Laser pointer discussion. Read/write reviews of laser pointers and laser pointer companies. Learn about all types of laser pointers and lasers

 Welcome to Laser Pointer Forums! If you are looking for a laser pointer or want to compare different laser pointer companies, you may want to check out the LPF Laser Pointer Company Database. The link will open in a new window for your convenience.

One laser store meets all your needs

 Laser Pointer Forums - Discuss Laser Pointers Lm317 Help

LPF List of Laser Pointer Companies (link opens new window)

03-02-2011, 06:05 PM #1
 Class 2M Laser Join Date: Mar 2011 Location: Texas Posts: 692 Rep Power: 52
justinjja
Class 2M Laser

Join Date: Mar 2011
Location: Texas
Posts: 692
Rep Power: 52
Lm317 Help

I am working on a simple driver for a a140 445nm blue diode.

I am using a simple constant current setup.
I have a set of resistors hooked up to a LM317,
set up so I can Adjust the current from 300ma to 1A.
Problem is the smallest pot radio shack had was 25ohm. So When I adjust current it is like an E^2 graph.
(Current starts at 300ma, I turn the pot half way and current is 350 3/4 of the way and its 450, then all of a suddent it jumps to 1a)

Does anyone know where to get a pot about 5 ohms or even 3 ohms?

I am currently using 2W resistors is that nessasary or would 1/4w ones work fine?

acording to my calculations there would be 1w max going through my resistors right?

LPF List of Laser Pointer Companies (link opens new window)

03-03-2011, 12:15 AM #2
 Class 3R Laser Join Date: Nov 2010 Location: Portugal Posts: 2,470 Rep Power: 84
anselm
Class 3R Laser

Join Date: Nov 2010
Location: Portugal
Posts: 2,470
Rep Power: 84
Re: Lm317 Help

Hello and welcome to the forum!

You can "tune" your potentiometer by soldering a resistor onto it's pins (in parallel).

Suppose your potentiometer gives you a range from 0.5Ohm to 25Ohm.
Now suppose you add a 4Ohm resistor in parallel.

Now your potentiometer has a range of 0.44Ohm to ~3.45Ohm
1/Rt = 1/R1+1/R2+....+1/Rn

1/Rt = 1/0.5 + 1/4 = 9/4 <=> Rt = 4/9 = 0.44_
1/Rt = 1/25 + 1/4 = 29/100 <=> Rt = 100/29 = 3.448...

I have done this very same thing in my 445nm project, 2nd link in my signature.

Stick around, read the stickies, and most of all be safe, it's a class IV laser we're talking 'bout.
__________________
I'm away from home and lasers until late July!
Kryton Groove switch workaround
Get your warning label stickers 0.90\$ or less, depending on qty
The INDEX to the LPF
Beware! Scams a-plenty, don't be a sucker!
___________________________
ATTENTION
This forum is fullfilled mit special electronische equippment. Fingergrabbing and pressing the cnoeppkes from the lasers is
allowed for die experts only! So all the “lefthanders” stay away and do not disturben the brainstorming von here working
intelligencies. Otherwise you will be out thrown and kicked anderswhere! Also: please keep still and only watchen astaunished the blinkenlights.

03-03-2011, 02:30 AM #3
 Class 4 Laser Join Date: Dec 2010 Posts: 8,491 Rep Power: 1392
rhd
Class 4 Laser

Join Date: Dec 2010
Posts: 8,491
Rep Power: 1392
Re: Lm317 Help

Even if your pot is linear, once you parallel it with a static resistor, I think you'll end up with an exponential pot.

At 25 ohms (100% of your pot's max), with a 4 ohm resistor in parallel, you'll get 3.45 ohms (your max resistance now)
At 20 ohms (80% of your pot's max), you'll get 3.33 ohms (96.6% of your max resistance)
At 15 ohms (60% of your pot's max), you'll get 3.16 ohms (91.6% of your max resistance)
At 10 ohms (40% of your pot's max), you'll get 2.86 ohms (82.9% of your max resistance)
At 5 ohms (20% of your pot's max), you'll get 2.22 ohms (64.4% of your max resistance)
At 0.2 ohms (1% of your pot's max), you'll get 0.19 ohms (5% of your max resistance)
__________________
CURRENT WAVELENGTHS:
405|441|450|467|473|495|505|520|532|556|PGLRG|589|594|632|638|660

SAFETY & IMPORTANT READING (threads authored and contributed to by various members of LPF):
- Info release from Laserglow - Default Canadian restrictions on portable lasers (link)
- The Necessity of Safety Goggles (link)

03-03-2011, 07:44 AM #4
 Class 2M Laser Join Date: Mar 2011 Location: Texas Posts: 692 Rep Power: 52
justinjja
Class 2M Laser

Join Date: Mar 2011
Location: Texas
Posts: 692
Rep Power: 52
Re: Lm317 Help

Yes My 25 ohm Pot in parallel with 3.3 ohms works, but I get a very uneven spread of current.

Anyway I have a working prototype:

Lol at my battery setup -- Lantern battery in series with a cr123 battery.

Can you recomend a lens for this.
The one I have now is acrilic (I think)
The guy who sold it to me said It would work upto about 1.4watts

Last edited by justinjja; 03-03-2011 at 07:47 AM.

03-03-2011, 07:48 AM #5
 Class 3R Laser Join Date: Jul 2010 Location: Hill Country, TX Posts: 2,185 Rep Power: 51
Coherent Light
Class 3R Laser

Join Date: Jul 2010
Location: Hill Country, TX
Posts: 2,185
Rep Power: 51
Re: Lm317 Help

look Béla Lugosi is alive.........
__________________
Coherent::

03-03-2011, 02:21 PM #6
 Class 2 Laser Join Date: Jan 2011 Posts: 428 Rep Power: 59
123splat
Class 2 Laser

Join Date: Jan 2011
Posts: 428
Rep Power: 59
Re: Lm317 Help

WOW!! Pocket portable, and classy looks! Love your heatsink and host!

Just kidding. Kudos for a valiant effort! You do not need to worry much about the wattage in the current limit loop (it is a sensing, not shunting, path) 1/4 wat will more than suffice. If you want low R linearity, you will probablly have to go with a trim pot or 10 turn (or 20 turn). Check somebody like JameCo or DigiKey. Good Luck and keep at it.

03-03-2011, 02:28 PM #7
 Class 3R Laser Join Date: Nov 2010 Location: Portugal Posts: 2,470 Rep Power: 84
anselm
Class 3R Laser

Join Date: Nov 2010
Location: Portugal
Posts: 2,470
Rep Power: 84
Re: Lm317 Help

Quote:
 Even if your pot is linear, once you parallel it with a static resistor, I think you'll end up with an exponential pot.
Quote:
 but I get a very uneven spread of current.
That's cool, because brightness doesn't increase linearly with current!
So things kinda even out one each other!

Mixing batteries like that, just can't be good, especially when you're drawing high currents.
+1 for the successful effort though!
__________________
I'm away from home and lasers until late July!
Kryton Groove switch workaround
Get your warning label stickers 0.90\$ or less, depending on qty
The INDEX to the LPF
Beware! Scams a-plenty, don't be a sucker!
___________________________
ATTENTION
This forum is fullfilled mit special electronische equippment. Fingergrabbing and pressing the cnoeppkes from the lasers is
allowed for die experts only! So all the “lefthanders” stay away and do not disturben the brainstorming von here working
intelligencies. Otherwise you will be out thrown and kicked anderswhere! Also: please keep still and only watchen astaunished the blinkenlights.

03-03-2011, 03:11 PM #8
 Class 4 Laser Join Date: Sep 2007 Location: Wisconsin Posts: 9,142 Rep Power: 9321
Cyparagon
Class 4 Laser

Join Date: Sep 2007
Location: Wisconsin
Posts: 9,142
Rep Power: 9321
Re: Lm317 Help

Quote:
 Originally Posted by justinjja Lantern battery in series with a cr123 battery.
Do NOT run that for more than a few minutes or you WILL ruin the CR123.
__________________
A problem well stated is a problem half solved.

03-04-2011, 02:00 PM #9
 Class 2 Laser Join Date: Jan 2011 Posts: 428 Rep Power: 59
123splat
Class 2 Laser

Join Date: Jan 2011
Posts: 428
Rep Power: 59
Re: Lm317 Help

WARNING WARNING WARNING!!!

Justinjja,
I'm supprised some of the 'gurus' didn't catch this. I LIED! I was thinking voltage regulator mode, not current regulator mode. In Vreg mode the current in the Adjust leg is in the 100uA (micro AMP) range and a 1/4 watt resistor is way more than sufficient.

When you are using a 317 as a current regulator, the R is in the current path and you must use higher wattage resistor(s). Apply Ohm's DC power calc.s to determin wattage of the output path (and thus the resistor(s) in the output path):
Power in Watts= Current in amps squared times Rt in Ohms, or Voltage in volts squared divided by R in Ohms, or Voltage in volts times current in Amps. Pick the one which serves you best, they are all the same.
300mA @ 4 Vdc = .3*4= 1.2 Watts ,, 1/4 W will work for a short time, but will get real hot.
1 A @ 4 Vdc = 4 Watts ,, 1/4 Watt will go brown to black, scorch the PCB and burn open fairly quick..

Sorry man, did not mean to miss lead you. I'm an old fart and mind does not always correctly engage with fingers.... Mind does not seem to engage at all sometimes....'
But, I eventually get there, I think, where am I anyway?

03-04-2011, 02:13 PM #10
 Class 4 Laser Join Date: Dec 2010 Posts: 8,491 Rep Power: 1392
rhd
Class 4 Laser

Join Date: Dec 2010
Posts: 8,491
Rep Power: 1392
Re: Lm317 Help

Slight correction here -

You're both right and wrong.

YES, in current regulating mode, the resistor IS in the current path, so you need a heftier resistor.

NO, it's not 300mA @ 4 Vdc (DiodeCurrent x DiodeVoltage) that you use to determine the Wattage of resistor required.

It's actually DiodeCurrent x 1.25 Vdc (regardless of DiodeVoltage) that you use to determine the required resistor wattage.

*Disclaimer* I don't entirely understand the "voodoo magic" of these wonderful ICs. But in essence, the current regulation comes from the LM317 trying to maintain a voltage of 1.25 accross ADJ and OUT. The resistor is what manipulates the amount of current across those two pins that is required in order to achieve this.

However, it's STILL just 1.25V running across those two pins, and across the resistor. While I don't quite grasp how the Voodoo Magic gets the diode it's required voltage, I DO know that it isn't shooting that magic voltage across the resistor.

So for 300mA, you're looking at 0.3 x 1.25 = 0.375 Watts (in other words, a 1/2 W resistor is fine)
__________________
CURRENT WAVELENGTHS:
405|441|450|467|473|495|505|520|532|556|PGLRG|589|594|632|638|660

SAFETY & IMPORTANT READING (threads authored and contributed to by various members of LPF):
- Info release from Laserglow - Default Canadian restrictions on portable lasers (link)
- The Necessity of Safety Goggles (link)

03-04-2011, 02:33 PM #11
 Class 3R Laser Join Date: Jul 2010 Location: Hill Country, TX Posts: 2,185 Rep Power: 51
Coherent Light
Class 3R Laser

Join Date: Jul 2010
Location: Hill Country, TX
Posts: 2,185
Rep Power: 51
Re: Lm317 Help

justinjja use these links to help calculate the resistor value and wattage required for your desired current.

LM317 Current Calculator - Electric Circuit

This link can help as well if you plug in a resistor value it will give you the output current and wattage needed.

LM317 / LM338 / LM350 Voltage and Current Regulator Calculators
__________________
Coherent::

03-04-2011, 03:55 PM #12
 Class 2 Laser Join Date: Jan 2011 Posts: 428 Rep Power: 59
123splat
Class 2 Laser

Join Date: Jan 2011
Posts: 428
Rep Power: 59
Re: Lm317 Help

Justinjja,
Coherent Light's links to the calculators look like a good idea/shortcut (haven't tried the yet though), but it is always nice to be able to figure out how things work and what is happening. Sorry if it seems like we are highjacking your thread, but we may BOTH be learning something here.

Update: I just tried out coherent's suggeted links and they bear out RHD's numbers. I still don't understand the logic, but (assuming the calculators are correct, as the do appear to be) must agree with and humblly accept RHD's correction.

Last edited by 123splat; 03-04-2011 at 04:03 PM. Reason: Update

03-04-2011, 04:12 PM #13
 Class 4 Laser Join Date: Dec 2010 Posts: 8,491 Rep Power: 1392
rhd
Class 4 Laser

Join Date: Dec 2010
Posts: 8,491
Rep Power: 1392
Re: Lm317 Help

Ok, I can probably explain better if I use Ohm's law. If someone else jumps in here and corrects me - trust them. Really, I feel like I get by on the foggiest of recollection from high-school physics classes, and not much else.

In terms of the IC setting the current
- To get the 1.25V drop accross ADJ and OUT, the regulator has to increase the current to 312.5 mA because:
V / R = C
1.25 / 4 = C
C = 0.3125 A

In terms of the resistor wattage you need
- To get the wattage rating of the resistor:
C^2 x R = W
0.3125^2 x 4 = W
0.09765625 x 4 = W
W = 0.390625

It's kind of cool that you can get the same WATTAGE figure much easier by just doing a simple CURRENT x 1.25 operation. But that's more abstracted from what's going on, so hopefully this helps clear it up?
__________________
CURRENT WAVELENGTHS:
405|441|450|467|473|495|505|520|532|556|PGLRG|589|594|632|638|660

SAFETY & IMPORTANT READING (threads authored and contributed to by various members of LPF):
- Info release from Laserglow - Default Canadian restrictions on portable lasers (link)
- The Necessity of Safety Goggles (link)

03-04-2011, 05:34 PM #14
 Class 1M Laser Join Date: Feb 2009 Posts: 199 Rep Power: 53
Illuminum3415
Class 1M Laser

Join Date: Feb 2009
Posts: 199
Rep Power: 53
Re: Lm317 Help

Quote:
 Originally Posted by justinjja Lol at my battery setup -- Lantern battery in series with a cr123 battery.
The CR123A will drain first, then be reverse charged in series by the 6V lantern battery...which may push it over the edge, start a fire, and destroy a perfectly good investment.
Why not parallel a couple 9Vs instead? simple, square, easy to mount, practical to carry.

03-05-2011, 04:52 PM #15
 Class 2 Laser Join Date: Jan 2011 Posts: 428 Rep Power: 59
123splat
Class 2 Laser

Join Date: Jan 2011
Posts: 428
Rep Power: 59
Re: Lm317 Help

RHD, (justin, if you don't like us hi-jacking your thread, just tell us to shut-up and go start our own. RHD, you'll have to do that, I'm new and don't exactly know how to yet), Now back to physics class. Got ch'a and agree with the Ohm's laws calculations. The part that is giving me problems (old, brain gets stuck in one gear and cann't shake it...) is that you are (and, b.t.w. everybody else,, so I must be in error) using the voltage of the reference loop (never goes to ground, goes to a comparator in the regulator IC) to calculate the wattage in the output leg. But, the work in the output leg is done across the resistance to ground (the LASER Diode).
I know it's a nit and everything shows me to be wrong, but I just cann't get the concept of why down. Thanks for letting an old fart ramble and it is educational to the noobs.

03-05-2011, 06:55 PM #16
 Class 4 Laser Join Date: Dec 2010 Posts: 8,491 Rep Power: 1392
rhd
Class 4 Laser

Join Date: Dec 2010
Posts: 8,491
Rep Power: 1392
Re: Lm317 Help

The way I'd conceptualize it:

You care about wattage because you want a resistor that can handle dissipating the amount of power you're expecting it to.

That's a function of the current across the resistor multiplied by (and ONLY multiplied by) the voltage that is ACTUALLY DROPPED by the resistor. That's what the resistor must turn into heat. Thats always 1.25v.
__________________
CURRENT WAVELENGTHS:
405|441|450|467|473|495|505|520|532|556|PGLRG|589|594|632|638|660

SAFETY & IMPORTANT READING (threads authored and contributed to by various members of LPF):
- Info release from Laserglow - Default Canadian restrictions on portable lasers (link)
- The Necessity of Safety Goggles (link)

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

All times are GMT. The time now is 08:17 PM.

 -- DarkShadows V5 -- Responsive LPF -2562016 -- Default Style Contact Us - Laser Pointer Forums - Archive - Top