3.3 v dc psu

First post of mine so please bear with me.

AC/DC adapter that came with my WiFi router got busted and I am in need of one. I could go get the replacement but I am looking for alternative solutions. I have computer power supply that is gathering dust. I could simply tap 3.3 V from there. Since my current requirement is around 1 Amp max, that wouldn't be a problem. But the cooling fan's noise bugs me.

Other alternative is to get 3.3 V from automotive battery. That way I won't have to worry about router turning off during power outage. However, getting 3.3 V for 1 Amp current doesn't sound like a easy task.

Sorry if this question has been already answered. I would appreciate to get some pointer for building an affordable (should cost less than $20) PSU for 3.3 V. Or should I simply stick with free solution of using computer power supply?

Thanks in advance.

I am not sure what your electronics knowledge is like, but your main problem here will be heat. The heat dissipated in your regulator will be (input voltage - output voltage) x current. With a 12V car battery and 3.3V output at 1A will be 8.7W which is lots of heat to get rid of.

My option would be to come down to 5V with a wall cube power supply (also called a plug top power supply). These have awful regulation though and are sometimes only in spec when under full load. So you then need to 'clean up' this voltage with an external regulator. I suggest an LM317 set to 3.3V output. This will dissipate heat though (5-3.3) x 1 = 1.7W so will still need a heatsink. Make sure your wall cube can output 1A

Finally, just make sure you wire up the connector to your WiFi router the right way round to save reverse voltaging your router

The guys in the component store should be able to help you with any further probs you have

Hope this helps

If you're using a computer supply for no more than 3.3V@1A then you don't need a cooling fan so you can safely disconnect it.

Thanks for quick replies!

Appreciate both suggestions. If I get a wall wart with 5V output, I could simply tag a resistor to drop off 1.7V. I don't know the current requirement of router yet. If it is 600 mA at the most, the resistor will be dissipating 1 watt max. LM317 option sounds good too; I will have to do some searching for the circuit.

That's nice to know i could disconnect the fan of PSU. If the heat buildup is too much, I could attach bigger heat sink I suppose.

You don't show your location but if you are in the US Jameco electronics www.jameco.com sells what you need. the part numbers are 251565 for a 1.5 Amp wall cube or 251600 for 2.5 Amps. They are priced at $11.95 and $12.95.