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-   -   Help me build my fixed driver! (http://laserpointerforums.com/f51/help-me-build-my-fixed-driver-46932.html)

Flugufrelsarinn 01-07-2010 10:53 PM

Help me build my fixed driver!
 
Okay, so I have two questions.

On the LM317, how do I know which prong is VIN , VOUT, ADJ?

And to figure out how much resistance I need, would I use the formula...
R= 1.2/Iout? So if I want 150 Ma I would use a 8 ohm resistor?

Hallucynogenyc 01-07-2010 11:05 PM

Re: Help me build my fixed driver!
 
It's r= 1.25/Iout

You can find everything on the datasheet, google it ;)

pyrotech 01-08-2010 01:07 AM

Re: Help me build my fixed driver!
 
Hallucynogenyc is right on with the formula. I come up with an 8.3 ohm resistor. You may not find that, but an 8 ohm will give you about 156Ma. Bear in mind almost any resistor can be 5% or 10% off and still be considered good, that will affect your Ma.
The pinouts confused me too. the schematics are for ease of drawing and do not necessarily represent accurate pinouts of the LM317. Pin 1 is Adj, there should be a dot on the plastic case to denote Pin 1. Pin 2 is Vout and Pin 3 is Vin.
I hope this is helpful...

Flugufrelsarinn 01-08-2010 04:30 AM

Re: Help me build my fixed driver!
 
Okay, thanks

Just to be safe with the PHR, I'll go with a 10 ohm resistor and 1k resistor. I was being dumb when I though 150 mA would last on the PHR. I'll ask here if I have any more problems!

Devilz Rej3ct 01-08-2010 08:13 AM

Re: Help me build my fixed driver!
 
If your running the 10 ohm and 1K resistor in parallel then correct me if I am wrong but you end up with 9.9 ohms.

pyrotech 01-08-2010 05:15 PM

Re: Help me build my fixed driver!
 
We kinda need to see your schematic.

Flugufrelsarinn 01-08-2010 08:41 PM

Re: Help me build my fixed driver!
 
Here's the best I could do

http://img268.imageshack.us/img268/6105/picture3kf.png



EDIT. Oops, forgot a switch, there will be a switch before the LM317

Bluefan 01-08-2010 08:45 PM

Re: Help me build my fixed driver!
 
I =U/R -> I = 1.25/10 = 125mA
The PHR uses about 4 volt, so there's 4mA through the 1K resistor -> 121 mA left, but check the resistor you're using, 1% is qute common, but 5% may be around too. Measuring low resistances is best done with a 4 wire method, if available.

pyrotech 01-08-2010 09:10 PM

Re: Help me build my fixed driver!
 
Bluefan has electronics experience that I lack. My only concern is that if you want long life out of a PHR you may want to target >100mA. I've burned them out at 120Ma in less than a second. Not all PHRs are created equal. If you start low you can always replace a resistor and boost things up a bit.

Bluefan 01-08-2010 09:18 PM

Re: Help me build my fixed driver!
 
from the diode compilation thread for the PHR:
Safe operating current: 90mA
Enthusiast operating current: 110mA
Maximum operating current: 120mA

But I'd question the lifetime of the diode when running close to the maximum, I'd go for 90mA and be happy with a longer life.

Flugufrelsarinn 01-08-2010 09:21 PM

Re: Help me build my fixed driver!
 
I'll probably play middle ground with it and run ~100 mA with a 12 ohm resistor.


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