small and board mount solutions for +5VDC AC-DC supply?

Hi - I have a board I'm finishing up the design of right now that needs a

5V DC supply. It already has 120V AC live, neutral, and ground on it - so ideally I'd like to be able to have something simple made use of those lines instead of using a wall wart. Current consumption should be fairly low - I believe around 30-50ma, certainly never over 100ma. I'm also hoping to find something fairly efficient, as there won't be much cooling available to this circuit. Any suggestions? Thanks!

-Michael J. Noone

Reply to
Michael Noone
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If the board doesn't have to be isolated, you can use a capacitor to block the line, followed by a bridge and a shunt regulator. Here is a technote by microchip that describes some techniques:

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Regards,
  Bob Monsen
Reply to
Bob Monsen

Since the board already has 120V AC live, neutral and ground, it will have to conform to the legal rules in any event.

I'd use a small step-down transformer, a diode bridge, about 1000uF of electrolytic reservour capacitor, and 5V linear regulator in a TO-220 package - something like the LM340 or an LM7805. A low-drop-out regulator wouldn't be worth the trouble in this sort of application.

A capacitative voltage dropper sounds attractive until you start working out to protect it from the fast, high-voltage spikes that show up from time to time on the mains.

----------- Bill Sloman, Nijmegen

Reply to
bill.sloman

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martin

"Wales is a big welsh-shaped rain collection device"

Reply to
martin griffith

Stick with the wallwart supply. By using an external powersupply, only this supply has to conform to the legal rules. Otherwise your gadget has to conform to the rules. Conforming to the rules can be a costly undertaking as the required tests differ quite a lot.

Rene

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Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
Reply to
Rene Tschaggelar

Would it be possible to use a transient voltage suppressor to help with this problem? How about something like this:

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Regards,
  Bob Monsen
Reply to
Bob Monsen

The highest voltage device in the range would clip just above the 170V peak of a nominal 120V rms waveform, so you could probably use it, with a series resistor to limit the clamping current to something finite, but you would end up with quite a lot of componenets.

------------ Bill Sloman, Nijmegen

Reply to
bill.sloman

It sounds the same as a transformer supply to me, except the transformer is replaced by the cap, transorb and resistor. Those 250V ac caps aren't small, either, so a small transformer might even win out over it in terms of size. I suspect this is particularly true of 100mA @ 5VDC, because the supply will require at least 3.3uF with a bridge diode, and twice that with a simple two diode rectifier. A lower current requirement would mean a far smaller cap.

However, it seems like one could put all of this (minus the cap) onto an IC... I wonder if some mfgr out there has done this already? That might tip the balance in favor of this type of supply, at least for this application.

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Regards,
  Bob Monsen
Reply to
Bob Monsen

hoping

Take a look at:

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Don Cleveland

Reply to
Don Cleveland

Ther are a number of switching regulators designed to do just that.

Reply to
Robert Baer

"Don Cleveland" wrote in news:B0Ome.8258$ snipped-for-privacy@nnrp1.uunet.ca:

Hi Don - that is *exactly* what I'm looking for. I contacted them and these units are new and have not made it out of production yet, and will not until August. Are there any companies out there that make similar products? Again - this is exactly what I'm looking for, but I'm hoping to get the parts sooner than that. Thanks,

-Michael Noone

Reply to
Michael Noone

martin griffith wrote in news: snipped-for-privacy@4ax.com:

I'm not quite sure what I should be looking for at this website? I looked through their product catalog and did not see anything at all like what I'm looking for. Thanks,

-Michael

Reply to
Michael Noone

snipped-for-privacy@ieee.org wrote in news:1117445015.906720.34530 @z14g2000cwz.googlegroups.com:

You're quite correct about the legalities Bill. My plan was to do like you said with a step down transformer, but I got to thinking that there just

*has* to be an easier way, as this seems like a pretty common task. Also all the transformers I've been looking at are fairly large, and I'm hoping to keep this board as small as possible.

-Michael

Reply to
Michael Noone

What if you just attached something like this to the board, instead of a transformer/rectifier/filter/regulator?

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I can't imagine this being the only thing like it - I just went to radioshack.com and looked up "adapters".

Cheers! Rich

Reply to
Rich Grise

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