Patent ID: 6118675
Filing Date: 2000-09-12
Classification: H02M,Y02B

Abstract:
A method for controlling a flyback DC-DC converter comprising a transformer for storing and transferring energy to a load, the transformer including a primary winding, a secondary winding and an auxiliary winding having a voltage induced by current in the secondary winding, a power switch connected to the primary winding, an output filter capacitor, and a fixed frequency oscillator having a frequency lower than a self-oscillating frequency control mode of the converter for a start-up charge transient of the output filter capacitor, the flyback DC-DC converter operating in a fixed frequency control mode for a low load, the method comprising:monitoring the auxiliary winding to regulate an amount of energy transferred for enabling the power switch driving the primary winding;enabling the power switch for a new conduction and energy storage phase; andcontrolling the amount of energy transferred from the primary winding to the secondary winding by introducing a delay to a turn-on instant of the power switch with respect to a turn-on command generated during the self-oscillating frequency control mode and modulating the power switch off time as a function of an overshoot of an output voltage on the secondary winding during both the fixed frequency control mode and the self-oscillating frequency control mode.