PSU using old computer SMPS
Do it yourself
Using Computer SMPS on your design bench
Hi friends, I tell you an interesting story of mine. During last few weeks SMPS in my PC was creating problem. The problem was also unique. The system used to reboot itself when the switch was on for the CD drive. The problem which I understood was that the power handling capacity for the SMPS has gone down. Instead of repairing that, I purchased the new one and installed that to my PC. I was not happy to see the old SMPS lying in my lab without any use. I was also requiring the DC power supply in my lab for testing.
I thought of changing the computer SMPS to the DC power supply for my lab.
The only problem to the SMPS was the low power handling capacity so I agreed with the power level which the SMPS was supplying, as that was sufficient for my projects.
I unscrewed that and identified the basic connections required for that to meet my lab requirement.
Below is the table showing the basic connections required?
The computer power supply is essentially a SMPS, with power handling capability up to 250 W. The output of the SMPS consists of number of wires fixed in number of connectors.
We must first examine the pin configuration of the connectors to make the full use of it.
And below is the procedure to change the computer SMPS to your lab PSU.
1. De-solder all the unnecessary output connection wires
2. Just make Yellow, Red, orange, black, Grey and green connected.
3. Mark the Yellow wire as +12V supply
4. Mark the Red wire as +5V supply
5. Mark the orange wire as +3.3V supply
6. Mark the black wire as ground supply
7. Put a switch between green wire and the black wire, this will act as the power supply on/off switch
8. Put a LED with 500ohm series resistance to the grey wire and the black wire , this will serve as the power on indication.
9. Put a 10ohm / 10W resistor connected permanently to the 5 volt supply.
Now the DC power supply requirement for my lab is fulfilled.
Using Computer SMPS on your design bench
Hi friends, I tell you an interesting story of mine. During last few weeks SMPS in my PC was creating problem. The problem was also unique. The system used to reboot itself when the switch was on for the CD drive. The problem which I understood was that the power handling capacity for the SMPS has gone down. Instead of repairing that, I purchased the new one and installed that to my PC. I was not happy to see the old SMPS lying in my lab without any use. I was also requiring the DC power supply in my lab for testing.
I thought of changing the computer SMPS to the DC power supply for my lab.
The only problem to the SMPS was the low power handling capacity so I agreed with the power level which the SMPS was supplying, as that was sufficient for my projects.
I unscrewed that and identified the basic connections required for that to meet my lab requirement.
Below is the table showing the basic connections required?
The computer power supply is essentially a SMPS, with power handling capability up to 250 W. The output of the SMPS consists of number of wires fixed in number of connectors.
We must first examine the pin configuration of the connectors to make the full use of it.
| Pin | Name | Color | Description | |
| 1 | 3.3V | Orange | +3.3 VDC | |
| 2 | 3.3V | Orange | +3.3 VDC | |
| 3 | COM | Black | Ground | |
| 4 | 5V | Red | +5 VDC | |
| 5 | COM | Black | Ground | |
| 6 | 5V | Red | +5 VDC | |
| 7 | COM | Black | Ground | |
| 8 | PWR_OK | Gray | Power Ok is a status signal generated by the power supply to notify the computer that the DC operating voltages are within the ranges required for proper computer operation (+5 VDC when power is Ok) | |
| 9 | 5VSB | Purple | +5 VDC Standby Voltage (max 10mA) | |
| 10 | 12V | Yellow | +12 VDC | |
| 11 | 12V | Yellow | +12 VDC | |
| 12 | 3.3V | Orange | +3.3 VDC | |
| 13 | 3.3V | Orange | +3.3 VDC | |
| 14 | -12V | Blue | -12 VDC | |
| 15 | COM | Black | Ground | |
| 16 | /PS_ON | Green | Power Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF. | |
| 17 | COM | Black | Ground | |
| 18 | COM | Black | Ground | |
| 19 | COM | Black | Ground | |
| 20 | -5V | White | -5 VDC (this is optional on newer ATX-2 supplies, it is for use with older AT class expansion cards and can be omitted on newer units) | |
| 21 | +5V | Red | +5 VDC | |
| 22 | +5V | Red | +5 VDC | |
| 23 | +5V | Red | +5 VDC | |
| 24 | COM | Black | Ground |
And below is the procedure to change the computer SMPS to your lab PSU.
1. De-solder all the unnecessary output connection wires
2. Just make Yellow, Red, orange, black, Grey and green connected.
3. Mark the Yellow wire as +12V supply
4. Mark the Red wire as +5V supply
5. Mark the orange wire as +3.3V supply
6. Mark the black wire as ground supply
7. Put a switch between green wire and the black wire, this will act as the power supply on/off switch
8. Put a LED with 500ohm series resistance to the grey wire and the black wire , this will serve as the power on indication.
9. Put a 10ohm / 10W resistor connected permanently to the 5 volt supply.
Now the DC power supply requirement for my lab is fulfilled.
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