Voltage on Daedal's driver build.

[DREW8110]

Ive built the driver described by Daedal. When testing it with 6V power , I get 5.25V & 250 mA, which drives my DVD diode from stonetech. When using 3V in, I get 2.7 V out, and no matter how high I turn up my pot, (250mA), the laser just want get very bright. I thought that 2.5-3V was what I wanted and 5V was to high for the DVD diode. Can anyone tell me what im missing.I would really appriciate any info on building drivers . Ive been putting them together on the breadboard before I do any soldering for days now and just dont have the confidence that im doing it right. Thanks for any response on this,

 

[chido]

It's possible your diode is dead, you see, the owner of the store got a bad batch of diodes which die at currents that used to be safe for the normal diodes.
Use at least an input of 7.2v with this driver, and how are you measuring the current going to the diode?

 

[DREW8110]

IM measuring the current and voltage with multimeter. THanks for reply.

 

[DREW8110]

Also im confused, but the more voltage put in, the more out ? Is this wrong?

 

[chido]

Yeah, it's obvious you're using a multimeter, but how are you measuring the current, are you using a 1ohm resistor in series with 4 1N4001 diodes, or are you using the laser diode with a 1ohm resistor in series?

 

[DREW8110]

I tryed to read spec sheat on LM317T, but I guess I dont have enough exp. in this. To complicated. How do you use it to controle voltage. Thanks again for answring .

 

[DREW8110]

IN his diagram I only saw 1 1n4001 and 2 10 Ohm resisters. If its to frustating to explain to someone without experience I understand. Thanks

 

[DREW8110]

Are you saying to use the 1N4001 in series to drop valtage?

 

[chido]

I'm not talking about the driver, I'm talking about how you connect the multimeter to the driver to measure the current.
You're supposed to hook it up like in this picture:

 

[jayrob]

Also im confused, but the more voltage put in, the more out ? Is this wrong?

With the DDL driver and a red Stonetek diode, you need to use a supply of over 6 volts. We have been using 2 X RCR123 3.6 volt batteries. The LM317 circuit will use up about 3 volts or more. The diode needs about 3 volts. You can supply this driver with up to 37 volts. (I believe it's 37) And the LD will still only get what it needs. Of course, you don't want to put that much voltage into it, because the LM317 will probably get too hot.
Anyway, that's why with a blu-ray diode using the DDL driver, you need more voltage supply. (like 9 volts) Because the diode needs around 4.5 and the circuit will need at least 3...
Jay

 

[DREW8110]

OK, Thanks I did not know that. Ill look at the diagram and see if thats my prob. Thanks again, as I said Im shure it gets old trying to explain to people that should do more homework before asking questions. My problem is I hate to read and get ahead of myself when excited about putting something together. Sorry!

 

[chido]

Don't worry about it. I suggest you watch your wallet though, if you're excited now, you're going to go crazy once you finish the laser. You're going to get the laser bug which is going to make you spend and spend and spend lots of money. ;D

Oh, and here's the complete thread on how to test the circuit:
http://www.laserpointerforums.com/forums/YaBB.pl?num=1197651171

 

[DREW8110]

One final question. If you are familiar with the 70mw laser with heat sink and driver sold by deal extreme for around $17.00; it should be possible to alter this driver for other lasers, correct? Stupid question but thout Id ask. Ive already done it , but wonder if im messing something up.

 

[DREW8110]

YOUR right about the mony. Ive made several with the 70mw deal exteme laser,baught 6, and nothed out 1 1/2" pvc pipe.Worked out nicey. Almost looks like store baught flashlight except its white pipe. Used the dx driver with DVD and other diodes I baught in these PVC holders. Thanks again for help.

 

[IgorT]

One final question. If you are familiar with the 70mw laser with heat sink and driver sold by deal extreme for around $17.00; it should be possible to alter this driver for other lasers, correct? Stupid question but thout Id ask. Ive already done it , but wonder if im messing something up.

I think i know which one you mean.. But that driver board is way too complicated.. The heatsink might be usefull tho..

The LM317 driver is more than enough for all your LDs..


I have one question tho.. You said you measured 5.2V out at 6V in and 2.7V out at 3V in...
Were you measuring the open circuit voltage? (no load)

Your results sound almost exactly like what happens in that case.. when the 317 is set up to regulate the current, it needs something for the current to flow through. Otherwise it can't regulate it.. It "thinks" the load needs more voltage to reach the current you set, and increases the output votage as much as possible, but since there is no load, it maxes out at around 5.2V with 6V in.


This is not the proper way to measure if it's behaving.. You need to give it a dummy load, like the one, that was posted above - the diodes and the 1 Ohm resistor..

Then you can measure the voltage on the diodes (between the first and the last), and you can measure the current going through them, by measuring the voltage drop across the 1 Ohm resistor, without disconnecting the load to put the meter in between.. Across a 1 Ohm resistor, the voltage drop in mV is the same as the current through it in mA.

Then you can turn the pot and see if the current increases / decreases, and this way you know if the circuit is working properly.



Otherwise (as has been mentioned already), the circuit needs 6 V OR MORE. If you give it exactly 6V of batteries, their voltage will start dropping immediatelly, and you won't get the constant current benefit of the driver circuit. The circuit can take up to 37V on the input, and keep the output constant.. So you need to select your batteries in a way, that they give you 6V when they are empty, and more than that when they are full..

6 Ni-MH cells or two Li-Po cells are perfect for this.. They give you 8.4V when full and 6V when empty. The laser gets the same current over this entire voltage range, instead of dropping with your batteries.



EDIT: When you were measuring the output, how did you measure the current? Did you just put the multimeter between the + and - of the circuit output?