LM317 Driver question

itsmei · Jan 3, 2011

Hi,
The plan is that i am going to build my own driver for when i get a 445nm A-140 1W diode, i will be running it at 1250mA and having 7.4v by using 2x 18650 batteries.

The parts:
LM317
1ohm resistor
47uF 35V capacitor
50ohm pot
IN4001 diode

A 1ohm resistor allows 1250mA to be drawn, that is the amount of current i am going set to the diode. I am going to get the 50ohm pot and make it come out of the "lab" style case so it the power input is adjustable, this way when the pot is set to maximum i will have 1250mA which is ~1 watt, if i want less power i will simply adjust the 50ohm pot lower. Does this sound a good idea?

The question is that if i keep turning the pot, will it eventually break or blow the diode?

Thanks

midias · Jan 3, 2011

You never said if you were going to be in series or parallel with the pot and the 1 ohm resistor. But it sounds like a good plan. Personally I would add a 0.1uf cap at both the in and output of the driver or at least at the input. Also at 1.25A don't forget the heatsink.

Ideal voltage for a bluray or 445 diode would be around 8.5V I am not sure if 7.4 will be enough I may add an extra 18650 batter in there. Also don't forget that at 1.25A across the resistor your PD is ~1.56W so get a resistor that can handle it accordingly.

Personally for higher wattage builds I prefer some parallel resistance as in 2 X 2 ohm resistors to cut the PD in each one in half then put the pot inline with one of the two. Here is a picture. You do not have to take my advice I just sometimes over build a little.

itsmei · Jan 3, 2011

That is great information you have given, i will be getting 2x 0.47ohm resistors in parallel with the pot inbetween. The resistors have a 7watt power rating, so they will not get hot. I will get 3 186500 batteries to get me 10.5v, i will put them in series. I am building a portable "lab" style laser, so a lot of it will be a heatsink, that way the driver and diode will be kept cool.

Can anyone answer another question which is, if i just turn a pot will it eventually break the pot or will it reset to 0 for the power input. I just don't want to risk killing my diode, as i am making an adjustable pot which comes out of the box so i can adjust it at any time.

Thanks

P.S can anyone suggest some good qualty glasses, i thought of these Laser Glasses - UV to Green Lasers Protection 190-548nm :: Laser Safety :: Dragon Lasers , i just don't want to risk my eyes. I want to keep my eyes, so i want a good pair!

midias · Jan 3, 2011

itsmei said:
That is great information you have given, i will be getting 2x 0.47ohm resistors in parallel with the pot inbetween. The resistors have a 7watt power rating, so they will not get hot. I will get 3 186500 batteries to get me 10.5v, i will put them in series. I am building a portable "lab" style laser, so a lot of it will be a heatsink, that way the driver and diode will be kept cool.

Can anyone answer another question which is, if i just turn a pot will it eventually break the pot or will it reset to 0 for the power input. I just don't want to risk killing my diode, as i am making an adjustable pot which comes out of the box so i can adjust it at any time.

Thanks

P.S can anyone suggest some good qualty glasses, i thought of these Laser Glasses - UV to Green Lasers Protection 190-548nm :: Laser Safety :: Dragon Lasers , i just don't want to risk my eyes. I want to keep my eyes, so i want a good pair!

Check this out for resistor adding
Adding components in series and parallel

2 0.47 resistors in parallel will = ~0.235 ohms you would want 2 x 2ohm resistors.

For the POT you will notice larger pots have a hard stop on them so you will not be able to turn it too far and break it by turning it.

itsmei · Jan 4, 2011

2 0.47 resistors in parallel will = ~0.235 ohms you would want 2 x 2ohm resistors.

Ahhh sorry! Got them mixed up.... Anyway i will get 2 x 2ohm resistors, in parallel.

For the POT you will notice larger pots have a hard stop on them so you will not be able to turn it too far and break it by turning it.

Will smaller pots have a stop, will this pot have a stop to it. If it does not have a pot, will it break?

SubMiniature Fully EnclosedCarbon Preset Potentiometers : Potentiometers : Maplin

midias · Jan 4, 2011

That pot does have a hard stop in it and should work just be careful because it is only .15w I made an excel sheet and it looks like worst case through the pot you will get ~400mw PD.

I have attached a Zip file with the sheet someone let me know if I calculated something wrong. This is just guessing you are using 2 1W resistors in parallel with the POT in series after them.

Kevlar · Jan 4, 2011

If you're making a lab style laser why don't you use a bigger pot that you can put a knob on instead of pulling out a screwdriver whenever you want to adjust it?

Like this one is a 25 Ohm 3 Watt: 25-Ohm 3-Watt Rheostat - RadioShack.com

Just a thought. :yh:

Cyparagon · Jan 4, 2011

^That one is a good choice. I use it with my set up. The only problem is the current is still under threshold for about 80% of the turn angle.

itsmei said:
Ahhh sorry! Got them mixed up.... Anyway i will get 2 x 2ohm resistors, in parallel.

If you already have 2 0.47Ω resistors, wire them in series instead.

midias · Jan 4, 2011

^true once you get over ~6 ohms total resistance your 445 will not do anything significant.

itsmei · Jan 4, 2011

If you're making a lab style laser why don't you use a bigger pot that you can put a knob on instead of pulling out a screwdriver whenever you want to adjust it?

Like this one is a 25 Ohm 3 Watt: 25-Ohm 3-Watt Rheostat - RadioShack.com

Just a thought.

ooooo thank you! I have been trying to find one so i can adjust it, thanks!

I was thinking, do you think as i am going to have a HUGE heatsink i will be able to power my A-140 diode up to 2w. I was thinking if i was going to do this i will need a better regulator, so i found one that supports 2A, which is here:
STMicroelectronics | Semiconductors | Power Management | Linear Regulator | Positive Voltage Regulators |L78S15CV
I will also get a good couple of resistors which will allow more than 2watt of current each so they do not get hot. I will be putting 2x 1ohm resistors in parallel. I will be adding a huge heatsink so heat isn't a worry. Will this work?

midias · Jan 4, 2011

itsmei said:
ooooo thank you! I have been trying to find one so i can adjust it, thanks!

I was thinking, do you think as i am going to have a HUGE heatsink i will be able to power my A-140 diode up to 2w. I was thinking if i was going to do this i will need a better regulator, so i found one that supports 2A, which is here:
STMicroelectronics | Semiconductors | Power Management | Linear Regulator | Positive Voltage Regulators |L78S15CV
I will also get a good couple of resistors which will allow more than 2watt of current each so they do not get hot. I will be putting 2x 1ohm resistors in parallel. I will be adding a huge heatsink so heat isn't a worry. Will this work?

That is a fixed 15V regulator I do not think it will work the same but somebody may correct me.

You could try this VREF is the same at 1.25V

Digi-Key - 497-1482-5-ND (Manufacturer - LD1085V)

You could also run 2 LM317s in parallel

Kevlar · Jan 4, 2011

Or a LM350, I believe it's rated up to 3A.

jib77 · Jan 4, 2011

Ive used the LD1085V for some stuff at work ... good stuff, but because its a LDO you will need at least 10uF caps on the Vin and Vout pins.

itsmei · Jan 5, 2011

my plan was that i was going to use 47uF 35 volt capacitors. If i get this, will it work for making a 2watt laser?
regulator: Digi-Key - 497-1482-5-ND (Manufacturer - LD1085V)
This pot:25-Ohm 3-Watt Rheostat - RadioShack.com
A 47uF 35v capacitor.
2xcapacitor of 1ohm each in parallel to get me 0.5ohm, i will use more than 2 watt input.
3x 18650 batteries which will make 9.1v.

Now i do you think the above is good?

I got a couple of questions though:
What Rectifier Diode do you recommend?
How many mA do you recommend running the A-140 diode at for best and most powerful results? And what mW would it give me?
What good safety glasses would you recommend? I was thinking of these: Laser Glasses - UV to Green Lasers Protection 190-548nm :: Laser Safety :: Dragon Lasers

Thanks!

anselm · Jan 5, 2011

3x 18650 batteries which will make 9.1v.

No 3x 18650 gives you ~12V

How many mA do you recommend running the A-140 diode at for best and most powerful results?

Hmm 800mA already makes for a strong and nice beam.
At 1200mA, it'll burn faster but it will not be signififcantly brighter.
I wouldn't push more than 1500mA if you want your diode to live a long and happy life.

jib77 · Jan 5, 2011

For a 3A continuous current rectifier I use a OnSemi 1N5401G. Put a cap on the input otherwise the LD1085V will not be stable(datasheet recommends 10uF, but another 47uF should be fine). Your resistors will need to handle 3.75W, make sure they are rated 2W each so you get a total 4W of available power dissipation.

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