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Old 04-14-2008, 11:50 PM #1
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Default which driver diagram is correct?

I've been poking around and eventually found 2 conflicting wiring diagrams for driver circuits. *Actually for all I know they do the same thing cuz I dunno advanced components that well. *But otherwise, which one of them is correct.
Btw I dunno why he added dual 10 ohm resistors. *Maybe he was out of 5's or it needed to handle more current.

EDIT: Too bad this board won't let me post html links, pictures, or even html links in code tags for who the hell knows why or the diagrams would actually be conveniently embedded. *Go check em out here but add http : // (with no spaces) before each of them:

i129.photobucket.com/albums/p227/wizzerd911/driver-circuit2.gif

i129.photobucket.com/albums/p227/wizzerd911/driver-circuit.gif


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Old 04-14-2008, 11:54 PM #2
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Default Re: which driver diagram is correct?





You're not allowed to post links until you have at least 20 posts. (it's to prevent spaming)

They're both correct, the difference is that the pot and the resistors are in different order and the resistors are not of the same value.
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Old 04-15-2008, 12:09 AM #3
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Default Re: which driver diagram is correct?

^What he said.

They'll both work fine, provided you hook the diode in the right way (its polarity isn't marked on there, but it'll only work in one direction). The only difference is the maximum allowed current by each. It basically sets a ceiling so that even if the potentiometer is turned all the way down, the diode will still be protected from excess current.

Assuming the Volt Reg is an LM317 like most people use for DIY, the max current allowed into the diode will be 1.25V divided by the value of the resistor. Turning up tho pot would then increase the resistance, thereby lowering the current into the diode.
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Old 04-15-2008, 12:16 AM #4
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Default Re: which driver diagram is correct?

well now that you mention it, they are just in a different order aren't they lol. So here's a dumb question, why would you add a 4-5 ohm resistor after an adjustable 25 ohm pot? *Couldn't you just turn the pot up 4 ohms?

or and for the person who snuck in a post while I was posting this and thus wasn't addressed by anything above this statement, don't most 5mw and dvd burner diodes need 3-3.2V to run or am I remembering that wrong? Or did you mean that calculation results in the amount of current? I'm confused lol. *And don't worry, I know how dangerous it is to put a one way diode in backwards. *Cuz if I did, logically it would cause the LD to do the opposite and suck in photos by forming a black hole and destroying the entire Earth That or it won't turn on lol.
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Old 04-15-2008, 12:20 AM #5
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Default Re: which driver diagram is correct?

It's for a back-up fail-safe kind of thing. In case you turn the pot down too low or lower than you intended to, it sets the maximum amount of current allowed into the diode. If you turn the pot all the way to zero accidently, the current will still be limited as a back-up.
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Old 04-15-2008, 12:23 AM #6
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Default Re: which driver diagram is correct?

oh I get it. Would the "emergency" resistor need to be a higher resistance amount if I were sendin 9V instead of 6V then in order to keep it safe? And why don't they just make pots that don't go to 0 ohms lol.
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Old 04-15-2008, 12:37 AM #7
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Default Re: which driver diagram is correct?

Nope. The LM317 will maintain 1.25V between its prongs no matter what the input voltage is. And since it's always 1.25V there, the resistance needed for a given current won't change. Any extra voltage you don't need will generate excess heat though, so with high-powered red diodes it's not be best idea to go way overboard on voltage, but it'll still work.

And pots that don't go to zero, I have no idea. But it doesn't even have to go to zero to ruin a diode if there's no resistor there. 1 ohm will give you 1.25 amps, theoretically. It would only have to go down to 2.5 ohms to put through .5 amps. These are too great for pretty much any red diode that's not actively cooled, like with a TEC.
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