Patent ID: 6301135
Filing Date: 2001-10-09
Classification: H02M

Abstract:
Control circuitry for an isolated switching-mode power supply operating under secondary-side control, comprising:a secondary-side controller operative to monitor an output voltage of the power supply and to generate a pulse-width-modulated (PWM) control signal, the PWM control signal being generated such that it can be used to control one or more primary-side switching elements in the power supply to maintain a predetermined output voltage level; anda primary-side controller operative to receive the PWM control signal and to generate a PWM drive signal to control the primary-side switching elements, the primary-side controller including:supervisory circuitry operative to detect certain primary-side operating conditions under which the modulation of the PWM drive signal is to be modified from that dictated by the PWM control signal; andpulse width determining circuitry operative to modulate the PWM drive signal as dictated by the PWM control signal and upon detection of the certain operating conditions to modify the modulation of said PWM drive signal accordingly.