Personal computer power supply with low-power standby mode activated by

Abstract

A power supply for a computer system includes a transformer having a primary side coupled to an AC main and a secondary side coupled to an output line, a charging circuit coupled between the secondary side of the transformer and the output line, an optical switch coupled to the secondary side of the transformer and comprised of an optical transmitter and an optical receiver, a secondary side power switch coupled to the optical receiver, a short circuit protection circuit coupled to the charging circuit, the output line and the optical receiver, a pulse width modulator coupled to an output of the optical receiver and a transformer switch coupled to an output of the pulse width modulator. The pulse width modulator generates a pulse sequence which alternates between first and second states, each having respective durations and frequencies. At each change between the first and second states, the transformer switch selectively connects or disconnects the primary side of the transformer with the input line. By changing the frequency and duration for which the transformer switch selectively connects or disconnects the primary side of the transformer, the charging circuit will have sufficient charge to power energy demanding components coupled to the output line when no short circuit has been detected and sufficient charge to power the optical switch so that the power switch may be used to reset the power supply but insufficient power to operate the energy demanding components when a short circuit has been detected.