High-Efficiency Multioutput LLC Resonant Converter With Multiwinding Transformer and Cost-Effective Analog Control Circuit

A new multioutput
LLC
resonant converter with a multiwinding transformer is proposed. In the proposed converter, the main output is controlled by the pulse frequency modulation of the primary switches, and the additional outputs are regulated by the pulsewidth modulation of the secondary synchronous rectifiers (SRs). Synchronization between the primary switches and the SRs can be easily achieved by sensing the voltage across the secondary side of the transformer at the main output with simple and cost-effective analog circuitry. The proposed converter features high efficiency because of the reduced transformer core loss and conduction losses in the primary switches. It also achieves high power density because of the small size of the transformer, resonant capacitor, and primary switches. The validity of the proposed converter is verified through experiments on a prototype for a 55-inch TV power supply converting 390 Vdc input to 13 V/6.3 A and 65–83 V/ 2.25 A outputs.