Description

This reference design implements the UCC28630 PSR controller in a flyback power supply. The UCC28630 is capable of operating in both Continuous and Discontinuous Conduction Modes which enables high efficiency while reducing inductor size and cost. Safety standards such as EN60950 require that any X-capacitors in EMC filters on the AC side of the bridge rectifier quickly discharge to a safe level when AC is disconnected.  Typically: this requirement is achieved by including a resistive discharge element in parallel with the X-capacitor. However: this resistance causes a continuous power dissipation that impacts the standby power performance. In order to reduce standby power and eliminate the standing loss associated with the conventional discharge resistors: the UCC28630 device incorporates active X-capacitor discharge circuitry. In this design: less than 100mW no load power comsumption and over 88% converter efficiency is achieved.