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Topic: Power from 24VAC (Read 4 times) previous topic - next topic


between + and - of the bridge output?

Doable, but not as good.

You can check out the staged regulator designs (pre-regulators) from Walter Jung. If that's too much, get a resistor or zener from Radioshack + another LM317/78xx series regulators and use the resistor / zener to raise the ground pin's potential, and then use the 2nd regulator to step it down further. A typical approach in LM317 datasheet to expand the (input) voltage range.


Thanks for the inputs.

The Recom is a neat device http://www.recom-power.com/pdf/Powerline-AC-DC/RAC01_02-SC.pdf

However, it is rated at 90vac minimum.  What happens when it is used at far below its rated minimum?

I guess that several billion wall module power supply designers are right and that a transformer is the best approach. 

Does anyone have any recommendations for a tiny transformer to go in front of the bridge?

As i looked at information on transformers, it became obvious that becoming familiar with all the varieties and specifications could take a long time.  Does anyone have any quick explanation on how to see the load imposed by the winding on a perpetual basis>

If this post seems redundant, I put one up a few minutes ago that didn't show up and decided to do it again.

Thanks again.


Search at mouser.com, there is a whole line of Recom Ac/Dc adapters.  I had line voltage on the brain when I selected that part.
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I looked at Mouser and they start at 80VAC


Same story at Digikey.

Do you have any quick thoughts on a tiny transformer?



You could use something like http://www.digikey.com/product-detail/en/FP30-200/237-1021-ND/242467. Connect the 2 secondaries in series across the 24V supply (I've chosen a 30V transformer because your supply is more than 24V unloaded). Leave the primary open circuit. Then you will get 15V across one of the secondaries, which you can rectify and feed to a 7805.

Or build your own switching regulator, as I suggested in a previous post.
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