power supplies

(snip)

Many "wall wart" type supplies are simple transformer, rectifier capacitor filter designs that are completely unregulated, so, at light load, they produce considerably more than their full load rated voltage. The output also varies as the line voltage wanders around. They are quite useful for many tasks, as long as the lack of regulation is okay for those tasks, and you don't expect them to protect themselves from overloads by doing anything more than failing. Adding an external solid state regulator (i.e. LM78xx series fixed voltage devices or the LM317 adjustable type) can make them even more useful and add some overload protection.

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Regards,

John Popelish

Something like this? -->

ch-Top-Power-Supply/

Yes, like that. Change R1 to 240 ohms instead of 560.

Ed

The 1.2A is no problem -- For any given circuit at any given voltage and condition, there'll be just one amount of current that it'll pull. The

1.2A tells what it's _capable_ of supplying at 12V, not that it'll _force_ your circuit to accept 1.2A at 12V (that would require amendments to the law of physics).

Consider it this way. Your car battery is _capable_ of delivering 100s of amps (for a short while) to your starter. Yet you can connect one little old light bulb to that battery, and it'll a couple of 100 milliamps, no problem -- the battery can't _make_ the bulb take more (but don't drop a wrench across those battery terminals!).

Your wall-wart is no different, except as John P. mentioned it'll tend to deliver more than 12V at no load, then less and less as the current draw goes up. What the rating _really_ says is that if you are pulling

1.2A from it, it'll deliver at least 12V -- and that's just what it says, we don't know if it's lying or not.

I save all my wall warts to reuse in stuff I build. They're very useful as long as you know their limitations.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

l .

Guys - thanks so much for the inputs. I'm glad I can go somewhere and actually ASK something without getting some super flamemaster saying RTFM. I eally try not to ask until I've done some googling on my own for a few hours. I've got the components and will build the above.

OT - I'm reading/perusing this newsgroup via web/linux. Any preferred news reader that I can install and import some filters others supply that would be beneficial to me? I'm not a fan of chinese athletic shoes.....

H. Dixon

I use Pan on my Linux machines, Thunderbird on my Windows box. Thunderbird will work, but Pan has better control over filters if you're willing to edit the text files directly. I'd use Pan on the Windows box too, except that I'm lazy.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html