A low-cost flyback converter with primary side regulation for a TV set top box

In consumer electronic products, there is a high demand for an off-line low-power Switched Mode Power Supply (SMPS). Applications invariably require the SMPS be small, lightweight, reliable, and low cost. This paper presents the design of a low-cost flyback converter to power a TV set top box. To reduce costs, the conventional output feedback circuit using an opto-coupler is removed and replaced by the feedback circuit using an auxiliary winding of the flyback transformer. This feedback technique is literally called Primary Side Regulation (PSR). In the PSR, the output regulation performance largely depends on good coupling between the secondary and auxiliary windings. The paper considers two transformer winding methods and their impacts on output voltage regulation are compared. Experimental results are provided to verify the output performance given by each winding technique.