Research And Design Of Protection Circuits In Switching Power Supply

As mainstream products of power markets, switching power supply get more and more attention of the designers. According to statistics, the probability to make the switching power supply failure is very small in the normal running work, and the damagement occurs in the bad environment and emergency conditions. When designing, it will satisfy the required electrical characteristics, and the design of protection circuits are indispensable, therefore the system can work safer and more reliable. In this paper, the main work is to design under voltage protection circuits and over current protection circuits of switching power supply, the main content and innovative achievements summarized as follows:1. With the reference voltage as comparing voltage, traditional under voltage protection circuits cannot be applied to the condition that minimum working voltage is low. Aiming at the shortcomings of the traditional under-voltage protection circuit, we put forward a circuit which can be used in low minimum working voltage. Adopting the principle of the temperature compensation, the designed circuit can work in wide temperature range, and the undervoltage threshold is small with the temperature drift.2. To overcome the large area of under voltage protection circuit, we design an under voltage protection circuit, which is smaller in occupied area. The circuit reduce the number of the resistance and the total resistance, therefore reduce the area of the module. At the same time, the circuit can also be applied to the condition that minimum working voltage is low.3. In view of the shortcomings of traditional over current protection circuit, that over current threshod varies greatly, we design a kind of over current protection circuit, whose over current threshod changes small with temperature drift. The circuit adopts PTAT current, which is associated with on resistance of rectifying tube to make compensation, and the on resistance of rectifying tube has positive temperature coefficient. With temperature changing the over current threshold of the designed circuit is small.4. We make detailed analysis and deduction, when amplifier is used as a comparator, including ICMR、CMRR、PSRR、DC gain、IOV and so on, at the same time, every parameters are simulated.Cadence and Hspice simulation software are used to validate the circuits’ functions.