200W ATX Power Supply Circuit

This an ATX power supply circuit diagram, dedicated for personal computer, but you may use this power supply for other electronic devices. The circuit is built using chip TL494, and will give you approximately 200W. It use push-pull transistor circuit with regulation of output voltage.

Line voltage goes via input filter circuit (C1, R1, T1, C4, T5) to the bridge rectifier. When voltage is switched from 230V to 115V, then rectifier works like a doubler. Varistors Z1 and Z2 have overvoltage secure function on the line input.

Thermistor NTCR1 limits input electric current until capacitors C5 and C6 are charged. R2 and R3 are only for discharge capacitors right after disconnecting power supply. When power supply is connected to the line voltage, then at very first are charged capacitors C5 and C6 together for about 300V.

Then take a run secondary power supply controlled by transistor Q12 and on its output is going to be voltage. Behind the voltage regulator IC3 would be voltage 5V, which goes in to the motherboard and it’s required for turn-on logic and for “Wake on something” functions.

The next unstabilized voltage goes via diode D30 to the primary control chip IC1 and control transistors Q3 and Q4. When primary power supply is running, then this voltage goes from +12V output via diode D.

ATX power supply circuit diagram, page source: http://www.pavouk.org/hw/en_atxps.html