A Proportional Drive for Discontinuous Mode DC-to-DC Converters

A conceptually simple and easy to design scheme to provide proportional base drive currents to bipolar-junction-transistors (BJT) used as power switches in switch mode power supplies (SMPS) is presented. The technique is presently restricted to use with SMPS which have magnetics designed to operate in discontinuous mode. This proportional inductance drive (PID) is so named to describe the circuitry used for implementation. The PID provides three important base drive functions in one simple circuit. It provides forward base current proportional to collector current during on time. It provides reverse base current proportional to collector current during storage time. It provides reverse bias clamping for base-emitter voltage. All three functions are performed by one simple magnetic circuit which is easily driven by most of the commercially available PWM control chips.