Primary Side Regulation Method for Fly-Back Converter With a Peak Detection Circuit in CCM/DCM

This article presents a new primary side regulation (PSR) method for the passive snubber fly-back converter. By incorporating a peak detection circuit in the feedback loop, the proposed method eliminates auxiliary winding and knee point detection of the conventional PSR method. To extract the output voltage and current values, this circuit converts the alternating current (ac) sensing signals of the drain-source voltage and primary switch current into direct-current (dc) sensing signals. In addition, a simple first order resistor capacitor (RC) filter is introduced prior to the peak detection circuit, so the signal conditioning circuit can eliminate the parasitic ringing and voltage spike due to the leakage inductance in the converter. Consequently, the proposed PSR methodology can precisely regulate the constant current (CC) and constant voltage (CV) regardless of the continuous conduction mode (CCM) and discontinuous conduction mode (DCM). A 15 W laboratory prototype operating in 10 V of CV and 1.5 A of CC was fabricated, and the feasibility of the proposed method was verified; it achieved PSR within the errors of 1.2% and 0.5% in the CV and CC mode, respectively.