DIY Homemade laser diode driver

awlego · Jan 4, 2010

Yes, that would work to make 5 ohms... but I want a max power of 125mA (I'm powering a PHR-803T) Shouldn't 10 ohms give me that? (1.25v / 10 ohms = 125mA)

BuildAbluraylaser · Jan 4, 2010

Well you have a pot, or are you only using a resistor? If you can't reach far enough, try lowering the resistor value. Once I had this problem, I couldn't get higher than 300mA, so I added another for 4 ohm resistor in parallel, and I was able to reach 0.96 Amps.

awlego · Jan 4, 2010

I have a 10 ohm resistor and a 25 ohm pot. I know I could always change my circuit to a 4 ohm resistor, but in theory the resistors I already have should give me my desired 125mA. So I'm just trying to figure out any possible reasons for my low readings. If nothing works, I'll just change the resistor values, but it would be nice to have everything working according to theory

Deleted member 8382 · Jan 6, 2010

@buildabluraylaser: wtf are you talking about. using the MM in amp mode is the best way to set the current on this and it perfectly works! Of course your're just shortening the circuit, but since this is a constant current driver using 0.0001 ohms as load will still make 125mA to go trough them!

Also, what do you really want the pot for? 125mA constant current is good enough, just put 5 ohms (or 2x 10 in paralel) and you're ready to go!

I still don't get your problem. Do it the way I said you and tell me again. Pots are always giving problems..

BuildAbluraylaser · Jan 6, 2010

That's exactly what I was saying....

Why did you give me negative rep.... :huh:

I'm just trying to help, I've built multiple DDL drivers, and I think I know what I am saying. I was talking about the pot because I didn't understand if he was using one or just resistors....

WTF?

And you are accusing me of false information.... ??

awlego · Jan 6, 2010

Thank you both for trying to help...

Anyways. I'm using the pot because I want to change the power on the fly. I'm building a RGV build and want to be able to easily adjust each power to make various colors.

So I understand not wanting to short the circuit, but I tried it anyways to test it, and it came out working correctly

So I guess my circuit is good, it's my test load that is bad.

Thank you both so much for your help. +1 to each. (buildabluraylaser - I couldn't give you more rep, because apparently I need to spread it around before giving to you again

) You've both been helpful, thanks.

-Awlego

Deleted member 8382 · Jan 7, 2010

You need a load to measure amps. You need to connect the DMM in series because it measure the current that goes through a circuit element. A DDM doesn't have enough resistance, so all you're doing is shorting the circuit. Not a good idea.

This is what I was talking about. See, the guy did what I said and ops, magic, it works! Anyway, I recognize I shouldn't have neg repped you for that, we all make mistakes. I'm really sorry but I was freaking angry because of a real life issue. I'll add you some rep as soon as the system allows me to do so, also, if someone can give this guy >25 rep points would help a lot. It won't happen again. I guess I need to go bed... :tired:

BuildAbluraylaser · Jan 7, 2010

For the rep, it's ok, at least you didn't get me in the negatives.

I don't really take the reputation system seriously either.. It was better on the other system.

Ok I admit my test load error, but I have to say I have always been thought to use one.
And I have never had any problems.

Well I'm glad that everything is sloved.

Deleted member 8382 · Jan 7, 2010

This is done to simulate the laser diode load, which is necessary in non-linear drivers such as the flexdrive. For the Rkcstr or the DDL driver the MM on amp mode is all you need

takirasan · Jan 11, 2010

dig dig dig dig
I like light

morganw · Jan 15, 2010

I was wondering if it would be ok to replace the 100 ohm pot with a 500 ohm 20 turn pot? Would this work ok or is the resistance too high?

Bluefan · Jan 16, 2010

It's a pot, it ca be turned to 0. But, first check if this provides you with an acceptable adjustment range. For a 250mA current, the minimum resistance is 5 ohm. Then,e ven witha 20 turn, a single turn is 25 ohm, and nearly all the adjustment will be in the last turn (~40mA -> 250mA). This gets better for lower currents, but worse for higher. Also check if the pot can take the power, a 20 turn pot is way too nice to smoke because of the high current. A pot hat a certain power, associated with a certain current, do not pass this.
There are even better alternatives for the LM317 based driver circuit that can make good use of the 20 turn pot, it's obvious you're not going for a pointer here. And it doesn't have to be that complex.

morganw · Jan 18, 2010

ok, thank you. I think that I might use a different pot then. I didn't really think about that.
Can you give me a schematic of a different circuit that can make use of a 20 turn pot?

brtaman · Jan 23, 2010

Hallucynogenyc said:
This is what I was talking about. See, the guy did what I said and ops, magic, it works! Anyway, I recognize I shouldn't have neg repped you for that, we all make mistakes. I'm really sorry but I was freaking angry because of a real life issue. I'll add you some rep as soon as the system allows me to do so, also, if someone can give this guy >25 rep points would help a lot. It won't happen again. I guess I need to go bed... :tired:

Just did. It wasn't really wrong information per se, just careful advice.

While I also just short LM317 drivers to measure current, which in the end isn't even needed due to the simple Vref calculations, you will no find many electrical engineers approving of shorting anything out. :evil:

nOIspheratu · Jan 24, 2010

I wired everything up like in the schematic but i´m only getting about 100mv over the resistor of my dummy diod. Could the Potentiometer be the reson because i used a mini version?

frostin · Jan 24, 2010

nOIspheratu said:
I wired everything up like in the schematic but i´m only getting about 100mv over the resistor of my dummy diod. Could the Potentiometer be the reson because i used a mini version?

Depends what pot you used and no your size of pot wont hurt it. And are you sure you hooked up the pot currectly?

DIY Homemade laser diode driver

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