Self-excited regulated power supply converter - uses tertiary winding and control transistor for output short circuit protection

摘要

The self-excited power supply converter comprises a switching transistor (Ts1) in series with a DC input and the primary of a heavy-duty transformer (Tr) whose rectified output feeds the load. The base of the transistor is controlled by a second transistor (Ts2) fed from one section of a tertiary winding (N3) and controlled by a regulator circuit which monitors the output (R) (Ts3). The second section of the tertiary winding of the transformer (N4) is connected to a fourth transistor (Ts4) which is in parallel with the base-emitter of the first transistor. During the cut-off time of the switching transistor, its base-emitter path is bridged by the fourth transistor which provides a connection to the negative side of the supply for the second transistor. In the event of a short-circuit across the load, the number of turns on the second section of the tertiary winding (N4) is chosen so that the voltage produced in its is sufficient to hold the fourth transistor in the conducting state and the main switching transistor is therefore not overloaded.