CN100449918C - DC-DC conversion circuit with adjustable output voltage - Google Patents

Abstract

The present invention provides a DC-DC conversion circuit, which includes a DC power supply, a DC-DC converter, a power management chip and a load, wherein the load can be a backlight source in a liquid crystal display. The power management chip controls the DC-DC converter to convert the DC voltage supplied by the DC power supply into an output voltage to supply the load, and controls the DC-DC converter to adjust its output voltage according to the minimum voltage change actually required by the load, so that the output voltage reaches the minimum voltage actually required by the load.

Description

DC to DC conversion circuit with adjustable output voltage

technical field

The invention relates to a direct current to direct current conversion circuit with adjustable output voltage, in particular to a direct current to direct current conversion circuit which can adjust the output voltage to the minimum voltage required by the load.

Background technique

As we all know, a backlight source is needed to light up the display screen in a general liquid crystal display, and the backlight source is the main power-consuming component in a liquid crystal display. If the power consumption of the backlight source can be effectively reduced, the power consumption of the liquid crystal display can be greatly reduced. overall power consumption. Therefore, how to reduce the power consumption of the backlight source has become one of the important issues in the circuit design of the liquid crystal display.

Please refer to FIG. 1 , which is a structural diagram showing an existing circuit for supplying load voltage, which includes a DC-to-DC converter 104 converting the voltage provided by the DC power supply 102 into an output voltage Vout to supply the load 108, where The load 108 can be a backlight of a liquid crystal display, and the backlight can be a plurality of light emitting diodes. A current feedback device 110 controls the current flowing through the load 108 to keep the current flowing through the load 108 stable. At the same time, the output voltage Vout is also supplied to the series connected resistors R1 and R2 so that the series connected resistors R1 and R2 divide the output voltage Vout and provide a feedback voltage Vfb between the resistors R1 and R2 to a power management chip 106 . The power management chip 106 controls the DC-DC converter 104 according to the feedback voltage Vfb to adjust the output voltage Vout to achieve the voltage actually required by the load 108 .

However, since the series resistors R1 and R2 are set to a constant value to match the voltage required by the load 108 . When the actual voltage required by the load 108 decreases, the output voltage Vout is still a constant value at this time, and the feedback voltage Vfb generated by the voltage division of the series resistors R1 and R2 will not change, so the power management chip will not be able to 106 controls the DC-DC converter 104 to actually reduce the output voltage Vout. At this time, the excessively high output voltage Vout will not only increase the power consumption of the load 108 , but also shorten the service life of the load 108 .

Therefore, if the change in the voltage required by the load 108 can be effectively fed back to the power management chip 106 to control the DC-to-DC converter 104 to generate an output voltage Vout suitable for the load 108, not only can the power consumption of the load 108 be effectively reduced The amount can also prolong the service life of the load 108.

Contents of the invention

Therefore, the main purpose of the present invention is to provide a DC-to-DC conversion circuit with adjustable output voltage, which can adjust its output voltage to the minimum voltage required by the load, so as to effectively reduce the power consumption of the load and prolong the use of the load. life.

According to the above object of the present invention, the present invention provides a DC-to-DC conversion circuit, which includes a DC power supply, a DC-to-DC converter (DC-DC Converter), a power management chip, a load, a controller, a A current control circuit and a resistance variable circuit, wherein the load can be a backlight in a liquid crystal display, and the backlight can be a plurality of light-emitting diodes connected in series. In the DC-to-DC conversion circuit of the present invention, the power management chip controls the DC-to-DC converter to convert the voltage supplied by a DC power supply into an output voltage to supply the load. The current control circuit is used to keep the current flowing through the load steady. When the voltage required by the load changes, its residual voltage will change accordingly, so that the controller can adjust the equivalent resistance value of the resistance variable circuit according to the change of the residual voltage. When the equivalent resistance value of the variable resistance circuit changes, the feedback voltage of the variable resistance circuit will change accordingly. Thereby, the power management chip can control the DC-DC converter to adjust its output voltage according to the change of the feedback voltage, so that the output voltage can reach the minimum voltage required by the load.

The DC-DC conversion circuit of the present invention can also use a voltage control circuit to replace the aforementioned controller and variable resistance circuit, so as to adjust the feedback voltage according to the variation of the residual voltage.

The DC-to-DC conversion circuit of the present invention can effectively feed back to the power management chip according to the actual voltage change required by the load, so as to control the DC-to-DC converter to generate the minimum output voltage actually required by the load, which can not only effectively reduce the load The power consumption can also prolong the service life of the load.

Description of drawings

FIG. 1 is a circuit structure diagram of a DC-DC conversion circuit in the prior art.

FIG. 2 is a circuit structure diagram of the first embodiment of the DC-DC conversion circuit of the present invention.

FIG. 3 is a circuit structure diagram of a second embodiment of the DC-DC conversion circuit of the present invention.

FIG. 4 is a circuit structure diagram of a third embodiment of the DC-DC conversion circuit of the present invention.

Fig. 5 is a detailed circuit diagram of the first embodiment of the present invention.

Fig. 6 is a detailed circuit diagram of a second embodiment of the present invention.

Fig. 7 is a detailed circuit diagram of a third embodiment of the present invention.

Description of reference symbols

202, 302, 402, 502, 602, 702 DC power supply

204, 304, 404, 504, 604, 704 DC to DC converter

206, 306, 406, 506, 606, 706 power management chip

208, 308, 408, 508, 608, 708 load

210, 310, 510, 610 Controller

212, 312, 412, 512, 612, 712 current control circuit

214, 314, 514, 614 Resistance variable circuit

316, 416, 616, 716 Minimum voltage selector

410, 710 Voltage control circuit

Vout Output Voltage

Vfb Feedback voltage

V1, V11, V12...V1n residual voltage

Detailed ways

Please refer to FIG. 2, which is a circuit architecture diagram of a first embodiment of a DC-to-DC conversion circuit of the present invention, which includes: a DC power supply 202, a DC-to-DC converter (DC-DC Converter) 204, and a power management chip 206. A load 208, a controller 210, a current control circuit 212, and a variable resistance circuit 214, wherein the load 208 can be a backlight in a liquid crystal display, and the backlight can be a plurality of light-emitting diodes connected in series . The power management chip 206 can be a pulse-width modulation chip (Pulse-Width Modulator IC, PWM IC). In the first embodiment, the power management chip 206 controls the DC-DC converter 204 to convert the voltage supplied by the DC power supply 202 into an output voltage Vout to supply the load 208 . The current control circuit 212 is used to keep the current flowing through the load 208 stable. When the actual voltage required by the load 208 changes, the residual voltage V1 is also changed accordingly, so that the controller 210 can adjust the equivalent resistance of the variable resistance circuit 214 according to the change of the residual voltage V1. When the equivalent resistance of the resistance variable circuit 214 changes, the feedback voltage Vfb between the series resistor R22 and the resistance variable circuit 214 will change accordingly. The power management chip 206 controls the DC-DC converter 204 to adjust the output voltage Vout according to the change of the feedback voltage Vfb, so that the output voltage Vout can reach the voltage actually required by the load 208 .

For example, when the voltage actually required by the load 208 decreases, the residual voltage V1 will increase, and the controller 210 will increase the equivalent resistance value of the resistance variable circuit 214, so that the resistance between the resistance R22 and the resistance variable circuit 214 The cross voltage becomes larger, that is, the feedback voltage Vfb rises accordingly. At this time, the power management chip 206 makes the DC-DC converter 204 reduce the output voltage Vout according to the rising feedback voltage Vfb, so as to reach the actual required voltage value of the current load 208 . Conversely, when the actual voltage required by the load 208 increases, the residual voltage V1 decreases, so that the controller 210 will reduce the equivalent resistance value of the resistance variable circuit 214, so that the span between the resistor R22 and the resistance variable circuit 214 The voltage becomes smaller, that is, the feedback voltage Vfb decreases accordingly. At this time, the power management chip 206 makes the DC-DC converter 204 increase the output voltage Vout according to the reduced feedback voltage Vfb. Thereby, the DC-DC conversion circuit of the present invention can adjust the output voltage Vout according to the voltage change actually required by the load 208 at any time, so as to keep the output voltage Vout at the minimum voltage value actually required by the load 208 .

Please refer to FIG. 3 , which is a circuit structure diagram of a second embodiment of the DC-to-DC conversion circuit of the present invention, which includes a DC power supply 302, a DC-to-DC converter 304, a power management chip 306, a load 308, a The controller 310 , a current control circuit 312 , a resistance variable circuit 314 and a minimum voltage selector 316 . The difference between the second embodiment and the first embodiment is that the load 208 in the first embodiment is a single string of light-emitting diodes, while the load 308 in the second embodiment is an array of light-emitting diodes, the array of light-emitting diodes includes There are multiple strings of light emitting diodes, and each string of light emitting diodes is a plurality of light emitting diodes connected in series. Since the load 308 in the second embodiment is multiple strings of light-emitting diodes, and the minimum voltage required by each string of light-emitting diodes is different, in order to ensure that each string of light-emitting diodes has enough voltage to maintain normal operation, the DC-to-DC converter The output voltage Vout of 304 must be based on the highest required voltage among the multiple strings of LEDs, and provide the minimum voltage required by these multiple strings of LEDs. Therefore, the lowest residual voltage V11, V12...V1n indicates that the voltage required by the string of LEDs is the highest, so the minimum voltage selector 316 is used to select the residual voltage V11, V12...V1n of each string of LEDs. The lowest one is provided to the controller 310 as a basis for adjusting the equivalent resistance value of the variable resistance circuit 314, and the power management chip 306 controls the DC-to-DC converter 304 to generate the actual required load 308 according to the change of the feedback voltage Vfb. The minimum output voltage Vout.

Please refer to FIG. 4 , which is a circuit structure diagram of a third embodiment of the DC-DC conversion circuit of the present invention. The third embodiment includes a DC power supply 402 , a DC-DC converter 404 , a power management chip 406 , a load 408 , a voltage control circuit 410 , a current control circuit 412 , and a minimum voltage selector 416 . The difference from the foregoing embodiments is that the third embodiment uses the lowest one among the residual voltages V11, V12...V1n of each string of light-emitting diodes selected by the voltage control circuit 410 according to the minimum voltage selector 416. The variation of the residual voltage is used to adjust the cross-voltage of the series resistors R41 and R42, so as to achieve the purpose of adjusting the feedback voltage Vfb. For example, when the required voltage value of the LED with the highest required voltage among multiple strings of LEDs decreases, the residual voltage value of the lowest residual voltage V11, V12 . . . V1n will increase, and the voltage control circuit 410 will The residual voltage increases the total voltage across the series resistors R41 and R42, and the feedback voltage Vfb increases accordingly. At this time, the power management chip 406 makes the DC-DC converter 404 reduce the output voltage Vout according to the rising feedback voltage Vfb, so as to meet the current voltage value required by the load 408 . Conversely, when the required voltage value of the highest required voltage among the multiple strings of LEDs rises, the residual voltage value of the lowest residual voltage V11, V12...V1n will decrease, and the voltage control circuit 410 then The voltage reduces the total voltage across the series resistors R41 and R42, and the feedback voltage Vfb decreases accordingly. At this time, the power management chip 406 increases the output voltage Vout of the DC-DC converter 404 according to the reduced feedback voltage Vfb to meet the current voltage value required by the load 408 .

Please refer to FIG. 5 , which is a detailed circuit diagram of the first embodiment. The power management chip 506 controls the DC-DC converter 504 to convert the voltage supplied by the DC power supply 502 into an output voltage Vout to supply the load 508 , wherein the load 508 can be a single string of LEDs. The current control circuit 512 keeps the current flowing through the load 508 steady. When the actual required voltage of the load 508 changes, the residual voltage V1 will change accordingly, and the controller 510 adjusts the equivalent resistance value of the variable resistance circuit 514 according to the change of the residual voltage V1. In FIG. 5, the controller 510 utilizes the amplifier A5 to inversely amplify the value of the residual voltage V1, and the variable resistance circuit 514 uses the transistor Q51 to adjust the equivalent resistance value of the variable resistance circuit 514 according to the reversely amplified value of the residual voltage V1. , wherein the transistor Q51 can be a bipolar junction transistor (Bipolar Junction Transistor, BJT), a field effect transistor (Field-Effect Transistor, FET) or other types of transistors.

The positive terminal input value of the aforementioned amplifier A5 is a reference voltage Vref, which must be equal to the value of the residual voltage V1, and the reference voltage Vref can be made Vref=V1 by using a proportional-integral controller (PI controller, not shown); The voltage V1 is input to the negative input terminal of the amplifier A5 through the resistor R51. When the actual voltage required by the load 508 decreases, the residual voltage V1 will increase. According to the ratio of the resistors R51 and R52 in the controller 510, the residual voltage V1 will be reversely amplified by the amplifier A5, and then output to the gate of the transistor Q51, so that the gate voltage of the transistor Q51 will increase, so its equivalent resistance will decrease. As the equivalent resistance of the variable resistance circuit 514 decreases, the voltage across the variable resistance circuit 514 also decreases, that is, the feedback voltage Vfb decreases. At this moment, the power management chip 506 makes the DC-DC converter 504 increase its output voltage Vout according to the reduced feedback voltage Vfb. Therefore, by adjusting the output voltage Vout, the output voltage Vout can be maintained at the minimum voltage value actually required by the load 508 . In Fig. 5, the design of the protection circuit is also included. When the circuit fault makes the transistor Q51 fully turned on, the resistor R55 can limit its maximum output voltage to achieve the purpose of overvoltage protection; and when the circuit fault makes the transistor Q51 completely cut off, The resistor R56 can prevent the feedback voltage Vfb from floating and cause circuit malfunction.

Please refer to FIG. 6 , which is a detailed circuit diagram of the second embodiment. Like the previous introduction to the second embodiment, the load 608 in FIG. 6 is an array of light emitting diodes, the array of light emitting diodes includes multiple strings of light emitting diodes, and each string of light emitting diodes is a plurality of light emitting diodes connected in series. Therefore, it is necessary to provide a minimum voltage selector 616 to select the lowest residual voltage value among the strings of LEDs. The minimum voltage selector 616 connects the ends of each string of light-emitting diodes to a diode, so that the residual voltage V11, V12...V1n of each string of light-emitting diodes is coupled to the input end of the controller 610 in a reverse-biased manner through the diode, In this way, the minimum residual voltage value of the residual voltages V11 , V12 . . . V1n can be selected.

Please refer to FIG. 7, which is a detailed circuit diagram of the third embodiment. In FIG. 7 , the present invention uses a voltage control circuit 710 to determine the lowest residual voltage V11, V12...V1n of each string of light-emitting diodes selected by the minimum voltage selector 716 according to the change amount of the lowest residual voltage. Adjust the voltage across the series resistors R75 and R76 to achieve the purpose of adjusting the feedback voltage Vfb. The voltage control circuit 710 utilizes an amplifier A7 to input the lowest of the residual voltages V11, V12 . The amplifier A7 amplifies the lowest residual voltage value according to the ratio of the resistors R73 and R74 to adjust the voltage across the series resistors R75 and R76 , thereby adjusting the feedback voltage Vfb. When the required voltage value of the highest required voltage among multiple strings of light-emitting diodes decreases, the residual voltage value of the lowest residual voltage V11, V12...V1n will increase, and the voltage control circuit 710 amplifies the residual voltage value so that the series resistance As the total cross-voltage of R75 and R76 increases, the feedback voltage Vfb increases accordingly. At this time, the power management chip 706 makes the DC-DC converter 704 lower its output voltage Vout according to the rising feedback voltage Vfb, so as to reach the actual required voltage value of the current load 708 .

Compared with the prior art, the DC-DC conversion circuit of the present invention can effectively feed back to the power management chip according to the voltage change actually required by the load to control the DC-DC converter to generate the minimum output voltage actually required by the load. Not only can effectively reduce the power consumption of the load, but also prolong the service life of the load.

The above is only a preferred embodiment of the present invention, and all equivalent modifications or changes made by those familiar with the technology of the present invention according to the spirit of the present invention are covered by the scope of the appended patent application.

Claims (19)

1. a direct current is to DC converting circuit, and it comprises:

One load;

One direct current is to direct current transducer, converts the direct voltage of a direct current power supply to an output voltage with offered load;

One resistance-variable circuit, it has variable equivalent resistance, and exports a feedback voltage according to this equivalence resistance value;

One controller changes the equivalent resistance of adjusting this resistance-variable circuit according to the residual voltage of this load, and then adjusts the feedback voltage of this resistance-variable circuit output; And

One power management chip in order to the feedback voltage of being exported according to this resistance-variable circuit, is controlled this direct current direct current transducer is adjusted its output voltage to the actual required voltage swing of this load.

2. direct current as claimed in claim 1 is to DC converting circuit, and wherein, this controller has an amplifier, in order to amplify this residual voltage; This resistance-variable circuit has a transistor, changes this transistorized equivalent resistance in order to the residual voltage according to this amplification.

3. direct current as claimed in claim 2 is to DC converting circuit, and wherein, this resistance-variable circuit comprises a protective circuit in addition, in order to when this transistor breaks away from its normal range of operation, avoids this direct current that DC converting circuit is produced misoperation.

4. direct current as claimed in claim 3 is to DC converting circuit, and wherein, it is in parallel with this transistor that this protective circuit has at least one resistance.

5. direct current as claimed in claim 1 is to DC converting circuit, and wherein, this load is a single string light-emitting diode, and it comprises the light-emitting diode of a plurality of series connection.

6. direct current as claimed in claim 1 is to DC converting circuit, and wherein, this load is an array formula light-emitting diode, and it comprises many string light-emitting diodes, and every string light-emitting diode has the light-emitting diode of a plurality of series connection.

7. direct current as claimed in claim 6 is to DC converting circuit, and other comprises a minimum voltage selector, in order to selecting minimum residual voltage in these many string light-emitting diodes, and exports this minimum residual voltage to this controller.

8. direct current as claimed in claim 7 is to DC converting circuit, wherein, this minimum voltage selector has a plurality of diodes, each diode is connected to respectively respectively goes here and there the tail end of light-emitting diode, makes respectively to go here and there the residual voltage of light-emitting diode and be coupled to this controller by this diode in the reverse bias mode.

9. direct current as claimed in claim 1 is to DC converting circuit, and wherein, this power management chip is a pulse width modulating chip.

10. direct current as claimed in claim 1 is to DC converting circuit, and other comprises a current control circuit, uses so that the electric current of this load of flowing through keeps stable.

11. a direct current is to DC converting circuit, it comprises:

One load;

Resistor assembly;

One direct current is to direct current transducer, converts an output voltage to for should load in order to the direct voltage that a direct current power supply is supplied;

One voltage control circuit changes the cross-pressure adjusted in this resistor assembly to produce a feedback voltage in order to the residual voltage according to this load; And

One power management chip in order to the feedback voltage of exporting according to this resistor assembly, is controlled this direct current direct current transducer is adjusted its output voltage to the actual required voltage swing of this load.

12. direct current as claimed in claim 11 is to DC converting circuit, wherein, this resistor assembly comprises two resistance of series connection, make the cross-pressure of voltage control circuit, produce a feedback voltage with the tie point between two resistance of this series connection according to the series circuit two ends of two resistance compositions of this series connection of residual voltage variation adjustment of this load.

13. direct current as claimed in claim 12 is to DC converting circuit, wherein, this voltage control circuit has an amplifier, and in order to amplifying this residual voltage, and the residual voltage that will amplify exports the series circuit that two resistance of this series connection are formed to.

14. direct current as claimed in claim 11 is to DC converting circuit, wherein, this load is a single string light-emitting diode, and it comprises the light-emitting diode of a plurality of series connection.

15. direct current as claimed in claim 11 is to DC converting circuit, wherein, this load is an array formula light-emitting diode, and it comprises many string light-emitting diodes, and every string light-emitting diode has the light-emitting diode of a plurality of series connection.

16. direct current as claimed in claim 15 is to DC converting circuit, other comprises a minimum voltage selector, in order to selecting minimum residual voltage in these many string light-emitting diodes, and exports this minimum residual voltage to voltage control circuit.

17. direct current as claimed in claim 16 is to DC converting circuit, wherein, this minimum voltage selector has a plurality of diodes, each diode is connected to respectively respectively goes here and there the tail end of light-emitting diode, makes respectively to go here and there the residual voltage of light-emitting diode and be coupled to this voltage control circuit by this diode in the reverse bias mode.

18. direct current as claimed in claim 11 is to DC converting circuit, wherein, this power management chip is a pulse width modulating chip.

19. direct current as claimed in claim 11 is to DC converting circuit, other comprises a current control circuit, uses so that the electric current of this load of flowing through keeps stable.

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