SG6105A controller is designed for switching-mode power supplies for desktop PCs. It provides all the functions necessary to monitor and control the output of the power supply. Remote ON/OFF control, power-good circuitry, and protection features against over-voltage and over-power are implemented. It directly senses all the output rails for OVP without the need for external dividers. An innovative AC-signal sampling circuitry provides a sufficient power-down warning signal for PG. A built-in timer generates accurate timing for the control circuit, including the PS-off delay. The cycle-by-cycle PWM switching prevents the power transformer from saturation and ensures the fastest response for the short-circuit protection, which greatly reduces stress for power transistors. Two internal precision TL431 shunt regulators provide stable reference voltage and a driver for 3.3V and 5V standby regulation. Utilizing minimum external components, the SG6105A includes the functions for push-pull and/or half-bridge topology, decreasing production cost and PCB space, and increasing the MTBF for power supply.