Research And Design Of Soft Start And Protect Circuit In Active Clamp Controllor

With the rapid development of the information age,many electronic devices that support the informatization of human's society are emerging.With the continuous emergence of various electronic devices and power electronic devices,switching power supplies have gradually occupied a large market which is ranging from personal computers to military industries because of its high efficiency,low power consumption,and light weight.This paper designs the protection circuit for the active clamp forward switching power supply,which combines the soft-start circuit with the over-current protection circuit to make an over-current restart protection circuit with a hiccup protection mode.The protection circuit designed in this paper includes four main parts: overtemperature protection circuit,under-voltage protection circuit,soft-start circuit and overcurrent protection circuit.The function of the over-temperature protection circuit is that when the temperature exceeds a certain value,the circuit will shutdown the chip,and have a hysteresis effect on the temperature to prevent hermal shock.The undervoltage protection circuit is a two-stage undervoltage protection.When the undervoltage value exceeds the first level,the dual power supply of the chip starts to supply.When the undervoltage value exceeds the second level,the chip starts to work normally,and each stage has hysteresis,which prevents error opening and error shutdown.The soft start circuit solves the problem that the error amplifier feedbacks too much during the start-up stage,using an op amp to limit the size of the VC.The over-current protection circuit detects whether the inductor current has an over-current condition.After entering the over-current condition,the circuit will enter a hiccup restart mode,which makes the chip far away from the situation that may cause over-current condition again.This article firstly introduced several common topological structure for switching power supplies,and introduced the working principle of active forward clamping,followed by introduction of several common protection circuits,then the author design a protection circuits in demand according to the characteristics of active clamp DCDC converters,and the protection circuits and their key sub-modules were analyzed and simulated.This simulation is based on HHGrace 0.5umBCD process,using Cadence to build the simulation circuit,and use HSPICE and SPECTRE for simulation,verification of function and performance.According to the simulation test,the circuit has shown good performance.