Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

LM317 based driver for 1W 445

Joined
Dec 18, 2009
Messages
112
Points
0
Okay guys so I ordered my 1W 445 diode last night. I plan on using an LM317 driver for it based on the photo. Obviously I will need a lower resistor to get the 1000 mW of power. My question is this, Is the capacitor shown and the diode okay to use in this circuit for the 1W 445 diode? My input voltage will be from a PSU from a computer. The 12 volt yellow wire.
 

Attachments

  • lm317bluray.jpg
    lm317bluray.jpg
    33.5 KB · Views: 27,968





Joined
Jul 17, 2010
Messages
2,160
Points
0
Your driver will get very hot using 12 volts! It will have to dump the extra voltage as heat, and I suggest You find an alternative power source.

My 0.02
 
Joined
Dec 18, 2009
Messages
112
Points
0
Thanks guys. What is the required voltage of the 445 diode? Any other driver suggestions? I really want to use the computer PSU. What if I screwed the LM317 to a larger heatsink with thermal paste?
 
Joined
Jul 17, 2010
Messages
2,160
Points
0
A heatsink is recommended. You need 2.5 volts of the operating voltage of the diode with a LM317 based driver. If memory is working at the moment 445's need 4.5v, so that you will need at least 7 volts with a LM317.
 

jaycey

0
Joined
Apr 10, 2009
Messages
480
Points
18
I use a 7.4v 850mah LiPo RC battery with mine, which works just fine and with a decent run time.

I also use a .5 ohm 1watt resistor.

All of my other components are as standard in your diagram.

You will need decent heatsinking on both your LM317 & diode.

At these currents things get hot quickly! And so does anything that gets in the way of the beam:eg:

Good luck with your build.
 

HIMNL9

0
Joined
May 26, 2009
Messages
5,318
Points
0
Just a little bit higher ..... 2.5V from IC dropout, plus 1.25V from Rset dropout for the LM317 ..... or 1.35V from the IC plus 1.25V from the Rset for a LM1117. (plus a little bit, say, half volt, for safety), if you want the full current capability (and a good heatsink)

So, 8.75 to 9 V for an LM317, or around 8V for an LM1117.
 
Joined
Jul 17, 2010
Messages
2,160
Points
0
Ooohh good catch I spaced the 1.25v Rset. I'll have to give you some Rep for that.

I did say at least...LOL
 
Joined
Sep 12, 2007
Messages
9,399
Points
113
I drive a 445 with 12V and lm317. I use a 3.3Ω 6W power resistor (from the junk pile) to drop ~3V which saves the lm317 from a lot of heat. It still needs a heat sink, but it is much smaller.
 
Joined
Dec 18, 2009
Messages
112
Points
0
Thanks all. So if my calculations are correct, I would need a 1.38 ohm resistor in order to push the 445 diode 900 mA of current?? Or would it be safe to use a 1 ohm resistor of higher wattage? You know the square white resistors.
 

anselm

0
Joined
Nov 22, 2010
Messages
2,448
Points
0
Or would it be safe to use a 1 ohm resistor of higher wattage? You know the square white resistors.
That should work just fine.;)
Just don't do as I did, using a 0Ohm "bypass", feeding 1.95Amps to the poor little diode.
 
Joined
Dec 18, 2009
Messages
112
Points
0
Yea I am currently using a 1 ohm 5 watt resistor in series with two 0.47 ohm resistors that are in parallel. During my tests, output remained a stable .99 amps. I do have the LM317 well heatsinked and am using 12 volts in. Now I just need to hurry up to wait on my 445 diode.;)
 

midias

0
Joined
Mar 14, 2010
Messages
631
Points
0
You could always use the 12V as your plus and the 3.3V as your -
 
Joined
Apr 7, 2011
Messages
22
Points
0
hi guys, a quick question, is it ok to connect the tab on the lm317 to the same heatsink than the 445 diode?, I was checking the diode and looks like isulated from the case, is that correct?

quick answer apreciatted, I'm setting up a quick lab for my diode just now, by the way, which driver with modulation and cheap could you recommend for a 7-13v range power?
thanks very much
 




Top