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Old 01-31-2013, 10:37 PM #1
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Default Lm317/338 improvement...

Thanks guys for your help so far.

I have built a couple LM317 based drivers, and have a couple units working.
Unlike most here, this setup is not for a focused burning, but rather for a wide beam night illumination hunting system.IR all the way.

you guys have me so worried about the dangers of lasers, I won't even turn it on in the house..gotta go outside and point at the field..

Ha,ha,ha...Yes I know big dummy..no goggles..but I'm careful..all testing done at lower power with a 5mw green..then outside.

I agree, I'm afraid of these things.

Anyhow, I read this on this board..and figured I would ask about it.

(You take the op amp, and use it to amplify the voltage to 1.25, so the regulator *thinks* that it's 1.25 volts, and will regulate the current as necessary. It would keep it at 250 mA, but there's a LOT less power dropped (only 6 mW!) across the resistor as a result. It makes it MUCH more efficient.

This method can be applied to any regulator, switching, or linear. You can make the famous LM317 work a lot better using this... instead of dropping 3 volts by default, it'll only drop around 1.5-2 volts instead! (basically, you won't need as much "default" voltage to get it regulating right)


Can anyone elaborate on this..how to wire it, opamp part# ect...drawing





FYI..I'm also making a Lardy/Marky light..for spotting..the IR laser is the shooter

Thanks...Brian



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Old 01-31-2013, 11:00 PM #2
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Default Re: Lm317/338 improvement...

hello,

I guess that means using a lower value shunt resistor, and using a differential amplifier with proper gain to feed into the ADJ pin?

If so, then I don't see the point in using a lm317 at all, a full blown current source using a bipolar transistor such as the die4drive would be more interesting.

PS: using a laser outside does not prevent it from reaching you eyes Buy googles asap, even cheap googles are better than nothing! IR lasers are more dangerous, since they are invisible!
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Old 02-01-2013, 01:36 AM #3
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Default Re: Lm317/338 improvement...

Quote:
Originally Posted by F4GRX View Post
hello,


PS: using a laser outside does not prevent it from reaching you eyes Buy googles asap, even cheap googles are better than nothing! IR lasers are more dangerous, since they are invisible!

Yea, I know. But when its mounted of the far end of a gun pointed at a field or objects 50-75 yards plus..in a 5 Ft wide dispersed beam. I'm really figured it was nothing to be worried about it.

Should I be?

I am looking through a scope and camera and screen system.
Should I worry about viewing the target area through this setup?
After all the scope gathers the light..sends it to the camera..then on to the screen.
I know there are other ir lasers out there that are designed for the same thing..but they are all 5-50mw.

I never considered this...is looking through the scope/camera/screen ..safe?

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Old 02-01-2013, 07:59 AM #4
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Default Re: Lm317/338 improvement...

Oh yeah there is a screen in this story

stop worrying now
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Old 02-02-2013, 05:07 PM #5
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Default Re: Lm317/338 improvement...

Or you can use a low dropout regulator instead. People don't want to build large circuits. If you're going to use an op amp, you might as well start from scratch and use the op amp to drive a pass transistor instead - then you get potentially less than 1V dropout.
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Old 02-03-2013, 02:16 AM #6
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Default Re: Lm317/338 improvement...

Yeah, I agree that you ought to look at other LDO regulators. The LM317 is a nice chip, but really made for situations where you don't care that much whatever power is being dissipated by the IC.

For a non-linear regulator circuit, you can rig something up like this circuit too.
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