ATX Power Supply | Electronic Project Circuits

Posts Tagged ‘ATX power supply’

Turn an ATX power supply into a lab PSU

With a couple hours of work, it’s pretty simple to pull the power supply from an old PC relic and turn it into a pretty decent bench system for powering your electronics projects. The standard ATX power supplys that you find in desktop computers have regulated 5 and 12 and 3.3 Volt outputs with sufficient power for most small project needs. You probably have a few of these just collecting dust in the basement, which means you could have a test bench PSU for quite a bit less than the 80 bucks you’d drop for one on
eBay.

WikiHow and Instructables both have a decent howto on the subject. As always, be careful when working with high voltage electronics. Nobody wants “almost saved $80″ on their epitaph, so mind those capacitors.

POWER SUPPLY ATX PC 200W

This power supply circuit uses chip TL494. Similar circuit is used in the most power supplies with output power about 200W.Device use push-pull transistor circuit with regulation of output voltage.

Stand-By mode

In stand-by mode is main power supply blocked by positive voltage on the PS-ON pin through resistor R23 from secondary power supply. Because of this voltage is opened transistor Q10, which opens Q1, which applies reference voltage +5V from pin 14 IO1 to pin 4 IO1. Switched circuit is totally blocked. Tranzistors Q3 and Q4 are both opened and short-circuit winding of auxiliary transformer T2.Due to short-circuit is no voltage on the power circuit. By voltage on pin 4 we can drive maximum pulse-width on the IO1 output. Zero voltage means the highest pulse-width. +5V means that pulse disappear.

PowerGood

Mainboard needs “PowerGood” signal. When all output voltages goes to stable, then PowerGood signal goes to +5V (logical one). PowerGood signal is usually connected to the RESET signal.

+3.3V Voltage stabilisation

Look at circuit connected to output voltage +3.3V. This circuit makes additional voltage stabilisation due to loss of voltage on cables. There are one auxiliary wire from connector for measure 3.3V voltage on motherboard.

Overvoltage circuit

For example when I by mistake short-circuit -5V with +5V, then positive voltage goes across D10, R28, D9 to the base Q6. This transistor is now opened and opens Q5. +5V from pin 14 IC1 comes across diode D11 to the pin 4 IC1 and power supply is blocked. Beyond that goes voltage again to base Q6. Power supply is still blocked, until he is disconnected from power line input.

ATX Power Connector

Pin	Signal	Color 1	Color 2	Pin	Signal	Color 1	Color 2
1	3.3V	orange	violet	11	3.3V	orange	violet
2	3.3V	orange	violet	12	-12V	blue	blue
3	GND	black	black	13	GND	black	black
4	5V	red	red	14	PS_ON	green	grey
5	GND	black	black	15	GND	black	black
6	5V	red	red	16	GND	black	black
7	GND	black	black	17	GND	black	black
8	PW_OK	grey	orange	18	-5V	white	white
9	5V_SB	violet	brown	19	5V	red	red
10	12V	yellow	yellow	20	5V	red	red