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Old 08-20-2007, 03:25 AM #1
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Default variable voltage and current power supply

Found this nifty little circuit for providing adjustable voltage and current:

voltage and current limited ps

http://www.repairfaq.org/sam/sgldtst1.gif

http://members.misty.com/don/sgldtst1.gif (Note: This is the mirror is above link off-line)

What's nice is that it uses a pair of LM317's to perform each task. I plan on trying this either with a blu-ray device at some point and/or a future red project.

UPDATE 8/21/07: Sam Goldwasser, in a newsgroup discussion, suggests the following to add to this circuit placed directly across the laser diode...."Not shown but highly recommended: A parallel combination of a 1K ohm resistor, 0.1 uF capacitor, and reverse polarity fast
diode permanently across the laser diode."


Jon


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Old 08-20-2007, 03:13 PM #2
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Default Re: variable voltage and current power supply

The link is not working for me - can you double check it please ?
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Old 08-20-2007, 03:18 PM #3
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Default Re: variable voltage and current power supply

Quote:
Originally Posted by SenKat
The link is not working for me - can you double check it please ?
The link is good. My guess is that it's offline for maintenance or something, but should be back up at some point as it is one of the main branches of the laserfaq.

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Old 08-20-2007, 03:45 PM #4
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Default Re: variable voltage and current power supply

I just found and added a mirror site for the same circuit in the event the original link is offline. See first post.

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Old 08-20-2007, 03:57 PM #5
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Default Re: variable voltage and current power supply

Crazy...

StumbledUpon took me to that site last night at random, and that was the FIRST schematic I went to.

;D
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Old 08-21-2007, 11:20 AM #6
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Default Re: variable voltage and current power supply

hmmm this is just what i wanted thank you very much
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Old 08-21-2007, 04:11 PM #7
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Default Re: variable voltage and current power supply

Thanks, all. This particular supply is more difficult to find in the various Sam's FAQ's as some of the mirrors describe it, but don't have the circuit.

The only thing I can think about that might be added is a reverse polarity diode in anti-parallel to the laser diode, similar to what Daedal has in his current regulator. In fact, to make things even simpler, I don't see why you couldn't use Daedal's current regulator fed by an LM317 configured in voltage regulation mode. It should look very similar to this circuit. Probably the LM317 data sheet has such a circuit.

Assuming Daedal is successful with his 200 mW feeler, I will definitely be using this dual LM317 to power the slightly more expensive diodes. Just safety reasons for me, but I don't see why Daedal's wouldn't be entirely satisfactory also. After all, it is simpler to just use a single 317.

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Old 08-22-2007, 11:09 AM #8
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Default Re: variable voltage and current power supply

I believe there is a way to regulate both current and voltage with one single LM317.

(looking at the data sheet) ... (Thinking) ... (looking some more) ... (maybe?)

Yep... a very, VERY, stable circuit is conveniently available on the data sheet. See top of page 17 here.
http://www.national.com/ds/LM/LM117.pdf

It's huge and confusing and requires many parts... but I don't think anything you would buy from meridith, roithner, or any other would be any better!

But, obviously, using 2 LM317's is the easier route :P and just as effective. Just less 'professional'

GL;
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Old 08-22-2007, 12:03 PM #9
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Default Re: variable voltage and current power supply

Quote:
Originally Posted by Daedal
I believe there is a way to regulate both current and voltage with one single LM317.
Yep... a very, VERY, stable circuit is conveniently available on the data sheet. See top of page 17 here.
http://www.national.com/ds/LM/LM117.pdf..........

GL;
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Thanks, Daedal. I remember seeing that one in the data sheets and thought the same thing about the "confusion". One drawback I can think of with this dual circuit I posted is the input voltage. I guess we're looking for at least 9 v input if we're loosing 3v across each 317 (correct me if I'm wrong here please), an issue the single circuit you mentioned might not have.

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Old 08-22-2007, 06:13 PM #10
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Default Re: variable voltage and current power supply

Hmmmm...interesting. I believe the easiest way to do this would be to use a 6 volt regulator, of course for regulating voltage. You would need a minimum of 8 volts to power everything.

http://www.newark.com/jsp/displayPro...mp;HBX_PK=7906
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