CN202475245U - Switching power supply circuit - Google Patents

Abstract

The utility model discloses a switching power supply circuit, which comprises a primary side circuit, a secondary side circuit, a transformer and a control circuit, the secondary side circuit comprises a main output circuit and an auxiliary output circuit, the control circuit comprises a microcontroller, a main output switch circuit, a standby The voltage control circuit and the working state sampling circuit; the output terminal of the working state sampling circuit and the signal input terminal of the main output switch circuit; the signal input terminals of the standby voltage control circuit are respectively connected to the microcontroller, and the output terminal of the standby voltage control circuit is connected to the PWM control circuit Controller control signal input. The utility model only needs one converter, the circuit structure is simple, and the realization cost is low; in the standby working state, the main output circuit is closed, and the standby voltage output by the auxiliary output circuit is lower than the auxiliary power supply voltage in the normal working state, so that the converter Can work in a more power-saving state to achieve lower standby power consumption.

Description

A switching power supply circuit

[technical field]

The utility model relates to a switching power supply, in particular to a switching power supply circuit.

[Background technique]

In order to save energy, countries all over the world have stricter and stricter energy consumption standards for various electronic products, and have established mandatory "green power supply" standard requirements, such as the famous European Energy Star Many electronic products are often in a standby state, and the standby power needs to continuously consume grid power. Although the absolute power of a single power supply is not large when it is in standby, the total power consumption is also very large because of the large number of products. In order to reduce these useless consumption, according to different types of products, strict standby power consumption requirements are put forward for the power supply. The typical requirements are that the standby power consumption is less than 0.5W, and some even require the standby power consumption to be less than 0.3W.

In order to meet the requirements of low power consumption, many power chip manufacturers have developed and produced various types of green-mode PWM controllers (Green-Mode PWM Controller), such as the single-chip FAN6756, which is a highly integrated green-mode PWM controller. . The common feature of these chips is that when the circuit enters the standby state, the chip also enters the energy-saving working mode, such as adopting the method of frequency conversion, reducing the working frequency with the reduction of output power or adopting intermittent working mode to reduce switching loss. To achieve the purpose of energy saving.

When electronic products are in standby mode, the auxiliary voltage is generally about 5V, and the main output may be one output or multiple outputs. Although the PWM chip can realize the "green" working mode, because various electronic products have different requirements for working voltage and power, there are high voltage, low voltage, single channel, multiple channels, high power, and power Small, so it is difficult to have the best of both worlds by using a green mode PWM chip to meet the various output requirements of the power supply and to meet the low power consumption requirements of standby at the same time.

As shown in Figure 1, in order to meet the requirements of standby power consumption, the current commonly used power supply scheme is to use two converters: one for standby and low-voltage circuit output; the other for main power output. When it is in the standby state, only the standby circuit works, the main output converter is turned off, and the main converter is started only after receiving the normal work command signal.

Although the dual-converter method is easy to achieve low standby power consumption requirements, the main disadvantages are high cost and complex circuits. In addition, if the PCB layout is not handled well, it is easy to cause the two converters to interfere with each other, resulting in abnormal operation.

[Content of the invention]

The technical problem to be solved by the utility model is to provide a switching power supply circuit with simple structure, low cost and low standby power consumption.

In order to solve the above-mentioned technical problems, the technical solution adopted by the utility model is that a switching power supply circuit includes a primary side circuit, a secondary side circuit, a transformer and a control circuit, and the primary side circuit and the secondary side circuit are coupled through a transformer; the primary side circuit includes An inverter circuit driven by a PWM controller, the secondary side circuit includes a main output circuit and an auxiliary output circuit, and the control circuit includes a microcontroller, a main output switch circuit, a standby voltage control circuit and a working state sampling circuit; The output terminal of the working state sampling circuit is connected to the microcontroller, the signal input terminal of the main output switch circuit is connected to the main output switch control signal output terminal of the microcontroller; the signal input terminal of the standby voltage control circuit is connected to the standby voltage control signal of the microcontroller The output terminal, the output terminal of the standby voltage control circuit is connected to the control signal input terminal of the PWM controller.

In the switching power supply circuit described above, the main output circuit includes a first secondary winding of the transformer, a first rectification filter circuit and an output port, and the output end of the first secondary winding is connected to the output port through the first rectification filter circuit; The main output switch circuit includes a switch tube, a first voltage divider circuit, a second voltage divider circuit and a first NPN triode; the first end of the switch tube is connected to the positive output end of the first rectifier filter circuit, and the second end Connect to the positive pole of the output port; the first voltage divider circuit includes a first resistor and a second resistor connected in series, one end of the first voltage divider circuit is connected to the first end of the switch tube, the other end is connected to the collector of the first NPN triode, and the first resistor The connection point between the second resistor and the control pole of the switch tube; the second voltage divider circuit includes the third resistor and the fourth resistor connected in series, and one end of the second voltage divider circuit is connected to the main output switch control signal output of the microcontroller terminal, and the other end is grounded; the connection point between the third resistor and the fourth resistor is connected to the base of the first NPN transistor, and the emitter of the first NPN transistor is grounded; the negative output terminal of the first rectification filter circuit is grounded.

The switching power supply circuit described above includes a constant voltage control circuit and an optocoupler, and the auxiliary output circuit includes a second secondary winding of a transformer and a second rectification filter circuit, and the output terminal of the second secondary winding is connected to the second rectification filter circuit; the positive output end of the second rectification filter circuit is used as the positive output end of the auxiliary output circuit, and the negative output end of the second rectification filter circuit is grounded; the constant voltage control circuit includes a third voltage divider circuit, a bias resistor and a first shunt regulator device, the third voltage divider circuit includes the fifth resistor and the sixth resistor connected in series, one end of the third voltage divider circuit is connected to the positive output end of the first rectification filter circuit, and the other end is grounded; the fifth resistor and the sixth resistor The connection point is connected to the reference voltage terminal of the first shunt regulator, the anode of the first shunt regulator is grounded, and the cathode is connected to the positive output end of the second rectification filter circuit through a bias resistor; the anode of the optocoupler light-emitting diode is connected to the second rectification filter circuit The positive output end of the positive pole, the cathode is connected to the cathode of the first shunt regulator; the collector of the optocoupler phototransistor is connected to the control signal input end of the PWM controller, and the emitter is grounded.

In the switching power supply circuit described above, the standby voltage control circuit includes a voltage regulator tube and a second NPN triode, the cathode of the voltage regulator tube is connected to the cathode of the optocoupler light-emitting diode; the base of the second NPN transistor is connected to the microcontroller The standby voltage control signal output terminal, the emitter is grounded, and the collector is connected to the anode of the voltage regulator tube.

In the switching power supply circuit described above, the working state sampling circuit includes a current sampling circuit, and the current sampling circuit includes a sampling resistor and an amplifying circuit, the input terminal of the amplifying circuit is connected to the negative pole of the output port, and the negative pole of the output port passes through the sampling resistor grounded, and the output terminal of the amplifying circuit is connected to the input terminal of the current sampling circuit of the microcontroller.

The switching power supply circuit described above includes a linear voltage stabilizing circuit, and the linear voltage stabilizing circuit includes a third NPN transistor, a fourth voltage dividing circuit, a base resistor and a second shunt regulator, and one end of the fourth voltage dividing circuit Connect to the emitter of the third NPN transistor, and the other end is grounded; the fourth voltage divider circuit includes the seventh resistor and the eighth resistor in series, and the connection point between the seventh resistor and the eighth resistor is connected to the reference voltage of the second shunt regulator terminal; the cathode of the second shunt regulator is connected to the base of the third NPN transistor, and the anode is grounded; the collector of the third NPN transistor is connected to the positive output end of the second rectification filter circuit, and the emitter is connected to the power input end of the microcontroller; The base of the third NPN transistor is connected to the collector of the third NPN transistor through a base resistor.

In the switching power supply circuit described above, the working state sampling circuit includes a load access test circuit, and the load access test circuit includes a fourth voltage divider circuit, and the fourth voltage divider circuit includes a seventh resistor and an eighth resistor connected in series. Resistor; one end of the fourth voltage divider circuit is connected to the power input end of the microcontroller, and the other end is connected to the load input signal test end of the microcontroller, and the connection point between the seventh resistor and the eighth resistor is used as a sample for load access point.

The switching power supply circuit described above is characterized in that the transformer T1 is a flyback transformer. The switching power supply circuit is a battery charging circuit.

All the voltage outputs of the switching power supply circuit of the utility model come from the same converter, the circuit structure is simple, and the realization cost is low. When in the standby working state, the main output circuit is turned off; when in the standby state, it is only necessary to ensure a stable output voltage of the standby circuit. Can work in a more power-saving state to achieve lower standby power consumption.

[Description of drawings]

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described in further detail.

FIG. 1 is a functional block diagram of a switching power supply circuit in the prior art.

Fig. 2 is a functional block diagram of the switching power supply circuit of the embodiment of the utility model.

Fig. 3 is a schematic diagram of the main circuit part of the switching power supply circuit of the embodiment of the present invention.

Fig. 4 is a schematic diagram of the control circuit part of the switching power supply circuit in the embodiment of the utility model.

[Detailed ways]

In the embodiment of the switching power supply circuit of the present invention shown in Fig. 2 to Fig. 4, the switching power supply circuit is a battery charging circuit, and the battery charging circuit includes a primary side circuit, a secondary side circuit, a transformer T1 and a control circuit; the primary side circuit and The secondary circuit is coupled through a transformer T1, which is a flyback transformer; the control circuit includes a microcontroller U2 (Samsung SCM S3F9454).

The flyback transformer is called "FLY-BACK Transformer" in English. During the working process, when the input main switching tube of the control transformer is turned on, the primary winding of the transformer, that is, the primary inductance, is turned on, the transformer stores energy, the secondary winding has no energy output, and the output energy is provided by the energy stored in the secondary capacitor ; When the input main switching tube is cut off, the transformer input winding stops energy storage. During the cut-off period, the energy stored in the transformer is released through the secondary winding, and the energy is transferred to the secondary energy storage capacitor and load. The characteristics of the flyback transformer are: The primary winding stores energy when it is turned on, and discharges energy when it is turned off, just like an energy storage inductor.

The opposite of the flyback converter is the forward converter. The output of the forward transformer needs to be connected to the energy storage inductor and the freewheeling diode, but the flyback transformer does not need the energy storage inductor and the freewheeling diode. The circuit is simple and it is easy to realize multiple outputs.

The primary side circuit includes a switch tube Q5, a primary side coil T1H of the transformer T1 and a PWM controller IC1. The rectifier bridge BG1 and the capacitor EC1 constitute the input rectification filter circuit, the series circuit of the switch tube Q5 and the primary coil T1H of the transformer T1 is connected to the output terminal of the input rectification filter circuit; the PWM signal of the PWM controller IC1 (green mode PWM chip LD7576) The output terminal (pin 5 of IC1) is connected to the control pole of the switching tube Q5, which constitutes an inverter circuit driven by a PWM controller.

The secondary circuit includes a main output circuit and an auxiliary output circuit; the control circuit includes a microcontroller, a main output switch circuit, a standby voltage control circuit, a constant voltage control circuit and a working state sampling circuit.

The main output circuit includes a first secondary winding T1Y of the transformer T1, a first rectification and filtering circuit, and output ports VB+ and VB- of the battery charging circuit. The first rectifying and filtering circuit includes a rectifying diode D1, capacitors EC4 and C24, and the negative output end of the first rectifying and filtering circuit is grounded.

The main output switch circuit includes a main switch tube Q1, an NPN transistor Q3, a voltage regulator tube Z1, diodes D7, D8, an isolation diode D2, a capacitor C5, and resistors R10, R11, R18, and R20.

The first end (pin number 3) of the main switch tube Q1 is connected to the positive output terminal Vout-1 of the first rectification filter circuit through the isolation diode D2, and the second end (pin number 2) is connected to the positive output port VB+ of the output port; resistors R10, R11 is connected in series to form the first voltage divider circuit, one end of the resistor R10 is connected to the first end of the main switching tube Q1, one end of the resistor R11 is connected to the collector of the NPN transistor Q3 through the diode D8, and the connection point between the resistors R10 and R11 is connected to the main switch. The control pole of the switch tube Q1. The cathode of the voltage regulator tube Z1 is connected to the first end of the main switch tube Q1, and the anode is connected to the control electrode of the main switch tube Q1; the capacitor C5 is connected in parallel with the voltage regulator tube Z1.

Resistors R18 and R20 are connected in series to form a second voltage divider circuit, and one end ON/OFF-2 of the resistor R20 is used as the control signal input terminal of the main output switch circuit to connect to the main output switch control signal output terminal ON/OFF-2 of the microcontroller U2, One end of the resistor R18 is grounded; the connection point between the resistors R18 and R20 is connected to the base of the NPN transistor Q3, and the emitter of the NPN transistor Q3 is grounded. The cathode of the diode D7 is connected to the base of the NPN transistor Q3, and the anode is connected to the emitter of the NPN transistor Q3.

When the signal of ON/OFF-2 is high level, the main switch tube Q1 is turned on, and the main output circuit can output; when the signal of ON/OFF-2 is low level, the main switch tube Q1 is turned off, and the main output circuit is closed .

The auxiliary output circuit includes a second secondary winding T1X of the transformer T1, a resistor R16, a rectifier diode D5, capacitors C4 and EC6. The output terminal of the second secondary winding T1X is connected to the second rectification filter circuit composed of the rectifier diode D5, capacitor C4 and EC6 through the resistor R16; the positive output terminal VAUX of the second rectification filter circuit is used as the positive output terminal of the auxiliary output circuit, and the second The negative output end of the rectification filter circuit is grounded.

The constant voltage control circuit of the main output (Vout-1) includes resistors R28, R29, R30, R31, R32, R82, RW1, capacitor C10, bias resistor R27 and shunt regulator U1 (TL431).

Resistors R28, R29, R30, R31, R32, R82, and RW1 form a third voltage divider circuit to obtain a voltage sampling signal at the main output terminal Vout-1. One end of the third voltage dividing circuit R30, R32 is connected as the signal input terminal Vout-1 of the constant voltage control circuit to the positive output terminal Vout-1 (42V/2A) of the first rectification filter circuit, and the third voltage dividing circuit R28, R31 One end is grounded; the connection point between the third voltage divider circuit R30, R32 and R28, R31 is connected to the voltage reference terminal R of the shunt regulator U1 (the signal input terminal R of the shunt regulator), the anode of the shunt regulator U1 is grounded, and the cathode passes through The bias resistor R27 is connected to the positive output terminal VAUX of the second rectification filter circuit; after the resistor R29 and the capacitor C10 are connected in series, one end is connected to the reference voltage terminal of the shunt regulator U1, and the other end is connected to the cathode of the shunt regulator U1; the optocoupler The anode of the P1 light-emitting diode is connected to the positive output terminal VAUX of the second rectification filter circuit through the resistor R26, and the cathode is connected to the cathode of the shunt regulator U1; the collector of the optocoupler P1 phototransistor is connected to the control signal input terminal of the PWM controller IC1 (IC1's Pin 2), the emitter is grounded.

When the voltage of the positive output terminal Vout-1 of the first rectification and filtering circuit changes, the voltage value of the reference terminal (R) of the shunt regulator U1 (TL431) of the constant voltage control circuit changes through the voltage sampling of the third voltage dividing circuit, and the After the signal is compared and amplified inside the shunt regulator, it is fed back to the control signal input terminal of the PWM controller IC1 through the optocoupler, so that the voltage of the positive output terminal Vout-1 of the first rectification and filtering circuit remains constant.

The standby voltage control circuit includes a voltage regulator tube Z4, resistors R62, R63 and NPN transistor Q9, the cathode of the voltage regulator tube Z4 is connected to the cathode of the light-emitting diode of the optocoupler P1 through the common electrical node VP; the base of the NPN transistor Q9 is connected to the micrometer through the resistor R63 The standby voltage control signal output terminal STB of the controller U2, the emitter is grounded, the collector is connected to the anode of the regulator tube Z4; the resistor R62 is connected between the base and the emitter of the NPN transistor Q9.

When the battery charging circuit is on standby, the standby voltage control signal output terminal STB of the microcontroller U2 sends a high level, the NPN transistor Q9 is turned on, and the anode of the voltage regulator tube Z4 is grounded, and the 5.1V voltage regulator tube Z4 is connected to the constant voltage In the voltage control circuit, the constant voltage control circuit of the main voltage output (Vout-1 terminal) is disabled, and fed back to the control signal input terminal of the PWM controller IC1 through the optocoupler, and at the same time, the output voltage VAUX of the auxiliary output circuit is changed from 25V down to 7.5V.

The output voltage VAUX of the auxiliary output circuit is supplied to the microcontroller U2 through a linear voltage regulator circuit to provide a standby voltage of 5V with high voltage regulation accuracy (VR=5V). The linear regulator circuit includes NPN transistor Q6, shunt regulator IC2, capacitor C11, resistors R38, R39, R40 and R48.

Resistors R39 and R40 are connected in series to form the fourth voltage divider circuit, one end of the fourth voltage divider circuit R39 is connected to the emitter of the NPN transistor Q6, and one end of the fourth voltage divider circuit R40 is grounded; the connection point between the resistors R39 and R40 is connected to the shunt regulator The reference voltage terminal of the regulator IC2; the cathode of the shunt regulator IC2 is connected to the base of the NPN transistor Q6, and the anode is grounded; the collector of the NPN transistor Q6 is connected to the positive output terminal VAUX of the second rectification filter circuit, and the emitter is connected to the microcontroller U2 Power supply input terminal Vdd; the base of NPN transistor Q6 is connected to the collector of NPN transistor Q6 through the base resistance composed of resistors R38 and R48 connected in parallel; capacitor C11 is connected between the reference voltage terminal and cathode of shunt regulator IC2.

The working state sampling circuit includes a current sampling circuit. The current sampling circuit includes a sampling resistor R19 and an amplifier circuit mainly composed of operational amplifier IC3B. The input terminal of the amplifier circuit is connected to the negative output port VB- of the battery charging circuit, and the negative output port VB- passes through the sampling The resistor R19 is grounded, the output terminal IS of the amplifying circuit is connected to the input terminal IS of the current sampling circuit of the microcontroller U2, and the microcontroller U2 determines the working state of the main output circuit through the current sampling signal.

The working state sampling circuit also includes a load access test circuit, the load access test circuit includes a fourth voltage divider circuit composed of resistors R45 and R46 in series, one end of the fourth voltage divider circuit is connected to the power input terminal Vdd of the microcontroller U2, The other end is connected to the load access signal test end of the microcontroller U2 (the 19th pin of U2), and the connection point NTC between the resistors R45 and R46 is used as a sampling point for external load access.

The NTC port of the load access test circuit is the input terminal of the battery pack access signal, and the signal is sent to the microcontroller U2 for detection to determine the access status of the battery pack and send out a "standby/work" signal.

When the battery is not connected or the battery is fully charged, the charging circuit stops charging and enters the standby state. When entering the standby state, the microcontroller U2 sends ON/OFF-2 low-level signal to turn off the main output switch Q1, the output port VB+, VB- has no output voltage, and the microcontroller U2 sends a STB high-level standby control signal (5V), the transistor Q9 is turned on, and the 5.1V voltage regulator tube Z4 is connected to the constant voltage control circuit, so that the constant voltage control circuit of the main output Vout-1 loses its control function, and the constant voltage control is performed by the standby voltage control circuit .

When it is detected that a battery is connected and needs to be charged normally, the microcontroller U2 sends a low-level signal of STB, the transistor Q9 is disconnected, the regulator tube Z4 loses its function, and the standby voltage control circuit is replaced by the constant voltage control circuit of the main output. The main output is 42V, and the auxiliary voltage Vaux output reaches 25V. At the same time, the microcontroller U2 sends an ON/OFF-2 high-level signal (5V), and the main output switch Q1 is turned on, allowing the battery pack to be charged.

When the charging circuit is in standby mode, the standby voltage control circuit only needs to maintain the stability of the auxiliary power supply (Vaux) at 7.5V to ensure that the microcontroller has a stable working voltage of 5V. The main output circuit switch Q1 is disconnected, regardless of the main voltage output. Voltage value, so the main output voltage is less than 42V. At this time, the green voltage PWM chip LD7576 works in the energy-saving mode of low frequency and low duty cycle. , D5) switching losses, conduction losses, false load (R17) losses are reduced to a minimum.

The above embodiments of the utility model have the following beneficial effects:

1. All voltage outputs come from the same converter, and the working process of the converter is controlled by the "green mode PWM chip". The circuit structure is simple and the cost is low.

2. The output circuit has two independent output voltage control loops, and only one voltage control loop works at the same time. When it is in the standby working state, the standby output voltage control loop works, the main output voltage control loop does not work, and the main output is turned off; when it is in the normal working state, the main output voltage control loop works, the standby voltage output control Loop doesn't work. The two voltage control loops are controlled by the standby/working control signal, the standby or normal working state is automatically detected by the control circuit, and the automatic switching is completed.

3. When in standby mode, since only the standby voltage control loop works, it is only necessary to ensure a stable output voltage (low voltage) of the standby circuit, the main circuit is turned off, and the output of the main voltage can be ignored, the green mode "PWM chip It can work in an energy-saving mode with a lower frequency and a lower duty cycle than under normal working conditions, so that the converter can work in a more power-saving state and achieve the goal of low standby power consumption and energy saving.

Claims (9)

1. a switching power circuit comprises former limit circuit, secondary circuit, transformer and control circuit, and former limit circuit and secondary circuit are through transformer coupled; Former limit circuit comprises the inverter circuit by the PWM controller drives; It is characterized in that; Described secondary circuit comprises main output circuit and auxiliary output circuit, and described control circuit comprises microcontroller, main output switch circuit, standby voltage control circuit and operating state sample circuit; The output termination microcontroller of operating state sample circuit, the signal input part of main output switch circuit connect the main output switch control signal output of microcontroller; The signal input part of standby voltage control circuit connects the standby voltage control signal output of microcontroller, the output termination PWM controller control signal input of standby voltage control circuit.

2. switching power circuit according to claim 1; It is characterized in that; Described main output circuit comprises the first secondary winding, first current rectifying and wave filtering circuit and the output port of transformer, and the output of the first secondary winding connects output port through first current rectifying and wave filtering circuit; Described main output switch circuit comprises switching tube, first bleeder circuit, second bleeder circuit and a NPN triode; The cathode output end of first termination, first current rectifying and wave filtering circuit of said switching tube, the second termination output port is anodal; First bleeder circuit comprises first resistance and second resistance of series connection, first end of a termination switching tube of first bleeder circuit, and the collector electrode of another termination the one NPN triode, the tie point between first resistance and second resistance connects the control utmost point of switching tube; Second bleeder circuit comprises the 3rd resistance and the 4th resistance of series connection, the main output switch control signal output of a termination microcontroller of second bleeder circuit, other end ground connection; Tie point between the 3rd resistance and the 4th resistance connects the base stage of a NPN triode, the grounded emitter of a NPN triode; The cathode output end ground connection of first current rectifying and wave filtering circuit.

3. switching power circuit according to claim 2; It is characterized in that; Comprise constant-voltage control circuit and optocoupler, described auxiliary output circuit comprises the second secondary winding and second current rectifying and wave filtering circuit of transformer, output termination second current rectifying and wave filtering circuit of the second secondary winding; The cathode output end of second current rectifying and wave filtering circuit is as the cathode output end of auxiliary output circuit, the cathode output end ground connection of second current rectifying and wave filtering circuit; Constant-voltage control circuit comprises the 3rd bleeder circuit, offset resistance and first parallel regulator, and the 3rd bleeder circuit comprises the 5th resistance and the 6th resistance of series connection, the cathode output end of a termination first current rectifying and wave filtering circuit of the 3rd bleeder circuit, other end ground connection; Tie point between the 5th resistance and the 6th resistance connects the reference voltage end of first parallel regulator, the plus earth of first parallel regulator, and negative electrode connects the cathode output end of second current rectifying and wave filtering circuit through offset resistance; The anode of optocoupler light-emitting diode connects the cathode output end of second current rectifying and wave filtering circuit, and negative electrode connects the negative electrode of first parallel regulator; The collector electrode of optocoupler phototriode connects PWM controller control signal input, grounded emitter.

4. switching power circuit according to claim 3 is characterized in that, described standby voltage control circuit comprises voltage-stabiliser tube and the 2nd NPN triode, and the negative electrode of voltage-stabiliser tube connects the negative electrode of optocoupler light-emitting diode; The base stage of the 2nd NPN triode connects the standby voltage control signal output of microcontroller, grounded emitter, and collector electrode connects the anode of voltage-stabiliser tube.

5. switching power circuit according to claim 1; It is characterized in that; Said operating state sample circuit comprises current sampling circuit, and described current sampling circuit comprises sampling resistor and amplifying circuit, the negative pole of the input termination output port of amplifying circuit; The negative pole of output port is through sampling resistor ground connection, the output termination microcontroller current sampling circuit input of amplifying circuit.

6. switching power circuit according to claim 1; It is characterized in that; Comprise linear voltage-stabilizing circuit; Described linear voltage-stabilizing circuit comprises the 3rd NPN triode, the 4th bleeder circuit, base resistance and second parallel regulator, the emitter of a termination the 3rd NPN triode of the 4th bleeder circuit, other end ground connection; The 4th bleeder circuit comprises the 7th resistance and the 8th resistance of series connection, and the tie point between the 7th resistance and the 8th resistance connects the reference voltage end of second parallel regulator; The negative electrode of second parallel regulator connects the base stage of the 3rd NPN triode, plus earth; The collector electrode of the 3rd NPN triode connects the cathode output end of second current rectifying and wave filtering circuit, and emitter connects the power input of microcontroller; The base stage of the 3rd NPN triode connects the collector electrode of the 3rd NPN triode through base resistance.

7. switching power circuit according to claim 1; It is characterized in that; Said operating state sample circuit comprises that load inserts test circuit, and described load inserts test circuit and comprises the 4th bleeder circuit, and the 4th bleeder circuit comprises the 7th resistance and the 8th resistance of series connection; The power input of one termination microcontroller of the 4th bleeder circuit, the load of another termination microcontroller inserts the signal testing end, the sampled point that the tie point between the 7th resistance and the 8th resistance inserts as load.

8. switching power circuit according to claim 1 is characterized in that, described transformer T1 is anti-violent change depressor.

9. switching power circuit according to claim 1 is characterized in that described switching power circuit is a battery charger.

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