Constant voltage output overvoltage protection circuit and method of flyback DC/DC converter and switching power supply

Abstract

The invention discloses a constant voltage output overvoltage protection circuit and method of a flyback DC / DC converter and a switching power supply. The circuit comprises an induction winding, a rectifier diode, an induction voltage filter capacitor, a resistor R1, a resistor R2, an operational amplifier, a backward diode, a resistor R3 and a sampling integrating capacitor. The induction winding is connected with the anode end of the rectifier diode; the resistor R1 and the resistor R2 are connected in series; the induced voltage filter capacitor is connected with the cathode end of the rectifier diode; the anti-phase end of the operational amplifier is connected between the resistor R1 and the resistor R2; the in-phase end of the operational amplifier is connected with the reference end of the PWM; the output end of the operational amplifier is connected with the cathode end of the backward diode, and the anode end of the backward diode is connected with the COMP end of the PWM; and the resistor R3 and the sampling integrating capacitor C5 are connected in series. By controlling the size of the PWM duty ratio, the output voltage is enabled to be constant at a set output value, so that a load chip is ensured not to be burnt down, the chip can work normally, and the reliability of the power supply and the whole electronic system is improved.

Description

technical field [0001] The invention belongs to the field of switching power supplies, and relates to a constant voltage output overvoltage protection circuit of a flyback DC / DC converter, a method and a switching power supply. Background technique [0002] The switching power supply is the core power supply unit in the electronic system, and its reliability directly determines the reliability of the electronic system. When the feedback loop of the switching power supply module is disconnected, abnormal, or the output tube legs are connected incorrectly, the output voltage of the switching power supply may drift high, resulting in The phenomenon that the load such as the post-stage chip is burned. At this time, it is necessary to turn off or reduce the output voltage to protect other components of the electronic system. At present, there are two commonly used overvoltage circuit protection circuits and implementation methods, one is to directly cut off the output voltage, an...

AI Technical Summary

Problems solved by technology

[0008] The output type overvoltage protection mode of turning off the power enable terminal can also effectively protect the output load, but there is also the problem that after the output is turned off, the load cannot work normally, and the electronic system interrupts the work. There are application restrictions in special application fields that do not allow interruption of work.

On the other hand, the isolated signal is transmitted through the photocoupler. Due to the radiation sensitivity of the photocoupler, there is a reliability risk when it is used in space, nuclear power plants, etc. where there are radiation environments.

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