Design of a Highly Accuracy PSR CC/CV AC-DC Converter Based on a Cable Compensation Scheme Without External Capacitor

With the development of portable electronic products, the requirement for chargers is also getting higher. In this paper, a highly accuracy CC/CV AC-DC flyback converter is proposed, and a novel cable compensation method without external capacitor is put forward. The converter adopts primary-side regulate(PSR) scheme, detecting the output voltage through the auxiliary winding, and adjusting switching frequency to achieve output voltage constant in CV mode. Compared to conventional cable compensation module, the proposed circuit applies a method of pre-filtering, averaging and re-filtering, to obtain the compensation voltage. This method eliminates the need of external capacitor, reducing cost and increasing reliability of the converter. In CC mode, the switching period is adjusted to be fixed multiple of the demagnetization time, thereby realizing the constant current output. The control chip was implemented in NEC 1μm HVCMOS process, and a 5V/1A prototype has been built to verify its feasibility. Experimental results show that the deviations of output voltage and current are within -0.9% and -3% under different inputs and loads, while maximum conversion efficiency can reach a level of 78.2%.