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Old 6th Mar 2019, 2:40 am   #1
M3VUV51
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Default CC/CV laser driver

Hi all,im building a 2 watt laser engraver for my cnc mill,its a 450nm laser diode,max voltage is 4.8v and it needs 1400ma ,im planing on using one 317 as a voltage regulator feeding a 2nd 317 as a current regulator,any reason why it shouldnt work,also as the 317 ref voltage is 1.25v i assume the first 317 will have to output 6.25v to the 2nd 317,im i right in thinking that?,also it can handle 1800ma puled,i againe assume it means pwn the power to it,if so any idea what frequency it should be,the diode is a nichia m-140,thanks in advance Paul m3-vuv.
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Old 6th Mar 2019, 4:10 am   #2
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Default Re: cc cv laser driver

Google 'laser diode drive circuit', plenty of hits.

You'll find the LM317 won't work as the current your asking is too high for a 317 (they are 1A devices, well, supposedly 1.5A for some but I've never found one that is happy on the limit).

6V input to the current limiter is about right, may need to be slightly higher.

Probably need an LM338 to do the job, but there are other circuits using op-amps and transistors.
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Old 6th Mar 2019, 8:20 pm   #3
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Default Re: CC/CV laser driver

well thats interesting,ive strung 6 1n series diodes in series feding into a 1ohm resistor,using a 317 calculator with the current adj resistor of .9 ohm im getting 600ma tops,acording to the calcs i should get 1480 ma approx,i wonder if ive a duff 317,im feeding 8v into it.m3-vuv
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Old 7th Mar 2019, 12:29 am   #4
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Default Re: CC/CV laser driver

They need a big heat sink for high current.
The thermal overload will otherwise kick in.
They make very good chargers for small SLA batteries at the initial current taken by a flat one will warm it up and the thermal limit will regulate the bulk of the charge cycle until it goes into constant voltage charge at the end.
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Old 7th Mar 2019, 3:47 am   #5
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Default Re: CC/CV laser driver

If you mean you did as in the first pic below (I've forgotten how to get the pics inline with the text), that's probably why the reading.

To check the current output of the 317, you do it as in the second pic, without a load, but, as mentioned above, add a BIGGG heatsink.
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Old 7th Mar 2019, 2:30 pm   #6
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Default Re: CC/CV laser driver

its as in the 2nd pic,ive just ordered some lm388 regs so they should do the job i hope.

ive actualy measured both ways as in both pics 600ma tops is all im getting,its on a big heatsink.
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Old 8th Mar 2019, 12:11 am   #7
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Default Re: CC/CV laser driver

Interesting.

I calculate that with 0.9 ohms, output current should 1389mA (output current = Iref/R and assuming Iref to be 1.25V).

Just as an exercise, if you have an adjustable supply that can provide the current, try bumping up the input voltage slowly and see if the current comes up.
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Old 8th Mar 2019, 8:34 am   #8
Craig Sawyers
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Default Re: CC/CV laser driver

Be very careful with lasers of that power. The scary thing is that anyone can buy these things for not much money at all. And they are so far above eye-safe as to be an acute hazard.

The eyesafe limit in the visible is 1mW (Class 2), which means that they cannot damage your eye before you blink. Class 4 (the highest class) kicks in at 500mW. At 2W, any direct viewing of the beam will drill a hole in your retina before you can blink, and cause local explosive boiling in the vitreous humour. Even if you do not get direct light in your eye, looking at the laser focus (and an engraving application will have a focus) for more than 1 minute will damage your eyes permanently.

Back in the day, when I was at the Laser Research Group at Southampton University, we had to go on a Laser Safety course. That was scary enough to get me wearing the correct goggles as a matter of rigorous routine. 100% of the time. I built a door interlock that shut the laser down if anyone opened the door. With a red light outside the door.

Buy the correct goggles, and wear them always before you turn on the laser. They are hot and inconvenient. But a lot less inconvenient than viewing the world with a black hole in your vision and seeing the world though your blood filled eyeball. And put a microswitch on the door to shut the thing down if anyone inadvertently opens the door.

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Old 8th Mar 2019, 11:32 am   #9
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Default Re: CC/CV laser driver

Quote:
Originally Posted by M3VUV51 View Post
well thats interesting,ive strung 6 1n series diodes in series feding into a 1ohm resistor,using a 317 calculator with the current adj resistor of .9 ohm im getting 600ma tops,acording to the calcs i should get 1480 ma approx,i wonder if ive a duff 317,im feeding 8v into it.m3-vuv
I've just measured Vf for a typical 1N4007 @ 1.4A as 0.97V.

To get 1.4A with 6 diodes + 1 ohm load then requires a minimum input voltage of:-

1.4 across load resistor
+ 5.8 (approx) across diodes
+ 1.25 across sense resistor
+ 3 across 317 (recommended minimum)

= 11.45 V

So , no chance with only an 8V input.

Cheers
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Old 8th Mar 2019, 7:24 pm   #10
julie_m
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Default Re: CC/CV laser driver

Isn't 1.4A pushing a 1N40xx a bit hard?
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