A ZVS-PWM controlled current-mode resonant converter previously propsoed includes an active-clamp circuit and a center-tap tpe synchronous rectifying circuit.This resonant converter has a high effictency for a specific input voltage.However

as the input voltage varies from the specifec value

the efficiency goes domn severely. This paper clarifies the cause of this efficiency drop through the atate transition analysis. To overcome the efficiency drop.we propose the usage of current-doubler type synchronous rectifying circuits with separate inductors and with a coupled inductor

and examine their steady-state characteristice. As a consequence

it is clarified that the propsoed redtifying circrits have achieved a high efficiency over 85% for a wide variation of input voltage under the load condition of 3.3V and 5A.