Transistor switch control circuit - has positive feedback and derives switching energy from load circuit with low losses

摘要

The control circuit, for a transistor switch, not only allows the power needed to switch the transistor to be derived from the load circuit itself but also reduces switching losses in the transistor. A control winding (nl) is coupled across the transistor switch base/emitter junction and is inductively coupled both to the clock circuit (T) and to an auxiliary winding (n3) in the transistor collector circuit. The transistor base current needed for switching is derived by positive feedback. The clock circuit is controlled at the beginning and end of the transistor 'on' interval by two short pulses opposite in polarity. The duration of these pulses is less than the clock circuit half period.