Patent ID: 8884551

Claim:
A circuit for controlling a switching regulator including a flyback transformer with primary and secondary windings and a switching transistor coupled to the primary side winding at a switching node SW, and configured to supply regulated current to a load that is isolated from a source of input power by the flyback transformer, the circuit comprising: controller circuitry configured to switch the transistor on at a time SW ON and off at a time SW OFF , such that a primary current I P through the primary side winding increases from substantially zero at SW ON to a primary peak current I PP at SW OFF , thereby inducing in the secondary side winding a secondary current I S that decreases from a peak current I SP at SW OFF to substantially zero before the transistor is switched on at a next SW ON , in accordance with discontinuous conduction mode operation; a zero crossing detect circuit configured to detect, after SW OFF , a zero crossing ZCD corresponding to a voltage V SW at the primary side switching node SW decreasing in magnitude to an input voltage V IN , which occurs after the secondary current I S is substantially zero and before the transistor is switched on at the next SW ON ; and time-integral circuitry configured to establish a time-integral window T-I_W with a leading edge corresponding to SW OFF and a trailing edge corresponding to ZCD; the controller circuitry operable to modulate at least the time SW OFF relative to SW ON based on the primary peak current IPP at SW OFF and the time-integral window T-I_W, such that a regulated load current is supplied to the load.