CN101420186B - Control circuit with frequency modulation for power supply - Google Patents

Abstract

The invention relates to a control circuit with frequency modulation for a power supply, which comprises an adjustable charging circuit, an oscillation signal generating circuit and a switching circuit, wherein the adjustable charging circuit generates a plurality of charging signals according to a first oscillation signal and transmits the charging signals to the oscillation signal generating circuit so that the oscillation signal generating circuit generates a second oscillation signal, the oscillation signal generating circuit modulates the second oscillation signal according to the charging signals to achieve the purpose of frequency modulation, the switching circuit generates a maximum conduction control signal according to the second oscillation signal, and the maximum conduction control signal is used for determining a switching period of a switching signal.

Description

Control circuit with frequency modulation for power supply

technical field

The present invention relates to a power supply, in particular to a control circuit with frequency modulation for the power supply.

Background technique

With the progress of today's technology, many electronic products have been developed to meet the needs of the people. The functions of these electronic products are becoming more and more powerful, and bring many conveniences to the lives of the people today. Most of the current electronic devices require a power supply to provide the power required by the electronic devices.

Please refer to FIG. 1 , which is a circuit diagram of a prior art power supply. As shown in the figure, the existing power supply includes a transformer T1. The transformer T1 has a primary winding N _P and a secondary winding _NS . One end of the primary winding N _P is coupled to an input voltage V _IN , the other end of the primary side winding N _P is coupled to a power switch Q1, the power switch Q1 is connected in series with a sensing resistor R _S , the power switch Q1 is coupled to one end of the sensing resistor R _S , and the other end of the sensing resistor R _S is coupled to At the ground terminal, the sensing resistor R _S is used to sense a switching current I _P of the power switch Q1 to generate a current signal V _S . One end of the secondary winding _NS of the transformer T1 is coupled to one end of a rectifier D _{O ,} and an output capacitor C _O is coupled between the other end of the rectifier D O and the other end of the secondary winding _NS . The output capacitor C _O It is also coupled to the output terminal of the power supply, and the output terminal of the power supply is used to provide the output voltage V _O .

Referring to FIG. 1 again, the existing power supply further includes a control chip 10 for generating a switching signal V _G to control the power switch Q1, and then switching the transformer T1. The control chip 10 is coupled to a resistor R _T and a capacitor C _T , the resistor _RT is coupled to a reference voltage V _R1 , the capacitor C _T is coupled between the ground terminal and the resistor _RT , and the reference voltage V _R1 is used to charge the capacitor C _T through the resistor _RT . The control chip 10 includes a discharge switch _SD and a discharge current source _IDCH , one end of the discharge switch _SD is coupled to the capacitor C _T , the other end of the discharge switch _SD is coupled to one end of the discharge current source _IDCH , and the discharge current The other end of the source _IDCH is coupled to the ground for discharging the capacitor _CT . The capacitor _CT is charged and discharged by the reference voltage V _R1 and the discharge current source _IDCH to generate an oscillating signal V _OSC .

Referring to FIG. 1 again, the control chip 10 further includes a first comparator 11 , a second comparator 12 and a flip-flop, and the flip-flop includes NAND gates 13 and 14 . The first comparator 11 compares the oscillating signal V _OSC with a high threshold signal V _H to generate a first comparison signal. The second comparator 12 compares the oscillating signal V _OSC with a low threshold signal V _L to generate a second comparison signal. The first comparison signal and the second comparison signal are sent to the flip-flop to generate a pulse signal PLS. The first input end of the first NAND gate 13 receives the first comparison signal, the first input end of the second NAND gate 14 receives the second comparison signal, and the output end of the second NAND gate 14 is coupled to the first NAND The second input terminal of the gate 13 and the output terminal of the first NAND gate 13 are coupled to the second input terminal of the second NAND gate 14 to generate a pulse signal PLS for controlling the discharge switch _SD .

Referring to FIG. 1 again, the negative input terminal of a comparator 15 receives the oscillating signal V _OSC , the positive input terminal of the comparator 15 receives a reference signal V _R2 , and the first input terminal of an AND gate 16 is coupled to the output of the comparator 15 The second input terminal of the AND gate 16 receives the pulse signal PLS through an inverter 17, and the output terminal of the AND gate 16 generates a maximum conduction control signal S _MAX and is coupled to the first input terminal of an AND gate 18 , the maximum conduction control signal S _MAX is used to control a maximum conduction time T _ON,MAX of the switching signal V _G , that is, to control the maximum conduction time of the power switch Q1 to control the maximum output power of the power supply. A comparator 19 receives a feedback signal V _FB and the current signal V _S to compare the feedback signal V _FB and the current signal V _S , and the output of the comparator 19 is coupled to the second input terminal of the AND gate 18 to cut off The signal V _G is switched to determine the conduction time T _ON of the power switch Q1 .

Please also refer to FIG. 2 , which is a waveform diagram of a conventional power supply. As shown in the figure, the reference signal V _R2 is a signal with a fixed level. When the oscillating signal V _OSC is smaller than the reference signal V _R2 and the pulse signal PLS is at a low level, the maximum conduction control signal S _MAX is enabled. , which is the conduction state of the high level. If the oscillating signal V _OSC is greater than the reference signal V _R2 , the maximum conduction control signal S _MAX is in a disabled state, that is, a low-level cut-off state. Therefore, the pulse signal PLS and the output of the comparator 15 can be used to determine the pulse width of the maximum conduction control signal S _MAX through the AND gate 16 . When the current signal V _S is greater than the feedback signal V _FB , the comparator 19 outputs a low level state, which is used to periodically cut off the switching signal V _G through the AND gate 18 to determine the conduction time T _ON of the power switch Q1. The maximum on-time T _{ON, MAX} of the switching signal V _G is determined by the maximum on-time control signal S _MAX through the AND gate 18 . It can be seen from the above that the oscillating signal V _OSC determines the switching period of the switching signal V _G , that is, controls the maximum on-time T _ON,MAX of the switching signal V _G , and controls the operating frequency of the power supply. Since the oscillating signal V _OSC is fixed, the operating frequency of the power supply is fixed, which is likely to generate high electromagnetic interference and affect the performance of the power supply.

Therefore, in order to reduce the electromagnetic interference of the power supply, the present invention proposes a frequency modulation control circuit of the power supply for the above problems, which can improve the above shortcomings, and further reduce the electromagnetic interference of the power supply to solve the problem above question.

Contents of the invention

The main purpose of the present invention is to provide a control circuit with frequency modulation for a power supply, which generates complex charging signals by an adjustable charging circuit to modulate the oscillating signal, and then modulate to control the power supply The frequency of the switching signal of the power supply can be reduced to reduce the electromagnetic interference of the power supply.

In order to realize the purpose of the present invention and solve its technical problems, it is achieved through the following technical solutions.

A control circuit with frequency modulation for a power supply according to the present invention, which includes:

A sampling circuit, sampling a first oscillating signal to generate a holding signal;

An adjustable charging circuit to generate multiple charging signals according to the holding signal;

An oscillating signal generating circuit generates a second oscillating signal according to the charging signals, and the oscillating signal generating circuit modulates the second oscillating signal according to the charging signals; and

A switching circuit, generating a maximum conduction control signal according to the second oscillating signal, the maximum conduction control signal is used to determine a switching period of a switching signal, and control the maximum output power of the power supply;

Wherein, the first oscillating signal and the second oscillating signal are sawtooth wave signals.

In the present invention, a conversion circuit is further included, which converts the holding signal into a reference current, and provides the reference current to the adjustable charging circuit to generate the charging signals.

In the present invention, the converting circuit is a voltage-current converting circuit.

In the present invention, a charging and discharging circuit is further included, which generates the first oscillating signal according to a reference voltage.

In the present invention, wherein the sampling circuit includes:

a hold capacitor for generating the hold signal; and

A sampling switch is coupled to the holding capacitor and samples the first oscillating signal for the holding capacitor to generate the holding signal.

In the present invention, the sampling circuit further includes a buffer, which buffers the first oscillating signal and is coupled to the sampling switch, and the sampling switch samples the buffered first oscillating signal.

In the present invention, wherein the adjustable charging circuit includes:

a frequency generator generating complex frequency control signals; and

The complex current mirrors generate the charging signals according to the frequency control signals.

In the present invention, wherein the frequency generator includes:

an input frequency generating circuit to generate an input frequency signal; and

A linear shift register generates the frequency control signals according to the input frequency signal.

In the present invention, the charging signals are charging currents with different magnitudes.

In the present invention, the oscillating signal generating circuit includes:

An oscillating capacitor generates the second oscillating signal according to the charging signals;

A discharge current source generates a discharge current to discharge the oscillating capacitor;

a discharge switch, coupled between the oscillating capacitor and the discharge current source;

a first comparator, receiving a high threshold signal and the second oscillating signal, and generating a first comparison signal;

A second comparator receives a low threshold signal and the second oscillating signal to generate a second comparison signal; and

A flip-flop receives the first comparison signal and the second comparison signal to generate a pulse signal to control the discharge switch.

In the present invention, the switching circuit includes a comparator, which compares a reference signal and the second oscillating signal to generate the maximum conduction control signal.

In the present invention, a protection circuit is further included, which generates a protection signal according to a feedback signal and a sensing signal to cut off the switching signal, wherein the feedback signal is related to an output voltage of the power supply.

The present invention also discloses a control circuit with frequency modulation for a power supply, which includes:

An adjustable charging circuit to generate multiple charging signals according to a first oscillating signal;

An oscillating signal generating circuit generates a second oscillating signal according to the charging signals, and the oscillating signal generating circuit modulates the second oscillating signal according to the charging signals; and

A switching circuit, generating a maximum conduction control signal according to the second oscillating signal, the maximum conduction control signal is used to determine a switching period of a switching signal, and control the maximum output power of the power supply;

Wherein, the first oscillating signal and the second oscillating signal are sawtooth wave signals.

In the present invention, a charging and discharging circuit is further included, which generates the first oscillating signal according to a reference voltage.

In the present invention, wherein the adjustable charging circuit includes:

a frequency generator generating complex frequency control signals; and

The complex current mirrors generate the charging signals according to the frequency control signals.

In the present invention, wherein the frequency generator includes:

an input frequency generating circuit to generate an input frequency signal; and

A linear shift register generates the frequency control signals according to the input frequency signal.

In the present invention, the charging signals are charging currents with different magnitudes.

In the present invention, the oscillating signal generating circuit includes:

An oscillating capacitor generates the second oscillating signal according to the charging signals;

A discharge current source generates a discharge current to discharge the oscillating capacitor;

a discharge switch, coupled between the oscillating capacitor and the discharge current source;

a first comparator, receiving a high threshold signal and the second oscillating signal, and generating a first comparison signal;

A second comparator receives a low threshold signal and the second oscillating signal to generate a second comparison signal; and

A flip-flop receives the first comparison signal and the second comparison signal to generate a pulse signal to control the discharge switch.

In the present invention, the switching circuit includes a comparator, which compares a reference signal and the second oscillating signal to generate the maximum conduction control signal.

In the present invention, a protection circuit is further included, which generates a protection signal according to a feedback signal and a sensing signal to cut off the switching signal, wherein the feedback signal is related to an output voltage of the power supply.

The present invention has the following beneficial effects: the control circuit with frequency modulation used in the power supply of the present invention includes an adjustable charging circuit, an oscillating signal generating circuit and a switching circuit, and the adjustable charging circuit generates complex numbers according to the first oscillating signal. The charging signal is used for the oscillating signal generation circuit to generate the second oscillating signal according to these charging signals, and modulate the second oscillating signal according to these charging signals, and the switching circuit generates the maximum conduction control signal according to the second oscillating signal, because the first The second oscillating signal can be modulated by these charging signals, so the switching period of the maximum conduction control signal can be modulated, and the frequency of the power supply can be modulated to reduce the electromagnetic interference of the power supply.

Description of drawings

FIG. 1 is a circuit diagram of a prior art power supply;

FIG. 2 is a waveform diagram of a prior art power supply;

3 is a circuit diagram of a power supply including a control circuit with frequency modulation according to a preferred embodiment of the present invention;

Fig. 4 is the circuit diagram of the frequency generator of a preferred embodiment of the present invention; And

5 is the waveforms of the first oscillating signal, clearing signal, sampling signal, holding signal and reference current of the control circuit with frequency modulation of the present invention.

[Simple description of figure number]

10 control chip 11 first comparator

12 Second comparator 13 First NAND gate

14 Second NAND gate 15 Comparator

16 AND Gate 17 Inverter

18 AND Gate 19 Comparator

20 control chip 30 sampling circuit

31 Discharge switch 32 Buffer

34 sampling switch 36 holding capacitor

40 Adjust charging circuit 50 Oscillating signal generating circuit

52 First Comparator 54 Second Comparator

56 The first NAND gate 58 The second NAND gate

60 Comparator 62 Resistor

70 Comparator 72 Inverter

74 AND Gate 76 AND Gate

80 Comparator 300 Frequency Generator

310 Input Frequency Generating Circuit 311 Hysteresis Inverter

312 Inverter 330 Linear Shift Register

331 flip-flop 332 flip-flop

335 Inverter 339 Exclusive OR Gate

CK Input Frequency Signal C _B Capacitance

C _O output capacitor C _OSC oscillation capacitor

C _T capacitor D _O rectifier

I _C1 charging signal I _C2 charging signal

I _C3 charging signal I _C4 charging signal

I _Cn charging signal I _CB charging current source

I _DCH Discharge Current Source I _P Switching Current

I _R reference current M ₁ frequency control signal

M _n frequency control signal N _P primary side winding

N _S secondary winding PLS pulse signal

Q1 Power switch R _S sense resistor

R _T Resistor SMP Hold Signal

CLR Clear signal V _SP Sample signal

S _D discharge switch S _DB discharge switch

S _MAX maximum conduction control signal T1 Transformer

V _CC supply voltage V _DD voltage source

V _FB feedback signal V _G switching signal

V _H high threshold signal V _IN input voltage

V _L low threshold signal V _O output voltage

V _OSC oscillating signal V _OSC1 first oscillating signal

V _OSC2 second oscillation signal VR ₁ reference voltage

V _R2 reference signal V _S current signal

X ₁ switch X ₂ switch

X ₃ switch X _n switch

W ₁ Transistor W ₂ Transistor

W ₃ Transistor W ₄ Transistor

W ₅ Transistor W _n Transistor

Detailed ways

In order to enable the examiner to have a further understanding and understanding of the structural features and achieved effects of the present invention, the preferred embodiments and accompanying drawings are used for detailed descriptions, as follows:

Please refer to FIG. 3 , which is a circuit diagram of a preferred embodiment of the present invention applied to a power supply. As shown in the figure, the power supply includes a transformer T1 that transfers energy from a primary side to a secondary side to provide a regulated output voltage V _O . The primary side and the secondary side of the transformer T1 respectively have a primary side winding N _P and a secondary side winding N _S , one end of the primary side winding N _P is coupled to an input voltage V _IN , and the other end of the primary side winding N _P Coupled to a power switch Q1, the power switch Q1 is connected in series with a sensing component, the sensing component is a sensing resistor R _S in this embodiment, one end of the power switch Q1 is coupled to one end of the sensing resistor R _S , and the sensing resistor The other end of R _S is coupled to the ground end, and the sensing resistor R _S is used to sense a switching current I _P of the power switch Q1 to generate a current signal V _S . The aforementioned power switch Q1 is used to switch the transformer T1 to control the output of the power supply, and a preferred embodiment thereof is a transistor. One end of the secondary winding _NS of the transformer T1 is coupled to one end of a rectifier D _O , and an output capacitor C _O is coupled between the other _end of the rectifier D O and the other end of the secondary winding _NS . The output capacitor C _O It is also coupled to the output terminal of the power supply, and the output terminal of the power supply is used to provide the output voltage V _O .

Referring again to FIG. 3 , the control circuit of the present invention is used to generate a switching signal V _G to control the power switch Q1 , and then switch the transformer T1 . The control circuit of the present invention includes a control chip 20, which is externally coupled to a resistor R _T and a capacitor C _T , the resistor R _T and the capacitor C _T are connected in series, the resistor R _T is coupled to a reference voltage V _R1 , and the capacitor C _T is coupled to Connected to the ground terminal, the reference voltage V _R1 is used to charge the capacitor C _T through the resistor _RT . The control chip 20 includes a discharge switch 31, one end of which is coupled to the capacitor _CT , and the other end of the discharge switch 31 is coupled to the ground for discharging the capacitor _CT . The discharge switch 31 is controlled by a clear signal CLR, Refer to Figure 5. There are many ways to generate the clear signal CLR, and one embodiment can be generated by the internal circuit of the control chip 20, which is a commonly used technology and will not be described in detail here. As mentioned above, the resistor R _T , the capacitor C _T and the discharge switch 31 are a charging and discharging circuit for charging and discharging the capacitor C _T according to the reference voltage V _R1 and the discharging switch 31 to generate a first oscillating signal V _OSC1 . An oscillating signal V _OSC1 is a sawtooth signal.

Referring to FIG. 3 again, the control chip 20 of the present invention further includes a sampling circuit 30 , an adjustable charging circuit 40 , and an oscillation signal generating circuit 50 . The sampling circuit 30 includes a buffer 32 , a sampling switch 34 and a holding capacitor 36 for sampling the first oscillating signal V _OSC1 to generate a holding signal SMP. The positive input terminal of the buffer 32 is coupled to the capacitor C _T to receive the first oscillating signal V _OSC1 , the output terminal of the buffer 32 is coupled to the negative input terminal of the buffer 32 , and one terminal of the sampling switch 34 is coupled to the buffer 32 The holding capacitor 36 is coupled between the other end of the sampling switch 34 and the ground. The sampling switch 34 is controlled by a sampling signal V _SP , as shown in FIG. 5 . There are many ways to generate the sampling signal V _SP , and one embodiment can be generated by the internal circuit of the control chip 20 , which is a commonly used technology and will not be described in detail here. The buffer 32 is used to buffer the first oscillating signal V _OSC1 for sampling by the sampling switch 34 and the sampling signal V _SP and for the holding capacitor 36 to generate the holding signal SMP.

Following the above, the hold signal SMP is sent to a conversion circuit to convert the hold signal SMP into a reference current I _R , and the conversion circuit is a voltage-current conversion circuit in this embodiment. The conversion circuit includes a comparator 60 and a resistor 62, the positive input of the comparator 60 receives the hold signal SMP, the negative input of the comparator 60 is coupled to the output of the comparator 60, and the resistor 62 is coupled to the output of the comparator 60 terminal and ground terminal.

_Referring to FIG. 3 again, _{the adjustable charging circuit 40 includes complex current mirrors, complex switches X 1 . .} . ₁ ... W _n sources are coupled to a voltage source V _DD , the gates of these transistors W ₁ ... W _n are coupled together with the drain of transistor W ₁ , and the drain of transistor W ₁ receives a reference The current I _R is used for the current mirrors to generate a plurality of charging signals I _C1 ... I _Cn , and the charging signals I _C1 ... I _Cn are charging currents with different magnitudes. The drains of the transistors W ₃ ...W _n are coupled to the switches X ₁ ...X _n . The frequency generator 300 is used to generate complex frequency control signals M ₁ ... M _n to control the on and off of the switches X ₁ ... X _n , that is, the current mirrors are based on the frequency control signals M ₁ ... M _n to generate the charging signals I _C2 ... I _Cn .

Referring to FIG. 3 again, the oscillating signal generating circuit 50 is used to generate a second oscillating signal V _OSC2 according to the charging signals I _C1 . . . I _Cn . It includes an oscillating capacitor C _OSC , a discharge switch _SD , a discharge current source _IDCH , a first comparator 52 , a second comparator 54 and a flip-flop, and the flip-flop includes a first NAND gate 56 and a second NAND gate 58 . The oscillating capacitor C _OSC is coupled between the adjustable charging circuit 40 and the ground terminal, and the charging signals I _C1 . . . I _Cn charge the oscillating capacitor C _OSC . The discharge switch _SD is coupled between the oscillating capacitor C _OSC and the discharge current source _IDCH , and the discharge current source _IDCH is coupled to the ground terminal for generating a discharge current to discharge the oscillating capacitor C _OSC . In the present invention, the oscillating capacitor C _OSC is charged and discharged by the charging signals _{I C1} . . . I _Cn and the discharge current source _IDCH to generate the second oscillating signal V _OSC2 , which is a sawtooth signal. Since the charging signals I _C2 ... I _Cn are controlled by the frequency control signals M ₁ ... M _n , the amount of charging the oscillating capacitor C _OSC can be adjusted, thus the second oscillation can be adjusted. Signal V _OSC2 .

Following the above, the positive input terminal of the first comparator 52 receives a high threshold signal V _H , the negative input terminal of the first comparator 52 receives the second oscillating signal V _OSC2 , and the first comparator 52 compares the second oscillating signal V _OSC2 with The threshold signal V _H is high, and a first comparison signal is generated at the output terminal. The positive input terminal and the negative input terminal of the second comparator 54 respectively receive the second oscillating signal V _OSC2 and a low threshold signal V _L , compare the second oscillating signal V _OSC2 with the low threshold signal V _L , and generate a The second comparison signal. The first comparison signal and the second comparison signal are sent to the flip-flop to generate a pulse signal PLS. The output terminal of the first comparator 52 is coupled to the first input terminal of the first NAND gate 56, that is, the first input terminal of the first NAND gate 56 receives the first comparison signal, and the output terminal of the second comparator 54 is coupled to the first input terminal of the first NAND gate 56. Connected to the first input end of the second NAND gate 58, to transmit the second comparison signal to the first input end of the second NAND gate 58, the output end of the second NAND gate 58 is coupled to the first NAND gate The second input terminal of the first NAND gate 56 and the output terminal of the first NAND gate 56 are coupled to the second input terminal of the second NAND gate 58 to generate a pulse signal PLS for controlling the discharge switch _SD .

Referring to FIG. 3 again, the control chip further includes a switching circuit for generating a switching signal V _G according to the second oscillating signal V _OSC2 to control the power switch Q1 , that is, to control the output of the power supply. The switching circuit includes a comparator 70, an inverter 72 and AND gates 74, 76. The negative input terminal of the comparator 70 receives the second oscillating signal V _OSC2 , and the positive input terminal of the comparator 70 receives a reference signal of a fixed level. V _R2 is used to compare the reference signal V _R2 with the second oscillating signal V _OSC2 to generate the switching signal V _G . The input end of the inverter 72 receives the pulse signal PLS, the output end of the comparator 70 and the output end of the inverter 72 are respectively coupled to the first input end and the second input end of the AND gate 74, and the output end of the AND gate 74 Generate a maximum conduction control signal S _MAX .

Following the above, the first input end of the AND gate 76 receives the maximum conduction control signal S _MAX , the maximum conduction control signal S _MAX is used to control a maximum conduction time T _{ON, MAX} of the switching signal V _G , that is, to control the power switch Q1 The maximum on-time to control the maximum output power of the power supply. The switching circuit of the present invention generates the switching signal V _G according to the second oscillating signal V _OSC2 , because the oscillating signal generating circuit 50 will modulate the second oscillating signal V _OSC2 according to the charging signals I _C1 ... I _Cn , so the switching signal The switching period of V _G is also modulated, so that the frequency of the power supply can be adjusted, so that the electromagnetic interference of the power supply can be reduced, and the performance of the power supply can be improved.

In order to further protect the power supply, the present invention further includes a protection circuit, which has a comparator 80, the positive input terminal of the comparator 80 receives a feedback signal V _FB , and the negative input terminal of the comparator 80 receives the current signal V _S , the comparator 80 compares the feedback signal V _FB and the current signal V _S to generate a protection signal at the output terminal, and transmits it to the second input terminal of the AND gate 76 to periodically cut off the switching signal V _G to The conduction time T _ON of the power switch Q1 is determined. The on-time T _ON of the switching signal V _G is determined by the comparator 80 , and the maximum on-time T _{ON, MAX} of the switching signal V _G is determined by the maximum on-time control signal S _MAX through the AND gate 76 . It is known that the feedback signal V _FB can be coupled to the output terminal of the power supply by an optocoupler or a feedback circuit to detect the output voltage V _O of the power supply. Therefore, the feedback signal V _FB is Correlates to the output voltage V _O .

Please refer to FIG. 4 , which is a circuit diagram of a frequency generator according to a preferred embodiment of the present invention. As shown in the figure, the frequency generator 300 includes an input frequency generating circuit 310 and a linear shift register 330, the input frequency generating circuit 310 is used to generate an input frequency signal CK, and the input frequency generating circuit 310 includes a charging current source I _CB , which is coupled to a supply voltage V _CC . A capacitor C _B is coupled between the charging current source I _CB and the ground, and the charging current source I _CB is used to charge the capacitor C _B. A discharge switch S _DB is connected in parallel with the capacitor C _B for discharging the capacitor C _B , and the discharge switch S _DB is controlled by the input frequency signal CK. The input end of a hysteresis inverter 311 is coupled to the capacitor C _B , the input end of an inverter 312 is coupled to the output end of the hysteresis inverter 311 , and the output end of the inverter 312 generates the input frequency signal CK .

Referring to FIG. 4 again, the linear shift register 330 is used to generate the frequency control signals M ₁ . . . M _n according to the input frequency signal CK. The linear shift register 330 includes complex flip-flops 331, 332...335 and a mutually exclusive OR gate 339, these flip-flops 331, 332...335 are connected in series, these flip-flops 331, 332.. The frequency input terminal CK of .335 receives the input frequency signal CK, the output terminals Q of these flip-flops 331, 332...335 are connected to the input terminal D, and the output of these flip-flops 331, 332...335 The terminal Q generates these frequency control signals M ₁ ...M _n and transmits them to the input terminal of the exclusive OR gate 339, and the output terminal of the exclusive OR gate 339 is coupled to the input terminal D of the flip-flop 331, these The reset terminal R of the flip-flops 331, 332...335 receives a reset signal RST for resetting the flip-flops 331, 332...335. There are many ways to generate the reset signal RST. One embodiment can be generated by controlling the internal circuit of the chip 20 , which is a commonly used technology and will not be described in detail here.

Please refer to FIG. 5 , which is the waveforms of the first oscillating signal, clearing signal, sampling signal, holding signal and reference current of the control circuit with frequency modulation of the present invention. As shown in the figure, by adjusting the resistance and capacitance of the externally coupled resistor R _T and capacitor C _T (refer to Figure 3), the first oscillation signal V _OSC1 with a sawtooth waveform with different slopes can be obtained. The sampling and holding of the circuit 30 (refer to FIG. 3 ) can obtain the holding signal SMP and the reference current I _R of different magnitudes. In other words, the first oscillating signal V _OSC1 of the sawtooth waveform with a larger slope can be sampled to a larger hold signal SMP to further obtain a larger reference current I _R , and this larger reference current I _R passes through the The current mirrors of these current mirrors generate larger charging signals I _C1 ... _{I Cn to} charge the oscillating capacitor C _OSC according to the frequency control signals M ₁ ... M n of FIG. A smaller switching period and a higher switching frequency are obtained. Conversely, the first oscillating signal V _OSC1 with a sawtooth waveform with a smaller slope can be sampled to a smaller holding signal SMP to further obtain a smaller reference current I _R , and the smaller reference current I _R passes through the current mirrors Current mapping, and according to the frequency control signals M ₁ ... M _n , the smaller charging signals I _C1 ... I _Cn are generated to charge the oscillating capacitor C _OSC , so that a larger switching period and a higher frequency can be obtained. low switching frequency.

To sum up, the control circuit with frequency modulation used in the power supply of the present invention includes an adjustable charging circuit, an oscillating signal generating circuit and a switching circuit, and the adjustable charging circuit generates multiple charging signals according to the first oscillating signal , for the oscillating signal generation circuit to generate the second oscillating signal according to the charging signals, and modulate the second oscillating signal according to the charging signals, and the switching circuit generates the maximum conduction control signal according to the second oscillating signal, because the second oscillating The signal can be modulated by these charging signals, so the switching period of the maximum conduction control signal can be modulated, and the frequency of the power supply can be modulated to reduce the electromagnetic interference of the power supply.

In summary, it is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. All changes made in accordance with the shape, structure, characteristics and spirit of the scope of the claims of the present invention are equivalent to Modifications should be included within the scope of the claims of the present invention.

Claims (19)

1. control circuit that is used for the tool frequency modulating of power supply unit is characterized in that it comprises:

One sample circuit, the one first concussion signal of taking a sample produces one and keeps signal;

One can adjust charging circuit, keeps signal to produce plural number charging signal according to this;

One concussion signal generating circuit produces one second concussion signal according to those charging signals, and this concussion signal generating circuit is according to this second concussion signal of those charging signal changings; And

One switches circuit, produces a maximum conducting controlling signal according to this second concussion signal, and this maximum conducting controlling signal is in order to determining one to switch a switching cycle of signal, and controls the peak power output of this power supply unit;

Wherein, this first concussion signal and this second concussion signal are the sawtooth waveforms signal;

This control circuit also comprises a change-over circuit, and it changes this maintenance signal is a reference current, and provides this reference current can adjust charging circuit to this, and to produce those charging signals, and this charging signal is a current signal.

2. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that wherein this change-over circuit is a voltage-current converter circuit.

3. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that, more comprises a charge-discharge circuit, and it produces this first concussion signal according to a reference voltage.

4. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that wherein this sample circuit comprises:

One keeps electric capacity, produces this maintenance signal; And

One sampling switch couples this maintenance electric capacity and this first concussion signal of taking a sample, and produces this maintenance signal for this maintenance electric capacity.

5. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 4, it is characterized in that wherein this sample circuit more comprises a buffer, it cushions this first concussion signal, and coupling this sampling switch, this sampling switch sampling is through this first concussion signal of buffering.

6. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that, wherein this can be adjusted charging circuit and comprises:

One frequency generator produces plural FREQUENCY CONTROL signal; And

The power plural current mirror produces those charging signals according to those FREQUENCY CONTROL signals.

7. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 6 is characterized in that wherein this frequency generator comprises:

One incoming frequency produces circuit, produces an incoming frequency signal; And

One linear shift register according to this incoming frequency signal, produces those FREQUENCY CONTROL signals.

8. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that, wherein those charging signals are the charging current that varies in size.

9. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that, wherein this concussion signal generating circuit comprises:

One concussion electric capacity according to those charging signals, produces this second concussion signal;

One discharging current source produces a discharging current, so that this is shaken capacitor discharge;

One discharge switch is coupled between this concussion electric capacity and this discharging current source;

One first comparator receives a high critical signal and this second concussion signal, produces one first and compares signal;

One second comparator receives a low critical signal and this second concussion signal, produces one second and compares signal; And

One flip-flop receives this first comparison signal and this second comparison signal, produces a pulse wave signal, to control this discharge switch.

10. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1 is characterized in that wherein this commutation circuit comprises a comparator, and it is a reference signal and this second concussion signal relatively, to produce this maximum conducting controlling signal.

11. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 1; it is characterized in that; more comprise a protective circuit; it produces a protection signal according to a back coupling signal and a sensing signal; to switch signal by this, wherein this back coupling signal is relevant to an output voltage of this power supply unit.

12. a control circuit that is used for the tool frequency modulating of power supply unit is characterized in that it comprises:

One can adjust charging circuit, produces plural number charging signal according to one first concussion signal;

One concussion signal generating circuit produces one second concussion signal according to those charging signals, and this concussion signal generating circuit is according to this second concussion signal of those charging signal changings; And

One switches circuit, produces a maximum conducting controlling signal according to this second concussion signal, and this maximum conducting controlling signal is in order to determining one to switch a switching cycle of signal, and controls the peak power output of this power supply unit;

Wherein, this first concussion signal and this second concussion signal are the sawtooth waveforms signal;

This control circuit also comprises a change-over circuit, and it changes this first shake

Swinging signal is a reference current, and provides this reference current can adjust charging circuit to this, and to produce those charging signals, and this charging signal is a current signal.

13. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 12 is characterized in that, more comprises a charge-discharge circuit, it produces this first concussion signal according to a reference voltage.

14. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 12 is characterized in that, wherein this can be adjusted charging circuit and comprises:

One frequency generator produces plural FREQUENCY CONTROL signal; And

The power plural current mirror produces those charging signals according to those FREQUENCY CONTROL signals.

15. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 14 is characterized in that wherein this frequency generator comprises:

One incoming frequency produces circuit, produces an incoming frequency signal; And

One linear shift register according to this incoming frequency signal, produces those FREQUENCY CONTROL signals.

16. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 12 is characterized in that, wherein those charging signals are the charging current that varies in size.

17. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 12 is characterized in that, wherein this concussion signal generating circuit comprises:

One concussion electric capacity according to those charging signals, produces this second concussion signal;

One discharging current source produces a discharging current, so that this is shaken capacitor discharge;

One discharge switch is coupled between this concussion electric capacity and this discharging current source;

One first comparator receives a high critical signal and this second concussion signal, produces one first and compares signal;

One second comparator receives a low critical signal and this second concussion signal, produces one second and compares signal; And

One flip-flop receives this first comparison signal and this second comparison signal, produces a pulse wave signal, to control this discharge switch.

18. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 12 is characterized in that wherein this commutation circuit comprises a comparator, it is a reference signal and this second concussion signal relatively, to produce this maximum conducting controlling signal.

19. the control circuit that is used for the tool frequency modulating of power supply unit according to claim 12; it is characterized in that; more comprise a protective circuit; it produces a protection signal according to a back coupling signal and a sensing signal; to switch signal by this, wherein this back coupling signal is relevant to an output voltage of this power supply unit.

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