IMPROVEMENT IN SWITCHED-MODE POWER SUPPLIES

摘要

A trapezoidal current-versus-time waveform output stage of simple construction for a switched-mode power supply avoids unwanted heat generation encountered while dropping the voltage of the D.C. supply to drive the base of the output transistor (10) by deriving the energy for output-transistor (10) base drive from a bias winding (20) on the output transformer (14), storing that energy in the form of a current flowing through an inductor (26), and steering that current by means of a shunt transistor 32 selectably either into the base-emitter junction of the power transistor (10) or so as to reverse bias the base emitter junction of the power transistor (10) to ensure that rapid removal therefrom of its stored charge.