Base drive circuit

A base drive circuit for driving a bipolar power switching device of the type which includes a collector, a base and an emitter (or equivalents thereto) to quasi saturation but not full saturation, the drive circuit comprising:

• first and second electronic switches, said first electronic switch being coupled between the collector and the base of the power switching device thereby to prevent the base-collector voltage from exceeding the collector-emitter voltage to prevent saturation of said bipolar power switching device, said second electronic switch being coupled between the base of the power switching device and a negative voltage source which is negative with reference to the emitter voltage, said first electronic switch having a gate and said second electronic switch having a gate, the gates of said switches being connected together;
• impedence means coupled between said gates of said first and second switches and a positive voltage source;
• a control electronic switch connected between said gates and said negative voltage source, said electronic control switch being responsive to a control input signal, and a reference voltage bus is connected between a voltage potential intermediate said positive and negative voltages and the emitter of the power switching device, said first switch being conductive and fully enhanced when a positive voltage is applied to the gate thereof and said second switch being conductive and fully enhanced when a negative voltage is applied to the gate thereof.