Switch control circuit under light load, switch control method and switch power supply

Abstract

The invention provides a switch control circuit, a switch control method and a switch power supply under light load, the switch control circuit comprises a voltage adjusting circuit and a switch driving circuit, the voltage adjusting circuit receives a first voltage representing the load size of the switch power supply and is used for adjusting a power supply voltage output by the voltage adjusting circuit according to the first voltage; the power supply voltage is in positive correlation with the first voltage; the switch driving circuit is connected with the control end of a power tube in the switch power supply, receives a switch control signal and is used for controlling the on-off state of the power tube, and the power supply voltage is used for supplying power to the switch driving circuit. During light load, the power supply voltage of the switch driving circuit can be continuously changed, so that charge and discharge charges of the grid electrode of the power tube are reduced, and the efficiency during light load is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a switch control circuit, a switch control method and a switch power supply under light load. Background Art

[0002] The switching power supply converts the input voltage to supply power to the load. When the switching power supply is lightly loaded (such as when the computer is in standby mode or the light is low), the loss caused by driving the power tube of the switching power supply greatly reduces the efficiency of the switching power supply when it is lightly loaded. The existing practice is to switch only some of the power tubes when it is lightly loaded, thereby reducing the charging and discharging of the gate of the power tube to reduce the switching loss. However, such hard switching will cause a sudden change in the current sampling ratio, which will cause instability in the switching power supply system. When the boundary load is hard-cut, the current of the power tube will fluctuate greatly, and the current sampling ratio will change back and forth, which will cause loop instability, resulting in output oscillation, switch device failure, high noise and other problems. Summary of the invention

[0003] The purpose of the present invention is to provide a switch control circuit, a switch control method and a switch power supply under light load, which are used to solve the problems of large power tube current fluctuation and system loop instability under light load in the prior art.

[0004] The present invention provides a switch control circuit under light load, which is used in a switching power supply, and includes a voltage adjustment circuit and a switch driving circuit. The voltage adjustment circuit receives a first voltage representing the load size of the switching power supply, and is used to adjust the output power supply voltage according to the first voltage, and the power supply voltage is positively correlated with the first voltage;

[0005] The switch driving circuit is connected to the control end of the power tube in the switching power supply, receives a switch control signal, and is used to control the switch state of the power tube. The supply voltage is used to power the switch driving circuit.

[0006] Optionally, when the switching power supply load enters a light load state, the voltage adjustment circuit reduces the supply voltage.

[0007] Optionally, when the switching power supply load enters a light load, the charge and discharge charge of the gate of the power tube decreases as the supply voltage decreases.

[0008] Optionally, within a preset load range, the supply voltage is positively correlated with the first voltage.

[0009] Optionally, when the switching power supply load enters a light load state and the switch control signal is valid, the power tube is in an on state.

[0010] Optionally, it further includes a first operational amplifier, which is used to perform operational amplification on the output feedback signal of the switching power supply and a reference signal to obtain a compensation voltage, wherein the compensation voltage is positively correlated with the load, and the compensation voltage is used as the first voltage;

[0011] A control unit receives the compensation voltage and obtains the switch control signal according to the compensation voltage.

[0012] Optionally, the power tube includes a first power tube and a second power tube, and the switch driving circuit includes a first switch driving circuit and a second switch driving circuit;

[0013] The first switch driving circuit is connected to the control end of the first power tube and is used to drive the first power tube; the second switch driving circuit is connected to the control end of the second power tube and is used to drive the second power tube;

[0014] The supply voltage supplies power to the first switch driving circuit and the second switch driving circuit respectively.

[0015] Optionally, the switch control signal includes a first switch control signal and a second switch control signal; the first switch drive circuit and the second switch drive circuit respectively receive the first switch control signal and the second switch control signal to respectively control the switch states of the first power tube and the second power tube; the switch states of the first power tube and the second power tube are complementary.

[0016] Optionally, the first end of the first power tube receives an input voltage, the second end of the first power tube is connected to the first end of the second power tube, and the second end of the second power tube is grounded;

[0017] The first switch driving circuit uses the common connection terminal of the first power tube and the second power tube as a reference ground, and the second switch driving circuit uses the ground terminal as a reference ground.

[0018] Optionally, the voltage adjustment circuit receives a power supply voltage and a first voltage to adjust the power supply voltage according to a magnitude of the first voltage, thereby obtaining the supply voltage;

[0019] The power supply voltage is obtained by taking power from the input terminal or the switch node of the switching power supply.

[0020] Optionally, the voltage adjustment circuit includes a first adjustment tube and a second operational amplifier, the first end of the first adjustment tube receives the power supply voltage, the second end of the first adjustment tube is grounded through a first resistor and a second resistor connected thereto, and a common connection end of the first resistor and the second resistor outputs a sampling voltage;

[0021] The second operational amplifier performs operational amplification on the first voltage and the sampled voltage, and an output end of the second operational amplifier is connected to a control end of the first adjustment tube;

[0022] The second end of the first adjustment tube outputs the supply voltage.

[0023] Optionally, the voltage adjustment circuit includes a first adjustment circuit, a second adjustment circuit, a second adjustment tube and a current source, the first adjustment circuit and the second adjustment circuit are respectively connected to the control end of the second adjustment tube, the first adjustment circuit generates a first current flowing into the gate of the power tube, and the second adjustment circuit generates a second current flowing out of the gate of the power tube;

[0024] The first end of the second adjustment tube receives the power supply voltage, the second end of the second adjustment tube is connected to the current source and the second adjustment circuit, and the second end of the second adjustment tube outputs the power supply voltage;

[0025] The first current and the second current are adjusted according to the first voltage, the first current is positively correlated with the first voltage, and the second current is negatively correlated with the first voltage.

[0026] The present invention discloses a switch control method under light load, which is used in a switching power supply, wherein the switching power supply comprises a power tube and a switch driving circuit thereof, wherein the switch driving circuit receives a switch control signal and controls the switch state of the power tube according to the switch control signal;

[0027] A supply voltage is obtained according to a first voltage representing the load size of the switching power supply, the supply voltage is positively correlated with the first voltage, and the supply voltage is used to power the switch driving circuit.

[0028] Optionally, when the switching power supply load enters a light load state, the supply voltage is reduced.

[0029] Optionally, when the switching power supply load enters a light load, the charge and discharge charge of the gate of the power tube decreases as the supply voltage decreases.

[0030] Optionally, when the switching power supply load enters a light load state and the switch control signal is valid, the power tube remains in an on state.

[0031] Optionally, within a preset load range, the supply voltage is positively correlated with the first voltage.

[0032] The present invention also provides a switching power supply, comprising a power tube and an inductor connected to each other, and also comprising any one of the above-mentioned switching control circuits, wherein the control circuit is used to control the switching state of the power tube.

[0033] Compared with the prior art, the present invention has the following advantages: the present invention adjusts the supply voltage according to the load size, the supply voltage is positively correlated with the load size, and the supply voltage is used to power the switch drive circuit of the power tube in the switching power supply. When the load is switched, the present invention can avoid problems such as large current fluctuation of the power tube and unstable loop, and can also save power loss when the load is light. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the principle diagram of the switching power supply of the present invention;

[0035] Figure 2 A curve diagram showing the relationship between the power supply voltage and the load size of the present invention;

[0036] Figure 3 is a schematic diagram of a first embodiment of a voltage regulating circuit of the present invention;

[0037] Figure 4 This is a schematic diagram of a second embodiment of the voltage regulation circuit of the present invention. DETAILED DESCRIPTION

[0038] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made on the spirit and range of the present invention.

[0039] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0040] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0041] Reference Figure 1 , which illustrates the principle diagram of the switching power supply of the present invention, Figure 1 The switching power supply in the present invention takes a step-down circuit as an example, but the present invention is not limited to the step-down circuit, and other switching power supplies including a power tube and the control circuit of the present invention are within the protection scope of the present invention. The switching power supply of the present invention includes a power tube M1 and a switch control circuit, the switch control circuit includes a voltage adjustment circuit and a first switch drive circuit, the voltage adjustment circuit receives a first voltage VC representing the load size of the switching power supply, and adjusts the size of the output power supply voltage VDD according to the size of the first voltage VC. The larger the first voltage VC, the larger the output power supply voltage VDD, that is, the power supply voltage VDD is positively correlated with the first voltage VC. Preferably, the power supply voltage VDD is proportional to the first voltage VC. Figure 1Among them, the switching power supply further includes an operational amplifier 01, which is used to perform operational amplification on the reference signal VREF and the output feedback signal FB to obtain a compensation voltage. When the compensation voltage is positively correlated with the load, the compensation voltage serves as the first voltage VC, which characterizes the load size of the switching power supply. When the compensation voltage is negatively correlated with the load, the compensation voltage is negatively correlated with the first voltage. In another embodiment, the first voltage VC characterizes the magnitude of the inductor current, that is, the inductor current can also characterize the load size of the switching power supply. In the present invention, the first voltage is equivalent to other signals that can characterize the load size.

[0042] Furthermore, the supply voltage VDD output by the voltage adjustment circuit is obtained from the power supply voltage VCC, and the magnitude of the supply voltage VDD is regulated by the first voltage VC. Further, the power supply voltage VCC can be obtained by taking power from the input end or the switching node of the switching power supply. For example, the input voltage VIN is used to charge a capacitor within a set time to obtain the power supply voltage VCC. The present invention does not specifically limit the method of obtaining the power supply voltage VCC, and any power acquisition method can be used.

[0043] The control end of the first switch driving circuit is connected to the gate of the power transistor M1, and the supply voltage VDD is used to supply power to the first switch driving circuit, enabling the first switch driving circuit to operate normally after being powered on. The first switch driving circuit receives the switch control signal TON and is used to control the switching state of the power transistor M1 according to the switch control signal TON.

[0044] Furthermore, the switching power supply further includes a power transistor M2, and the switch control circuit further includes a second switch driving circuit. The second switch driving circuit is connected to the gate of the power transistor M2, and the obtained supply voltage VDD supplies power to the second switch driving circuit at the same time, enabling the second switch driving circuit to operate normally after being powered on. The second switch driving circuit receives the switch control signal BON and is used to control the switching state of the power transistor M2 according to the switch control signal BON.

[0045] Furthermore, the switching power supply further includes a control unit (not shown in the figure). The control unit is used to generate the switch control signals TON and BON. In one embodiment, the control unit generates the switch control signals TON and BON according to the sampling signals of the compensation voltage and the inductor current. In another embodiment, the control unit generates the switch control signals TON and BON according to the compensation voltage and a given ramp signal. In different control methods, the methods of generating the switch control signals are also different, and the switch control signals can also be directly given. The present invention does not limit this.

[0046] In the switching power supply as a buck circuit, a boost circuit or other bridge circuit, the power tube M1 and the power tube M2 are connected between the input terminal and the ground terminal of the switching power supply, and the switch states of the power tube M1 and the power tube M2 are complementary. Specifically, the first end of the power tube M0 receives the input voltage VIN, and the second end is connected to the first end of the power tube M1, and the second end of the power tube M1 is grounded. Further, the first switch driving circuit uses the common connection end of the power tube M0 and the power tube M1 as the reference ground end, and the second switch driving circuit uses the system ground end as the reference ground end to perform switch control.

[0047] According to the relationship between the charge and discharge charge of the power tube gate and the power supply voltage, Q=Cg*VDD, where Cg is the parasitic capacitance of the power tube gate. According to the power supply principle of the control circuit introduced above, when the load of the switching power supply is heavy, the first voltage VC rises, and the control supply voltage VDD rises, thereby increasing the charge and discharge charge of the power tube gate; when the load of the switching power supply is light, the first voltage VC decreases, and the control supply voltage VDD decreases, thereby reducing the charge and discharge charge of the power tube gate. The present invention can adjust the supply voltage VDD according to the load state. When the load is switched, the supply voltage VDD is continuously adjusted following the load change. The current of the power tube will not change suddenly, the current floating is small, and the sampling ratio of the power tube current will not be affected, and the circuit loop will not be unstable, causing system failure. When the switching power supply is switched from heavy load to light load, the supply voltage VDD is continuously reduced, the power tube current will not change suddenly, the system loop is stable, and the power supply power consumption is saved at the same time, avoiding the instability of the system caused by hard shutting down of some power tubes to save power consumption.

[0048] Further, within a certain load range, the control supply voltage VDD is positively correlated with the first voltage VC representing the load, and the load range is determined according to the relationship between the power consumption generated by the gate of the power tube and the total power consumption generated on the power tube, where the power consumption generated by the gate is the power consumption generated by the gate charge charging and discharging, and the total power consumption includes the sum of the power consumption generated by the gate and the power consumption generated by the current flowing through the power tube. For each load, the power tube corresponds to an optimal power consumption, which is determined by the characteristics of the power tube itself. Under light load conditions, the power consumption generated by the gate accounts for a large proportion of the total power consumption of the power tube, and under heavy load conditions, the power consumption generated by the current flowing through the power tube accounts for a large proportion of the total power consumption of the power tube. Therefore, when the ratio of the gate power consumption to the total power consumption is greater than a certain value, such as 1 / 2, it indicates that the load at this time is small, and the load range can be determined accordingly. When the load is reduced, reducing the supply voltage VDD can significantly reduce the loss generated by the power tube and ensure good control stability of the loop, and there will be no oscillation caused by hard-off switching. If under heavy load conditions, the total power consumption of the power tube is mainly determined by the current flowing through the power tube, if the load is reduced, reducing the supply voltage will not significantly reduce the loss of the power tube.

[0049] like Figure 2As shown, a curve diagram of the relationship between the power supply voltage and the load size is illustrated. In the figure, VC represents the load size, VDD is the power supply voltage, and the power supply voltage VDD is positively correlated with the VC representing the load size. When the load decreases, the power supply voltage VDD also decreases. When the load decreases and enters a light load, the power supply voltage VDD decreases accordingly. The power supply voltage VDD can be proportional to the VC representing the load size, as shown in waveform ① in the figure; the power supply voltage VDD can also change in stages with the VC representing the load size, and the change rate in different stages is different, as shown in waveform ② in the figure; the power supply voltage VDD can also change in steps with the size of VC, which is not shown in the figure. Preferably, the load is within a preset range, such as VC is within the range of VC1-VC2 in the figure, the power supply voltage VDD is positively correlated with VC, when the load decreases, the power supply voltage VDD also decreases, and when the load decreases and enters a light load, the power supply voltage VDD decreases accordingly. The power supply voltage VDD of the present invention changes in a positive correlation with the load size, but the present invention does not limit the form of change of the power supply voltage VDD.

[0050] like Figure 3 As shown, a schematic diagram of an embodiment of the voltage adjustment circuit of the present invention is illustrated, including a second operational amplifier U2 and an adjustment tube Q1, the first end of the adjustment tube Q1 receives the power supply voltage VCC, the second end of the adjustment tube Q1 is grounded through the connected sampling resistors R1 and R2, the common connection end of the sampling resistors R1 and R2 outputs the sampling voltage VS1, the in-phase input end of the second operational amplifier U2 receives the first voltage VC, the second input end receives the sampling voltage VS1, the second operational amplifier U2 outputs the driving voltage VG1, the control end of the adjustment tube Q1 receives the driving voltage VG1, and the second end of the adjustment tube Q1 outputs the power supply voltage VDD. When the load decreases, the first voltage VC decreases, and according to the characteristics of the operational amplifier, the sampling voltage VS1 decreases, and then the power supply voltage VDD decreases; similarly, when the load increases, the power supply voltage VDD increases accordingly. The voltage adjustment circuit realizes the adjustment of the power supply voltage VDD according to the load size, and the power supply voltage VDD is positively correlated with the load size.

[0051] like Figure 4As shown, a schematic diagram of the second embodiment of the voltage adjustment circuit of the present invention is illustrated, including a first adjustment circuit, a second adjustment circuit, an adjustment tube Q2 and a current source I3. The first end of the first adjustment tube circuit receives the power supply voltage VCC, and the second end is connected to the gate of the adjustment tube Q2. The first adjustment circuit outputs a first current I1 that flows into the gate of the adjustment tube Q2 to pull up the voltage of the gate of the adjustment tube Q2. The first adjustment circuit also receives a first voltage VC that represents the load size, which is used to adjust the size of the first current I1. The larger the first voltage VC is, the larger the first current I1 is. The first end of the second adjustment circuit is connected to the gate of the adjustment tube Q2, and the second end is grounded. The second adjustment circuit generates a second current I2, and the second current I2 flows out from the gate of the adjustment tube Q2 to pull down the gate voltage of the adjustment tube Q2. The second adjustment circuit also receives the first voltage VC to adjust the size of the second current I2. The larger the first voltage VC is, the smaller the second current I2 is. The first end of the adjustment tube Q2 receives the power supply voltage VCC, and the second end is connected to the current source I3 and the second adjustment circuit. The second end of the adjustment tube Q2 outputs the power supply voltage VDD.

[0052] When the first voltage VC increases, the first current I1 increases, and the second current I2 decreases, so the gate voltage of the adjustment tube Q2 increases, the current flowing through the adjustment tube Q2 increases, and then the voltage at the second end of the adjustment tube Q2 increases; when the first voltage VC decreases, the first current I1 decreases, and the second current I2 increases, so the gate voltage of the adjustment tube decreases, the current flowing through the adjustment tube Q2 decreases, and then the voltage at the second end of the adjustment tube Q2 decreases.

[0053] The embodiments of the voltage regulating circuit of the present invention are not limited to Figure 3 , 4 As shown in the schematic diagram, other circuit embodiments can solve the technical problem of the present invention, that is, the technical problem of unstable loop current when load is switched, as long as the power supply voltage VDD is adjusted according to the load and the positive correlation between the power supply voltage VDD and the load is satisfied. The power supply method of the present invention has the technical effect that the loop current is stable when the load is switched and the power supply loss can be saved when the load is light.

[0054] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0055] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A light-load switch control circuit for use in a switching power supply, characterized in that: It includes a voltage adjustment circuit and a switch driving circuit, wherein the voltage adjustment circuit receives a first voltage representing the load size of the switch power supply and is used to adjust the output power supply voltage according to the first voltage, and the power supply voltage is positively correlated with the first voltage; The switch driving circuit is connected to the control end of the power tube in the switching power supply, receives a switch control signal, and is used to control the switch state of the power tube. The supply voltage is used to power the switch driving circuit.

2. The switch control circuit according to claim 1, characterized in that: When the switching power supply enters a light load state, the voltage regulating circuit reduces the supply voltage.

3. The switch control circuit according to claim 2, characterized in that: When the switching power supply enters a light load state, the charge and discharge charge of the gate of the power tube decreases as the supply voltage decreases.

4. The switch control circuit according to claim 1, characterized in that: Within a preset load range, the supply voltage is positively correlated with the first voltage.

5. The switch control circuit according to claim 1, characterized in that: When the switch power supply load enters a light load state and the switch control signal is valid, the power tube is in an on state.

6. The switch control circuit according to claim 1, characterized in that: It also includes a first operational amplifier, which is used to perform operational amplification on the output feedback signal of the switching power supply and the reference signal to obtain a compensation voltage, wherein the compensation voltage is positively correlated with the load, and the compensation voltage is used as the first voltage; A control unit receives the compensation voltage and obtains the switch control signal according to the compensation voltage.

7. The switch control circuit according to claim 1, characterized in that: The power tube includes a first power tube and a second power tube, and the switch driving circuit includes a first switch driving circuit and a second switch driving circuit; The first switch driving circuit is connected to the control end of the first power tube and is used to drive the first power tube; The second switch driving circuit is connected to the control end of the second power tube and is used to drive the second power tube; The supply voltage supplies power to the first switch driving circuit and the second switch driving circuit respectively.

8. The switch control circuit according to claim 7, characterized in that: The switch control signal includes a first switch control signal and a second switch control signal; the first switch drive circuit and the second switch drive circuit receive the first switch control signal and the second switch control signal respectively to control the switch states of the first power tube and the second power tube respectively; the switch states of the first power tube and the second power tube are complementary.

9. The switch control circuit according to claim 7, characterized in that: The first end of the first power tube receives an input voltage, the second end of the first power tube is connected to the first end of the second power tube, and the second end of the second power tube is grounded; The first switch driving circuit uses the common connection terminal of the first power tube and the second power tube as a reference ground, and the second switch driving circuit uses the ground terminal as a reference ground.

10. The switch control circuit according to claim 1, characterized in that: The voltage adjustment circuit receives a power supply voltage and a first voltage to adjust the power supply voltage according to the magnitude of the first voltage, thereby obtaining the supply voltage; The power supply voltage is obtained by taking power from the input terminal or the switch node of the switching power supply.

11. The switch control circuit according to claim 10, characterized in that: The voltage adjustment circuit includes a first adjustment tube and a second operational amplifier, wherein a first end of the first adjustment tube receives the power supply voltage, a second end of the first adjustment tube is grounded through a first resistor and a second resistor connected thereto, and a common connection end of the first resistor and the second resistor outputs a sampling voltage; The second operational amplifier performs operational amplification on the first voltage and the sampled voltage, and an output end of the second operational amplifier is connected to a control end of the first adjustment tube; The second end of the first adjustment tube outputs the supply voltage.

12. The switch control circuit according to claim 10, characterized in that: The voltage adjustment circuit comprises a first adjustment circuit, a second adjustment circuit, a second adjustment tube and a current source, wherein the first adjustment circuit and the second adjustment circuit are respectively connected to the control end of the second adjustment tube, the first adjustment circuit generates a first current flowing into the gate of the power tube, and the second adjustment circuit generates a second current flowing out of the gate of the power tube; The first end of the second adjustment tube receives the power supply voltage, the second end of the second adjustment tube is connected to the current source and the second adjustment circuit, and the second end of the second adjustment tube outputs the power supply voltage; The first current and the second current are adjusted according to the first voltage, the first current is positively correlated with the first voltage, and the second current is negatively correlated with the first voltage.

13. A switch control method under light load, used in a switching power supply, the switching power supply comprising a power tube and a switch drive circuit thereof, characterized in that: The switch driving circuit receives a switch control signal and controls the switch state of the power tube according to the switch control signal; A supply voltage is obtained according to a first voltage representing the load size of the switching power supply, the supply voltage is positively correlated with the first voltage, and the supply voltage is used to power the switch driving circuit.

14. The control method according to claim 13, characterized in that: When the switching power supply enters a light load state, the supply voltage decreases.

15. The control circuit of the switching power supply according to claim 14, characterized in that: When the switching power supply enters a light load state, the charge and discharge charge of the gate of the power tube decreases as the supply voltage decreases.

16. The control method according to claim 14, characterized in that: When the switch power supply load enters a light load state and the switch control signal is valid, the power tube remains in an on state.

17. The control method according to claim 13, characterized in that: Within a preset load range, the supply voltage is positively correlated with the first voltage.

18. A switching power supply, comprising a power tube and an inductor connected together, characterized in that: It also includes the switch control circuit described in any one of claims 1-12, wherein the control circuit is used to control the switch state of the power tube.

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