CN207460003U - A kind of rearrangeable switch power supply based on BUCK circuits - Google Patents

Abstract

The utility model discloses an adjustable switching power supply based on a BUCK circuit, which comprises a first linear voltage stabilizing power supply circuit, a low voltage shutdown and soft start circuit, a PWM control circuit, a constant voltage and constant current control circuit, a bootstrap suspension drive circuit, Current shutdown circuit, MOS tube, constant current load circuit and voltage and current sampling circuit, the first linear regulated power supply circuit provides the regulated power supply of the system, the low voltage shutdown and soft start circuit is used for low voltage protection and soft start, and the bootstrap suspension drive The circuit is used to drive the MOS tube with push-pull output, the constant current load circuit is used to provide load for the system output to realize the stable output of the system, the voltage and current sampling circuit is used to collect the voltage or current output by the system, and the over-current shutdown circuit is used to Current protection, constant voltage and constant current control circuit is used to feedback and control the duty cycle of PWM output to adjust the voltage or current output by the system. The output of the power supply is automatically switched between constant voltage and constant current, and the output voltage and current are continuously linearly adjustable.

Description

An adjustable switching power supply based on BUCK circuit

technical field

The utility model relates to a switching power supply, in particular to an adjustable switching power supply based on a BUCK circuit.

Background technique

With the development of electronic technology, the status of electronic equipment in people's life and production is becoming more and more important, and many electronic equipment also put forward higher requirements for the required power supply. A considerable number of electronic devices cannot directly use the AC power provided by the power grid, but need a stable DC power supply. Therefore, the requirements for the performance, volume, and weight of the DC power supply are also constantly increasing. The traditional switching power supply, because it is a fixed output, even if it is adjustable, it is fine-tuning, which is difficult to meet the requirements of modern electronic products.

Utility model content

Aiming at the defects existing in the prior art, the utility model proposes an adjustable switching power supply based on the BUCK circuit, whose output constant voltage and constant current are automatically switched, the output voltage is continuously linearly adjustable from 0V, and the output current is continuously adjustable from 0A Linear adjustable.

For realizing above-mentioned utility model purpose, the technical scheme that the utility model adopts is:

An adjustable switching power supply based on a BUCK circuit, including a first linear regulated power supply circuit, a low-voltage shutdown and soft-start circuit, a PWM control circuit, a constant voltage and constant current control circuit, a bootstrap suspension drive circuit, an overcurrent shutdown circuit, MOS tube, constant current load circuit and voltage and current sampling circuit, the first linear regulated power supply circuit is used to provide regulated power supply to the PWM control circuit and the constant voltage and constant current control circuit, the low voltage shutdown and soft The startup circuit is used to soft start the PWM control circuit and turn off the PWM output of the PWM control circuit when low voltage occurs, the bootstrap suspension drive circuit is used to drive the MOS tube with a push-pull output, and the constant current The load circuit is used to provide a load for the system output to achieve a stable system output, the voltage and current sampling circuit is used to collect the voltage or current output by the system and feed it back to the overcurrent shutdown circuit and the constant voltage constant current control circuit, The over-current shutdown circuit is used to shut off the PWM output of the PWM control circuit when the output current of the system is too large, and the constant voltage and constant current control circuit is used to compare the system output voltage with the voltage adjusted by the potentiometer , when the system output voltage or current is not equal to the voltage or current adjusted by the potentiometer, the system output voltage or current is adjusted by feedback controlling the duty cycle of the PWM output of the PWM control circuit.

Preferably, the PWM control circuit includes a TL494 chip, an eighth triode, a fifth diode, a seventeenth capacitor, a twenty-fourth resistor, a third resistor, and a twenty-third resistor, and the TL494 chip 11 pins of the third resistor are respectively connected to one end of the third resistor, one end of the twenty-third resistor and one end of the seventeenth capacitor, and the other end of the third resistor is connected to the output end of the linear voltage stabilizing power supply circuit , the other end of the twenty-third resistor and the seventeenth capacitor are respectively connected to the base of the eighth triode and one end of the twenty-fourth resistor, the eighth triode The emitter is connected to the anode of the fifth diode, the cathode of the fifth diode and the other end of the twenty-fourth resistor are both connected to the output end of the voltage and current sampling circuit, and the eighth third The collector of the pole tube is connected to the input terminal of the bootstrap suspension drive circuit.

Preferably, the bootstrap suspension drive circuit includes a second linear regulated power supply circuit, a fourth transistor, a fifth transistor, a PNP third transistor, a fourteenth resistor, a thirteenth resistor, The tenth resistor, the eleventh resistor and the twelfth resistor, the collector of the eighth triode is respectively connected to one end of the tenth resistor and one end of the twelfth resistor, and the other end of the tenth resistor One end is respectively connected to the collector of the fifth triode, the collector of the fourth triode and the output end of the second linear voltage stabilizing power supply circuit, and the input end of the second linear voltage stabilizing power supply circuit connected to the DC input terminal, the other end of the twelfth resistor is respectively connected to the base of the fifth triode and the base of the PNP third triode, and the emitter of the fifth triode One end of the eleventh resistor and the base of the fourth transistor are respectively connected, and the other end of the eleventh resistor and the emitter of the fourth transistor are respectively connected to the tenth One end of the four resistors is connected to the emitter of the third PNP triode, and the other end of the fourteenth resistor is respectively connected to one end of the thirteenth resistor and the gate of the MOS transistor, and the MOS transistor The drain of the PNP type third transistor is connected to the DC input terminal, the collector of the third PNP transistor and the other end of the thirteenth resistor are respectively connected to the source of the MOS transistor and one end of a first inductor, and the The other end of the first inductor is the output end of the voltage and current of the system.

Preferably, the constant current load circuit includes a charge pump circuit, a twenty-first capacitor, a tenth diode, a ninth diode, a twenty-second capacitor, a twenty-ninth resistor and a ninth triode , the 5-pin of the TL494 is connected to the input end of the charge pump circuit, the output end of the charge pump circuit is connected to one end of the twenty-first capacitor, and the other end of the twenty-first capacitor is respectively connected to the The anode of the tenth diode and the cathode of the ninth diode, the anode of the ninth diode are respectively connected to one end of the twenty-second capacitor and one end of the twenty-ninth resistor, The collector of the ninth triode is connected to the other end of the first inductor, the emitter is connected to the other end of the twenty-ninth resistor, the base is connected to the input ground, and the tenth diode The cathode and the other end of the twenty-second capacitor are respectively connected to the base of the ninth triode.

Preferably, the constant voltage and constant current control circuit includes a double operational amplifier, a second light emitting diode and a first light emitting diode, the voltage output by the system is compared with the voltage adjusted by the potentiometer on the double operational amplifier, when the system outputs When the voltage is not equal to the voltage adjusted by the potentiometer, the duty cycle of the PWM output of the TL494 chip is feedback-controlled to adjust the output voltage of the system; the second light-emitting diode is used to emit light in constant voltage mode, and the The first light emitting diode is used for emitting light in a constant current mode.

Preferably, the low-voltage shutdown and soft-start circuit includes a first resistor, a second resistor, a sixth resistor, a PNP-type second transistor and a third capacitor, and pin 12 of the TL494 chip is connected to the second resistor One end of the second resistor, the other end of the second resistor is respectively connected to one end of the first resistor and the base of the PNP type second triode, and the 14 pins of the TL494 chip are respectively connected to the PNP type second three The emitter of the pole tube and one end of the third capacitor, the other end of the first resistor and one end of the sixth resistor are grounded, the other end of the sixth resistor, the PNP type second triode The collector of the tube and the other end of the third capacitor are respectively connected to pin 4 of the TL494 chip.

Preferably, the first linear voltage regulator power supply circuit includes a first voltage regulator tube, a first triode, a fourth resistor and a fifth resistor, the anode of the first voltage regulator tube is grounded, and the cathode is connected to the first voltage regulator tube. The base of a triode, one end of the fourth resistor, one end of the fifth resistor and the collector of the first triode are connected to the DC input terminal, the fourth resistor and the fifth resistor The other end of the first triode is connected to the base of the first triode, and the emitter of the first triode outputs a stable voltage.

Preferably, the over-current shutdown circuit includes a seventh diode, a thirty-third resistor, a PNP-type twelfth triode, a thirteenth triode, a twentieth capacitor and a thirty-fourth resistor , the output end of the PWM control circuit is connected to the anode of the seventh diode, and the cathode of the seventh diode is respectively connected to one end of the thirty-third resistor R33 and the PNP type twelfth-third the emitter of the thirteenth triode, the other end of the thirty-third resistor is respectively connected to the base of the PNP-type twelfth triode and the collector of the thirteenth triode, and the thirteenth and third The emitter of the transistor is connected to the output end of the voltage and current sampling circuit and one end of the twentieth capacitor, and the base of the thirteenth triode is respectively connected to the other end of the twentieth capacitor, the The collector of the twelfth PNP triode and one end of the thirty-fourth resistor, and the other end of the thirty-fourth resistor is grounded.

Preferably, the voltage and current sampling circuit includes a current detection resistor, one end of the current detection resistor is connected to the emitter of the thirteenth triode, and the other end is connected to the output terminals of the voltage and current of the system.

Preferably, the switching power supply includes a Schottky diode, the cathode of the Schottky diode is connected to the source of the MOS transistor, and the anode of the Schottky diode is connected to one end of the current detection resistor.

Compared with the prior art, the beneficial technical effect of the utility model is:

①The DC input voltage range is 12-50V, and the output voltage is adjusted from 0V. When the input is greater than 36V, the maximum output is 30V, and the output current is adjustable from 0-10A;

② Output CC/CV constant voltage and constant current automatic switching, continuous linear adjustment of voltage and current values;

③ Ensure stable output under light load and low voltage conditions;

④ With input low voltage protection, overcurrent protection, soft start.

Of course, any product implementing the present utility model does not necessarily need to achieve all the above-mentioned advantages at the same time.

Description of drawings

Fig. 1 is the system block diagram of a kind of adjustable switching power supply based on BUCK circuit of the present utility model;

Fig. 2 is the schematic diagram of the first linear voltage stabilizing power supply circuit of the present utility model;

Fig. 3 is the schematic diagram of the PWM control circuit of the present utility model;

Fig. 4 is the schematic diagram of the overcurrent shutdown circuit of the present invention;

Fig. 5 is a schematic diagram of the bootstrap suspension driving circuit of the present invention;

Fig. 6 is the schematic diagram of the constant current load circuit of the present utility model;

7 is a schematic diagram of the constant voltage and constant current control circuit of the present invention;

Fig. 8 is the schematic diagram of the low-voltage shutdown and soft-start circuit of the present invention;

FIG. 9 is a schematic diagram of an adjustable switching power supply based on a BUCK circuit of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present utility model clearer, various implementation modes of the present utility model will be described in detail below in conjunction with the accompanying drawings.

Please refer to Figure 1 to Figure 9 below, an adjustable switching power supply based on the BUCK circuit, including the first linear regulated power supply circuit, low-voltage shutdown and soft-start circuit, PWM control circuit, constant voltage and constant current control circuit, bootstrap Suspension drive circuit, over-current shutdown circuit, MOS tube, constant current load circuit and voltage and current sampling circuit, the first linear regulated power supply circuit is used to provide regulated power supply to the PWM control circuit and constant voltage and constant current control circuit, low voltage shutdown And the soft start circuit is used to soft start the PWM control circuit and turn off the PWM output of the PWM control circuit when low voltage occurs, the bootstrap suspension drive circuit is used to drive the MOS tube with push-pull output, and the constant current load circuit is used to provide system output Load to achieve stable output of the system, the voltage and current sampling circuit is used to collect the voltage or current output by the system and feed back to the over-current shutdown circuit and constant voltage constant current control circuit, the over-current shutdown circuit is used to When the PWM output of the PWM control circuit is turned off, the constant voltage and constant current control circuit is used to compare the system output voltage with the voltage adjusted by the potentiometer. When the system output voltage or current is not equal to the voltage or current adjusted by the potentiometer, the feedback Control the duty cycle of the PWM output of the PWM control circuit to adjust the voltage or current output by the system.

As shown in Figure 2, the first linear voltage regulator power supply circuit includes a first voltage regulator tube ZD1, a first triode Q1, a fourth resistor R4 and a fifth resistor R5, the anode of the first voltage regulator tube ZD1 is grounded, and the cathode is connected to The base of the first transistor Q1, one end of the fourth resistor R4, one end of the fifth resistor R5, and the collector of the first transistor Q1 are connected to the DC input terminal, and the other end of the fourth resistor R4 and the fifth resistor R5 Connected to the base of the first triode Q1, the emitter of the first triode Q1 outputs a stable voltage. In this design, the system power supply requires a DC voltage of 9V. A linear regulated power supply composed of the first regulator ZD1 and the first triode Q1 is used. When the DC input passes through the fourth resistor R4, the fifth resistor R5 and the first A voltage regulator ZD1 obtains a voltage of 9.1V, which is applied to the base of the first transistor Q1, so that the emitter of the first transistor Q1 outputs a voltage of approximately 9V.

As shown in Figure 3, the PWM control circuit includes a TL494 chip, an eighth transistor Q8, a fifth diode D5, a seventeenth capacitor C17, a twenty-fourth resistor R24, a third resistor R3 and a twenty-third resistor R23, pin 11 of the TL494 chip are respectively connected to one end of the third resistor R3, one end of the twenty-third resistor R23 and one end of the seventeenth capacitor C17, and the other end of the third resistor R3 is connected to the output end of the linear regulated power supply circuit , the other end of the twenty-third resistor R23 and the seventeenth capacitor C17 are respectively connected to the base of the eighth triode Q8 and one end of the twenty-fourth resistor R24, and the emitter of the eighth triode Q8 is connected to the fifth The anode of the diode D5, the cathode of the fifth diode D5 and the other end of the twenty-fourth resistor R24 are all connected to the output end of the voltage and current sampling circuit, and the collector of the eighth triode Q8 is connected to the bootstrap suspension drive circuit input terminal. In this design, the TL494 chip is a fixed-frequency pulse width modulation circuit with a built-in linear sawtooth oscillator, and the oscillation frequency is determined by the sixteenth resistor and the twelfth capacitor externally. The 3rd pin of the TL494 chip is the feedback pin to receive the feedback signal of the constant voltage constant current control circuit, the 11th pin outputs PWM through the eighth transistor Q8 to increase the driving capability, and the 14th pin outputs a 5V reference source.

As shown in Figure 4, the over-current shutdown circuit includes a seventh diode D7, a thirty-third resistor R33, a PNP-type twelfth triode Q12, a thirteenth triode Q13, a twentieth capacitor C20 and The thirty-fourth resistor R34, the output end of the PWM control circuit is connected to the anode of the seventh diode D7, and the cathode of the seventh diode D7 is respectively connected to one end of the thirty-third resistor R33 and the PNP type twelfth triode The emitter of Q12, the other end of the thirty-third resistor R33 are respectively connected to the base of the PNP-type twelfth triode Q12 and the collector of the thirteenth triode Q13, and the emitter of the thirteenth triode Q13 Connect the output end of the voltage and current sampling circuit to one end of the twentieth capacitor C20, the base of the thirteenth triode Q13 is respectively connected to the other end of the twentieth capacitor C20, and the collector of the PNP-type twelfth triode Q12 and one end of the thirty-fourth resistor R34, and the other end of the thirty-fourth resistor R34 is grounded. In this design, when the output current of the system increases, the emitter voltage of the thirteenth triode Q13 decreases, and when it is low to a certain value, the thirteenth triode Q13 is turned on, and then the PNP type twelfth-third The transistor Q12 is turned on, and the twelfth transistor Q12 and the PNP-type thirteenth transistor Q13 form a single-key start switch circuit, which is equivalent to a one-way thyristor.

The voltage and current sampling circuit includes a current detection resistor, one end of the current detection resistor is connected to the emitter of the thirteenth triode Q13, and the other end is connected to the output terminals of the voltage and current of the system. Further, the switching power supply includes a Schottky diode, the cathode of the Schottky diode is connected to the source of the MOS transistor, and the anode of the Schottky diode is connected to one end of the current detection resistor.

As shown in Figure 5, the bootstrap suspension drive circuit includes a second linear voltage stabilized power supply circuit, a fourth transistor Q4, a fifth transistor Q5, a PNP third transistor Q3, a fourteenth resistor R14, a The thirteenth resistor R13, the tenth resistor R10, the eleventh resistor R11 and the twelfth resistor R12, the collector of the eighth triode Q8 are respectively connected to one end of the tenth resistor R10 and one end of the twelfth resistor R12, the tenth resistor The other end of the resistor R10 is respectively connected to the collector of the fifth triode Q5, the collector of the fourth triode Q4 and the output terminal of the second linear regulated power supply circuit, and the input terminal of the second linear regulated power supply circuit is connected to the DC The other end of the twelfth resistor R12 is connected to the base of the fifth transistor Q5 and the base of the PNP third transistor Q3 respectively, and the emitter of the fifth transistor Q5 is connected to the eleventh transistor Q5 respectively. One end of the resistor R11 and the base of the fourth transistor Q4, the other end of the eleventh resistor R11 and the emitter of the fourth transistor Q4 are respectively connected to one end of the fourteenth resistor R14 and the third PNP type transistor The emitter of the tube Q3, the other end of the fourteenth resistor R14 are respectively connected to one end of the thirteenth resistor R13 and the gate of the MOS tube, the drain of the MOS tube is connected to the DC input terminal, and the collector of the PNP type third transistor Q3 The electrodes and the other end of the thirteenth resistor R13 are respectively connected to the source of the MOS transistor and one end of a first inductance, and the other end of the first inductance is the output end of the voltage and current of the system; further, the second linear regulator The power supply circuit includes the seventh triode Q7, the twenty-fifth resistor R25, the second regulator ZD2, the fourteenth capacitor C14 and the eighteenth capacitor C18, the DC input terminal is connected to the anode of the fourth diode D4, and the The cathodes of the four diodes D4 are respectively connected to the collector of the seventh triode Q7, one end of the eighteenth capacitor C18 and one end of the twenty-fifth resistor R25, and the other end of the twenty-fifth resistor R25 is respectively connected to the seventh third The base of the pole tube Q7 and the cathode of the second regulator tube ZD2, the emitter of the seventh triode Q7 are respectively connected to the other end of the tenth resistor R10, the collector of the fifth triode Q5, and the fourteenth capacitor C14 One end of the capacitor is connected to the collector of the fourth transistor Q4, the anode of the second voltage regulator transistor ZD2, the other end of the fourteenth capacitor C14 and the other end of the eighteenth capacitor C18 are respectively connected to one end of the first inductor. In this design, the driven output of PWM belongs to the pull-up mode output, and the driving ability is not strong enough at high level, so the fifth triode Q5 and the fourth triode Q4 form a composite tube to have a good drive at high level ability, and the composite tube and the PNP third transistor Q3 form a push-pull output mode to drive the MOS tube.

As shown in Figure 6, the constant current load circuit includes a charge pump circuit, a twenty-first capacitor C21, a tenth diode D10, a ninth diode D9, a twenty-second capacitor C22, a twenty-ninth resistor R29 and Ninth triode Q9, pin 5 of TL494 is connected to the input end of the charge pump circuit, the output end of the charge pump circuit is connected to one end of the twenty-first capacitor C21, and the other end of the twenty-first capacitor C21 is respectively connected to the twelfth The anode of the pole tube D10 and the cathode of the ninth diode D9, the anode of the ninth diode D9 are respectively connected to one end of the twenty-second capacitor C22 and one end of the twenty-ninth resistor R29, and the ninth triode Q9 The collector is connected to the other end of the first inductor, the emitter is connected to the other end of the twenty-ninth resistor R29, the base is connected to the input ground, the cathode of the tenth diode D10 is connected to the other end of the twenty-second capacitor C22 are respectively connected to the base of the ninth triode Q9. Further, the charge pump circuit includes a twenty-seventh resistor R27, a thirty-eighth resistor R38, a fourteenth transistor Q14, a thirty-ninth resistor R39, a fifteenth transistor Q15, and a PNP type sixteenth-third The pole tube Q16, pin 5 of the TL494 chip is connected to one end of the twenty-seventh resistor R27, and the other end of the twenty-seventh resistor R27 is respectively connected to one end of the thirty-eighth resistor R38 and the base of the fourteenth triode Q14, The other end of the thirty-eighth resistor R38 is connected to the emitter of the fourteenth triode Q14, and the collector of the fourteenth triode Q14 is respectively connected to one end of the thirty-ninth resistor R39 and the fifteenth triode Q15. and the base of the PNP-type sixteenth transistor Q16, the other end of the thirty-ninth resistor R39 is connected to the collector of the fifteenth transistor Q15, and the collector of the PNP-type sixteenth transistor Q16 The electrodes are respectively connected to the emitter of the fourteenth triode Q14 and the cathode of the tenth diode D10, and one end of the twenty-first capacitor C21 is respectively connected to the emitter of the fifteenth triode Q15 and the PNP type sixteenth three The emitter of the pole tube Q16. In this design, the twenty-seventh resistor R27 is connected to the oscillating pin of the TL494 chip. The charge pump circuit makes the twenty-second capacitor C22 generate a voltage of about -6V relative to the input ground, and the base of the ninth transistor Q9 pole is connected to the input ground, so that the lowest voltage of the emitter of the ninth triode Q9 is -0.7V relative to the input ground, so that a voltage of about 5.3V is loaded on the twenty-ninth resistor R29, and flows through the twenty-ninth resistor R29 The current of the resistor R29 is approximately equal to the collector current of the ninth triode Q9, thus achieving the purpose of constant current.

As shown in Figure 7, the constant voltage and constant current control circuit includes dual operational amplifiers LM358, the second light-emitting diode D2 and the first light-emitting diode D1, and the voltage output by the system is compared with the voltage adjusted by the potentiometer on the dual operational amplifier LM358. When the voltage output by the system is not equal to the voltage adjusted by the potentiometer, the duty cycle of the PWM output of the TL494 chip is feedback controlled to adjust the output voltage of the system; the second light-emitting diode D2 is used to emit light in constant voltage mode, while the first light-emitting diode D1 Used to emit light in constant current mode.

As shown in Figure 8, the low-voltage shutdown and soft-start circuit includes a first resistor R1, a second resistor R2, a sixth resistor R6, a PNP-type second transistor Q2, and a third capacitor C3. Pin 12 of the TL494 chip is connected to the second One end of the resistor R2 and the other end of the second resistor R2 are respectively connected to one end of the first resistor R1 and the base of the PNP second transistor Q2, and pin 14 of the TL494 chip is respectively connected to the emitter of the PNP second transistor Q2. pole and one end of the third capacitor C3, the other end of the first resistor R1 and one end of the sixth resistor R6 are grounded, the other end of the sixth resistor R6, the collector of the PNP type second transistor Q2 and the third capacitor C3 The other end of the TL494 chip is connected to the 4 pins. In this design, if the input voltage is too low, the second PNP transistor Q2 will be turned on, making pin 4 of the TL494 chip high, thereby turning off the PWM output. At the moment of power-on, because the voltage at both ends of the third capacitor cannot change suddenly, pin 4 of the TL494 chip is at high level without PWM output. When the third capacitor C3 is slowly charged to make pin 4 low, the PWM output is normal.

Test the switching power supply of the present utility model, input 36Vdc no-load and output 30Vdc under load test, the test data is as follows:

Current A 0 1 2 3 4 5 6 Voltage V 30.00 30.01 30.00 30.00 30.01 29.99 30.01

The above is only a preferred embodiment of the utility model, but the scope of protection of the utility model is not limited thereto, and any person familiar with the technical field can easily think of All changes or replacements should fall within the protection scope of the present utility model. Therefore, the protection scope of the present utility model should be based on the protection scope of the claims.

Claims (10)

1. An adjustable switching power supply based on a BUCK circuit, characterized in that it comprises a first linear voltage stabilized power supply circuit, a low voltage shutdown and a soft start circuit, a PWM control circuit, a constant voltage and constant current control circuit, a bootstrap suspension drive circuit, an overcurrent shutdown circuit, a MOS tube, a constant current load circuit, and a voltage and current sampling circuit, the first linear regulated power supply circuit is used to provide a regulated power supply to the PWM control circuit and the constant voltage and constant current control circuit, The low-voltage shutdown and soft-start circuit is used to soft-start the PWM control circuit and turn off the PWM output of the PWM control circuit when a low voltage occurs, and the bootstrap suspension drive circuit is used to drive the MOS with a push-pull output tube, the constant current load circuit is used to provide a load for the system output to achieve a stable output of the system, the voltage and current sampling circuit is used to collect the voltage or current output by the system and feed it back to the over-current shutdown circuit and the constant A voltage constant current control circuit, the overcurrent shutdown circuit is used to shut off the PWM output of the PWM control circuit when the output current of the system is too large, and the constant voltage constant current control circuit is used to connect the system output voltage and potential Compared with the voltage regulated by the potentiometer, when the system output voltage or current is not equal to the voltage or current regulated by the potentiometer, the duty cycle of the PWM output of the PWM control circuit is feedback controlled to adjust the system output voltage or current. 2. An adjustable switching power supply based on a BUCK circuit according to claim 1, wherein the PWM control circuit includes a TL494 chip, an eighth triode, a fifth diode, a seventeenth capacitor, The twenty-fourth resistor, the third resistor and the twenty-third resistor, the 11 pins of the TL494 chip are respectively connected to one end of the third resistor, one end of the twenty-third resistor and one end of the seventeenth capacitor , the other end of the third resistor is connected to the output end of the linear regulated power supply circuit, and the other end of the twenty-third resistor and the seventeenth capacitor are respectively connected to the base of the eighth triode electrode and one end of the twenty-fourth resistor, the emitter of the eighth triode is connected to the anode of the fifth diode, the cathode of the fifth diode is connected to the twenty-fourth resistor The other ends of the eighth triode are connected to the output end of the voltage and current sampling circuit, and the collector of the eighth triode is connected to the input end of the bootstrap suspension drive circuit. 3. The adjustable switching power supply based on the BUCK circuit according to claim 2, wherein the bootstrap suspension drive circuit includes a second linear voltage regulator power supply circuit, a fourth triode, a fifth triode tube and PNP type third triode, fourteenth resistor, thirteenth resistor, tenth resistor, eleventh resistor and twelfth resistor, the collector of the eighth triode is respectively connected to the tenth One end of the resistor and one end of the twelfth resistor, and the other end of the tenth resistor is respectively connected to the collector of the fifth triode, the collector of the fourth triode and the second linear The output end of the voltage stabilizing power supply circuit, the input end of the second linear voltage stabilizing power supply circuit is connected to the DC input end, and the other end of the twelfth resistor is respectively connected to the base of the fifth triode and the The base of the PNP type third transistor, the emitter of the fifth transistor is respectively connected to one end of the eleventh resistor and the base of the fourth transistor, and the eleventh resistor is connected to the base of the fourth transistor. The other end and the emitter of the fourth transistor are respectively connected to one end of the fourteenth resistor and the emitter of the PNP type third transistor, and the other end of the fourteenth resistor is respectively connected to the One end of the thirteenth resistor and the gate of the MOS transistor, the drain of the MOS transistor is connected to the DC input end, the collector of the PNP third transistor is connected to the other end of the thirteenth resistor Both are respectively connected to the source of the MOS transistor and one end of a first inductance, and the other end of the first inductance is the output end of the voltage and current of the system. 4. The adjustable switching power supply based on a BUCK circuit according to claim 3, wherein the constant current load circuit includes a charge pump circuit, a twenty-first capacitor, a tenth diode, a ninety-second pole tube, the twenty-second capacitor, the twenty-ninth resistor and the ninth triode, the 5 pin of the TL494 is connected to the input end of the charge pump circuit, and the output end of the charge pump circuit is connected to the first One end of the twenty-first capacitor, the other end of the twenty-first capacitor is respectively connected to the anode of the tenth diode and the cathode of the ninth diode, and the anode of the ninth diode is respectively connected to One end of the twenty-second capacitor and one end of the twenty-ninth resistor, the collector of the ninth transistor is connected to the other end of the first inductor, and the emitter is connected to the twenty-ninth resistor. The other end of the resistor is connected, the base is connected to the input ground, the cathode of the tenth diode and the other end of the twenty-second capacitor are respectively connected to the base of the ninth triode. 5. A kind of adjustable switching power supply based on BUCK circuit according to claim 2, it is characterized in that, described constant voltage and constant current control circuit comprises double operational amplifier, the second light-emitting diode and the first light-emitting diode, the output of the system The voltage is compared with the voltage adjusted by the potentiometer on the dual operational amplifier. When the voltage output by the system is not equal to the voltage adjusted by the potentiometer, the duty cycle of the PWM output of the TL494 chip is feedback controlled to adjust the output of the system. voltage; the second light emitting diode is used to emit light in a constant voltage mode, and the first light emitting diode is used to emit light in a constant current mode. 6. An adjustable switching power supply based on a BUCK circuit according to claim 2, wherein the low-voltage shutdown and soft-start circuit includes a first resistor, a second resistor, a sixth resistor, a PNP type second and third resistors An electrode tube and a third capacitor, the 12-pin of the TL494 chip is connected to one end of the second resistor, and the other end of the second resistor is respectively connected to one end of the first resistor and the PNP type second triode The base of the TL494 chip, the 14 pins of the TL494 chip are respectively connected to the emitter of the PNP type second transistor and one end of the third capacitor, the other end of the first resistor and one end of the sixth resistor Both are grounded, and the other end of the sixth resistor, the collector of the PNP-type second transistor and the other end of the third capacitor are respectively connected to pin 4 of the TL494 chip. 7. The adjustable switching power supply based on BUCK circuit according to claim 1, characterized in that, the first linear regulated power supply circuit comprises a first voltage regulator tube, a first triode, a fourth resistor and The fifth resistor, the anode of the first voltage regulator tube is grounded, the cathode is connected to the base of the first triode, one end of the fourth resistor, one end of the fifth resistor and the first triode The collector of the tube is connected to the DC input terminal, the other terminals of the fourth resistor and the fifth resistor are connected to the base of the first triode, and the emitter of the first triode outputs a stable voltage. 8. An adjustable switching power supply based on a BUCK circuit according to claim 1, wherein the over-current shutdown circuit comprises a seventh diode, a thirty-third resistor, a PNP type twelfth-third pole tube, a thirteenth triode, a twentieth capacitor and a thirty-fourth resistor, the output end of the PWM control circuit is connected to the anode of the seventh diode, and the cathode of the seventh diode is respectively One end of the thirty-third resistor is connected to the emitter of the PNP-type twelfth triode, and the other end of the thirty-third resistor is respectively connected to the base of the PNP-type twelfth triode and the collector of the thirteenth triode, the emitter of the thirteenth triode is connected to the output terminal of the voltage and current sampling circuit and one end of the twentieth capacitor, the thirteenth three The base of the transistor is respectively connected to the other end of the twentieth capacitor, the collector of the PNP-type twelfth triode and one end of the thirty-fourth resistor, and the other end of the thirty-fourth resistor One end is grounded. 9. The adjustable switching power supply based on the BUCK circuit according to claim 8, wherein the voltage and current sampling circuit includes a current detection resistor, and one end of the current detection resistor is connected to the thirteenth three-pole The emitter of the tube, the other end is connected to the output end of the voltage and current of the system. 10. A kind of adjustable switching power supply based on BUCK circuit according to claim 9, is characterized in that, comprises a Schottky diode, and the cathode of described Schottky diode is connected with the source of described MOS tube, and described The anode of the Schottky diode is connected to one end of the current detection resistor.