These devices are specifically designed to meet the requirements for increased integration and reliability in off-line flyback (STR-S6401) and forward (STR-S6401F) converters operating in a fixed-frequency PWM mode. Each device incorporates the primary control and drive circuits with an avalanche-rated power MOSFET. Crucial system parameters such as switching frequency and maximum duty cycle are fixed during manufacture. The STR-S6401 and STR-S6401F differ only in their maximum duty cycle. Control circuit decoupling and layout are optimized within each device.