You have 24VAC and you want 5V to run a uc, here is a circuit I designed

metron9

Actually it is a circuit that I found to run a indicator LED directly from 110VAC mains. I increased the capacitor size and added a low dropout 5V regulator. What I had was a standard 24VAC transformer from an old furnace that I wanted to use to drive a 220VAC relay with a 24VAC coil.
Originally I blew up a 7805 because the transformer when put through a bridge rectifier actually output about 38 volts. I could not find a regulator that would allow over 38VDC input so I made this. I can get a stiff 22mA at 5VDC using the following circuit. I thought it might be instructive for others needing a bit of low voltage to run a uc when only high voltage AC is available.


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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

sam_sam_sam

Take a look at this if you need·a little more in the way of more amps ·I have used in a project and it works very well with a 24 volt tranformer

You can get a kit with a board and all parts for this regulator at the Nuts and Volts Store online

I was able to power a Basic Stamp and a 2 line LCD Display with a back light and power a·optic sensor and a Ds1302 time chip ·it was·for a project that·I built

http://www.national.com/ds/LM/LM2576.pdf

I hope this helps

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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 10/20/2008 5:00:51 AM GMT

metron9

I shall file it in my datasheet collection, thanks.

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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!

Beau Schwabe

metron9,

Just curious... why a full wave bridge rectifier?· A single diode (half-wave rectifier) would provide a more reasonable output voltage closer to 24V and certainly allow more current than 22mA.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.