# Voltage regulator setup

I'm building a circuit that requires 5v and 3.3v.

basic estimated specs:

3.3v average current 100ma, max 600ma 5v average current 300ma, max 800ma

I will use a 12v 1amp wall wart.

what do you think is the best way I should go about doing this.

12v --> 7805 --> ez1084(3.3 regulator w/ low dropout) or 12v --> 7805 and ez1084?

3.3v average current 100ma, max 600ma (12-3.3) * .6 = 5.22Watts 5v average current 300ma, max 800ma (12-5) * .8 = 5.6Watts

Things will get hot.

Use a 5volt regulated wall wart. Add a 3.3volt regulator. (5-3.3) * .6 = ~1watt. Leo..

i will need that 12v also ::)

When I say max I mean only on startup or every 30 mins for 1 second. TO-220 package should be able to handle that?

I'm trying to not use a heat sink.

efficiency isn't required but lm2575 -5.0 is also a option but more parts

The 5volt regulator will dissipate (12-5) * 0.3 = 2.1watt. The chip inside the regulator will be ~150C without heatsink. It will shut down if you're lucky.

Get a \$2 buck converter from ebay. Feed 12volt into it, and adjust for 5volt output. Make 3.3volt from 5volt with a small lineair regulator.

A step-down/buck converter also drops the input current. e.g. 5volt/500mA out needs 12volt/~250mA in.

Also look at micro converters. Higher efficiency = less heat. https://www.pololu.com/product/2843 Leo..

Also keep in mind, if you use the 12V and 800mA @ 5V and 600mA @ 3,3V you overload the wal wartâ€¦

switchmode from 12V to 5V, then 3.3V linear regulator from 5V to 3.3V perhaps?

Yes, i will switchmode to 5v. Thank you.