Abstract: The present invention discloses a method applied in a controller unit of a feedback circuit for controlling a resonant converter. When the operation mode of the resonant converter turns from no load (or light load) to full load (or heave load), the controller unit is configured by the method of the present invention to control a power switch unit in the resonant converter to switch ON and OFF according to an operation frequency of full load (such as 100 KHz), in the case of the fact that an instantaneous drop of the output voltage and a variation of the output current of the resonant converter are over predicted. As a result, the instantaneous drop of the output voltage is largely reduced. Therefore, this method is able to make the resonant converter provide the output voltage stably during the switch between the no-load operation mode and the full-load operation mode.

Abstract: A resonant control device and a resonant control method thereof controls a resonant converter connected with a load. An output voltage is applied across the load. Firstly, a setting voltage is used to perform voltage compensation on the output voltage to generate a control value. Then, pulse modulation signals are generated according to the control value and a switch value, so as to drive the resonant converter to regulate the output voltage. Each pulse modulation signal has the maximum frequency and the minimum frequency. The switch value is equal to the minimum frequency divided by the maximum frequency and less than 0.5. Finally, the process determines whether the control value is less than the switch value. If the answer is yes, PWM signals as the pulse modulation signals are generated, and their frequency is less than the maximum frequency to increase a lower-limit range of the output voltage.