CN205583659U - A switching power supply circuit - Google Patents

Abstract

The utility model discloses a switching power supply circuit, include: the overvoltage detection module is connected with the power supply module; the power supply module comprises a power supply input end, a controlled end and a power supply output end; the overvoltage detection module comprises a first sampling end and a comparison signal output end; the feedback loop control module comprises a second sampling end and a feedback output end; the power supply control module comprises a feedback input end and a power supply control end; and the comparison signal output end of the overvoltage detection module is connected with the second sampling end of the feedback loop control module. The utility model discloses a combine original feedback loop control circuit and overvoltage protection control circuit in the switching power supply circuit to realize overvoltage protection to reduce the quantity of components and parts among the switching power supply circuit, reach the purpose that reduces circuit cost and improve circuit security.

Description

A switching power supply circuit

technical field

The utility model relates to the field of electronic technology, in particular to a switching power supply circuit.

Background technique

The feedback loop control circuit in the switching power supply is usually realized by "optocoupler + op amp", which is used to control the output voltage to keep it stable under all conditions.

The function of the output overvoltage protection circuit in the switching power supply is: when the output voltage exceeds the design value, the output voltage is limited within a safe value range. When the internal voltage stabilization loop of the switching power supply fails or the output overvoltage occurs due to improper operation by the user, the overvoltage protection circuit will protect it to prevent damage to the subsequent electrical equipment.

In the existing technical solutions, most of the output overvoltage protection is realized by "comparator/op amp + optocoupler", that is, the output voltage is sampled through the "comparator/op amp", and then compared with the reference voltage. When the output voltage exceeds the reference voltage, the comparator outputs a high level, which turns the optocoupler on, thereby pulling down the feedback input terminal of the switching power supply control chip, and at the same time forms a positive feedback through the diode, so that the feedback input terminal of the power supply control chip is always Pull low to achieve overvoltage protection lockout. Although this solution can provide accurate overvoltage protection for the output voltage, the optocoupler is a safety component, and it is connected between the hot and cold grounds. If it is damaged, it may cause safety problems, and the existing switching power supply circuit needs to use more To achieve overvoltage protection with advanced components, the circuit cost is relatively high.

Utility model content

The technical problem to be solved by the utility model is to provide a switching power supply circuit, which combines the original feedback loop control circuit and overvoltage protection circuit in the switching power supply circuit to realize overvoltage protection, so as to reduce the components in the switching power supply circuit. Quantity, to achieve the purpose of reducing the cost of the circuit and improving the safety of the circuit.

In order to solve the above technical problems, the utility model proposes a switching power supply circuit, including: a power supply module, an overvoltage detection module, a feedback loop control module and a power supply control module;

The power module includes a power input terminal, a controlled terminal and a power output terminal; the overvoltage detection module includes a first sampling terminal and a comparison signal output terminal; the feedback loop control module includes a second sampling terminal and a feedback output terminal ; The power control module includes a feedback input terminal and a power control terminal;

The first sampling end of the overvoltage detection module is connected to the power supply output end of the power module, and the comparison signal output end of the overvoltage detection module is connected to the second sampling end of the feedback loop control module; the feedback loop The feedback output end of the power control module is connected to the feedback input end of the power control module; the power control end of the power control module is connected to the controlled end of the power module.

Further, the feedback loop control module includes a first reference voltage unit, a first operational amplifier, an optocoupler, a first resistor and a second resistor; the first reference voltage unit includes a first reference voltage input terminal and a first Reference voltage output terminal;

The first inverting input terminal of the first operational amplifier is the second sampling terminal of the feedback loop control module, and the first non-inverting input terminal of the first operational amplifier is connected to the first reference voltage unit. A reference voltage output end, the first output end of the first operational amplifier is connected to the second input end of the optocoupler; the second input end of the optocoupler is also connected to the second end of the second resistor, so The first input end of the optocoupler is connected to the first end of the second resistor and the second end of the first resistor, and the first output end of the optocoupler is the feedback output end of the feedback loop control module , the second output end of the optocoupler is grounded; the first end of the first resistor is connected to the first power supply signal.

Further, the overvoltage detection module includes a voltage comparison unit, a latch unit and a first diode; the voltage comparison unit includes a voltage input terminal and a second output terminal; the latch unit includes a data input terminal and a data output terminal;

The voltage input terminal of the voltage comparison unit is the first sampling terminal of the overvoltage detection module, the voltage input terminal is connected to the data output terminal of the latch unit, and the second output terminal of the voltage comparison unit is connected to the The anode of the first diode and the data input end of the latch unit; the cathode of the first diode is the comparison signal output end of the overvoltage detection module.

Furthermore, the overvoltage detection module also includes a second reference voltage unit; the second reference voltage unit includes a second reference voltage input terminal and a second reference voltage output terminal; the voltage comparison unit also includes a third reference voltage voltage input;

The second reference voltage output terminal of the second reference voltage unit is connected to the third reference voltage input terminal of the voltage comparison unit.

Preferably, the second reference voltage unit includes a third resistor, a fourth resistor and a first capacitor;

The first end of the third resistor is the second reference voltage input end of the second reference voltage unit, the second end of the third resistor is connected to the first end of the fourth resistor; the fourth resistor The first end of the second reference voltage unit is the second reference voltage output end of the second reference voltage unit, and the second end of the fourth resistor is grounded; the first capacitor is connected in parallel with the fourth resistor.

Preferably, the second reference voltage unit includes a Zener diode, a fifth resistor and a sixth resistor;

The first end of the fifth resistor is the second reference voltage input end of the second reference voltage unit, and the second end of the fifth resistor is connected to the negative pole of the Zener diode; the negative pole of the Zener diode It is the second reference voltage output terminal of the second reference voltage unit, and the anode of the Zener diode is grounded; the sixth resistor is connected in parallel with the Zener diode.

Preferably, the second reference voltage unit includes a three-terminal voltage regulator, a seventh resistor, an eighth resistor, and a ninth resistor; the three-terminal voltage regulator includes an anode, a cathode, and a reference voltage terminal;

The first end of the seventh resistor is the second reference voltage input end of the second reference voltage unit, and the second end of the seventh resistor is connected to the cathode of the three-terminal voltage regulator; The cathode of the pressure tube is the second reference voltage output terminal of the second reference voltage unit, the cathode of the three-terminal voltage regulator is also connected to the first end of the eighth resistor, and the reference of the three-terminal voltage regulator is The voltage end is connected to the second end of the eighth resistor and the first end of the ninth resistor, and the anode of the three-terminal voltage regulator tube is connected to the second end of the ninth resistor; the first end of the ninth resistor Both ends are grounded.

Further, the voltage comparison unit is a second operational amplifier;

The second operational amplifier includes a second non-inverting input terminal, a second inverting input terminal and a third output terminal; the second non-inverting input terminal of the second operational amplifier is the voltage input terminal of the voltage comparison unit, and the The second inverting input terminal of the second operational amplifier is the third reference voltage input terminal of the voltage comparison unit, and the third output terminal of the second operational amplifier is the second output terminal of the voltage comparison unit.

Furthermore, the overvoltage detection module further includes a first voltage dividing unit; the first voltage dividing unit includes a tenth resistor, an eleventh resistor and a second capacitor;

The first end of the tenth resistor is the first sampling end of the overvoltage detection module, the second end of the tenth resistor is connected to the first end of the eleventh resistor; The second end is grounded; the second capacitor is connected in parallel with the eleventh resistor.

Preferably, the latch unit is a second diode, the anode of the second diode is the data input end of the latch unit, and the cathode of the second diode is the latch unit data output terminal.

Implementing the utility model has the following beneficial effects:

In the switching power supply circuit provided by the utility model, the comparison signal output terminal of the overvoltage detection module is connected to the feedback output terminal of the feedback loop control module. When the output voltage of the power supply module is greater than the threshold value, the overvoltage detection module continues to output high-level signals , the feedback output terminal of the feedback loop control module continuously outputs a low-level signal, the feedback input terminal of the power control module is pulled low, the power control module is turned off, and the entire power supply stops working to achieve the purpose of overvoltage protection. The utility model combines the original feedback loop control circuit and the overvoltage protection circuit in the switching power supply circuit to realize the overvoltage protection, reduces the number of components, reduces the circuit cost and improves the safety of the circuit.

Description of drawings

Fig. 1 is the circuit schematic diagram of the feedback loop control circuit in the existing switching power supply circuit;

Fig. 2 is a circuit schematic diagram of an overvoltage protection circuit in an existing switching power supply circuit;

Fig. 3 is a structural schematic diagram of an embodiment of a switching power supply circuit provided by the utility model;

Fig. 4 is a structural schematic diagram of another embodiment of a switching power supply circuit provided by the utility model;

Fig. 5 is a schematic circuit diagram of an embodiment of an overvoltage detection module provided by the present invention;

Fig. 6 is a schematic circuit diagram of another embodiment of an overvoltage detection module provided by the present invention;

Fig. 7 is a schematic circuit diagram of another embodiment of an overvoltage detection module provided by the present invention.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. example. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

Referring to FIG. 3 , it is a schematic structural diagram of an embodiment of a switching power supply circuit provided by the present invention.

In this embodiment, the switching power supply circuit includes: a power supply module 1, an overvoltage detection module 4, a feedback loop control module 3 and a power supply control module 2;

The power module 1 includes a power input terminal Vin, a controlled terminal and a power output terminal Vout; the overvoltage detection module 4 includes a first sampling terminal and a comparison signal output terminal; the feedback loop control module 3 includes a second sampling terminal end and a feedback output end; the power control module 2 includes a feedback input end FB and a power control end;

The first sampling terminal of the overvoltage detection module 4 is connected to the power supply output terminal Vout of the power supply module 1, and the comparison signal output terminal of the overvoltage detection module 4 is connected to the second sampling terminal of the feedback loop control module 3 The feedback output terminal of the feedback loop control module 3 is connected to the feedback input terminal FB of the power control module 2 ; the power control terminal of the power control module 2 is connected to the controlled terminal of the power module 1 .

It should be noted that the power supply module 1 includes a transient filter circuit, an input rectification filter circuit, a switch tube, a main transformer and an output rectification filter circuit; The peak of the input rectification filter circuit is used to rectify and filter the voltage signal output by the transient filter circuit. The primary side of the main transformer is connected to the switch tube, and the secondary side is connected to the output rectification filter circuit, which can provide low-voltage DC output of the power supply. The power supply control module 2 is a switching power supply chip, and the input voltage of the power supply input terminal Vin is rectified and filtered by the power supply module 1 and then added to the power supply end of the switching power supply chip to provide a starting voltage for the switching power supply chip, and the switching power supply chip works normally. The power control terminal of the power control module 2 is the output terminal of the switching power supply chip, which can drive the power tube to adjust the output signal of the switching power supply. The feedback input terminal FB of the power control module 2 is the COMP pin of the switching power supply chip. When the COMP pin of the switching power supply chip is pulled low, the switching power supply chip is turned off, and the whole power supply stops working. A specific embodiment of the switching power supply chip is UC3842 switching power supply control chip.

Referring to FIG. 4 , it is a structural schematic diagram of another embodiment of a switching power supply circuit provided by the present invention.

On the basis of the above embodiment shown in FIG. 3 , further, the feedback loop control module 3 includes a first reference voltage unit U1, a first operational amplifier A1, an optocoupler OC, a first resistor R1 and a second resistor R2 ; The first reference voltage unit U1 includes a first reference voltage input terminal Vref1 and a first reference voltage output terminal;

The first inverting input terminal of the first operational amplifier A1 is the second sampling terminal of the feedback loop control module 3, and the first non-inverting input terminal of the first operational amplifier A1 is connected to the first reference voltage The first reference voltage output terminal of the unit U1, the first output terminal of the first operational amplifier A1 is connected to the second input terminal of the optocoupler OC; the second input terminal of the optocoupler OC is also connected to the second The second end of the resistor R2, the first input end of the optocoupler OC is connected to the first end of the second resistor R2 and the second end of the first resistor R1, the first output end of the optocoupler OC is the feedback output terminal of the feedback loop control module 3 , the second output terminal of the optocoupler OC is grounded; the first terminal of the first resistor R1 is connected to the first power supply signal Vcc. Wherein, the first power signal Vcc is a power supply with a voltage value of +5V.

Further, the overvoltage detection module 4 includes a voltage comparison unit, a latch unit 42 and a first diode D1; the voltage comparison unit includes a voltage input terminal and a second output terminal; the latch unit 42 includes a data input and data output;

The voltage input terminal of the voltage comparison unit is the first sampling terminal of the overvoltage detection module 4, the voltage input terminal is connected to the data output terminal of the latch unit 42, and the second output terminal of the voltage comparison unit The anode of the first diode D1 is connected to the data input end of the latch unit 42 ; the cathode of the first diode D1 is the comparison signal output end of the overvoltage detection module 4 .

Further, the latch unit 42 is a second diode D2, the anode of the second diode D2 is the data input terminal of the latch unit 42, and the cathode of the second diode D2 is is the data output terminal of the latch unit 42 .

Further, the overvoltage detection module 4 also includes a second reference voltage unit U2; the second reference voltage unit U2 includes a second reference voltage input terminal Vref2 and a second reference voltage output terminal; the voltage comparison unit also including a third reference voltage input terminal;

The second reference voltage output terminal of the second reference voltage unit U2 is connected to the third reference voltage input terminal of the voltage comparison unit.

Specifically, the voltage comparison unit is a second operational amplifier A2; the second operational amplifier A2 includes a second non-inverting input terminal, a second inverting input terminal and a third output terminal; the second operational amplifier A2 The two non-inverting input terminals are the voltage input terminals of the voltage comparison unit, the second inverting input terminal of the second operational amplifier A2 is the third reference voltage input terminal of the voltage comparison unit, and the second operational amplifier A2 The third output terminal of is the second output terminal of the voltage comparison unit.

Further, the overvoltage detection module 4 also includes a first voltage dividing unit 41; the first voltage dividing unit 41 includes a tenth resistor R10, an eleventh resistor R11 and a second capacitor C2;

The first end of the tenth resistor R10 is the first sampling end of the overvoltage detection module 4, the second end of the tenth resistor R10 is connected to the first end of the eleventh resistor R11; The second end of the eleventh resistor R11 is grounded; the second capacitor C2 is connected in parallel with the eleventh resistor R11.

It should be noted that, in this embodiment, the latch unit 42 plays the role of positive feedback, and the purpose of latching is achieved through positive feedback, so that the second output terminal of the voltage comparison unit in the overvoltage detection module 4 continues to output high level signal. The first diode D1 functions to prevent backflow, so that the signal can only be transmitted in one direction, that is, it can only be output from the overvoltage detection module 4 to the feedback loop control module 3 . The latch unit 42 and the first diode D1 can be implemented using a BAW56 element.

The working principle of the switching power supply circuit provided in this embodiment is as follows:

After the output voltage of the power module 1 is divided by the tenth resistor R10 and the eleventh resistor R11, it is input to the second non-inverting input terminal of the second operational amplifier A2, and the second reference voltage is input to the second inverting input of the second operational amplifier A2 Terminal, when the voltage of the second non-inverting input terminal in the second operational amplifier A2 is greater than the voltage of the second inverting input terminal, that is, when the output voltage of the power module 1 is higher than the threshold value, the third output terminal of the second operational amplifier A2 outputs a high level At the same time, a positive feedback is formed through the second diode D2, so that the third output terminal of the second operational amplifier A2 keeps outputting a high-level signal, and this high-level signal is output to the The first inverting input terminal of the first operational amplifier A1 in the feedback loop control module 3, the first reference voltage is input from the first non-inverting input terminal of the first operational amplifier A1, and the high level signal output by the overvoltage detection module makes The voltage of the first inverting input terminal in the first operational amplifier A1 is greater than the voltage of the first non-inverting input terminal, the second output terminal of the first operational amplifier A1 outputs a low-level signal, the optocoupler OC is turned on, and the feedback of the power control module 2 The input terminal FB is pulled low, the power control module 2 is turned off, and the whole power supply stops working, so as to realize the purpose of overvoltage protection.

Referring to FIG. 5 , it is a schematic circuit diagram of an embodiment of an overvoltage detection module 4 provided by the present invention.

The difference between this embodiment and the overvoltage detection module 4 in the embodiment shown in FIG. 4 is that the second reference voltage unit U2 in this embodiment includes a third resistor R3, a fourth resistor R4 and a first capacitor C1; The first terminal of the third resistor R3 is the second reference voltage input terminal Vref2 of the second reference voltage unit U2, and the second terminal of the third resistor R3 is connected to the first terminal of the fourth resistor R4; The first end of the fourth resistor R4 is the second reference voltage output end of the second reference voltage unit U2, the second end of the fourth resistor R4 is grounded; the first capacitor C1 and the fourth Resistor R4 is connected in parallel.

Further, the overvoltage detection module 4 also includes a third capacitor C3 and a fourth capacitor C4; the positive pole of the third capacitor C3 is connected to the positive pole of the fourth capacitor C4, and the negative pole of the third capacitor C3 is connected to the The negative pole of the fourth capacitor C4, the positive pole of the third capacitor C3 is also connected to the first power supply signal Vcc and the positive power supply terminal of the voltage comparison unit, and the negative pole of the third capacitor C3 is grounded. Wherein, the third capacitor C3 and the fourth capacitor C4 are used for filtering and decoupling.

It should be noted that the third resistor R3 and the fourth resistor R4 are voltage dividing resistors, and the second reference voltage is divided by the third resistor R3 and the fourth resistor R4 and then sent to the second operational amplifier A2. Inverting input. The function of the first capacitor C1 is to prevent false triggering.

Referring to FIG. 6 , it is a schematic circuit diagram of another embodiment of an overvoltage detection module 4 provided by the present invention.

The difference between this embodiment and the overvoltage detection module 4 in the embodiment shown in FIG. 5 is that the second reference voltage unit U2 in this embodiment includes a Zener diode D3, a fifth resistor R5 and a sixth resistor R6; The first terminal of the fifth resistor R5 is the second reference voltage input terminal Vref2 of the second reference voltage unit U2, and the second terminal of the fifth resistor R5 is connected to the cathode of the Zener diode D3; the The cathode of the voltage stabilizing diode D3 is the second reference voltage output terminal of the second reference voltage unit U2, and the anode of the voltage stabilizing diode D3 is grounded; the sixth resistor R6 is connected in parallel with the voltage stabilizing diode D3.

It should be noted that the fifth resistor R5 acts as a voltage regulator to ensure that the output voltage is basically constant.

Referring to FIG. 7 , it is a schematic circuit diagram of another embodiment of an overvoltage detection module 4 provided by the present invention.

The difference between this embodiment and the overvoltage detection module 4 in the embodiment shown in FIG. 6 is that the second reference voltage unit U2 in this embodiment includes a three-terminal regulator D4, a seventh resistor R7, R8 and the ninth resistor R9; the three-terminal regulator D4 includes an anode, a cathode and a reference voltage terminal; the first terminal of the seventh resistor R7 is the second reference voltage input terminal of the second reference voltage unit U2 Vref2, the second end of the seventh resistor R7 is connected to the cathode of the three-terminal voltage regulator D4; the cathode of the three-terminal voltage regulator D4 is the second reference voltage output terminal of the second reference voltage unit U2 , the cathode of the three-terminal voltage regulator D4 is also connected to the first end of the eighth resistor R8, and the reference voltage terminal of the three-terminal voltage regulator D4 is connected to the second end of the eighth resistor R8 and the The first end of the ninth resistor R9 and the anode of the three-terminal regulator D4 are connected to the second end of the ninth resistor R9; the second end of the ninth resistor R9 is grounded.

Wherein, the three-terminal regulator D4 may be a TL431 three-terminal regulator D4. The TL431 series chip is a three-terminal adjustable shunt reference source with good thermal stability. Its output voltage can be set to any value from 2.5V to 36V with two resistors.

It should be noted that, in the switching power supply circuit provided in the above-mentioned embodiments, the voltage comparison unit and the latch unit 42 adopt “operational amplifier + diode”. In other embodiments, the voltage comparison unit and the latch unit 42 can also be Combination methods such as "operational amplifier + latch", "operational amplifier + relay" or "microcontroller + AD converter".

In addition, in the existing switching power supply circuit, the feedback loop control module 3 is used to control the output voltage to keep it stable under all circumstances. In the constant current switching power supply, the second sampling terminal of the feedback loop control module 3 is connected to a sampling resistor for current sampling in the switching power supply. In the constant voltage switching power supply, the second sampling terminal of the feedback loop control module 3 is connected to the voltage output terminal of the switching power supply to collect the output voltage signal. The utility model connects the comparison signal output terminal of the overvoltage detection module 4 to the second sampling terminal of the feedback loop control module 3, but the overvoltage detection module 4 only outputs a high-level signal when the output voltage of the switching power supply exceeds the threshold. The working state of the first operational amplifier A1 in the feedback loop control module 3 , when the output voltage of the switching power supply is normal, the overvoltage detection module 4 will not affect the work of the feedback loop control module 3 .

Compared with the prior art, the beneficial effects of a switching power supply circuit of the present invention are:

In the switching power supply circuit provided by the utility model, the comparison signal output terminal of the overvoltage detection module is connected to the feedback output terminal of the feedback loop control module. When the output voltage of the power supply module is greater than the threshold value, the overvoltage detection module continues to output high-level signals , the feedback output terminal of the feedback loop control module continuously outputs a low-level signal, the feedback input terminal of the power control module is pulled low, the power control module is turned off, and the entire power supply stops working to achieve the purpose of overvoltage protection. The utility model combines the original feedback loop control circuit and the overvoltage protection circuit in the switching power supply circuit to realize the overvoltage protection, reduces the number of components, reduces the circuit cost and improves the safety of the circuit.

The above is a preferred embodiment of the present utility model, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present utility model, some improvements and deformations can also be made, these improvements and deformations It is also regarded as the protection scope of the present utility model.

Claims (10)

1. a switching power circuit, it is characterised in that including: power module, overvoltage detection module, feedback loop control module and energy supply control module；

Described power module includes power input, controlled end and power output end；Described overvoltage detection module includes the first sampling end and comparison signal outfan；Described feedback loop control module includes the second sampling end and feedback output end；Described energy supply control module includes feedback input end and power control terminal；

First sampling end of described overvoltage detection module connects the power output end of described power module, and the comparison signal outfan of described overvoltage detection module connects the second sampling end of described feedback loop control module；The feedback output end of described feedback loop control module connects the feedback input end of described energy supply control module；The power control terminal of described energy supply control module connects the controlled end of described power module.

2. switching power circuit as claimed in claim 1, it is characterised in that described feedback loop control module includes the first reference voltage unit, the first operational amplifier, optocoupler, the first resistance and the second resistance；Described first reference voltage unit includes the first reference voltage input and the first reference voltage output end；

First inverting input of described first operational amplifier is the second sampling end of described feedback loop control module, first in-phase input end of described first operational amplifier connects the first reference voltage output end of described first reference voltage unit, and the first outfan of described first operational amplifier connects the second input of described optocoupler；Second input of described optocoupler is also connected with the second end of described second resistance, the first input end of described optocoupler connects the first end and second end of described first resistance of described second resistance, first outfan of described optocoupler is the feedback output end of described feedback loop control module, the second output head grounding of described optocoupler；The first of described first resistance terminates into the first power supply signal.

3. switching power circuit as claimed in claim 1, it is characterised in that described overvoltage detection module includes voltage comparison unit, latch units and the first diode；Described voltage comparison unit includes voltage input end and the second outfan；Described latch units includes data input pin and data output end；

The voltage input end of described voltage comparison unit is the first sampling end of described overvoltage detection module, described voltage input end connects the data output end of described latch units, and the second outfan of described voltage comparison unit connects anode and the data input pin of described latch units of described first diode；The negative electrode of described first diode is the comparison signal outfan of described overvoltage detection module.

4. switching power circuit as claimed in claim 3, it is characterised in that described overvoltage detection module also includes the second reference voltage unit；Described second reference voltage unit includes the second reference voltage input and the second reference voltage output end；Described voltage comparison unit also includes the 3rd reference voltage input；

Second reference voltage output end of described second reference voltage unit connects the 3rd reference voltage input of described voltage comparison unit.

5. switching power circuit as claimed in claim 4, it is characterised in that described second reference voltage unit includes the 3rd resistance, the 4th resistance and the first electric capacity；

Second reference voltage input that first end is described second reference voltage unit of described 3rd resistance, the second end of described 3rd resistance connects the first end of described 4th resistance；Second reference voltage output end that first end is described second reference voltage unit of described 4th resistance, the second end ground connection of described 4th resistance；Described first electric capacity and described 4th resistor coupled in parallel.

6. switching power circuit as claimed in claim 4, it is characterised in that described second reference voltage unit includes Zener diode, the 5th resistance and the 6th resistance；

Second reference voltage input that first end is described second reference voltage unit of described 5th resistance, the second end of described 5th resistance connects the negative pole of described Zener diode；The negative pole of described Zener diode is the second reference voltage output end of described second reference voltage unit, the plus earth of described Zener diode；Described 6th resistance is in parallel with described Zener diode.

7. switching power circuit as claimed in claim 4, it is characterised in that described second reference voltage unit includes three-terminal voltage-stabilizing pipe, the 7th resistance, the 8th resistance and the 9th resistance；Described three-terminal voltage-stabilizing pipe includes anode, negative electrode and reference voltage end；

Second reference voltage input that first end is described second reference voltage unit of described 7th resistance, the second end of described 7th resistance connects the negative electrode of described three-terminal voltage-stabilizing pipe；The negative electrode of described three-terminal voltage-stabilizing pipe is the second reference voltage output end of described second reference voltage unit, the negative electrode of described three-terminal voltage-stabilizing pipe is also connected with the first end of described 8th resistance, the reference voltage end of described three-terminal voltage-stabilizing pipe connects the second end and first end of described 9th resistance of described 8th resistance, and the anode of described three-terminal voltage-stabilizing pipe connects the second end of described 9th resistance；Second end ground connection of described 9th resistance.

8. switching power circuit as claimed in claim 4, it is characterised in that described voltage comparison unit is the second operational amplifier；

Described second operational amplifier includes the second in-phase input end, the second inverting input and the 3rd outfan；The voltage input end that second in-phase input end is described voltage comparison unit of described second operational amplifier, the 3rd reference voltage input that second inverting input is described voltage comparison unit of described second operational amplifier, second outfan that the 3rd outfan is described voltage comparison unit of described second operational amplifier.

9. the switching power circuit as described in any one of claim 1 to 7, it is characterised in that described overvoltage detection module also includes the first partial pressure unit；Described first partial pressure unit includes the tenth resistance, the 11st resistance and the second electric capacity；

First sampling end that first end is described overvoltage detection module of described tenth resistance, the second end of described tenth resistance connects the first end of described 11st resistance；Second end ground connection of described 11st resistance；Described second electric capacity and described 11st resistor coupled in parallel.

10. the switching power circuit as described in any one of claim 3 to 7, it is characterized in that, described latch units is the second diode, the data input pin that anode is described latch units of described second diode, the data output end that negative electrode is described latch units of described second diode.