Primary-Side Controlled Flyback Converter with Propagation-Delay Compensation

Primary-side regulation (PSR) flyback converter has advantages of compact size, lower cost, and less power loss on devices because secondary-side feedback circuit is needless. In general, PSR flyback converter uses current sensing resistor to sense primary-side current peak value, and auxiliary winding to detect output diode conduction period, then output current can be estimated. However, it exists error between the sensed value and the real value of primary-side current peak value because of the time delay between power switch turn-off instant and output diode conducting instant. In prior researches, the compensation method of primaryside current peak value is to detect the delay period and estimate the current error with assuming that primary-side current increases linearly, but parasitic capacitances of power switch let primary-side current change nonlinearly actually. The current error compensation can be achieved by detecting the sink current of the gate driver circuit. Finally, the output current control is implemented with digital controller TMS320F28335, and applied to an input voltage at 130 V, output current of 5 A, output voltage of 12 V, and output power of 60 W flyback converter to verify the feasibility of proposed compensation method.