I am working on a circuit that is completly powered by 5VDC from a USB port. The circuit uses SSR's to turn on and off 120VAC from a standard wall plug; the 120VAC powers a high-power heater of sorts. Now it appears as though I am also going to need to add a PC fan into the mix. Most of the PC fans that I have seen run off 12 VDC. So what would be the cheapest and easiest way to get 12VDC to my fan. I am thinking that it doesn't have to be well regulated and smooth becuase the ONLY thing it will be used for is powering this fan. I will likely use another lower power SSR to turn the 12VDC on and off from my MCU. Extra points for a space saving solution as well!
Looks like MPJA.com has 12V, 300mA power supplies for $1.25 and if you buy 50 they're $0.99. That is hard to beat! But they aren't the smallest solution.
You could just get a 12VDC wall supply. Has the transformer, rectifier, filter and regulator built in. can get fans cheap also. Check these links, $8.50 for all.
Why would you not just use a 5 volt fan?
Ok here's my best guess.
I can get a transform at Radioshack for $4.49 that will drop the 120VAC down to 12.6VAC. (Suprising I couldn't find a transformer of this type cheaper on digikey or mouser) Transformer: http://www.radioshack.com/product/index.jsp?productId=2102494#inTheBox
Then I could use four 1N4007 diodes to make a full wave rectifier. Cost of diodes is about a dollar total.
Finally stick a large capacitor at the output to smooth out the signal.
This puts the total cost around $7.
I know the output won't be prefect and it will be a little higher than 12VDC but I think it should be fine for a PC fan...
I'd think outside the box on this one: Go get a 12VDC wall wart from Goodwill and switch with a relay on the DC side (or a solid-state solution to taste). For your $2 you may even be able to find one with an on/off switch.