Author Options:

fast and easy way to get 3.3v from 5v without a lm317? Answered

i got a dvd player but the power supply was missing. i can get the 5v and the 12v, but other than a lm317 (which i dont have) i cant get 3.3v. ive looked at all sorts of things to try and find a 3.3v regulator, but everything i have searched up lead to several misleading results.

so i was wondering, what value resistor could i use to get 3.3v from 5v
what devices could i look in to find a 3.3v regulator? i have several computer motherboards, a bunch of cd drives, a couple hard drives, etc.

please help!

thanks in advance,


Don't use a resistor - The voltage would vary depending on the load.
A dirty way of getting to 3.3V it is to drop the 5V rail with a couple of diodes.
A silicon diode (e.g. IN4001) gives a voltage drop of around 0.7V, but different types do vary slightly and by experiment (100R load without the MP3 connected) you should be able to get 3.3V within 0.1V which would be close enough.

thanks, i will check into that if i cant find any other method for getting the 3.3v, i really want to see if this dvd player works.


5 weeks ago

Use AM1117 with cap on both in and out

The small SMD SOT-223 package AMS1117-3.3's work a treat, as they are a
voltage regulator, and are pretty ubiquitous on motherboards, and sound
cards. If i remember correctly, 5v falls within the typical specs of
the device (5v - 7v) with the max range being around 12v - 15v.

Of coarse, you'll need a couple of capacitors, and resistors, but they should be available in small enough packages to suit your need...

Here's a typical circuit for using the device:


You could, as has been suggested, use series diodes, but imo it would be far simpler to purchase a step-down dc/dc converter IC and build a small board to supply your 3.3V needs.

A PC power supply generates 3.3V directly.

You may well find a single regulator on a PC motherboard, but they are likely to be switchers, and hard to transplant. THey are often found near some coils on the board - take a look.

Otherwise: http://www.sparkfun.com/products/526
...or similar,. depening on the current requirements,


i would use a pc power supply but its a bit too big to fit into this dvd player, and i fear it might get too hot.

by switchers do you mean a regulator with multiple output capabilities?

No, I mean "Switch mode" - where you need a couple of extra parts as well as the "regulator" to make the power supply, and it works by chopping the DC input up, stuffing it through an inductor and smoothing it out again.

Try the PC supply first, if it works, an old Xbox would also yield a small-ish PSU