Transformer-coupled direct base drive technology for high-power, high-voltage, bipolar transistor PWM converters

The drive requirements of large high-voltage bipolar power transistors as applied in pulsewidth modulation (PWM) converters and the fundamentally different topologies for efficient high-power transformer-coupled base drives delivering up to 100 A are discussed. Possibilities for high-power base drives with a single transformer were examined, and the limitations of high-efficiency pulsed direct base drives are discussed. The main disadvantage of all pulsed transformer-coupled drives is the absence of continuous negative base-emitter voltage. This is essential in PWM applications in high-voltage converters, and transformer-coupled drives require carrier wave systems. The high-frequency carrier wave system as optimal topology for high-power transformer-coupled direct base drives is analyzed. The different base drive topologies are evaluated in terms of capability, losses, component count, and physical size. Some aspects of the design of a 1 MHz carrier wave transformer-coupled base drive are discussed and experimental results, including efficiency, are shown.>