DC supply circuit fed from AC mains - uses oscillating transistor voltage converter to derive voltage from AC mains and has storage capacitor in starting unit

摘要

A circuit arrangement is used to derive a DC supply from an AC mains source. It includes an oscillating transistorised voltage transducer which is set in operation by means of a starting unit containing a transistor. The starting unit includes a reservoir capacitor (3) which is charged by way of an ohmic resistor (R5) from a DC source derived by rectification of the mains AC. The output of the starting transistor is fed to a threshold value circuit (GR5). When the instantaneous voltage across the reservoir capacitor exceeds the threshold voltage, the transistor switches on and commences to oscillate. The time constant of the reservoir capacitor and the charging resistor is very large in comparison with the period of oscillation of the voltage transducer circuit.