Each product in the FSDx321 (x for H, L) family consists of an integrated Pulse Width Modulator (PWM) and Sense FET, and is specifically designed for high performance off-line Switch Mode Power Supplies (SMPS) with minimal external components. Both devices are integrated high voltage power switching regulators which combine an avalanche rugged Sense FET with a current mode PWM control block. The integrated PWM controller features include: a fixed oscillator with frequency modulation for reduced EMI, Under Voltage Lock Out (UVLO) protection, Leading Edge Blanking (LEB), an optimized gate turn-on/turn-off driver, Thermal Shut Down (TSD) protection, Abnormal Over Current Protection (AOCP) and temperature compensated precision current sources for loop compensation and fault protection circuitry. When compared to a discrete MOSFET and controller or RCC switching converter solution, the FSDx321 devices reduce total component count, design size, weight while increasing efficiency, productivity and system reliability. Both devices provide a basic platform that is well suited for the design of cost-effective flyback converters.