Design Guidelines for Flyback Converters Using FSQ-series Fairchild Power Switch (FPSTM)

The FSQ-series FPSTM (Fairchild Power Switch) is an integrated Pulse Width Modulation (PWM) controller and Sense FET specifically designed for quasi-resonant off-line Switch Mode Power Supplies (SMPS) with minimal external components. Figure 1 shows the internal block diagram of the FSQ-series. Compared with discrete MOSFET and PWM controller solution, it can reduce total cost, component count, size and weight, while simultaneously increasing efficiency, productivity, and system reliability. The FSQ-series employs an advanced control technique that allows converter to operate with narrow frequency variation, while keeping the quasi-resonant operation. When the converter operates in discontinuous conduction mode (DCM), the controller finds the valley of the drain voltage and turns on the MOSFET at the minimum drain voltage. Meanwhile, the converter can operate with fixed frequency when operating in continuous conduction mode (CCM), which allows converter design as simple as conventional PWM converters.