Television power supply with polarity-independent charging paths

Abstract

A television receiver has a switched mode power supply controller, which may be deflection synchronized, which produces pulses in a power transformer. To power the controller during startup, before the internal power supply has started, a storage capacitor on the power supply input of the controller is coupled through a current limiting resistance to a rectified voltage from the AC mains so as to charge the storage capacitor during first polarity phases of the AC mains. The current limiting resistance includes a positive temperature coefficient (PTC) element which increases its impedance as it heats, to reduce power dissipation after initial connection of the television receiver to AC mains. In addition, a diode is coupled in a current path to the storage capacitor to charge the capacitor to the same polarity during opposite polarity phases of the AC mains. The two paths for charging the capacitor allow a relatively smaller value for the current limiting resistance, which remains coupled to the storage capacitor, and provides sufficient power to the controller without undue power dissipation over a wide range of power mains voltages.

Dependencies are inferred from the claim text.