Power control circuit for DC supply - includes transistor cutting current periodically to primary of transformer with winding to base, led and phototransistor providing feedback

摘要

The circuit uses a continuous (DC) supply to limit the power delivered to a load by a periodic cutting of the supply. The DC source is connected to the primary winding of a transformer (LP), and a transistor (Q1) is connected in series. A control circuit periodically blocks this transistor by a connection to the transistor base via an additional transformer winding (ER). A further winding (EU) derives the output voltage which is applied across the terminals of a capacitor (C3) to the load. A light emitting diode connected to the output terminals provides a light output related to the output voltage. This LED is optically coupled to a phototransistor (Q2) in the control circuit, providing a feedback loop by which the power is controlled.