CN112332649B

CN112332649B - Power supply switching circuit and control method thereof

Info

Publication number: CN112332649B
Application number: CN201910714861.9A
Authority: CN
Inventors: 刘中唯; 蒋永恒; 李立民; 林婧婧
Original assignee: Wuxi U Nikc Semiconductor Co ltd
Current assignee: Wuxi U Nikc Semiconductor Co ltd
Priority date: 2019-08-05
Filing date: 2019-08-05
Publication date: 2023-10-31
Anticipated expiration: 2039-08-05
Also published as: CN112332649A

Abstract

The invention provides a power supply switching circuit, which is mainly improved in that the power supply switching circuit comprises: the first transistor switch module is coupled with a first power supply voltage and an output end and is used for controlling the first power supply voltage to provide power to the output end; the second transistor switch module is coupled with a second power supply voltage and the output end and used for controlling the second power supply voltage to provide power to the output end; one end of the starting circuit is coupled with the second transistor switch module, the other end of the starting circuit is coupled with a control circuit, and the second transistor switch module which is coupled with the starting circuit is started in a segmented mode; the control circuit is respectively coupled with the first transistor switch module and the starting circuit; the first power supply voltage is less than the second power supply voltage. The invention can avoid the problem that the high-voltage power supply is pulled down or the output has larger power failure when the low voltage is converted into the high voltage, and can prevent the backward current from damaging the front-stage circuit when the high voltage is converted into the low voltage.

Description

Power supply switching circuit and control method thereof

Technical Field

The present invention relates to a power switching circuit and a control method thereof, and more particularly to a power switching circuit capable of being started in a segmented manner and a control method thereof.

Background

Along with the increasing demand of electronic devices on power supply systems, such as server power supply systems, automotive electrical systems, computer mainboards, graphics cards, USB interfaces, etc., when power is supplied to different loads, a single set of power supply cannot meet the demand, so that two or more sets of power supplies are required to be switched for power supply, thereby achieving the purposes of energy saving, consumption reduction, etc.

Fig. 1 is a schematic diagram of a prior art power switching circuit, which includes a first power voltage VIN1, a second power voltage VIN2, a back-to-back switch 1 and 2, a back-to-back switch 3 and 4, a control circuit and a load. The first power voltage VIN1 and the second power voltage VIN2 are respectively supplied to the load terminal through the back-to-back switches 1 and 2 and the back-to-back switches 3 and 4 to obtain an output voltage Vo. The control circuit receives a control signal S1 and outputs a gate driving signal VG1 and a gate driving signal VG2, the gate driving signal VG1 controls the on and off of the switches 1 and 2, and the gate driving signal VG2 controls the on and off of the switches 3 and 4.

Fig. 2 is a waveform diagram of the switching mode shown in fig. 1 when the low voltage is changed to the high voltage, assuming that the first power voltage VIN1 is smaller than the second power voltage VIN2, when the control signal S1 is changed from the low voltage to the high voltage, the gate driving signal VG1 is changed from the high voltage to the low voltage rapidly, the switches 1 and 2 are turned off, the gate driving signal VG2 is changed from the low voltage to the high voltage rapidly (the high voltage of the gate driving signal VG2 is higher than the high voltage of the gate driving signal VG 1), and the switches 3 and 4 are turned on, the output voltage Vo is changed to the second power voltage VIN2 rapidly. The output terminal is commonly connected with a large capacitor, so that the output voltage Vo rises rapidly, and a large current is needed to charge the output capacitor, and when the charging current is greater than the maximum current that can be provided by the second power voltage VIN2, the second power voltage VIN2 is pulled down. Although the second power voltage VIN2 eventually returns to the original voltage value as the voltage of the output capacitor increases, the sudden power failure of the second power voltage VIN2 during the switching process may cause abnormal operation of other module circuits powered by the second power voltage VIN2.

Fig. 3 is a schematic diagram of another conventional power switching circuit, which is different from fig. 1 in that the power switching circuit further includes a start-up circuit, one end of which is coupled to the control circuit, and the other end of which is coupled to the back-to-back switches 3 and 4. The control circuit receives a control signal S1, outputs a gate drive signal VG1 to the back-to-back switches 1 and 2, and also outputs another control signal S2 to the start-up circuit, which outputs a gate drive signal VG2 to the back-to-back switches 3 and 4. The gate driving signal VG1 controls the on and off of the switches 1 and 2, and the gate driving signal VG2 controls the on and off of the switches 3 and 4.

Fig. 4 is a waveform diagram of the switching mode shown in fig. 3 when the low voltage is changed to the high voltage, assuming that the first power voltage VIN1 is smaller than the second power voltage VIN2, when the control signal S1 is changed from the low voltage to the high voltage, the gate driving signal VG1 is changed from the high voltage to the low voltage rapidly, and the switches 1 and 2 are turned off. At the same time, the control circuit outputs a control signal S2 to the start-up circuit, so that the gate driving signal VG2 output by the start-up circuit rises at a slow speed. When the gate driving signal VG2 is less than vo+V _TH At this time, the switches 3 and 4 are also in the off state, and the output voltage Vo decreases due to the load discharge. When the gate driving signal VG2 is greater than vo+V _TH When the output voltage Vo slowly rises along with the gate driving signal VG2, only a small current is needed to charge the output capacitor, the charging current is smaller than the maximum current that can be provided by the second power voltage VIN2, and the second power voltage VIN2 remains unchanged. Although the method can ensure that the second power voltage VIN2 is not powered down, the power failure of the output voltage Vo may cause abnormal operation of the load system.

Fig. 5 is a waveform diagram showing the switching mode of fig. 1 from high voltage to low voltage, assuming that the first power voltage VIN1 is smaller than the second power voltage VIN2, when the control signal S1 changes from high voltage to low voltage, the gate driving signal VG2 changes from high voltage to low voltage rapidly, the switches 3 and 4 are turned off, the gate driving signal VG1 changes from low voltage to high voltage rapidly (the high voltage of the gate driving signal VG2 is higher than the high voltage of the gate driving signal VG 1), and the switches 1 and 2 are turned on. Before the output voltage Vo drops to the first power voltage VIN1, a reverse current flows into the first power voltage VIN1 to pull the first power voltage VIN1 high, which may damage the pre-stage circuit. When the first power voltage VIN1 and the second power voltage VIN2 are different from each other, the switches 1 and 2 may be damaged when the reverse current is large.

In summary, in the current power switching application, more than two sets of power supplies may be used to supply power simultaneously, and the voltages of different power supplies are different (e.g. 3.3V, 5V, 12V, 48V), if the switching is incorrect, there may be reverse current, the high voltage power supply is pulled down, or the output has a larger power failure.

Disclosure of Invention

In view of the foregoing problems of the prior art, the present invention provides a power switching circuit capable of being started in segments and a control method thereof, in which when a low voltage is converted to a high voltage, a corresponding switch module is started quickly and then slowly by a starting circuit, so as to avoid the problem that the high voltage power is pulled down or the output has a large power failure, and when the high voltage is converted to the low voltage, a detecting circuit detects a voltage difference between an output end and the low voltage, so as to prevent a backward current from damaging a front-stage circuit. The technical scheme adopted by the invention is as follows:

in a power switching circuit, the main improvement comprising:

the first transistor switch module is coupled with a first power supply voltage and an output end and is used for controlling the first power supply voltage to provide power to the output end;

the second transistor switch module is coupled with a second power supply voltage and the output end and used for controlling the second power supply voltage to provide power to the output end;

one end of the starting circuit is coupled with the second transistor switch module, the other end of the starting circuit is coupled with a control circuit, and the second transistor switch module which is coupled with the starting circuit is started in a segmented mode;

the control circuit is respectively coupled with the first transistor switch module and the starting circuit so as to control the on and off of the two transistor switch modules;

the first power supply voltage is less than the second power supply voltage.

Further, the segmented start includes a first start segment and a second start segment, the start speed of the first start segment being greater than the start speed of the second start segment.

Further, the start slope of the second start-up section is adjustable.

Further, the power supply switching circuit further includes:

and the detection circuit is respectively coupled with the first transistor switch module and the control circuit, and detects the voltage difference between the output end and the first power supply voltage and feeds back the voltage difference to the control circuit.

Further, when the switching mode of the power supply switching circuit is low voltage to high voltage, the detected voltage difference between the output end and the first power supply voltage is used as a node for starting in a sectional mode; when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the first starting section enters the second starting section;

when the switching mode of the power supply switching circuit is that the high voltage is changed into the low voltage, the first transistor switching module is kept in an off state, and when the relative value or absolute value of the voltage difference between the output end and the first power supply voltage is smaller than or equal to a second preset value, the first transistor switching module is turned on.

Further, the starting circuit comprises a first starting module, a second starting module, a power supply unit and a capacitor C1; one end of the first starting module and one end of the second starting module are respectively connected with the power supply unit, and the other end of the first starting module and the other end of the second starting module are respectively connected with the capacitor C1 and the switch control end of the second transistor switch module;

the segment starting mode comprises one of the following two modes:

when the switching mode is low voltage to high voltage, the control signal of the starting circuit controls the first starting module and the second starting module to charge the capacitor C1 at the same time, and when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the control signal of the starting circuit controls one starting module to stop charging the capacitor C1, and the other starting module continues to charge the capacitor C1, so that the charging speed is reduced, and the sectional starting is realized;

when the switching mode is low voltage to high voltage, the charging current of the first starting module to the capacitor C1 is larger than the charging current of the second starting module to the capacitor C1; the control signal of the starting circuit controls the first starting module to charge the capacitor C1, when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the control signal of the starting circuit controls the first starting module to stop charging, the second starting module charges the capacitor C1, and the charging speed is reduced, so that the sectional starting is realized.

Further, for the segment start mode (one), the charging current of the first start module to the capacitor C1 is greater than or equal to the charging current of the second start module to the capacitor C1; when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the control signal of the starting circuit controls the first starting module to stop charging the capacitor C1, and the second starting module continues to charge the capacitor C1.

Further, the first starting module includes a current source I1, a switch SW1; the second starting module comprises a current source I2 and a switch SW2; the input end of the current source I1 is connected with the power supply unit, and the output end of the current source I1 is connected with the capacitor C1 through the switch SW1; the input end of the current source I2 is connected with the power supply unit, and the output end of the current source I2 is connected with the capacitor C1 through the switch SW 2.

Still further, the method further comprises the steps of,

for the segment start mode (one), the current of the first current source I1 is greater than or equal to the current of the second current source I2;

for the segment start mode (two), the current of the first current source I1 is larger than the current of the second current source I2.

Or, further, the first starting module includes a resistor R1 and a switch SW1; the second starting module comprises a resistor R2 and a switch SW2; one end of the resistor R1 is connected with the power supply unit, and the other end of the resistor R1 is connected with the capacitor C1 through the switch SW1; one end of the resistor R2 is connected with the power supply unit, and the other end of the resistor R2 is connected with the capacitor C1 through the switch SW2; r1< R2.

A control method of a power supply switching circuit, comprising:

the first power supply voltage provides power to an output end through the first transistor switch module;

the second power supply voltage provides power to the output end through a second transistor switch module;

the first power supply voltage is smaller than the second power supply voltage;

when the switching mode is low voltage to high voltage, the first transistor switch module is controlled to be turned off; the method comprises the steps of starting a second transistor switch module in a segmented mode, wherein the segmented starting comprises a first starting section and a second starting section, and the starting speed of the first starting section is greater than that of the second starting section; taking the detected voltage difference between the output end and the first power supply voltage as a node for starting in a segmented mode; when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the first starting section enters the second starting section;

when the switching mode is high voltage to low voltage, the second transistor switch module is controlled to be turned off; the first transistor switch module is kept in an off state, and is turned on when the relative value or absolute value of the voltage difference between the output end and the first power supply voltage is smaller than or equal to a second preset value.

The invention has the advantages that: according to the power supply switching circuit, when the low voltage is converted into the high voltage, the corresponding switch module is started quickly and then slowly by the starting circuit, so that the problem that the high voltage power supply is pulled down or the output has larger power failure is avoided, and when the high voltage is converted into the low voltage, the voltage difference between the output end and the low voltage is detected by the detecting circuit, so that the backward current is prevented from damaging the front-stage circuit.

Drawings

Fig. 1 is a schematic diagram of a prior art power switching circuit.

Fig. 2 is a waveform diagram of the switching mode shown in fig. 1 when switching from low voltage to high voltage.

FIG. 3 is a schematic diagram of another conventional power switching circuit

Fig. 4 is another waveform diagram of the switching mode shown in fig. 3 when switching from low voltage to high voltage.

Fig. 5 is a waveform diagram showing the switching mode of fig. 1 from high voltage to low voltage.

Fig. 6 is a power switching circuit according to a preferred embodiment of the invention.

Fig. 7 is a waveform diagram of the embodiment shown in fig. 6 when the switching mode is low voltage to high voltage.

Fig. 8 is a waveform diagram of the embodiment shown in fig. 6 when the switching mode is changed from high voltage to low voltage.

FIG. 9 is a schematic diagram of a detection circuit and a start-up circuit according to a preferred embodiment of the present invention.

Detailed Description

For purposes of clarity, technical solutions and advantages of the present invention, a preferred embodiment of the present invention will be described in detail, and elements/components using the same reference numerals or letters in the drawings and the embodiments represent the same or similar parts.

Referring to fig. 6, fig. 6 is a power switching circuit according to a preferred embodiment of the invention. The power switching circuit 100 includes a first power voltage VIN1, a second power voltage VIN2, a first transistor switch module 101, a second transistor switch module 102, a control circuit 103, an output Vo, a load 104, a detection circuit 105 and a start-up circuit 106. The first transistor switch module 101 is coupled to the first power voltage VIN1 and an output terminal Vo for controlling the first power voltage VIN1 to provide power to the output terminal Vo; the second transistor switch module 102 is coupled to the second power voltage VIN2 and the output terminal Vo for controlling the second power voltage VIN2 to provide power to the output terminal Vo. The starting circuit 106 has one end coupled to the second transistor switch module 102 and the other end coupled to a control circuit 103, and starts the coupled second transistor switch module 102 in a segmented manner; the control circuit 103 is coupled to the first transistor switch module 101 and the start circuit 106 respectively to control the on and off of the two transistor switch modules; the control circuit 103 receives a control signal S1, and outputs a gate driving signal VG1 and a control signal S2, wherein the gate driving signal VG1 controls the on and off of the first transistor switch module 101. The start-up circuit 106 receives the control signal S2 and outputs the gate driving signal VG2 to control the on and off of the second transistor switch module 102. In the present embodiment, the first transistor switch module 101 is a back-to-back NMOS transistor switch 1 and a switch 2, and the second transistor switch module 102 is a back-to-back NMOS transistor switch 3 and a switch 4, and in other embodiments, the first transistor switch module 101 and the second transistor switch module 102 may be other switch elements such as back-to-back PMOS transistors, IGBTs, BJTs, and the like.

In the present embodiment, the first power voltage VIN1 and the second power voltage VIN2 are not equal, wherein the first power voltage VIN1 is smaller than the second power voltage VIN2; the detection circuit 105 is coupled to the first transistor switch module 101 and the control circuit 103, and detects a voltage difference between the output terminal Vo and the first power voltage VIN1 and feeds back the voltage difference to the control circuit 103. One end of the start-up circuit 106 is coupled to the second transistor switch module 102, and is configured to output the gate driving signal VG2 to start up the second transistor switch module 102 in a segmented manner.

Referring to fig. 7 and fig. 8, fig. 7 is a waveform diagram illustrating the switching mode from low voltage to high voltage in the embodiment shown in fig. 6. Since the first power voltage VIN1 is smaller than the second power voltage VIN2, when the control signal S1 changes from a low voltage to a high voltage, the gate driving signal VG1 changes from a high voltage to a low voltage rapidly, turning off the switches 1 and 2. Meanwhile, the control circuit 103 outputs a control signal S2 to the start-up circuit 106, and the start-up circuit 106 outputs the gate driving signal VG2 according to the control signal S2, where the control signal S2 may be a signal or a group of signals. In the first start-up section, the gate driving signal VG2 is first quickly increased to an intermediate voltage, and the switches 3 and 4 are turned on, so that the problem of power failure of the output terminal Vo due to too slow opening of the switches 3 and 4 is avoided. In the second start-up section, the gate driving signal VG2 rises from the intermediate voltage to the high voltage (the high voltage of the gate driving signal VG2 is higher than the high voltage of the gate driving signal VG 1) at a slower speed, and the start-up slope of the second start-up section is adjustable, and different designs are made according to different needs. The start-up circuit 106 uses the voltage difference between the output terminal Vo and the first power voltage VIN1 detected by the detection circuit 105 as a node for segment start-up; when the voltage difference between the output end Vo and the first power voltage VIN1 is detected to be more than or equal to a first preset value, the first starting section is started to enter the second starting section; the starting speed of the first starting section is larger than that of the second starting section, and the voltage of the output end Vo drops less when the starting speed of the first starting section is larger. In this embodiment, the output end Vo does not have a rapid change in the whole switching process, so that the problem that the second power supply voltage VIN2 is powered down during rapid switching is avoided, and the problem that the output end Vo is powered down during the power-up of the gate driving signal VG2 at a slow speed is also avoided.

Fig. 8 is a waveform diagram of the embodiment shown in fig. 6 when the switching mode is changed from high voltage to low voltage. Because the first power voltage VIN1 is smaller than the second power voltage VIN2, when the control signal S1 changes from high voltage to low voltage, the control circuit 103 receives the control signal S1 and outputs the control signal S2, and the start-up circuit 106 controls the gate driving signal VG2 to quickly change from high voltage to low voltage according to the control signal S2, so that the switches 3 and 4 are turned off, and the gate driving signal VG1 is kept at low voltage at this time, so that the first transistor switch module 101 is kept in the off state until the detection circuit 105 detects that the relative value or the absolute value of the voltage difference between the output terminal Vo and the first power voltage is smaller than or equal to a second preset value, and the gate driving signal VG1 quickly changes from low voltage to high voltage, so that the switches 1 and 2 are turned on, thereby preventing the current from flowing backward and protecting the front-stage circuit from being damaged.

With continued reference to fig. 9, fig. 9 is a schematic diagram of a detection circuit and a start-up circuit according to a preferred embodiment of the invention. The detection circuit 105 includes a comparator CMP, which compares the voltage difference between the output terminal Vo and the first power voltage VIN1, and outputs a detection signal VS1, and the control circuit 103 controls the switching timing of the two transistor switch modules according to the detection signal VS 1.

The starting circuit 106 includes a first starting module 116, a second starting module 126, a power supply unit, and a capacitor C1; one end of the first starting module 116 and one end of the second starting module 126 are respectively connected with a power supply unit, and the other end of the first starting module 116 and the other end of the second starting module 126 are respectively connected with a capacitor C1 and a switch control end of the second transistor switch module; the power supply unit may be the charge pump 136 of fig. 9 or another power supply voltage;

there are two types of segment start modes:

when the switching mode is low voltage to high voltage, the control signal S2 of the starting circuit controls the first starting module 116 and the second starting module 126 to charge the capacitor C1 at the same time, the charging speed is fast, and when the voltage difference between the output end Vo and the first power voltage VIN1 is larger than or equal to a first preset value, the control signal S2 of the starting circuit controls one starting module to stop charging the capacitor C1, and the other starting module continues to charge the capacitor C1, so that the charging speed is slow, and the segmented starting is realized;

(II) when the switching mode is low voltage to high voltage, the charging current of the capacitor C1 by the first starting module 116 is greater than the charging current of the capacitor C1 by the second starting module 126; the control signal S2 of the starting circuit controls the first starting module 116 to charge the capacitor C1, the charging speed is fast, when the voltage difference between the output end Vo and the first power supply voltage VIN1 is greater than or equal to a first preset value, the control signal S2 of the starting circuit controls the first starting module 116 to stop charging, and the second starting module 126 charges the capacitor C1, the charging speed is slow, and therefore segmented starting is achieved;

the first start-up module 116 includes a current source I1, a switch SW1, wherein SW1 may be a MOS switch;

the second starting module 126 includes a current source I2, a switch SW2, where SW2 may be a MOS switch;

the input end of the current source I1 is connected with the power supply unit, and the output end of the current source I1 is connected with the capacitor C1 through the switch SW1;

the input end of the current source I2 is connected with the power supply unit, and the output end of the current source I2 is connected with the capacitor C1 through the switch SW2;

for the segment starting mode (one), the current of the first current source I1 is greater than or equal to the current of the second current source I2, the control signal S2 of the starting circuit controls the switches SW1 and SW2 to be closed at the same time, the first current source I1 and the second current source I2 charge the capacitor C1 at the same time, the charging speed is fast, when the voltage difference between the output end Vo and the first power voltage VIN1 is greater than or equal to a first preset value, the control signal S2 of the starting circuit controls the switch SW1 to be opened, the switch SW2 still keeps to be closed, only the second current source I2 charges the capacitor C1 at the moment, and the charging speed is slow, so that segment starting is realized.

For the segment starting mode (II), the current of the first current source I1 is larger than that of the second current source I2, the control signal S2 of the starting circuit firstly controls the switch SW1 to be closed and the switch SW2 to be opened, the first current source I1 charges the capacitor C1, when the voltage difference between the output end Vo and the first power voltage VIN1 is larger than or equal to a first preset value, the control signal S2 of the starting circuit controls the switch SW1 to be opened, the switch SW2 is closed, and at the moment, the second current source I2 charges the C1, and the charging speed is slowed down, so that segment starting is realized.

In other embodiments, current source I1 may be replaced with a resistor R1, current source I2 may be replaced with a resistor R2, R1< R2;

when the switching mode is high voltage to low voltage, the control signal S2 of the starting circuit controls the switches SW1 and SW2 to be switched off, and controls the switch 3 and the switch 4 to be switched off;

for the connection line between the control circuit 103 and the start circuit 106, there may be a plurality of parallel lines to control the switches SW1, SW2 and the second transistor switch module 102, respectively; a serial line may also be used, but a serial-parallel conversion module is required to be arranged in the starting circuit at this time, so that the serial signal can be converted into control signals on a plurality of parallel lines, thereby controlling the switches SW1 and SW2 and the second transistor switch module 102;

in summary, in the power supply switching circuit of the present invention, when the low voltage is switched to the high voltage, the corresponding transistor switch module is started up quickly and then slowly by the starting circuit, so as to avoid the problem that the high voltage power supply is pulled down or the output has a larger power failure, and when the high voltage is switched to the low voltage, the detecting circuit detects the voltage difference between the output end and the low voltage to prevent the backward current from damaging the front-stage circuit.

Finally, it should be noted that the above-mentioned embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications and equivalents may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention, and all such modifications and equivalents are intended to be encompassed in the scope of the claims of the present invention.

Claims

1. A power switching circuit, the power switching circuit comprising:

the first power supply voltage is less than the second power supply voltage;

the detection circuit is respectively coupled with the first transistor switch module and the control circuit, and detects the voltage difference between the output end and the first power supply voltage and feeds the voltage difference back to the control circuit;

the starting circuit comprises a first starting module, a second starting module, a power supply unit and a capacitor C1; one end of the first starting module and one end of the second starting module are respectively connected with the power supply unit, and the other end of the first starting module and the other end of the second starting module are respectively connected with the capacitor C1 and the switch control end of the second transistor switch module;

the segment starting mode comprises one of the following two modes:

2. The power switching circuit according to claim 1, wherein,

the segmented start comprises a first start section and a second start section, wherein the start speed of the first start section is larger than that of the second start section.

3. The power switching circuit according to claim 2, wherein,

the start-up slope of the second start-up section is adjustable.

4. The power switching circuit according to claim 1, wherein,

when the switching mode of the power supply switching circuit is low voltage to high voltage, the detected voltage difference between the output end and the first power supply voltage is used as a node for starting in a sectional mode; when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the first starting section enters the second starting section;

5. The power switching circuit according to claim 1, wherein,

for the segment starting mode (I), the charging current of the first starting module to the capacitor C1 is larger than or equal to the charging current of the second starting module to the capacitor C1; when the voltage difference between the output end and the first power supply voltage is larger than or equal to a first preset value, the control signal of the starting circuit controls the first starting module to stop charging the capacitor C1, and the second starting module continues to charge the capacitor C1.

6. The power switching circuit according to claim 1, wherein,

the first starting module comprises a current source I1 and a switch SW1; the second starting module comprises a current source I2 and a switch SW2; the input end of the current source I1 is connected with the power supply unit, and the output end of the current source I1 is connected with the capacitor C1 through the switch SW1; the input end of the current source I2 is connected with the power supply unit, and the output end of the current source I2 is connected with the capacitor C1 through the switch SW 2.

7. The power switching circuit according to claim 6, wherein,

8. The power switching circuit according to claim 1, wherein,

the first starting module comprises a resistor R1 and a switch SW1; the second starting module comprises a resistor R2 and a switch SW2; one end of the resistor R1 is connected with the power supply unit, and the other end of the resistor R1 is connected with the capacitor C1 through the switch SW1; one end of the resistor R2 is connected with the power supply unit, and the other end of the resistor R2 is connected with the capacitor C1 through the switch SW2; r1< R2.

9. A control method of a power supply switching circuit, comprising:

the first power supply voltage is smaller than the second power supply voltage;