Schematic of a 12V PC power supply

I'm looking for a schematic of a power supply for a PC (486/Pentium I) that can run off a 12V battery (ie. Don't have to step it up and then the power supply steps it down again - loss in efficiency).

Thanks
Sputnik :idea:

486 pc power supply

Check out

www.ludvigsen.nu/1-2-octaviamp3/1-2-octaviamp3.pdf

This shows schematic for 5V and 12V supplies. Can be modified top provide 3.3V if required.

pin detail ic dbl494

You probably would like to consider using TL494. You can modify the circuit show in this link **broken link removed**

12v pc power

Thank you very much for your helpful responses. I only have a slight problem, I don't know how many of these components are available where I am. I tried searching my local electronic store's website and they don't have them. If any components can be substituted for more common components, could someone list them, please!

The following components need to be substituted:
Component ................... Replacement found
-MBR340 .............................. 1N5822
-MBR745
-MAX787
-LM2587T12(5)
-SA30A
-MUR120
-TL494 ................................. DBL494 (Same difference)

I also need the power supply to have -12V and -5V.

Thanks
Sputnik :idea:

12v pc power supply schematic

TL494 is a popular IC used in switching regulator. If you have old PC power supply, you may find the IC insides it. By the way, you can also apply FREE TL494 sample from Texas Instruments ( https://focus.ti.com/docs/prod/folders/print/tl494.html#samples ), providing that TI has the policy to deliver sample to your country.

You also can apply FREE MAX787 sample from Maxim ( **broken link removed** ). Again, it depends whether Maxim has the policy to send sample to your country.


MBR340 is a 3A 40V Schottky Rectifier, meaning it can do fast switching. I think you can find one fast switching rectifier/diode to replace. You also can order FREE MBR340 from On Semiconductor ( https://www.onsemi.com/site/products/summary/0,4450,MBR340,00.html ). However, customer needs to pay 'handling charge'.

power supply old pc regulate

In the following schematic, I know I would increase output current by changing the transistor and inductor, but what components would I alter in order to change the output voltage? And how do I make the 1mH inductor?

Thanks
Sputnik :idea:

ka7500 examples

The circuit regulate the pulse width in such a way , that the voltage difference between comparator inputs 1 and 2 must be equal 0 volt.
If you divide by half the output voltage that is apply to pin 1 (for example by inserting 5,1 kohm resistor between pin 1 and pins (4,7,9,10) , the regulator output voltage must rise to 10 V in order to get 5V at pin 1.

To reduce the output voltage you should lover the reference voltage (generated at pin 14 and applied to pin 2 via 5,1 k resistor) leaving the full (not divided) output voltage applied to pin 1 (via 5,1 kohm resistor).

May be it would be also good to keep the equivalent resistance of divider equal 5 kohm (as in original circuit-without the divider) , to realise this, two 10 kohm resistors should be used to build the divider.
(5,1 k should be replaced by 10 kohm and another 10 k should be added to pin 4,7,9,10)

I must say, that all written above is my "mind game". You can experiment, but on your own risk.