CN106558978B - Switching power supply and its control circuit and control method - Google Patents

Abstract

The present invention provides a switching power supply and its control circuit and control method. The switching power supply is used to convert an input voltage into an output voltage. The switching power supply includes a power stage circuit and a control circuit. The power stage circuit switches at least one power switch according to an operation signal to convert the input voltage into an output voltage. The control circuit is coupled to the power stage circuit to generate an operation signal. The control circuit includes a threshold value adjustment circuit, which is used to generate and adaptively adjust an overcurrent protection threshold value according to an input voltage or an input current. The input current flows through the power stage circuit. The overcurrent protection threshold value is used to limit the input current. When the input current exceeds the overcurrent protection threshold value, the control circuit does not turn on the power switch.

Description

Switching power supply and its control circuit and control method

technical field

The present invention relates to a switching power supply and its control circuit and control method, in particular to a switching power supply with the function of adaptively adjusting the critical value of overcurrent protection and its control circuit and control method.

Background technique

FIG. 1A shows a schematic diagram of a conventional switching power supply 100 . As shown in FIG. 1A , the switching power supply 100 is used to receive power to drive the display panel 10 . The switching power supply 100 includes: a power stage circuit 101 , a control circuit 102 , and a display driving circuit 103 . As shown in the figure, the power stage circuit 101 receives an input voltage Vin, and operates a power switch therein according to an operation signal generated by the control circuit 102 to generate an output voltage Vout. The display driver circuit 103 receives an output voltage for driving the display panel 10 .

One of the problems of the above-mentioned prior art is that, from receiving power to driving the display panel 10, the switching power supply 100 will pass through many circuits, including wires, etc., and the sum of their resistance values can be regarded as shown in the figure The wire resistance, has impedance R. Since the wire resistance has an impedance R, when the input current Iin flows through the power stage circuit 101 , a voltage drop of the input current Iin multiplied by the impedance R is generated. When the display panel 10 is refreshing during screen switching, there will be a period of liquid crystal inversion, which is called a blanking interval. During the blanking period, the control circuit 102 will request to increase the input current Iin, and increase the duty ratio of the operation signal, thus generating a relatively high voltage drop, causing the input voltage Vin to drop. FIG. 1B shows a schematic diagram of signal waveforms of the input voltage Vin, the output voltage Vout, and the input current Iin during normal operation. As shown in FIG. 1B , during the blanking period, the input current Iin increases, the input voltage Vin decreases, and the output voltage Vout increases. During the blanking period, due to the drop of the input voltage Vin, the input voltage Vin may be lower than the undervoltage lockout (undervoltage lock out, UVLO) level, and the entire system is shut down.

Figure 2 shows a schematic diagram of reducing the UVLO level to avoid system shutdown. As shown in Figure 2, reducing the undervoltage lockout level from UVLO to UVLO' can indeed prevent the system from shutting down due to the low input voltage Vin during the blanking period. However, this increases the operational risk of the switch mode power supply 100, and the UVLO level needs to be set at a higher level in many applications, which also makes this unfeasible.

Invention application US 6,445,144 shows a method to solve the above problems. It detects the input current and feedbacks the control switch to limit the upper and lower limits of the input current. However, in this way, many power switches and circuits need to be added, which increases power consumption and manufacturing cost.

In view of this, the present invention proposes a switching power supply and its control circuit and control method to address the shortcomings of the above-mentioned prior art. According to the input voltage or input current, the present invention adaptively adjusts the critical value of over-current protection, not only can reduce the input current when necessary, and prevent the input voltage from being lower than the under-voltage lock-out level without lowering the under-voltage lock-out level; There is no need to add additional power circuits to control manufacturing costs and power consumption.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies and defects of the prior art, and propose a switching power supply and its control circuit and control method. According to the input voltage or input current, the over-current protection critical value can be adaptively adjusted, which can not only The input current can be lowered to prevent the input voltage from falling below the under-voltage lockout level without lowering the under-voltage lockout level; and there is no need to add additional power circuits to control manufacturing costs and power consumption.

In order to achieve the above purpose, from one point of view, the present invention provides a switching power supply for converting an input voltage into an output voltage, the switching power supply includes: a power stage circuit, according to an operating signal for switching at least one of the power switches to convert the input voltage to the output voltage; and a control circuit coupled to the power stage circuit for generating the operating signal, the control circuit including a threshold adjustment circuit , used to generate and adaptively adjust an over-current protection threshold according to the input voltage or an input current; wherein, the input current flows through the power stage circuit; wherein, the over-current protection threshold is used to limit the input current; wherein, the control circuit does not turn on the power switch when the input current exceeds the overcurrent protection threshold.

In one of the preferred embodiments, the threshold adjustment circuit adaptively lowers the over-current protection threshold when the input voltage drops, and when the input voltage drops to not higher than a default first input voltage When the over-current protection threshold value is maintained at a minimum threshold value of over-current protection; and when the input voltage rises, the over-current protection threshold value is adaptively raised, and when the input voltage rises to no less than a When the default second input voltage is used, the over-current protection threshold is maintained at a maximum over-current protection threshold; wherein, the default first input voltage is lower than the default second input voltage, and the over-current protection minimum threshold is The value is lower than the maximum critical value of the overcurrent protection.

In one of the preferred embodiments, when the input current rises, the threshold adjustment circuit adaptively lowers the over-current protection threshold, and when the input current rises to a preset first input current, maintaining the over-current protection threshold at a very small over-current protection threshold, and maintaining the input current at the preset first input current; and adaptively increasing the over-current protection threshold when the input current drops , and when the input current drops to not higher than a preset second input current, the over-current protection threshold is maintained at a maximum over-current protection threshold; wherein, the preset first input current is higher than the The second input current is preset, and the over-current protection minimum threshold is lower than the over-current protection maximum threshold.

In one of the preferred embodiments, the threshold adjustment circuit adaptively adjusts the over-current protection threshold so that the input voltage will not be lower than a preset under voltage lockout (under voltage lockout, UVLO) level.

In one preferred embodiment, the output voltage is used to supply a display panel, and during a blanking interval, the threshold adjustment circuit adaptively adjusts the threshold value according to the input voltage or the input current. an over-current protection threshold; and outside the blanking period, the threshold adjustment circuit maintains the over-current protection threshold at a fixed preset over-current protection threshold.

In one of the preferred embodiments, the threshold adjustment circuit includes: a voltage-current conversion circuit for converting the input voltage or its related signal into a first current; a first current modulation circuit, Coupled with the voltage-current conversion circuit, it is used to convert the first current into a first amplified current proportional to it, and generate a second current according to the difference between an overcurrent protection upper limit current and the first amplified current ; a second current modulation circuit, coupled with the first current modulation circuit, for converting the second current into a second amplified current proportional to it, and according to an overcurrent protection lower limit current and the second amplifying the difference of the current to generate a third current; a third current modulation circuit, coupled with the second current modulation circuit, for converting the third current into a third amplified current proportional to it, and Generate a modulated current according to an overcurrent protection minimum critical value current and the third current; and a current-voltage conversion circuit coupled to the third current modulation circuit for converting the modulated current into the third current Overcurrent protection threshold.

In the foregoing embodiments, the second current modulating circuit preferably further includes an enabling switch circuit for determining whether to generate the second amplified current according to an enabling signal.

In the aforementioned embodiment, the enable signal preferably determines to generate the second amplified current during a blanking period; and determines not to generate the second amplified current outside the blanking period; wherein, the output The voltage is used to supply a display panel, and the blanking period is related to the period from the end of a front frame scan to the start of a rear frame scan of the display panel.

In one of the preferred embodiments, the threshold adjustment circuit includes: an input current sensing circuit for sensing the input current to generate a current sensing signal; a voltage-current conversion circuit for converting The current sensing signal is converted into a first current; a first current modulation circuit is coupled with the voltage-current conversion circuit, and is used to convert the first current into a first amplified current proportional thereto, and according to The difference between the first amplified current and an overcurrent protection lower limit current generates a second current; a second current modulation circuit, coupled with the first current modulation circuit, is used to convert the second current into A second amplified current proportional to it, and a third current is generated according to the difference between an overcurrent protection upper limit current and the second amplified current; a third current amplifying circuit, coupled with the second current modulation circuit , used to convert the third current into a third amplified current proportional to it; a third current modulation circuit, coupled with the second current modulation circuit, used to convert the third current into a proportional current A third amplified current, and generates a modulated current according to an overcurrent protection minimum threshold current and the third current; and a current-voltage conversion circuit, coupled with the third current modulation circuit, for converting The modulated current is converted into the over-current protection threshold.

In the foregoing embodiments, the second current modulating circuit preferably further includes an enabling switch circuit for determining whether to generate the second amplified current according to an enabling signal.

In the foregoing embodiment, the enable signal preferably determines to generate the third current during a blanking period; and determines not to generate the third current outside the blanking period; wherein, the output voltage is determined by To supply a display panel, and the blanking period is related to the period from the end of a front frame scan to the start of a rear frame scan of the display panel.

To achieve the above purpose, from another point of view, the present invention provides a control method of a switching power supply, wherein the switching power supply is used to convert an input voltage into an output voltage, and the switching power supply The control method of the supplier includes: operating at least one power switch in a power stage circuit according to an operation signal to convert the input voltage into the output voltage; and generating and adaptively adjusting a power switch according to the input voltage or an input current An over-current protection critical value; limiting the input current with the over-current protection critical value; and not turning on the power switch when the input current exceeds the over-current protection critical value; wherein, the input current flows through the power stage circuit.

In one of the preferred embodiments, the step of generating and adaptively adjusting the overcurrent protection threshold according to the input voltage or the input current includes: adaptively lowering the overcurrent when the input voltage drops protection threshold, and when the input voltage drops to not higher than a default first input voltage, the over-current protection threshold is maintained at a minimum over-current protection threshold; and when the input voltage rises, the adaptability increasing the over-current protection threshold, and maintaining the over-current protection threshold at a maximum over-current protection threshold when the input voltage rises to no lower than a default second input voltage; wherein, the default first An input voltage is lower than the default second input voltage, and the over-current protection minimum threshold is lower than the over-current protection maximum threshold.

In one of the preferred embodiments, the step of generating and adaptively adjusting the overcurrent protection threshold according to the input voltage or the input current includes: adaptively lowering the overcurrent when the input current rises protection threshold, and when the input current rises to a preset first input current, the over-current protection threshold is maintained at a minimum over-current protection threshold, and the input current is maintained at the preset first input current; and when the input current drops, adaptively increase the over-current protection threshold, and when the input current drops to not higher than a preset second input current, maintain the over-current protection threshold at a Overcurrent protection maximum threshold; wherein, the preset first input current is higher than the preset second input current, and the overcurrent protection minimum threshold is lower than the overcurrent protection maximum threshold.

In one of the preferred embodiments, the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage or the input current further includes: preventing the input voltage from falling due to the input current being too high at a preset under voltage lockout (under voltage lockout, UVLO) level.

In a preferred embodiment, the output voltage is used to supply a display panel, and the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage or the input current includes: During the blanking period, adaptively adjust the over-current protection threshold according to the input voltage or the input current; and maintain the over-current protection threshold at a fixed preset over-current protection threshold outside the blanking period.

In one preferred embodiment, the step of generating and adaptively adjusting the overcurrent protection threshold according to the input voltage includes: converting the input voltage or a related signal thereof into a first current; The first current is converted into a first amplified current proportional to it, and a second current is generated according to the difference between an overcurrent protection upper limit current and the first amplified current; the second current is converted into a first amplified current proportional to it Two amplified currents, and generate a third current according to the difference between an overcurrent protection lower limit current and the second amplified current; convert the third current into a third amplified current proportional to it, and generate a third current according to an overcurrent protection The very small threshold current and the third current generate a modulated current; and convert the modulated current into the overcurrent protection threshold.

In the foregoing embodiment, the step of converting the second current into a second amplified current proportional to it, and generating a third current according to the difference between an overcurrent protection lower limit current and the second amplified current is relatively Preferably, it also includes: determining whether to generate the second amplified current according to an enabling signal.

In the foregoing embodiment, the enable signal preferably determines to generate the third current during a blanking period; and determines not to generate the third current outside the blanking period; wherein, the output voltage is determined by To supply a display panel, and the blanking period is related to the period from the end of a front frame scan to the start of a rear frame scan of the display panel.

In one of the preferred embodiments, the step of generating and adaptively adjusting the over-current protection threshold according to the input current includes: sensing the input current to generate a current sensing signal; sensing the current The measurement signal is converted into a first current; the first current is converted into a first amplified current proportional to it, and a second current is generated according to the difference between the first amplified current and an overcurrent protection lower limit current; converting the second current into a second amplified current proportional to it, and generating a third current according to the difference between an overcurrent protection upper limit current and the second amplified current; converting the third current into a proportional to it A third amplified current; convert the third amplified current into a fourth amplified current proportional to it, and generate a modulated current according to an overcurrent protection minimum critical value current and the fourth amplified current; and The modulated current is converted to the overcurrent protection threshold.

In the foregoing embodiments, the step of converting the second current into a second amplified current proportional thereto preferably further includes: determining whether to generate the second amplified current according to an enabling signal.

In the aforementioned embodiment, the enable signal preferably determines to generate the second amplified current during a blanking period; and determines not to generate the second amplified current outside the blanking period; wherein, the output The voltage is used to supply a display panel, and the blanking period is related to the period from the end of a front frame scan to the start of a rear frame scan of the display panel.

In order to achieve the above purpose, from another point of view, the present invention provides a control circuit in a switching power supply, which is used to generate an operation signal to switch at least one power switch in the switching power supply, and a The input voltage is converted into an output voltage, wherein the control circuit includes a threshold adjustment circuit for generating and adaptively adjusting an over-current protection threshold according to the input voltage to limit the input current, wherein the threshold adjustment The circuit includes: a voltage-current conversion circuit, used to convert the input voltage or its related signal into a first current; a first current modulation circuit, coupled with the voltage-current conversion circuit, used to convert the first current The current is converted into a first amplified current proportional to it, and a second current is generated according to the difference between an overcurrent protection upper limit current and the first amplified current; a second current modulating circuit, and the first current modulating circuit The transformer circuit is used to convert the second current into a second amplified current proportional to it, and generate a third current according to the difference between an overcurrent protection lower limit current and the second amplified current; a third A current modulation circuit, coupled with the second current modulation circuit, is used to convert the third current into a third amplified current proportional to it, and protect the extremely small threshold current and the third current according to an overcurrent , to generate a modulated current; and a current-voltage conversion circuit, coupled to the third current modulation circuit, for converting the modulated current into the over-current protection critical value; wherein the over-current protection critical value is used to limit the input current; wherein the control circuit does not turn on the power switch when the input current exceeds the over-current protection critical value.

In one of the preferred embodiments, when the input voltage drops, the over-current protection threshold is adaptively lowered, and when the input voltage drops to not higher than a default first input voltage, the over-current The protection threshold is maintained at an over-current protection minimum threshold; and when the input voltage rises, the over-current protection threshold is adaptively raised, and when the input voltage rises to no less than a default second input voltage , so that the over-current protection threshold is maintained at a maximum over-current protection threshold.

In order to achieve the above purpose, from another point of view, the present invention provides a control circuit in a switching power supply, which is used to generate an operation signal to switch at least one power switch in the switching power supply, and a The input voltage is converted into an output voltage, wherein the control circuit includes a threshold adjustment circuit for generating and adaptively adjusting an over-current protection threshold according to the input current to limit the input current, wherein the threshold adjustment The circuit includes: an input current sensing circuit for sensing the input current to generate a current sensing signal; a voltage-current conversion circuit for converting the current sensing signal into a first current; a first A current modulation circuit, coupled with the voltage-current conversion circuit, is used to convert the first current into a first amplified current proportional to it, and based on the difference between the first amplified current and an overcurrent protection lower limit current , to generate a second current; a second current modulation circuit, coupled with the first current modulation circuit, is used to convert the second current into a second amplified current proportional to it, and according to an over-current protection The difference between the upper limit current and the second amplified current generates a third current; a third current amplifying circuit is coupled with the second current modulating circuit to convert the third current into a first proportional current Three amplified currents; a fourth current modulation circuit, coupled with the third current amplifying circuit, is used to convert the third amplified current into a fourth amplified current proportional to it, and protect the minimum threshold according to an overcurrent the value current and the fourth amplified current to generate a modulated current; and a current-to-voltage conversion circuit coupled to the third current modulation circuit for converting the modulated current into the overcurrent protection threshold.

In one of the preferred embodiments, when the input current rises, the threshold adjustment circuit adaptively lowers the over-current protection threshold, and when the input current rises to a preset first input current, maintaining the over-current protection threshold at a very small over-current protection threshold, and maintaining the input current at the preset first input current; and adaptively increasing the over-current protection threshold when the input current drops , and when the input current drops to not higher than a preset second input current, the over-current protection threshold is maintained at a maximum over-current protection threshold; wherein, the preset first input current is higher than the The second input current is preset, and the over-current protection minimum threshold is lower than the over-current protection maximum threshold.

In one preferred embodiment, the control circuit adaptively adjusts the overcurrent protection threshold so that the input voltage is not lower than a default under voltage lockout (under voltage lockout, UVLO) level.

In one preferred embodiment, the output voltage is used to supply a display panel, and during a blanking period, the control circuit adaptively adjusts the overcurrent protection threshold according to the input voltage or the input current; And outside the blanking period, the control circuit maintains the over-current protection threshold at a fixed preset over-current protection threshold.

The following will be described in detail through specific examples, when it is easier to understand the purpose, technical content, characteristics and effects of the present invention.

Description of drawings

FIG. 1A shows a schematic diagram of a switching power supply 100 in the prior art;

FIG. 1B shows a schematic diagram of signal waveforms of the input voltage Vin, the output voltage Vout, and the input current Iin during normal operation;

Figure 2 shows a schematic diagram of reducing the UVLO level to avoid system shutdown;

Figure 3 shows a first embodiment of the present invention;

4A-4K show synchronous or asynchronous buck, boost, reverse, buck-boost, boost reverse, or flyback power stage circuits;

FIG. 5 shows a schematic diagram of the relationship between the overcurrent protection threshold OCP and the input voltage Vin according to an embodiment of the present invention;

Figure 6 shows a second embodiment of the present invention;

Figure 7 shows a third embodiment of the present invention;

FIG. 8 shows a schematic diagram of input voltage and input current signal waveforms according to the present invention;

FIG. 9 shows a schematic diagram of the relationship between the overcurrent protection threshold OCP and the input current Iin according to an embodiment of the present invention;

Figure 10 shows a fourth embodiment of the present invention;

Fig. 11 shows a fifth embodiment of the present invention.

Explanation of symbols in the figure

10 display panel

100,200 Switching Mode Power Supplies

101,201 Power stage circuits

102,202 Control circuits

103,203 Display driver circuits

2021 Threshold Adjustment Circuit

2022,3022 Voltage-current conversion circuit

2023, 3023 The first current modulation circuit

2024, 3024 Second current modulation circuit

2025 The third current modulation circuit

2026,3026 Current-voltage conversion circuit

3021 Input Current Sensing Circuit

3025 The third current amplifier circuit

3027 Fourth current modulation circuit

EN enable signal

I1,Ic1 first current

I1’, Ic1’ first amplified current

I2,Ic2 second current

I2’, Ic2’ second amplified current

I3, Ic3 third current

I3', Ic3' the third amplified current

Ic4 fourth amplified current

Iin input current

Iin1 preset first input current

Iin2 Default second input voltage

Ilol,Ilo overcurrent protection lower limit current

Imin overcurrent protection minimum threshold current

Imod modulation current

Iupl,Iup Overcurrent protection upper limit current

OCP Overcurrent Protection Threshold

OCPmax overcurrent protection maximum critical value

OCPmin overcurrent protection minimum critical value

R impedance

R1, R2, Rsen resistors

SW enable switch circuit

UVLO,UVLO’ undervoltage lockout level

Vin input voltage

Vin1 default first input voltage

Vin2 default second input voltage

Vout output voltage

Detailed ways

The drawings in the present invention are all schematic, mainly intended to show the coupling relationship between various circuits, and the relationship between various signal waveforms. As for the circuits, signal waveforms and frequencies, they are not drawn to scale.

Figure 3 shows a first embodiment of the invention. As shown in FIG. 3 , the switching power supply 200 is used to convert the input voltage Vin into an output voltage Vout, and the display driving circuit 203 drives the display panel 10 . The switching power supply 200 includes a power stage circuit 201 , a control circuit 202 , and a display driver circuit 203 . The power stage circuit 201 switches at least one of the power switches to convert the input voltage Vin to the output voltage Vout according to the operation signal. The power stage circuit 201 includes at least one power switch, which can be a synchronous or asynchronous buck type, boost type, reverse voltage type, buck-boost type, boost reverse voltage type, or flyback type power stage circuit, as shown in Figure 4A -4K shown. The display driver circuit 203 drives the display panel 10 in order to receive the output voltage Vout, which is not the focus of the present application, and will not be described in detail here.

The control circuit 202 is coupled to the power stage circuit 201 for generating an operation signal. The control circuit 202 includes a threshold adjustment circuit 2021 for generating and adaptively adjusting the over-current protection threshold OCP according to the input voltage Vin or the input current Iin. Wherein, the input current Iin flows through the power stage circuit 201 . Wherein, the over-current protection critical value OCP is used to limit the input current Iin. The control circuit 202 does not turn on the power switch when the input current Iin exceeds the overcurrent protection threshold OCP. Based on this mechanism, the control circuit 202 feeds back and controls the input current Iin so that the input current Iin will not be too high and the input voltage Vin will not be lower than a preset under voltage lockout (UVLO) level. The so-called standard for the input current Iin to be too high or not to be too high mainly lies in the voltage drop caused by the input current Iin multiplied by the impedance R of the line group, resulting in a drop in the input voltage Vin, so that the input voltage Vin is lower than the default undervoltage When the under voltage lockout (UVLO) level is locked, the input current Iin is too high; if the input voltage Vin is kept higher than the default under voltage lockout level, the input current Iin is not too high.

In this embodiment, the threshold adjustment circuit 2021 includes, for example, a voltage-current conversion circuit 2022 , a first current modulation circuit 2023 , a second current modulation circuit 2024 , a third current modulation circuit 2025 , and a current-voltage conversion circuit 2026 . For example, as shown in FIG. 5 , the threshold adjustment circuit 2021 adaptively lowers the over-current protection threshold OCP when the input voltage Vin drops, and when the input voltage Vin is not higher than the default first input voltage Vin1, Maintain the over-current protection critical value OCP at the minimum over-current protection critical value OCPmin; and when the input voltage rises, adaptively increase the over-current protection critical value OCP, and when the input voltage Vin is not lower than the default second input voltage Vin2 , keep the over-current protection critical value OCP at the over-current protection maximum critical value OCPmax; wherein, the default first input voltage Vin1 is lower than the default second input voltage Vin2, and the over-current protection minimum critical value OCPmin is lower than the over-current Protect the maximum critical value OCPmax.

Fig. 6 shows a second embodiment of the present invention. This embodiment shows a more specific embodiment of the threshold adjustment circuit 2021 . As shown in FIG. 6 , the threshold adjustment circuit 2021 includes, for example, a voltage-current conversion circuit 2022 , a first current modulation circuit 2023 , a second current modulation circuit 2024 , a third current modulation circuit 2025 , and a current-voltage conversion circuit 2026 . Wherein, the voltage-current conversion circuit 2022 is used to convert the input voltage Vin or its related signals into the first current I1. It should be noted that the so-called signal related to the input voltage Vin refers to a signal related to the input voltage Vin. Due to various factors, the voltage-current conversion circuit 2022 does not have to directly receive the input voltage Vin, but can receive a signal that has the same signal as the input voltage Vin. Proportional, or other signals with a linear function relationship, which are proportional to or have a linear function relationship with the input voltage Vin, are the relevant signals of the input voltage Vin. As shown in the figure, the voltage-to-current conversion circuit 2022 receives the input voltage Vin, and converts the input voltage Vin to a first voltage via a low-dropout regulator (LDO) as shown in the figure, which includes a resistor R1. A current I1.

The first current modulation circuit 2023 is coupled to the voltage-current conversion circuit 2022, and is used to convert the first current I1 into a proportional first amplified current I1', for example, at a ratio of 1:M1, and according to the over-current protection upper limit current Iupl The difference with the first amplified current I1' generates a second current I2. In this embodiment, the first current modulation circuit 2023 includes, for example but not limited to, a current mirror circuit and a fixed current source, and the current mirror circuit converts the first current I1 into a first amplified current I1' proportional to it, and the overcurrent The protection upper limit current Iupl is provided, for example, by a fixed current source; wherein, the relationship between the second current I2, the first amplified current I1', and the overcurrent protection upper limit current Iupl is: I2=Iupl-I1'.

The second current modulating circuit 2024 is coupled to the first current modulating circuit 2023, and is used to convert the second current I2 into a proportional second amplified current I2', for example, at a ratio of 1:M2, and according to an over-current protection The difference between the lower limit current Ilo1 and the second amplified current I2' generates a third current I3. In this embodiment, the second current modulation circuit 2024 includes, for example but not limited to, a current mirror circuit and a fixed current source, and the current mirror circuit converts the second current I2 into a second amplified current I2' proportional to it, and the overcurrent The protection lower limit current Ilol is provided by a fixed current source, for example; wherein, the relationship between the third current I3, the second amplified current I2', and the overcurrent protection lower limit current Ilol is: I3=Ilol-I2'.

The third current modulation circuit 2025 is coupled to the second current modulation circuit 2024, and is used to convert the third current I3 into a third amplified current I3' proportional to it, for example, at a ratio of 1:M3. The small threshold current Imin and the third amplified current I3' generate a modulated current Imod. In this embodiment, the third current modulation circuit 2025 includes, for example but not limited to, a current mirror circuit and a fixed current source, and the current mirror circuit converts the third current I3 into a third amplified current I3' proportional to it, and the overcurrent The protection minimum threshold current Imin is provided by a fixed current source, for example; wherein, the relationship between the modulating current Imod, the third amplified current I3', and the overcurrent protection minimum threshold current Imin is: Imod=I3'+Imin .

The current-voltage conversion circuit 2026 is coupled to the third current modulation circuit 2025 for converting the modulation current Imod into an over-current protection threshold OCP. Wherein, the current-to-voltage conversion circuit 2026 includes, for example, a resistor R2, and the voltage difference generated by modulating the current Imod flowing through the resistor R2 is used as the over-current protection threshold OCP.

In this embodiment, the value of the overcurrent protection minimum critical value OCPmin is:

OCPmin=Imin×R2

The value of the maximum critical value OCPmax of overcurrent protection is:

OCPmax=(Imin+Ilol×M3)×R2

According to this embodiment, the default first input voltage Vin1 is:

The default second input voltage Vin2 is:

And in FIG. 5 , between the default first input voltage Vin1 and the default second input voltage Vin2 , the rising slope slop of the overcurrent protection threshold OCP is:

That is to say, the user can properly select the resistors R1, R2, overcurrent protection upper limit current Iupl, overcurrent protection lower limit current Ilol, overcurrent protection minimum critical value current Imin, and current mirror amplification ratios M1 and M2 according to needs. , M3, to obtain the over-current protection minimum threshold OCPmin, the over-current protection maximum threshold OCPmax, the first input voltage Vin1, the default second input voltage Vin2, and the rising slope slop of the over-current protection threshold OCP.

Fig. 7 shows a third embodiment of the present invention. The difference between this implementation and the second embodiment is that in this embodiment, the second current modulation circuit 2024 also includes an enable switch circuit SW, which is used to determine whether to generate the second amplified current I2' according to the enable signal EN. . In this embodiment, the enable signal EN can determine to generate the second amplified current I2' during the blanking period; and can determine not to generate the second amplified current I2' outside the blanking period, and can , the threshold adjustment circuit 2021 maintains the overcurrent protection threshold OCP at a fixed preset overcurrent protection threshold, that is, a fixed value related to the overcurrent protection lower limit current Ilol, the overcurrent protection minimum threshold current Imin and the resistor R2 . Wherein, the output voltage Vout is used to supply the display panel 10 , and the blanking period is related to the period from the end of the scanning of the front frame of the display panel 10 to the start of scanning of the rear frame of the display panel 10 .

FIG. 8 shows a schematic diagram of the signal waveforms of the input voltage Vin and the input current Iin according to the present invention. Compared with the prior art, the present invention adaptively adjusts the overcurrent protection threshold OCP according to the change of the input voltage Vin or the input current Iin, especially during the aforementioned blanking period, the drop of the input voltage Vin and the rise of the input current. The over-current protection mechanism limits the input current Iin to prevent the input voltage Vin from falling below the default undervoltage lockout (under voltage lockout, UVLO) level (especially during the blanking period). The thick solid line in the figure represents the signal waveform diagram of the input voltage Vin and the input current Iin according to the present invention, and the thick dotted line represents the signal waveform diagram of the input voltage Vin and the input current Iin in the prior art.

FIG. 9 shows a schematic diagram of the relationship between the over-current protection threshold OCP and the input current Iin according to an embodiment of the present invention. It shows that the present invention can use the threshold adjustment circuit 2021 to adaptively reduce the over-current protection threshold OCP when the input current Iin rises, and when the input current Iin rises to reach the preset first input current Iin1, the over-current protection threshold OCP is maintained at the minimum threshold value OCPmin of the over-current protection, and the input current Iin is maintained at the preset first input current Iin1; and when the input current Iin drops, the over-current protection threshold value OCP is adaptively raised, and the input current Iin When not higher than the preset second input current Iin2, the overcurrent protection threshold OCP is maintained at the overcurrent protection maximum threshold OCPmax; wherein, the preset first input current Iin1 is higher than the preset second input current Iin2, and The overcurrent protection minimum critical value OCPmin is lower than the overcurrent protection maximum critical value OCPmax.

Fig. 10 shows a fourth embodiment of the present invention. This embodiment shows another more specific embodiment of the threshold adjustment circuit 2021 . As shown in FIG. 10, the threshold adjustment circuit 2021 includes, for example, an input current sensing circuit 3021, a voltage-current conversion circuit 3022, a first current modulation circuit 3023, a second current modulation circuit 3024, a third current amplification circuit 3025, a Four current modulation circuits 3027 and a current-voltage conversion circuit 3026 . The input current sensing circuit 3021 is used to sense the input current Iin to generate a current sensing signal. For example, the resistor Rsen is connected in series with the power stage circuit 101 to obtain the voltage across the resistor Rsen as the current sensing signal. The voltage-current conversion circuit 3022 is used to convert the current sensing signal into the first current Ic1. As shown in the figure, the voltage-current conversion circuit 3022 includes, for example, an error amplifier circuit and a low-dropout regulator (LDO) to convert the current sensing signal into the first current Ic1.

The first current modulation circuit 3023 is coupled to the voltage-current conversion circuit 2022, and is used to convert the first current Ic1 into a first amplified current Ic1' proportional to it, for example, at a ratio of 1:M1, and according to the first amplified current Ic1' The difference with the overcurrent protection lower limit current Ilo generates a second current Ic2. In this embodiment, the first current modulation circuit 3023 includes, for example but not limited to, a current mirror circuit and a fixed current source, and the current mirror circuit converts the first current Ic1 into a first amplified current Ic1' proportional to it, and the overcurrent The protection lower limit current Ilo is provided by a fixed current source, for example; wherein, the relationship between the second current Ic2 , the first amplified current Ic1 ′, and the overcurrent protection lower limit current Ilo is: Ic2=Ic1 ′−Ilo.

The second current modulation circuit 3024 is coupled to the first current modulation circuit 3023, and is used to convert the second current Ic2 into a second amplified current Ic2' proportional to it, for example, at a ratio of 1:M2, and according to the upper limit of the overcurrent protection The difference between the current Iup and the second amplified current Ic2' generates a third current Ic3. In this embodiment, the second current modulation circuit 3024 includes, for example but not limited to, a current mirror circuit and a fixed current source, and the current mirror circuit converts the second current Ic2 into a second amplified current Ic2' proportional to it, and the overcurrent The protection upper limit current Iup is provided, for example, by a fixed current source; wherein, the relationship between the third current Ic3, the second amplified current Ic2', and the overcurrent protection upper limit current Iup is: Ic3=Iup-Ic2'.

The third current amplifying circuit 3025 is coupled to the second current modulating circuit 3024 for converting the third current Ic3 into a third amplified current Ic3' proportional to it, for example, at a ratio of 1:M3. In this embodiment, the third current amplifying circuit 3025 includes, for example but not limited to, a current mirror circuit.

The fourth current modulating circuit 3027 is coupled to the third current amplifying circuit 3025 for converting the third amplified current Ic3' into a fourth amplified current Ic4 proportional to it, and according to the overcurrent protection minimum threshold current Imin and the first Four amplify the current Ic4 to generate the modulated current Imod. In this embodiment, the fourth current modulating circuit 3027 includes, for example but not limited to, a current mirror circuit and a fixed current source, and the current mirror circuit converts the third amplified current Ic3' into a fourth amplified current Ic4 that is proportional to it. The current protection minimum threshold current Imin is provided by a fixed current source, for example; wherein, the relationship between the modulating current Imod, the fourth amplified current Ic4, and the overcurrent protection minimum threshold current Imin is: Imod=Ic4+Imin.

The current-voltage conversion circuit 3026 is coupled to the fourth current modulation circuit 3027 for converting the modulation current Imod into an over-current protection threshold OCP. Wherein, the current-to-voltage conversion circuit 3026 includes, for example, a resistor R2, and the voltage difference generated by modulating the current Imod flowing through the resistor R2 is used as the over-current protection threshold OCP.

Fig. 11 shows a fifth embodiment of the present invention. The difference between this embodiment and the fourth embodiment is that in this embodiment, the second current modulation circuit 3024 further includes an enable switch circuit SW, which is used to determine whether to generate the second amplified current Ic2 according to the enable signal EN. '. In this embodiment, the enable signal EN can determine to generate the second amplified current Ic2' during the blanking period; and can determine not to generate the second amplified current Ic2' outside the blanking period, and can determine not to generate the second amplified current Ic2' outside the blanking period. , the threshold adjustment circuit 2021 maintains the overcurrent protection threshold OCP at a fixed preset overcurrent protection threshold, that is, a fixed value related to the overcurrent protection upper limit current Iup, the overcurrent protection minimum threshold current Imin and the resistor R2 . Wherein, the output voltage Vout is used to supply the display panel 10 , and the blanking period is related to the period from the end of the scanning of the front frame of the display panel 10 to the start of scanning of the rear frame of the display panel 10 .

The present invention has been described above with reference to preferred embodiments, and the above description is only for those skilled in the art to easily understand the content of the present invention, and is not intended to limit the scope of rights of the present invention. Under the same spirit of the present invention, various equivalent changes can be conceived by those skilled in the art. For example, other circuits or components that do not affect the main functions may be inserted between two circuits or components that are directly connected in the figures shown in the embodiments, so "coupling" should be regarded as including direct and indirect connections. Another example is to amplify the current in a positive ratio, not limited to the current mirror circuit, but also to other circuits with the same amplification effect; as another example, the positive and negative terminals of the amplifier circuit and the comparator circuit can be interchanged, and only the relevant circuits need to be modified accordingly Or the meaning of signal high and low levels. All these can be deduced according to the teaching of the present invention, therefore, the scope of the present invention should cover the above and all other equivalent changes.

Claims (26)

1. A switching power supply for converting an input voltage to an output voltage, the switching power supply comprising:

a power stage circuit, which switches at least one power switch to convert the input voltage into the output voltage according to an operation signal; and

a control circuit coupled to the power stage circuit for generating the operation signal, the control circuit including a threshold adjustment circuit for generating and adaptively adjusting an over-current protection threshold according to the input voltage;

wherein an input current flows through the power stage circuit;

wherein, the over-current protection threshold is used for limiting the input current;

when the input current exceeds the overcurrent protection critical value, the control circuit does not conduct the power switch;

wherein, this critical value adjustment circuit includes:

a voltage-current conversion circuit for converting the input voltage or the related signal into a first current;

a first current modulation circuit coupled to the voltage-current conversion circuit for converting the first current into a first amplified current proportional to the first current, and generating a second current according to a difference between an over-current protection upper-limit current and the first amplified current;

a second current modulation circuit coupled to the first current modulation circuit for converting the second current into a second amplified current proportional to the second current, and generating a third current according to a difference between an overcurrent protection lower limit current and the second amplified current;

a third current modulation circuit coupled to the second current modulation circuit for converting the third current into a third amplified current proportional thereto, and generating a modulation current according to an overcurrent protection minimum threshold current and the third amplified current; and

a current-voltage conversion circuit coupled to the third current modulation circuit for converting the modulation current into the over-current protection threshold.

2. The switching power supply of claim 1, wherein the threshold adjustment circuit adaptively adjusts the over-current protection threshold when the input voltage decreases, and maintains the over-current protection threshold at an over-current protection minimum threshold when the input voltage decreases to not higher than a default first input voltage; when the input voltage rises, the overcurrent protection critical value is adaptively adjusted, and when the input voltage rises to be not lower than a default second input voltage, the overcurrent protection critical value is maintained at an overcurrent protection maximum critical value;

the default first input voltage is lower than the default second input voltage, and the minimum overcurrent protection threshold is lower than the maximum overcurrent protection threshold.

3. The switching power supply of claim 1, wherein the threshold adjustment circuit adaptively adjusts the over-current protection threshold when the input current rises, and maintains the over-current protection threshold at an over-current protection minimum threshold and maintains the input current at a predetermined first input current when the input current rises to a predetermined first input current; when the input current is reduced, the overcurrent protection critical value is adaptively increased, and when the input current is reduced to be not higher than a preset second input current, the overcurrent protection critical value is maintained at an overcurrent protection maximum critical value;

the predetermined first input current is higher than the predetermined second input current, and the minimum over-current protection threshold is lower than the maximum over-current protection threshold.

4. The switching power supply of claim 1, wherein the threshold adjustment circuit adaptively adjusts the over-current protection threshold such that the input voltage is not below a predetermined under-voltage lockout level due to the input current being too high.

5. The switching power supply of claim 1, wherein the output voltage is used to supply a display panel, and the threshold adjustment circuit adaptively adjusts the over-current protection threshold according to the input voltage or the input current during a blanking period; and the threshold value adjusting circuit maintains the over-current protection threshold value at a fixed preset over-current protection threshold value outside the blanking period.

6. The switching power supply of claim 1, wherein the second current modulation circuit further comprises an enable switch circuit for determining whether to generate the second amplified current according to an enable signal.

7. The switching power supply of claim 6, wherein the enable signal determines to generate the second amplified current during a blanking period; and determining not to generate the second amplified current outside the blanking period; the output voltage is used for supplying a display panel, and the blanking period is related to a period from the end of scanning a front picture to the beginning of scanning a rear picture of the display panel.

8. A switching power supply for converting an input voltage to an output voltage, the switching power supply comprising:

a power stage circuit, which switches at least one power switch to convert the input voltage into the output voltage according to an operation signal; and

a control circuit coupled to the power stage circuit for generating the operation signal, the control circuit including a threshold adjustment circuit for generating and adaptively adjusting an overcurrent protection threshold according to an input current;

wherein the input current flows through the power stage circuit;

wherein, the over-current protection threshold is used for limiting the input current;

when the input current exceeds the overcurrent protection critical value, the control circuit does not conduct the power switch;

wherein, this critical value adjustment circuit includes:

an input current sensing circuit for sensing the input current and generating a current sensing signal;

a voltage-current conversion circuit for converting the current sensing signal into a first current;

a first current modulation circuit coupled to the voltage-current conversion circuit for converting the first current into a first amplified current proportional to the first current, and generating a second current according to a difference between the first amplified current and an overcurrent protection lower limit current;

a second current modulation circuit coupled to the first current modulation circuit for converting the second current into a second amplified current proportional to the second current, and generating a third current according to a difference between an over-current protection upper limit current and the second amplified current;

a third current amplifying circuit coupled to the second current modulating circuit for converting the third current into a third amplified current proportional thereto;

a fourth current modulation circuit coupled to the third current amplifying circuit for converting the third amplified current into a fourth amplified current proportional thereto, and generating a modulation current according to an overcurrent protection minimum threshold current and the fourth amplified current; and

a current-to-voltage conversion circuit coupled to the fourth current modulation circuit for converting the modulated current to the over-current protection threshold.

9. The switching power supply of claim 8, wherein the second current modulation circuit further comprises an enable switch circuit for determining whether to generate the second amplified current according to an enable signal.

10. The switching power supply of claim 9, wherein the enable signal determines to generate the second amplified current during a blanking period; and determining not to generate the second amplified current outside the blanking period; the output voltage is used for supplying a display panel, and the blanking period is related to a period from the end of scanning a front picture to the beginning of scanning a rear picture of the display panel.

11. A control method of a switching power supply, wherein the switching power supply is used for converting an input voltage into an output voltage, the control method of the switching power supply comprises:

operating at least one power switch in a power stage circuit according to an operation signal to convert the input voltage into the output voltage; and

generating and adaptively adjusting an overcurrent protection threshold according to the input voltage;

limiting an input current by the over-current protection threshold value; and

when the input current exceeds the overcurrent protection critical value, the power switch is not conducted;

wherein the input current flows through the power stage circuit;

wherein, the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage comprises:

converting the input voltage or the related signal into a first current;

converting the first current into a first amplified current in proportion to the first current, and generating a second current according to a difference value between an overcurrent protection upper limit current and the first amplified current;

converting the second current into a second amplified current in proportion to the second current, and generating a third current according to a difference value between an overcurrent protection lower limit current and the second amplified current;

converting the third current into a third amplified current in proportion to the third current, and generating a modulation current according to an over-current protection minimum critical value current and the third current; and

converting the modulation current into the over-current protection threshold.

12. The method as claimed in claim 11, wherein the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage comprises:

when the input voltage is reduced, the overcurrent protection critical value is adaptively reduced, and when the input voltage is reduced to be not higher than a default first input voltage, the overcurrent protection critical value is maintained at an overcurrent protection minimum critical value; and

when the input voltage rises, the overcurrent protection critical value is adaptively adjusted, and when the input voltage rises to be not lower than a default second input voltage, the overcurrent protection critical value is maintained at an overcurrent protection maximum critical value;

the default first input voltage is lower than the default second input voltage, and the minimum overcurrent protection threshold is lower than the maximum overcurrent protection threshold.

13. The method as claimed in claim 11, wherein the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage comprises:

when the input current rises, the overcurrent protection critical value is adjusted and reduced adaptively, and when the input current rises to reach a preset first input current, the overcurrent protection critical value is maintained at an overcurrent protection minimum critical value, and the input current is maintained at the preset first input current; and

when the input current is reduced, the overcurrent protection critical value is adaptively increased, and when the input current is reduced to be not higher than a preset second input current, the overcurrent protection critical value is maintained at an overcurrent protection maximum critical value;

the predetermined first input current is higher than the predetermined second input current, and the minimum over-current protection threshold is lower than the maximum over-current protection threshold.

14. The method as claimed in claim 11, wherein the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage further comprises: so that the input voltage is not lower than a predetermined under-voltage locking level due to the over-high input current.

15. The method as claimed in claim 11, wherein the output voltage is used for supplying a display panel, and the step of generating and adaptively adjusting the over-current protection threshold according to the input voltage comprises:

during a blanking period, the overcurrent protection critical value is adaptively adjusted according to the input voltage or the input current; and

and maintaining the over-current protection threshold value at a fixed preset over-current protection threshold value outside the blanking period.

16. The method as claimed in claim 11, wherein the step of converting the second current into a second amplified current proportional thereto and generating a third current according to a difference between an overcurrent protection lower limit current and the second amplified current further comprises: determining whether to generate the second amplified current according to an enable signal.

17. The method according to claim 16, wherein the enable signal determines to generate the second amplified current during a blanking period; and determining not to generate the second amplified current outside the blanking period; the output voltage is used for supplying a display panel, and the blanking period is related to a period from the end of scanning a front picture to the beginning of scanning a rear picture of the display panel.

18. A control method of a switching power supply, wherein the switching power supply is used for converting an input voltage into an output voltage, the control method of the switching power supply comprises:

operating at least one power switch in a power stage circuit according to an operation signal to convert the input voltage into the output voltage; and

generating and adaptively adjusting an overcurrent protection threshold according to an input current;

limiting the input current by the over-current protection threshold value; and

when the input current exceeds the overcurrent protection critical value, the power switch is not conducted;

wherein the input current flows through the power stage circuit;

wherein, the step of generating and adaptively adjusting the over-current protection threshold according to the input current comprises:

sensing the input current to generate a current sensing signal;

converting the current sensing signal into a first current;

converting the first current into a first amplified current in proportion to the first current, and generating a second current according to a difference value between the first amplified current and an overcurrent protection lower limit current;

converting the second current into a second amplified current in proportion to the second current, and generating a third current according to a difference value between an overcurrent protection upper limit current and the second amplified current;

converting the third current into a third amplified current in proportion thereto;

converting the third amplified current into a fourth amplified current in proportion to the third amplified current, and generating a modulation current according to an over-current protection minimum critical value current and the fourth amplified current; and

converting the modulation current into the over-current protection threshold.

19. The method as claimed in claim 18, wherein the step of converting the second current into a second amplified current proportional thereto further comprises: determining whether to generate the second amplified current according to an enable signal.

20. The method according to claim 19, wherein the enable signal determines to generate the second amplified current during a blanking period; and determining not to generate the second amplified current outside the blanking period; the output voltage is used for supplying a display panel, and the blanking period is related to a period from the end of scanning a front picture to the beginning of scanning a rear picture of the display panel.

21. A control circuit in a switching power supply for generating an operation signal to switch at least one power switch of the switching power supply to convert an input voltage into an output voltage, the control circuit comprising a threshold adjustment circuit for generating and adaptively adjusting an overcurrent protection threshold according to the input voltage to limit an input current, wherein the threshold adjustment circuit comprises:

a voltage-current conversion circuit for converting the input voltage or the related signal into a first current;

a first current modulation circuit coupled to the voltage-current conversion circuit for converting the first current into a first amplified current proportional to the first current, and generating a second current according to a difference between an over-current protection upper-limit current and the first amplified current;

a second current modulation circuit coupled to the first current modulation circuit for converting the second current into a second amplified current proportional to the second current, and generating a third current according to a difference between an overcurrent protection lower limit current and the second amplified current;

a third current modulation circuit coupled to the second current modulation circuit for converting the third current into a third amplified current proportional to the third current, and generating a modulation current according to an overcurrent protection minimum threshold current and the third current; and

a current-voltage conversion circuit coupled to the third current modulation circuit for converting the modulation current into the over-current protection threshold;

wherein the over-current protection threshold is used for limiting the input current;

the control circuit does not conduct the power switch when the input current exceeds the overcurrent protection critical value.

22. The control circuit of claim 21, wherein the over-current protection threshold is adaptively adjusted to decrease when the input voltage decreases, and is maintained at an over-current protection minimum threshold when the input voltage decreases to not higher than a default first input voltage; when the input voltage rises, the overcurrent protection threshold value is adaptively adjusted, and when the input voltage rises to be not lower than a default second input voltage, the overcurrent protection threshold value is maintained at an overcurrent protection maximum threshold value.

23. A control circuit in a switching power supply for generating an operation signal to switch at least one power switch of the switching power supply to convert an input voltage into an output voltage, the control circuit comprising a threshold adjustment circuit for generating and adaptively adjusting an overcurrent protection threshold according to an input current to limit the input current, wherein the threshold adjustment circuit comprises:

an input current sensing circuit for sensing the input current and generating a current sensing signal;

a voltage-current conversion circuit for converting the current sensing signal into a first current;

a first current modulation circuit coupled to the voltage-current conversion circuit for converting the first current into a first amplified current proportional to the first current, and generating a second current according to a difference between the first amplified current and an overcurrent protection lower limit current;

a second current modulation circuit coupled to the first current modulation circuit for converting the second current into a second amplified current proportional to the second current, and generating a third current according to a difference between an over-current protection upper limit current and the second amplified current;

a third current amplifying circuit coupled to the second current modulating circuit for converting the third current into a third amplified current proportional thereto;

a fourth current modulation circuit coupled to the third current amplifying circuit for converting the third amplified current into a fourth amplified current proportional thereto, and generating a modulation current according to an overcurrent protection minimum threshold current and the fourth amplified current; and

a current-to-voltage conversion circuit coupled to the fourth current modulation circuit for converting the modulated current to the over-current protection threshold.

24. The control circuit of claim 23, wherein the threshold adjustment circuit adaptively adjusts the over-current protection threshold when the input current rises, and maintains the over-current protection threshold at an over-current protection minimum threshold and maintains the input current at a predetermined first input current when the input current rises to a predetermined first input current; when the input current is reduced, the overcurrent protection critical value is adaptively increased, and when the input current is reduced to be not higher than a preset second input current, the overcurrent protection critical value is maintained at an overcurrent protection maximum critical value;

the predetermined first input current is higher than the predetermined second input current, and the minimum over-current protection threshold is lower than the maximum over-current protection threshold.

25. The control circuit of claim 21 or 23, wherein the control circuit is adapted to adjust the over-current protection threshold such that the input voltage does not fall below a predetermined under-voltage lockout level.

26. The control circuit of claim 21 or 23, wherein the output voltage is used to supply a display panel, and the control circuit adaptively adjusts the over-current protection threshold according to the input voltage or the input current during a blanking period; and the control circuit maintains the over-current protection threshold value at a fixed preset over-current protection threshold value outside the blanking period.