Patent ID: 6188588
Filing Date: 2001-02-13
Classification: H02M

Abstract:
A switching controller for use in a power converter having a controllable switch and operable in a critically continuous conduction mode (CCCM), said switching controller comprising:an error amplifier for sensing an electrical characteristic of said power converter and comparing said electrical characteristic to a reference electrical characteristic to generate an error signal;a drive signal generator, coupled to said controllable switch, for comparing said error signal to a reference waveform and providing, in response thereto, a drive signal to said controllable switch; anda waveform shaping circuit, coupled to said power converter, for comparing a sensed voltage across said controllable switch to a sensed time-varying input voltage and providing, in response to said sensed voltage being lower than said input voltage, a modifying signal to said drive signal generator, said modifying signal modifying said reference waveform and causing said drive signal generator to turn-on said controllable switch, said waveform shaping circuit including:an operational amplifier configured as an comparator, wherein said sensed voltage and said input voltage are coupled to an inverting node and a noninverting node, respectively, of said operational amplifier;an exclusive OR gate, said gate inputs are coupled to an output of said operational amplifier and to said drive signal of said drive signal generator; anda second controllable switch coupled to an output of said gate.