CONTROL OF POWER TRANSMISSION BY FLYBACK CONVERTER BY MODULATING OFF-PHASE OF LOAD FUNCTION

PROBLEM TO BE SOLVED: To prevent a burst mode function and, at the same time, to reduce overshooting by modulating the turning-off period of a power switch by using a combinatory function of operating parameters until a limit output voltage condition is reached when mode transition is made from a self-exciting oscillation mode to a fixed oscillator frequency mode. SOLUTION: A primary control loop controls the output voltage Vout of a flyback converter by controlling the voltage Vcs of the self-feeding power of a control circuit by means of an error amplifier Error Amp and a secondary control loop directly controls the output voltage Vout by optically coupling the amplifier Error Amp and control circuit to a Vcomp pin. Then the turning- off period of a power switch is continued until the energy stored in a transformer during the turning-on period of the power switch is completely transferred to an output circuit by operating a bistable circuit LATCH in accordance with the voltage Vcomp compensation capacitor Ccomp through a comparator Ccomp.