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Old 03-02-2015, 09:12 PM #1
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Default Issues with driver circuit for M140 laser

Hello,

I have been all over the internet trying to find a good schematic for a driver to power my M140.

I've found this circuit and ordered the components to build it, but am having issues getting anything to work.
Two watt blue laser driver 445nm - BOGIN, JR.

I'm no electronics expert by any means, but thought I could follow the schematic exactly with positive results. This has not been the case.

I have soldered all connections exactly like the schematic (this could be the problem because there may be some things that are just assumed for experienced electronics people and left out of the schematic. I have literally soldered it together like the image) and used an IRFZ44 for the MOSFET. In addition to these connections I have attached VCC and ground to the LM358 and a test circuit in place of the LD and I get no juice. (testing in mv across a 1 ohm resistor in the test circuit.)

A few confusing things about this schematic:
1. at the switch it has 12V marked. Do I also attach VCC here? (I think i tried that and smoked that resistor beside it)

2. I'm not certain I know how to properly read a POT in a schematic. I have the 6k8 only attached on the center and 1 side pin. On the 4k7 I have the center pin going to the pos of the op amp and the other 2 pins connected to the other POT and the cathode of the LED.

3. Not sure what value this LED needs to be. I tried replacing it with a diode to rule that out, but that may not help, or matter, I'm not sure.

4. Is there anywhere on this circuit that needs power or ground from the source? (other that the + - on the op amp)

5. I've seen circuits using MOSFETs where 2 of the pins are bridged with a resistor or grounded. This may be the norm for MOSFETs and the author didn't bother to notate it. I wouldn't know.

6. .22 microfarad seems low compared to other schematics I've looked at.

7. When I get something functional and decide to add the LD. Do I need to use the white wire?(case) and if so, how?

And finally, how much juice do I need to make this thing work? I planned on using 12V and ~2.5A, but I have some 12v Li-Po batteries that can provide much more if needed.

I don't know if these are easy questions or if I'm asking a lot. If anyone has an alternative driver schematic (perhaps something simpler) to recommend I'm all ears.

Thanks,
Aixeslyd007


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Old 03-02-2015, 11:03 PM #2
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Default Re: Issues with driver circuit for M140 laser

1) "VCC" is a generic term for positive voltage supply, 12V in this case. So your question is redundant. Are you asking if the VCC pin of the LM358 goes to VCC? If so, the answer is yes.

2) Pots have three pins. All three should be used. In the case of 6k8, center pin (aka "wiper") should be connected to one of the others. He's drawn it as connected to the LED anode, but it's not too important. 4k7 sounds correct.

3) He is using the LED as an indicator and a voltage reference. Any standard colored 5mm LED will work.

4) You should have 5 pins connected on your op amp.

5) Yes, I would put 100k between the FET's source and gate if I were you.

6) I don't see how this is a question. 220n is fine.

7) No.

8?) This is a linear driver, which means the current sense resistor and the pass FET will drop the extra voltage as needed, and current input will be roughly the same as current output. 12V/2.5A supply should be sufficient for most blue diodes.
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irfz44n, lm358, m140 blue laser diode





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