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5v to 3.3v for low power device

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Old 02-12-09, 12:58 PM Thread Starter   #1
nd4spdbh2
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5v to 3.3v for low power device


OK i got a usb wireless nic from my asus p5wdh... it uses the usb interface along with a 3.3v supply... it draws 120ma on the 3.3v rail is all so i need some type of voltage regulator to get 3.3v from the usb 5v as i wanna make an external usb wifi adaptor for any computer i plug it into.

So simply i need to get 3.3v from 5v efficiently... i could use an adjustable voltage regulator but thats overkill really.

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Old 02-13-09, 08:33 PM   #2
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There are a couple ways.

A regulator would do the trick as long as you choose a low drop-out regulator since the run of the mill regulators require >3V difference from supply voltage to regulated voltage.

You could also use two silicon diodes in series. These would drop ~0.7V each regardless of the current draw and should work pretty well even with a current draw of a couple hundred microamps.

If your load is going to be a constant 120mA you could check some spec sheets on digikey and select diodes that will give you the exact voltage drop for that current. You will be dissipating very little in the diodes and this would be the most efficient way to go.

Either way you go, make sure you do something to take the heat out of your component. A hot glue tack to the computer chassis would be fine.

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Old 02-17-09, 11:38 AM Thread Starter   #3
nd4spdbh2
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Quote:
Originally Posted by Bomber5000 View Post
There are a couple ways.

A regulator would do the trick as long as you choose a low drop-out regulator since the run of the mill regulators require >3V difference from supply voltage to regulated voltage.

You could also use two silicon diodes in series. These would drop ~0.7V each regardless of the current draw and should work pretty well even with a current draw of a couple hundred microamps.

If your load is going to be a constant 120mA you could check some spec sheets on digikey and select diodes that will give you the exact voltage drop for that current. You will be dissipating very little in the diodes and this would be the most efficient way to go.

Either way you go, make sure you do something to take the heat out of your component. A hot glue tack to the computer chassis would be fine.
ooo ya some diodes in a series might do the trick... i made a fan controler out of some a while back... worked quite well.... forgot bout that.

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