Overload protection switch for power supplies operating on the switchboard principle

摘要

An overload protective circuit for direct current switching or flyback power supplies which senses for build up of internal transistor stress during operation of the main power transistor output stage. Normally, setting an internal overload limit for the main power transistor dissipation is difficult to achieve because the load current to be sensed is out of phase with input driver current. The invention provides for sensing a change in base drive input voltage during a departure from normal operating saturation of Baker clamped main power transistors and initiating a reduction in the width of the drive pulses to reduce internal transistor stress and to reduce power input prior to transistor damage.