Research And Design Of Protection Circuits In BUCK Type DC-DC Converter

Modern electronic product is becoming lighter,thinner and smaller depending on the development of hardware circuit.As a kind of power supply,switching power supply is widely used in the market because of its high integration,small size,high efficiency,anti-interference ability,and other advantages.While pursuing high performance of product,people more focus on the reliability.In the normal working environment,the probability of damage to switching power supply is small.The damage to the circuit is generally occurred in the harsh working environment and sudden abnormal situation.In design process,we need to design the protection circuit to ensure that the chip can work safely and reliably in the abnormal environment.The main work of this paper is to study and design the under-voltage lockout circuit and short-circuit protection circuit in the BUCK type DC-DC converter.The design goal is completed through simulation verification.By studying the relevant literature about switching power supply,the background of which is understood in detail,the protective circuit of domestic and foreign research is obtained.The topology and working principle of BUCK type DC-DC converter in switching power supply are analyzed,and its modulation mode and control mode are described in detail,and their advantages and disadvantages are summarized.The realization method and working process of under-voltage lockout circuit and short protection circuit are introduced in detail.Based on the principle of traditional protection circuit structure,two kinds of low power-consumption and fast response under-voltage lockout circuit which can be applied to BUCK type switching power supply and a short-circuit protection circuit which can effectively reduce the output short current are designed.The working principles of two types of circuit are analyzed respectively in detail.The first under-voltage lockout circuit has a novel self-bias current which changes with the input voltage at a quadratic rate so as to improve the response speed of the circuit.On this basis,the temperature compensation is added to the second under-voltage lockout circuit to the make it has better temperature characteristics.The short-circuit protection circuit includes an output voltage short-circuit judgment circuit,a down-conversion circuit and a hiccup-mode soft start circuit,so that the converter can reduce the short current to avoid turning off the converter directly causes the loop can't be restarted after the short circuit condition is removed.In this paper,the structural characteristics and small signal characteristics of two kinds of commonly used comparators are analyzed.0.18um BCD process is used in circuit design.Cadence software is used to draw the circuit,the Hspice software is used to verify the circuit performance.The simulation results show that the under-voltage lockout circuit has the advantages of fast response and low power consumption.After adding the temperature compensation,the under-voltage lockout circuit has a smaller temperature drift which is only 0.04V.Short protection circuit can limit the output short-circuit peak current is less than 4A and short-circuit average current less than 2A when the system is shorted.The proposed circuit meet the design requirements.