Analysis of a novel drive circuit for bipolar transistor switches in DC-DC converters

When employing a bipolar transistor as a main switch in the dc-dc converter, the driving circuit with the current transformer is widely used to improve the power efficiency. However, it is also known that there exists low limit of the turn on time of the main switch in this conventional driving circuit. In this paper, a novel driving circuit for DC-DC converter is presented, in which the bipolar transistor as an auxiliary switch is connected in parallel with the bipolar transistor as a main switch. In this case, the power capacity and switching speed of the auxiliary switch are smaller and faster than those of the main one. Only when the short trigger pulse for the turn on is added to the auxiliary switch, it is turned on and its emitter current is detected by the current transformer, which is used as the base current of the main switch. Consequently the turn on time of the main switch is made sufficiently short and its switching power loss is decreased. The equivalent circuit analysis and experiments of the proposed driving circuit are performed and its validity is confirmed.