Power supply input system.

摘要

A power supply input system in which a bidirectional triode thyristor (TRIAC) (25) is connected in series with a switch mode power supply, characterised in that the system includes a control circuit (28) which compares the voltage across the power supply DC input bus (E,F) to a reference voltage and varies the conduction angle of the TRIAC by producing an error signal which determines the phase delay between a mains input zero crossing and the production of a firing pulse. At the time of application of power the conduction angle is zero and slowly increases to that demanded by the control circuit.