Patent ID: 7583519

Claim:
A system for estimating an output current of a Switch Mode Power Supply (“SMPS”), said SMPS including a transformer with at least a primary winding coupled to an input of the SMPS and a secondary winding coupled to an output of the SMPS, the system comprising: an input to sense a current in said primary winding of said transformer; an averager to average a signal from said sensed current over a period when current is flowing in said primary winding to provide an average current signal; a first subsystem to determine an estimate of a discharge time of current through said secondary winding of said transformer; and a second subsystem to scale said average current signal using said discharge time to estimate said SMPS output current; and wherein said averager comprises a low-pass filter including a resistor and a capacitor, wherein said resistor is implemented by a switched capacitor resistor, said switched capacitor resistor comprising: a first switched capacitor resistor terminal; a second switched capacitor resistor terminal; a common terminal; an intermediate terminal; a capacitor coupled between said intermediate terminal and said common terminal; a first controllable switch coupled between said first terminal and said intermediate terminal; a second controllable switch coupled between said second terminal and said intermediate terminal; and at least one resistor connected in series with one of said first and second switches between one of said first and second terminals and said intermediate terminal.