High‐speed switching of the power transistor in a DC‐DC converter with current feedback and core saturation

To reduce the size and weight of a switching dc‐dc converter, it is effective to increase its switching frequency. This requires the reduction of the switching time and switching loss. This paper introduces a dc‐dc converter with a short turn‐off time and a high efficiency at a switching frequency up to the order of megahertz. This is achieved by using a bipolar transistor with current feedback and core saturation. The turn‐off mechanism was analyzed by using an equivalent circuit. The turn‐off time was found to be considerably shortened by the quick discharge of the excess carrier in the base region. This is due to the formation of an LC circuit consisting of the saturated inductance of the current feedback transformer which magnetically saturates during the turn‐off period, and the base‐emitter capacitance of the switching transistor. This phenomenon can be used widely for high‐speed and high current switchings.