A Saturable Transformer Based Approach to Drive a Synchronous Rectifier

Abstract

This paper presents a new and an improved approach for driving a synchronous rectifier (SR) in a switching power converter. This approach consists to use a saturable transformer (ST) in series with a synchronous rectifier to detect the synchronous rectifier transition at turn off. The saturable transformer generates a very narrow signal (100 ns to 200 ns) at turn OFF when the current in the synchronous rectifier reaches zero. This signal will be used by the gate drive circuit to drive the synchronous rectifier at turn off. The saturable transformer approach presented in this paper is topology independent and it can be applied to any power converter. In addition, it offers the possibility of parallel connection of power converters without the risk of power sinking. The two-switch forward power converter with two synchronous rectifiers has been implemented to test the functionality of the synchronous rectifier driving method. In this experimental prototype, the input voltage is equal to 100 V the output voltage is equal to 9 V and the output load is 20 A. At the 180 Watts output load, the minimum measured efficiency was 93 % at 9 V.