Switched-mode self oscillating supply voltage circuit

Claim 1

A switched-mode self-oscillating supply voltage circuit for converting an input voltage into an output d.c. voltage which is substantially independent of variations of the input voltage and/or of a load connected to the terminals of the output voltage, comprising a transformer having a primary and a feedback winding, a first controllable switch connected in series with the primary winding, the series arrangement thus formed being coupled between terminals for the input voltage, a second controllable switch coupled via a turn-off capacitor to the control electrode of the first switch to turn it off, means coupling the feedback winding to said control electrode, a transformer winding being coupled via a rectifier to an output capacitor having terminals which supply the output voltage, an output voltage-dependent control voltage being present on a control electrode of the second switch for controlling the conduction period of the first switch, the circuit being switchable between an operating state and a stand-by state in which relative to the operating state the supply energy supplied to the load is considerably reduced, a starting network connected to a terminal for the input voltage, means for adjusting the control voltage in the stand-by state to a value at which the first controllable switch is cut-off, a connection which carries current during the conduction period for the second controllable switch being provided between the starting network and said second switch, and means providing a connection between the starting network and the control electrode of the first switch, which connection does not carry current in the stand-by state.