STANDBY OPERATION OF A RESONANT POWER CONVERTOR
A control method is proposed that enables to drive a resonant (LLC) power converter at low loads with substantially reduced power losses for realizing a stand-by power. The reduction is achieved by a sub-critical operation several times below Resonance Frequency while still keeping zero voltage switching. One half-bridge switch is turned on for a short pulse - in the remaining time of the sub-critical switching period the resonant current oscillates through the other switch. Zero voltage switching is obtained by evaluating the resonant capacitor voltage. The pulse length determines the stand-by power and is used as controlling variable. The power supply is suitable for Consumer Electronics products that require a low power standby supply.