CN103441661A

CN103441661A - Method for achieving soft starting of PWM convertor

Info

Publication number: CN103441661A
Application number: CN2013102752484A
Authority: CN
Inventors: 杨香兵; 蔡宝龙
Original assignee: 724th Research Institute of CSIC
Current assignee: 724th Research Institute of CSIC
Priority date: 2013-07-03
Filing date: 2013-07-03
Publication date: 2013-12-11

Abstract

The invention relates to a method for achieving soft starting of a PWM convertor. According to the method, a sawtooth wave generating circuit, a voltage comparator and an AND gate are utilized for achieving soft starting of the PWM convertor. The functional block diagram for achieving the technology is shown as the attached picture. The treatment process comprises that firstly, the sawtooth wave generating circuit is utilized for converting an input drive signal into a sawtooth wave, wherein the frequency and the duty ratio of the sawtooth wave is unchanged; then the voltage comparator is adopted for comparing the sawtooth wave and a slowly-rising reference voltage, and a pulse voltage signal is obtained, wherein the duty ratio of the pulse voltage signal is gradually increased; finally, the pulse voltage signal and an input drive voltage are compared through the AND gate to obtain an output drive voltage, wherein the duty ratio of the output drive voltage is gradually increased. At the moment of starting up, the duty ratio of the drive voltage is gradually increased, after a switching power supply works normally, the voltage comparator outputs a high level all the time, and the output drive voltage and the input drive voltage are completely equal. Therefore, soft starting of the PWM convertor is achieved, and the method has broad application prospects in the field of power sources.

Description

A kind of implementation method of pwm converter soft start

Technical field

The invention belongs to the special power supply technology, is a kind of implementation method of pwm converter soft start.

Background technology

Pwm converter is a kind of of Switching Power Supply, and in the PWM working method, converter switches plumber working frequency is constant, by sampling, comparison, error, after amplifying, goes the ON time of control switch pipe, thereby realizes the output voltage voltage stabilizing control of Switching Power Supply.

At the Switching Power Supply booting moment, if the duty ratio of the driving signal that the drive circuit of converter produces is maximum, the ON time of switching tube in one-period is the longest, electric current by switching tube in ON time is very large, once the electric current passed through has surpassed the limiting value of switching tube, switching tube will damage.Therefore, the driving that needs a duty ratio to increase gradually after power supply start, thus realize the soft start of power supply.

Thinking of the present invention is to utilize simple and reliable method to realize the pwm converter soft start, and the ON time of the rear switching tube of power supply start is increased gradually, improves the reliability of Switching Power Supply.

Summary of the invention

Content of the present invention is a kind of implementation method of pwm converter soft start.At first, utilize PWM to drive signal to produce a sawtooth waveforms that frequency is identical with duty ratio; Then, sawtooth waveforms is sent into to voltage comparator and reference voltage compares, obtain a voltage signal; Finally, drive signal to send into and the door comparison output voltage of voltage comparator and PWM, obtain new driving signal.

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The accompanying drawing explanation

Fig. 1 is the theory diagram of realizing the pwm converter soft start.

Fig. 2 is the electrical schematic diagram of realizing the pwm converter soft start.

Embodiment

The concrete implementation step of implementation method of a kind of pwm converter soft start of the present invention is referring to Fig. 1:

1. utilize saw-tooth wave generating circuit to produce a frequency and drive with PWM the sawtooth waveforms that signal is identical with duty ratio;

2. sawtooth waveforms is sent into to voltage comparator and reference voltage compares, obtain a voltage signal;

3. drive signal to send into and the door comparison output voltage of voltage comparator and PWM, obtain new driving signal.

The implementation method circuit theory diagrams of a kind of pwm converter soft start of the present invention are referring to Fig. 2, N1 NAND gate in figure, and model is H006, and N2 is operational amplifier, and model is LM111, and N3 is and door that model is H002.

1. N1, R1, R2, R3, V1 and C1 form sawtooth wave generating circuit.When input drive signal is low level, the 3 pin output high level of N1, the V1 conducting, C1 discharges by V1, and after electric discharge finishes, the C1 both end voltage is 0; When input drive signal is high level, the 3 pin output low levels of N1, V1 turn-offs, and C1 is by R1, R3 charging, and regulator potentiometer R1 can change the rate of climb of sawtooth voltage.

2. R4 and C2 provide reference voltage for N2, and after start, the voltage at C2 two ends is since 0 rising.When the 2 pin voltages of N2 higher than 3 pin voltages, the 7 pin output high level of N2, otherwise output low level.Because the voltage at C2 two ends rises slowly, so booting moment, the pulse voltage duty ratio of N2 output increases gradually, and when the C2 charging finishes, when two ends reach VCC, N7 exports high level always.

3. the pulse voltage signal that N7 produces and input drive signal are by producing output drive signal with door.Booting moment, the duty ratio of output drive signal increases gradually, and after the Switching Power Supply normal operation, output drive signal duty ratio and input drive signal are in full accord, have realized the soft start of pwm converter.

Claims

1. the implementation method of a pwm converter soft start, it is characterized in that: at first utilize saw-tooth wave generating circuit to produce a frequency and drive with PWM the sawtooth waveforms that signal is identical with duty ratio, then sawtooth waveforms is sent into to voltage comparator and reference voltage compares, obtain a voltage signal, this voltage signal and PWM driving signal are sent into door and are compared, obtain new driving signal, this driving signal is that duty ratio becomes large gradually from zero, thereby has realized the soft start of converter.

2. the implementation method of a kind of pwm converter soft start according to claim 1, it is characterized in that: saw-tooth wave generating circuit is by NAND gate N1, triode V1, potentiometer R1, resistance R 2, resistance R 3 and capacitor C 1 form, and the output that its concrete form is NAND gate N1 is connected with the base stage of triode V1 by resistance R 2, N1 drives signal to produce low and high level according to the PWM of input, controls conducting and the cut-off of V1; Capacitor C 1 is attempted by the emitter and collector two ends of triode V1, then with potentiometer R1 and resistance R 3, connects, and that utilizes electric capacity discharges and recharges the generation sawtooth waveforms; Adjust the slope that potentiometer R1 can change sawtooth waveforms in saw-tooth wave generating circuit, realize the adjustment to the converter soft-start time.

3. the implementation method of a kind of pwm converter soft start according to claim 1, it is characterized in that: the sawtooth waveforms that described saw-tooth wave generating circuit produces drives signal to produce according to PWM, its frequency drives signal identical with duty ratio with PWM, guarantees that new driving signal is identical with the PWM driving signal frequency.