Circuit for a picture display device for converting an input d.c. voltage into an output d.c. voltage

Claim 1

A circuit for a picture display device for converting an input d.c. voltage into an output d.c. voltage which is substantially independent of variations of the input voltage and/or variations of a load connected to the output voltage, comprising a transformer whose primary winding is part of a first resonant network which also includes a first and a second capacitor, switching means operations at line frequency to apply the voltage across the first capacitor to the primary winding, the switching means comprising a controllable switch connected in series with a first diode coupled with a second diode connected in parallel with the series connection of the switch and the first diode an inductance having one end connected to a first terminal of the input voltage and the other end to the primary winding, means connecting the switch to a second terminal of the input voltage, means coupling the inductance 155 to the resonant network via a third diode, a secondary winding of the transformer to a fourth diode connected in turn to a smoothing capacitor for generating the output voltage, a sawtooth current flowing during operation through the primary winding flowing during a first portion of the trace period thereof through the first diode and during the remaining, second portion of the trace period through the second diode and through the switch, a supply current flowing through the inductance causing energy to be stored therein while a current flowing during the cut-off period of the switch through the third diode and through the inductance replenishes energy losses, the retrace period of the said sawtooth current being determined by the elements of the first resonant network and the conduction period of the switch being dependent on the output voltage, a fifth diode series connected to the controllable switch and a sixth diode coupled in parallel with the series connection of the switch and fifth diode; a second resonant network comprising a second inductance, a trace and a retrace capacitor being included between the connecting point of the fifth and the sixth diode and the connecting point of the fourth diode and the smoothing capacitor, through which second inductance there flows during operation a second sawtooth current of line frequency which flows during a first portion of the trace period thereof through the sixth diode and during the remaining, second portion thereof through the fifth diode and the switch, the retrace period of the second sawtooth current being determined by the elements of the second resonant network and the starting moment of the retrace period of the second sawtooth current coinciding with the starting moment of the retrace period of the said first sawtooth current.