CN205490211U - Miniwatt switching power supply circuit of multiplexed output - Google Patents

Abstract

The utility model discloses a low-power switching power supply circuit with multi-channel output, which comprises a pre-stage protection circuit, a rectification circuit, a peak current suppression circuit, a switching transformer, a high-frequency rectification output circuit, a main control circuit, and a current detection circuit connected in sequence. circuit, voltage feedback circuit and reference voltage circuit; the main control circuit is connected to the rectifier circuit, peak current suppression circuit, switching transformer, current detection circuit and voltage feedback circuit respectively, and the reference voltage circuit is connected to the voltage feedback circuit and high-frequency rectification output circuit respectively , the switching transformer is multi-channel output; the main control circuit is connected with the peak current suppression circuit through the switching device, which is used to stabilize the output of multiple DC voltages by controlling the ratio between the turn-on and turn-off time of the switch device, and is used to control the output voltage. Value through the reference voltage circuit and voltage feedback circuit to achieve closed-loop feedback control. To achieve wide voltage operation, it has the ability to output multiple stable voltages, which can meet different voltage requirements.

Description

A low-power switching power supply circuit with multiple outputs

technical field

The utility model relates to a switching power supply circuit, in particular to a low-power switching power supply circuit with multiple outputs, and belongs to the technical field of switching power supplies.

Background technique

Alternating current is the most commonly used energy source in daily life. With the continuous development of power electronic conversion technology and switching power supply technology, switching power supply, as an alternating current conversion device, has been widely used in electronic products based on its small size and high conversion efficiency. .

However, the current switching power supply still has the disadvantages of single output, unable to meet various requirements of life and industry, unable to operate with wide voltage, unable to adapt to more occasions, poor load capacity, and high production cost.

Utility model content

The main purpose of the utility model is to overcome the deficiencies in the prior art and provide a low-power switching power supply circuit with multi-channel output, which is especially suitable for various complex low-power electric places.

The technical problem to be solved by the utility model is to provide a low-power switching power supply circuit with compact structure, convenient disassembly and assembly, easy manufacture, safety, reliability and strong practicability, which can operate at a wide voltage and has the ability to output multiple voltages. The invention can meet different voltage requirements, and has stable output voltage, low cost, and extremely has industrial utilization value.

In order to achieve the above object, the technical solution adopted in the utility model is:

A low-power switching power supply circuit with multiple outputs, including a pre-protection circuit, a rectification circuit, a peak current suppression circuit, a switching transformer and a high-frequency rectification output circuit connected in sequence, as well as a main control circuit, a current detection circuit, and a voltage feedback circuit and a reference voltage circuit; the main control circuit is respectively connected with a rectifier circuit, a peak current suppression circuit, a switching transformer, a current detection circuit and a voltage feedback circuit, and the reference voltage circuit is connected with a voltage feedback circuit and a high-frequency rectification output circuit respectively.

Wherein, the switching transformer includes a primary winding and a feedback winding on the input side, a primary output winding and a secondary output winding on the output side; the primary winding of the switching transformer is connected to the output terminal of the peak current suppression circuit, and the feedback of the switching transformer The winding feedback is connected to the main control circuit, and the main output winding of the switching transformer is connected to the reference voltage circuit through the voltage value output by the high-frequency rectification output circuit.

Moreover, the input terminal of the pre-stage protection circuit is connected to the alternating current, the main control circuit is connected to the peak current suppressing circuit through the switch device, and the main control circuit is used to control the ratio between the on time and the off time of the switch device To stabilize the output of multiple DC voltages, and to realize closed-loop feedback control of the output voltage value through the reference voltage circuit and the voltage feedback circuit.

The utility model is further configured as follows: the pre-stage protection circuit includes a fuse and a thermistor connected in series with the two output terminals of the alternating current respectively, a conjugate inductor connected in series with the fuse and the thermistor, and a conjugate inductor connected in parallel with the conjugate inductor safety capacitor.

The utility model is further set as: the rectifier circuit is a rectifier bridge circuit, including a bridge rectifier and a filter capacitor, the two input terminals of the bridge rectifier are connected with the output terminals of the previous stage protection circuit, and the two output terminals of the bridge rectifier respectively connected to the positive pole and the negative pole of the filter capacitor; the positive pole of the filter capacitor is connected to the input terminal of the peak current suppression circuit, and the negative pole of the filter capacitor is grounded.

The utility model is further set as: the peak current suppression circuit includes an RCD circuit and a transient suppression diode, and the RCD circuit is connected in parallel with both ends of the primary winding of the switching transformer; the RCD circuit includes a first resistor and a first capacitor An RC parallel branch connected in parallel, and a protection diode connected in series with the RC parallel branch; the transient suppression diode is connected in parallel with the RC parallel branch; one end of the first resistor, one end of the first capacitor and the transient The anodes of the suppression diodes are all connected to one end of the primary winding of the switching transformer, and the anodes of the protection diodes are connected to the other end of the primary winding of the switching transformer.

The utility model is further configured as follows: the switching transformer is a three-way output transformer, and the main output winding and the secondary output winding on the output side are respectively two-way output and one-way output.

The utility model is further set as: the high-frequency rectification output circuit includes a plurality of rectification units with the same structure respectively connected to each output of the switching transformer output side, and the rectification unit includes an output rectification circuit, a π-type filter circuit and a DCR circuit.

Wherein, the output rectification circuit includes a Schottky diode, a second resistor and a second capacitor, and the second resistor and the second capacitor are connected in parallel at both ends of the Schottky diode in series; the π-type filter circuit includes sequentially A third capacitor, a first inductor and a fourth capacitor connected in series, the DCR circuit includes a first diode, a ceramic capacitor and a third resistor connected in parallel in sequence; one end of the first inductor is connected to the negative pole of the Schottky diode The other end of the first inductor is connected to the cathode of the first diode; the cathode of the third capacitor, the cathode of the fourth capacitor and the anode of the first diode are all grounded.

The utility model is further configured as follows: the main control circuit includes a UC3842 chip, and the switching device is an N-MOS tube.

Wherein, the power supply terminal of the UC3842 chip is connected to the output terminal of the rectifier circuit through a starting resistor, grounded through a starting capacitor, and connected to the feedback winding of a switching transformer through a fourth resistor and a rectifying diode connected in series in sequence, the starting capacitor The cathode is grounded, and the cathode of the rectifier diode is connected to the fourth resistor;

Wherein, the feedback voltage input terminal of the UC3842 chip is connected with the output terminal of the voltage feedback circuit, the feedback current input terminal of the UC3842 chip is connected with the source of the N-MOS tube through the current detection circuit; the drain of the N-MOS tube It is connected to the peak current suppression circuit, and the gate of the N-MOS transistor is connected to the push-pull output terminal of the UC3842 chip through the second diode; the anode of the second diode is connected to the gate of the N-MOS transistor, and the second diode A fifth resistor is connected in parallel on both sides of the second diode, and the anode of the second diode is connected to the ground terminal of the UC3842 chip through the sixth resistor.

The utility model is further configured as: the current detection circuit includes a seventh resistor and an eighth resistor connected in sequence, one end of the seventh resistor is connected to the main control circuit, the other end of the seventh resistor and one end of the eighth resistor are both It is connected with the switching device, and the other end of the eighth resistor is grounded.

The utility model is further set as: the voltage feedback circuit includes a photoelectric coupler, one input end of the photoelectric coupler is grounded through the ninth resistor and the fifth capacitor connected in series in sequence, and the other input end is connected to the output end of the reference voltage circuit connected, and a sixth capacitor is connected in parallel between the two output terminals of the optocoupler.

The utility model is further set as: the reference voltage circuit includes TL431, the cathode of the TL431 is connected to the voltage feedback circuit, and connected to the output voltage value through the tenth resistor, the seventh capacitor and the eleventh resistor connected in sequence, The anode of the TL431 is grounded and connected to the input terminal of the eleventh resistor through an adjustable resistor, and the reference terminal of the TL431 is connected to the adjustment terminal of the adjustable resistor.

Compared with the prior art, the utility model has the beneficial effects of:

Through the setting of the pre-stage protection circuit, rectification circuit, peak current suppression circuit, switching transformer and high-frequency rectification output circuit, as well as the main control circuit, current detection circuit, voltage feedback circuit and reference voltage circuit, the switching transformer includes the input side The primary winding and the feedback winding, the main output winding and the secondary output winding on the output side, provide a switching transformer for multi-channel DC-DC voltage conversion; and control the ratio between the turn-on time and the turn-off time of the switching device through the main control circuit. Stable output of multiple DC voltages, and the closed-loop feedback control of the output voltage value through the reference voltage circuit and voltage feedback circuit, can operate at a wide voltage, and has the ability to output multiple voltages, so as to meet different voltage requirements and ensure output The voltage is stable.

The above content is only an overview of the technical solution of the utility model. In order to understand the technical means of the utility model more clearly, the utility model will be further described below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is the circuit diagram of a kind of multi-channel output low-power switching power supply circuit of the utility model;

Fig. 2 is the circuit diagram of the pre-stage protection circuit and the rectifier circuit in a kind of multi-channel output low power switching power supply circuit of the utility model;

Fig. 3 is the circuit diagram of peak current suppressing circuit and switching transformer in the low-power switching power supply circuit of a kind of multi-channel output of the utility model;

Fig. 4 is the circuit diagram of switching transformer in the low-power switching power supply circuit of a kind of multi-channel output of the utility model;

Fig. 5 is a circuit diagram of a switching transformer and a high-frequency rectification output circuit in a low-power switching power supply circuit with multiple outputs of the present invention;

Fig. 6 is a circuit diagram of the main control circuit and the current detection circuit in the low-power switching power supply circuit of a kind of multi-channel output of the utility model;

FIG. 7 is a circuit diagram of a voltage feedback circuit and a reference voltage circuit in a multi-output low-power switching power supply circuit of the present invention.

detailed description

Below in conjunction with accompanying drawing of description, the utility model is described further.

A low-power switching power supply circuit with multiple outputs as shown in Figure 1, including a pre-stage protection circuit 1, a rectification circuit 2, a peak current suppression circuit 3, a switching transformer U1 and a high-frequency rectification output circuit 4 connected in sequence, and The main control circuit 5, the current detection circuit 6, the voltage feedback circuit 7 and the reference voltage circuit 8; the main control circuit 5 is respectively connected with the rectification circuit 2, the peak current suppression circuit 3, the switching transformer U1, the current detection circuit 6 and the voltage feedback circuit 7, and the reference voltage circuit 8 is connected to the voltage feedback circuit 7 and the high frequency rectification output circuit 4 respectively.

As shown in Figures 1 and 4, the switching transformer U1 includes a primary winding (tap 0, 1) and a feedback winding (tap 2, 3) on the input side, and a main output winding (tap 6, 7, 8) on the output side. taps) and secondary output windings (4, 5 taps); the primary winding of the switching transformer U1 is connected to the output terminal of the peak current suppression circuit 3, the feedback winding of the switching transformer U1 is connected to the main control circuit 5, and the switching transformer U1’s The main output winding is connected to the reference voltage circuit 8 through the voltage value output by the high frequency rectification output circuit 4 .

As shown in Figure 1, the input terminal of the pre-stage protection circuit 1 is connected to the alternating current, the main control circuit 5 is connected to the peak current suppression circuit 3 through the switching device K1, and the main control circuit 5 is used to control the switching device K1 The ratio between the turn-on time and the turn-off time is used to stabilize the output of multiple DC voltages, and is used to realize closed-loop feedback control of the output voltage value through the reference voltage circuit 8 and the voltage feedback circuit 7 .

As shown in Figure 2, the pre-stage protection circuit 1 includes a fuse fuse1 and a thermistor R5 connected in series with the two output terminals of the alternating current, a conjugate inductance L1 connected in series with the fuse fuse1 and the thermistor R5, and The safety capacitor C1 connected in parallel with the conjugate inductance L1 can prevent basic circuit problems such as short circuit and overload in the previous stage, and can suppress electromagnetic interference and prevent electromagnetic channeling in the power supply from flowing into the power grid.

As shown in Figure 2, the rectifier circuit 2 is a rectifier bridge circuit, including a bridge rectifier and a filter capacitor C7, the two input terminals of the bridge rectifier are connected with the output terminals of the pre-stage protection circuit 1, and the two input terminals of the bridge rectifier are connected to each other. The output terminals are respectively connected to the positive pole and the negative pole of the filter capacitor C7; the positive pole of the filter capacitor C7 is connected to the input terminal of the peak current suppression circuit 3, and the negative pole of the filter capacitor C7 is grounded.

As shown in Figure 3, the peak current suppression circuit 3 includes an RCD circuit and a transient suppression diode D2, and the RCD circuit is connected in parallel with both ends of the primary winding of the switching transformer U1; the RCD circuit includes a first resistor R2 and a The RC parallel branch connected in parallel with the first capacitor phase C6, and the protection diode D4 connected in series with the RC parallel branch; the transient suppression diode D2 is connected in parallel with the RC parallel branch; one end of the first resistor R2, the second One end of a capacitor C6 and the anode of the transient suppression diode D2 are both connected to one end of the primary winding of the switching transformer U1, and the anode of the protective diode D4 is connected to the other end of the primary winding of the switching transformer U1. Since the switching devices of the switching power supply will be frequently turned on and off during the working process, the existence of capacitance and inductance in the circuit will generate surge voltage and noise. The existence of surge voltage and noise not only affects the quality and stability of the power supply output, but also There is a lot of damage to the circuit components, so adding a peak current suppression circuit 3 on the primary winding side of the switching transformer can ensure the stability of the output voltage.

As shown in Figure 3 and Figure 4, the switching transformer U1 is a three-way output transformer, and the main output winding (6, 7, 8 taps) and the secondary output winding (4, 5 taps) on the output side are respectively two-way output and one output; and the secondary output winding is independent from the primary output winding. Among them, the No. 6 and No. 7 taps of the switching transformer U1 are one output, and the No. 7 and No. 8 taps of the switching transformer U1 are one output; the No. 7 tap is the reference voltage of the positive and negative power supply, which is not zero level. The component is connected to the negative terminal of TL431.

In this embodiment, taps 6, 7, and 8 of the switching transformer U1 can output positive and negative DC power of 12V, and taps 4 and 5 can output positive DC power of 5V; the 5V DC power is output independently and does not share the ground with other outputs. Among them, the winding process of switching transformer U1 is as follows: the primary winding is wound first, and the winding method is to wind 36 turns with a 0.3mm diameter enameled wire from pin 1 (that is, the tap), and then end on pin 0; then wind the main output winding, The winding method starts with 2 wires with a diameter of 0.8mm and winds 6 times from pin 8, and then ends on pin 7; then winds 6 times and also adds two layers of high-temperature tape for insulation treatment, and ends on pin 6; then wind the secondary winding , The winding method uses an enameled wire with a diameter of 0.8mm to start from the 5th foot and wind it 4 times and return to the 4th foot to complete the winding of the secondary output winding. Finally, the feedback winding is wound, and the winding method uses an enameled wire with a diameter of 0.8mm to wind 7 times from pin 2 back to pin 3 and end.

As shown in Figure 5, the high-frequency rectification output circuit 4 includes a number of rectification units with the same structure connected to each output of the switching transformer U1 output side, the rectification unit includes an output rectification circuit 41, a π-type filter circuit 42 and DCR circuit 43.

Wherein, the rectification unit takes 5V single output as an example. The output rectification circuit 41 includes a Schottky diode SR3, a second resistor R10 and a second capacitor C16, and the second resistor R10 and the second capacitor C16 are connected in parallel at both ends of the Schottky diode SR3 after being connected in series; the π The type filter circuit 42 includes a third capacitor C13, a first inductor L3 and a fourth capacitor C14 connected in series in sequence, and the DCR circuit 43 includes a first diode D5, a ceramic chip capacitor C15 and a third resistor R9 connected in parallel in sequence; One end of the first inductance L3 is connected to the cathode of the Schottky diode SR3, and the other end of the first inductance L3 is connected to the cathode of the first diode D5; the cathode of the third capacitor C13 and the cathode of the fourth capacitor C14 and the anode of the first diode D5 are grounded.

As shown in FIG. 6 , the main control circuit 5 includes a UC3842 chip U2, and the switching device K1 is an N-MOS transistor.

Wherein, the power supply terminal (pin 7) of the UC3842 chip U2 is connected to the output terminal of the rectifier circuit 2 through the start-up resistor R1, grounded through the start-up capacitor C12, and connected to the switch through the fourth resistor R14 and the rectifier diode D7 connected in series in sequence. The feedback winding T3 of the transformer U1 is connected, the cathode of the starting capacitor C12 is grounded, the cathode of the rectifier diode D7 is connected to the fourth resistor R14; the feedback voltage input terminal (pin 1) of the UC3842 chip U2 is connected to the voltage feedback circuit 7, the feedback current input terminal (pin 3) of the UC3842 chip U2 is connected to the source D terminal of the N-MOS tube through the current detection circuit 6; the drain S terminal of the N-MOS tube is connected to the peak current The suppression circuit 3 is connected, and the gate of the N-MOS transistor is connected to the push-pull output terminal (pin 6) of the UC3842 chip U2 through the second diode D6; the anode of the second diode D6 is connected to the N-MOS transistor The gate of the second diode D6 is connected in parallel with the fifth resistor R11, and the anode of the second diode D6 is connected to the ground terminal (pin 5) of the UC3842 chip U2 through the sixth resistor R15.

As shown in Figure 6, the current detection circuit 6 includes a seventh resistor R13 and an eighth resistor R18 connected in sequence, one end of the seventh resistor R13 is connected to the main control circuit 5, and the other end of the seventh resistor R13 is connected to the eighth resistor R13. One ends of the eight resistors R18 are all connected to the switch device, and the other end of the eighth resistor R18 is grounded.

As shown in FIG. 7 , the voltage feedback circuit 7 includes a photocoupler PC1, one input terminal of the photocoupler PC1 is grounded through the ninth resistor R17 and the fifth capacitor C18 connected in series in sequence, and the other input terminal is connected to the reference voltage The output terminals of the circuit 8 are connected, and a sixth capacitor C21 is connected in parallel between the two output terminals of the photocoupler PC1.

As shown in FIG. 7, the reference voltage circuit 8 includes a TL431, the cathode of the TL431 is connected to the voltage feedback circuit 7, and is connected to the output through the tenth resistor R16, the seventh capacitor C20 and the eleventh resistor R12 connected in sequence. The voltage values are connected, the anode of the TL431 is grounded and connected to the input terminal of the eleventh resistor R12 through the adjustable resistor RW, and the reference terminal of the TL431 is connected to the adjusting terminal of the adjustable resistor RW.

The utility model provides a switching power supply circuit based on the UC3842 chip, which is a multi-output switching power supply circuit, which directly samples the output voltage, processes the output voltage and transmits the voltage signal to the main control circuit 5, and has output positive 12V DC and negative 12V DC, and the ability to output independent 5V DC. Among them, the UC3842 chip used is a high-performance single-ended output current-controlled pulse width modulator chip.

The input and output process is as follows: input AC voltage in the range of 86V ~ 265V, the AC power passes through the pre-stage protection circuit, and then rectifies into DC power through the rectifier bridge. Connect a switching device controlled by a PWM wave, the secondary output is rectified and filtered by a high-frequency rectifier circuit, the output voltage value passes through a reference voltage circuit based on TL431, and the secondary voltage signal is converted by a voltage feedback circuit composed of a photocoupler Feedback to the main control circuit of the main stage; the main control circuit changes the duty cycle of the PWM wave controlling the switching device through the feedback voltage signal and current signal. In the whole process, the main control circuit with the UC3842 chip as the core realizes the adjustment of the voltage value to achieve a constant output.

The above are only preferred embodiments of the present utility model, and do not limit the utility model in any form. Although the utility model has been disclosed as above with preferred embodiments, it is not intended to limit the utility model. Any Those who are familiar with this profession, without departing from the scope of the technical solutions of the present utility model, can use the technical content disclosed above to make some changes or modify equivalent embodiments with equivalent changes, but all without departing from the technical solutions of the present utility model The content of the scheme, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the utility model still belong to the scope of the technical solution of the utility model.

Claims (10)

1. the small-power switching power-supply circuit of a multiple-channel output; it is characterized in that: include prime protection circuit, rectification circuit, peak current suppression circuit, switch transformer and the high-frequency rectification output circuit being sequentially connected, and governor circuit, current detection circuit, voltage feedback circuit and reference voltage circuit；Described governor circuit is connected with rectification circuit, peak current suppression circuit, switch transformer, current detection circuit and voltage feedback circuit respectively, and described reference voltage circuit is connected with voltage feedback circuit and high-frequency rectification output circuit respectively；

Described switch transformer includes armature winding and the feedback winding being positioned at input side, is positioned at main output winding and time output winding of outlet side；The armature winding of described switch transformer is connected with the outfan of peak current suppression circuit, the feedback winding feedback of switch transformer is connected to governor circuit, and the magnitude of voltage that the main output winding of switch transformer exports through high-frequency rectification output circuit is connected with reference voltage circuit；

The input of described prime protection circuit is connected with alternating current; described governor circuit is connected with peak current suppression circuit by switching device, and governor circuit ratio between service time and the turn-off time by controlling switching device stablizes the DC voltage of output multi-channel and for the magnitude of voltage of output is realized closed loop feedback control by reference voltage circuit and voltage feedback circuit.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1; it is characterized in that: described prime protection circuit include respectively with alternating current two outfans series winding electric fuse and critesistor; the conjugation inductance being all in series with electric fuse and critesistor, and the safety electric capacity being in parallel with conjugation inductance.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1; it is characterized in that: described rectification circuit is rectifier circuit, includes bridge rectifier and filter capacitor, two inputs of described bridge rectifier are connected with the outfan of prime protection circuit, two outfans of bridge rectifier are connected with positive pole and the negative pole of filter capacitor respectively；The positive pole of described filter capacitor is connected with the input of peak current suppression circuit, the minus earth of filter capacitor.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterised in that: described peak current suppression circuit includes a RCD circuit and Transient Suppression Diode, and described RCD circuit in parallel is in the armature winding two ends of switch transformer；Described RCD circuit includes the RC parallel branch being in parallel by the first resistance and the first electric capacity, and the protection diode being in series with RC parallel branch；Described Transient Suppression Diode is in parallel with RC parallel branch；One end of described first resistance, one end of the first electric capacity are all connected with armature winding one end of switch transformer with the positive pole of Transient Suppression Diode, and the positive pole of described protection diode is connected with the armature winding other end of switch transformer.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterised in that: described switch transformer is three tunnel output transformators, and the main output winding and time output winding that are positioned at outlet side are respectively two-way output and road output.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterized in that: if described high-frequency rectification output circuit includes the rectification unit of the identical structure in main line being connected respectively with every road output of switch transformer outlet side, described rectification unit includes output rectification circuit, π type filter circuit and DCR circuit；

Described output rectification circuit includes Schottky diode, the second resistance and the second electric capacity, is connected in parallel on the two ends of Schottky diode after described second resistance and the second capacitances in series；Described π type filter circuit includes that the 3rd electric capacity, the first inductance and the 4th electric capacity being sequentially connected in series, described DCR circuit include the first diode, ceramic disc capacitor and the 3rd resistance in parallel successively；

Described one end of first inductance is connected with the negative pole of Schottky diode, and the other end of the first inductance and the negative pole of the first diode are connected；The equal ground connection of positive pole of negative pole, the negative pole of the 4th electric capacity and first diode of described 3rd electric capacity.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterised in that: described governor circuit includes that UC3842 chip, described switching device are N-MOS pipe；

The 4th resistance and commutation diode that the feeder ear of described UC3842 chip is sequentially connected in series by starting resistance and be connected with the outfan of rectification circuit and pass through start-up capacitance ground connection and passing through are connected with the feedback winding of switch transformer, the minus earth of described start-up capacitance, the negative pole of described commutation diode and the 4th resistance are connected；

The feedback voltage input of described UC3842 chip is connected with the outfan of voltage feedback circuit, and the feedback current input of UC3842 chip is connected with the source electrode of N-MOS pipe by current detection circuit；The drain electrode of described N-MOS pipe is connected with peak current suppression circuit, and the grid of N-MOS pipe is connected with the outfan of recommending of UC3842 chip by the second diode；The positive pole of described second diode is connected with the grid of N-MOS pipe, and the both sides of the second diode are parallel with the 5th resistance, and the positive pole of the second diode is connected with the earth terminal of UC3842 chip by the 6th resistance.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterized in that: described current detection circuit includes the 7th resistance and the 8th resistance being sequentially connected, one end of described 7th resistance is connected with governor circuit, the other end of the 7th resistance and one end of the 8th resistance are all connected with switching device, the other end ground connection of described 8th resistance.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterized in that: described voltage feedback circuit includes photoelectrical coupler, one input of described photoelectrical coupler is connected with the outfan of reference voltage circuit by the 9th resistance and the 5th capacity earth, another input being sequentially connected in series, and is parallel with the 6th electric capacity between two outfans of described photoelectrical coupler.

The small-power switching power-supply circuit of a kind of multiple-channel output the most according to claim 1, it is characterized in that: described reference voltage circuit includes TL431, the negative electrode of described TL431 is connected with voltage feedback circuit and the tenth resistance, the 7th electric capacity and the 11st resistance that pass through to be sequentially connected are connected with the magnitude of voltage of output, the plus earth of described TL431 is also connected by the input of adjustable resistance and the 11st resistance, and the reference edge of described TL431 is connected with the adjustable side of adjustable resistance.