Switching power supply over-current protection circuit

Abstract

A switching power supply over-current protection circuit includes an alternating-current rectification and filtering circuit, a transformer, a direct-current rectification and filtering circuit, a switching circuit, a control circuit and a feedback circuit; the control circuit comprises a pulse width modulation chip and a sampling resistor. When voltage outputted by the direct-current rectification and filtering circuit is higher a voltage threshold value, the feedback circuit sends a feedback signal to a frequency compensation end of the pulse width modulation chip, such that the potential of the frequency compensation end is pulled low; the pulse width modulation chip compares a current signal collected by the sampling resistor with the voltage of the frequency compensation end; and the output end of the pulse width modulation chip outputs a PWM signal to control the switching on and switching off of the switching circuit, such that the switched-on and switched-off states of the transformer can be controlled, and therefore, stabilized voltage output can be realized. Since the feedback signal is sent directly to the frequency compensation end of the pulse width modulation chip, the feedback signal does not need to pass through a high-gain error amplifier inside the pulse width modulation chip, and therefore, the transmission time of the feedback signal is shortened. The switching power supply over-current protection circuit is advantageous in sensitive response over-current protection and short response time.

Description

technical field [0001] The invention relates to the field of switching power supply circuits, in particular to a switching power supply overcurrent protection circuit. Background technique [0002] The application of switching power supply has become more and more extensive. In order to improve the reliability of switching power supply, a reasonable protection circuit must be designed. Overcurrent protection is one of the protection circuits, used to protect the power supply and power switching devices when the output is overloaded or short-circuited. There are usually two methods of overcurrent protection for switching power supplies, pulse width modulation and frequency modulation. The pulse width modulation (PWM) method keeps the pulse frequency constant and controls the output voltage by changing the pulse width. It is the most commonly used modulation method for switching power supplies. [0003] figure 2 It is a block diagram of the internal principle of a pulse widt...

AI Technical Summary

Problems solved by technology

This inductive component presents a large impedance at high frequencies, so it will dissipate a lot of power

As the frequency increases, because the response time required by the pulse width modulation chip from obtaining the feedback signal to outputting the PWM signal is longer, the current flowing through the sampling resistor may not be discharged before the next oscillation cycle arrives, and the sampling resistor withstands The current will become larger and larger, which will cause misoperation of the pulse width modulation chip, and even cause a bombing

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