Active Clamp Forward Converter With a New Switch Control Technique for Reducing Transient Voltage Overshoot

An active clamp forward converter is popular in low- and medium-power applications. However, due to the voltage overshoot on the clamp capacitor in the transient state, the switches can suffer from high voltage stress, causing the adoption of higher voltage-rated switches and threatens system stability. This article proposes a new switch control technique to reduce the voltage overshoot. The overshoot occurs as the clamp capacitor voltage increases when the transformer primary current flows to clamp capacitor. Thus, to block voltage increase during the corresponding interval, the proposed technique reduces clamp capacitor current by bypassing transformer current to the main switch. For bypass operation, main switch operates as a current source by decreasing gate-to-source voltage. Because the bypass operation does not change voltage gain between input and output, the proposed technique can alleviate the overshoot without affecting the feedback controller designs. To verify the effectiveness, a 300 W prototype is experimented.