Isolated Dc / Dc Switching Power Supply Output With A Pre-bias Voltage To Start The Research

Along with development of electrical and computer technology, the IC (integrated circuit) like DSP (digital signal process) and CPU (center process unit) which need low voltage and high current is used in system design constantly. Then, two changes are caused by the development of IC: 1. synchronous rectifier must be used in new DC/DC power supply to improve efficiency and thermal performance. Multi power supplies with different output voltage are used in new system. At this situation, there is a bad short circuit on output of the power supply with synchronous rectifier because energy on output flow to input when pre-bias output voltage exists.Taking the example of active clamp forward converter, a detailed analysis on the phenomenon is given in this paper by analyzing the operating stage of the circuit. Comparing the synchronous rectifier to normal circuit by calculating the efficiency indicates that forestay is much better on efficiency and thermal performance.A simple circuit with good consistency, high efficiency, high reliability and low cost is presented in this paper. The feasibility is proved by emulating with computer.Finally, a prototype of active clamp forward converter is debugged. The result of comparing the two situation with or without the circuit advanced improved the validity of the technique. this circuit can be widely used in other topology, such as flyback converter, half bridge converter, full bridge converter and push-pull converter with synchronous rectifier.