# Good inexpensive step-down voltage regulator

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#### vvanders

##### New Member
I'm currently building a device that's somewhat cost sensitive(want to keep parts under $50) and I'm looking for a decent voltage regulator IC. It's USB bus powered(5v source) and I need 3.3v and 1.8v around 300ma or so. I'd really like to use a switching regulator if I can but that best I can find is a LTC3417 which runs ~$7 and I need to run two inductors and all the required capacitors/etc that I can easily see getting up to \$12.

Anyone know of any reasonable dual supply ICs that don't cost an arm and a leg?

#### Hero999

##### Banned
It depends on how cheap and how good it needs to be. You can make a switching regulator with a couple of transistors. The regulation won't be perfect but it's quite efficient.

2-transistor Black Regulator

#### moe7404

##### New Member
low cost reg

well i havent posted lately. and i am not good at deisgning circuts. but would a LM 317 work? i have used them some. and they are easy to use. and i have found some sites that will do the math for you. if you get one from radio shack be warned the digram on there package is wrong. above the grd sign the two wires that cross should have a dot. there package has been like that for decades. i hope this helps if iam wrong sorry.

#### RCinFLA

##### Well-Known Member
An LM317 needs greater then 2v from input to output to work properly so getting 3.3 vdc output with 5 vdc input will violate this.

It will be fine for the 1.8v supply.

A 220 ohm between output and adjust pin. 100 ohm between adjust pin and ground. You are going to have 1 watt of heat when drawing 300 mA @ 1.8v output so you should put a small heat sink on LM317.

You need to look for a low dropout regulator for 3.3 vdc. LM1117 comes in a 3.3 vdc version.

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