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# Help with fiber coupled pld 40 diode 30w

#### Branson33

##### Member
Alright so say I’ll set it to 2 volts and current limit it to 5 amps, at 2 volts it probably won’t draw 5 amps correct? So I’ll crank up the voltage until it hits five amps and I should be good to go right?
And please answer that question I quoted and last but not least if I place it directly on a peltier cooler with only a small aluminum sheet between the two will it hurt it? Would it be too cold? It can get down to -3c

#### paul1598419

##### Well-known member
No, not set AT 2 volts. Set it to 2 volts above the maximum voltage drop you would expect the diode to do at whatever current you are limiting the diode to draw. For instance, if you are setting the current for 5 amps and it normally drops 5.5 volts, then set it for 7.5 volts. You won't hurt the diode by getting it too cold with a TEC. The TEC will act as a heat pump and move heat away from the diode to the other side of the TEC.

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#### Branson33

##### Member
Alright so this diode is made for 12amps but I’m going to limit it to 5 because that’s all I have and the voltage drop is around 4.8 volts at 12 amps so if I am limiting it to 5 amps I will set the voltage 2 over 4.8 so 6.8 volts and it should work correct? And I would do 6.8 volts for 12 amps too? Or what

#### paul1598419

##### Well-known member
No, at 12 amps it will surely have a larger Vf, or forward voltage drop. Just guessing I would say at 12 amps to set the voltage for 10-12 volts. Since you don't have a PS that can deliver 12 amps, you will need a driver that will. If the driver is set to 12 amps you can deliver 12 volts to the driver and it will only drop as much voltage as is necessary to keep it drawing 12 amps, no matter what the diode needs in the way of voltage.

#### Branson33

##### Member
Okay guys I’m getting confused, the data sheet says at 12 amps the forward voltage is 4.8 volts and that’s at 12 amps so what would the forward voltage be if I lowered it to 5 amps only?

#### paul1598419

##### Well-known member
If your power supply is rated at 5 amps it may, or may not be able to supply that. I would set it to the maximum current and after it is turned on, with the voltage set to 0 volts, short the leads before connecting it to your diode. Then increase the voltage slowly until it reads whatever maximum current it will supply. You can increase the voltage a bit higher as its forward voltage will go up as the diode heats up. I would only do this after I had heat sinked the diode to keep it from over heating.

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#### Branson33

##### Member
That’s the answer I wanted something nice and simple!! Thank you! And I’ll have it right on top of a tec so I think it will be okay right?

#### paul1598419

##### Well-known member
Yes. A TEC can't get it too cold.

#### Branson33

##### Member
Alright just wondering because mine can go down to -3c

#### paul1598419

##### Well-known member
Don't worry about it. It won't stay there with the diode heating up. Even if it did, that won't hurt the diode.

#### DashApple

##### Well-known member
No, at 12 amps it will surely have a larger Vf, or forward voltage drop. Just guessing I would say at 12 amps to set the voltage for 10-12 volts. Since you don't have a PS that can deliver 12 amps, you will need a driver that will. If the driver is set to 12 amps you can deliver 12 volts to the driver and it will only drop as much voltage as is necessary to keep it drawing 12 amps, no matter what the diode needs in the way of voltage.
he is just using a bench supply to run it not a CC driver , if he was actually using a CC driver and assuming its linear he would need around 7 - 9 Volts in .

I need 6.8V on my setup with a drive current of 12A / 4Vf .

Also be careful of the fibre they do break easily and you need to take care of the bare fibre end .

#### Branson33

##### Member
Is running it with a bench supply okay? Mines supports constant current and constant voltage is that okay to use for this diode? And should I still just hook it up and set it to the max amperage setting and set it at zero volts then slowly raise the voltage until it is drawing the max amount of amps for my supply? Would that be okay and not hurt the diode?

Hello guys?

#### DashApple

##### Well-known member
If you do the same thing with other laser diodes , this is no different , so I guess your ok .

#### Branson33

##### Member
Alright sounds good.

#### Branson33

##### Member
Alright here is the supply I have 302289510899 so is it okay to use just set it to 5 amps, zero volts turn it on and short the leads, then un short the leads, connect them to the diode and slowly ramp up the voltage until it is drawing 5 amps correct? Then once it is drawing 5 amps raise the voltage a little bit more because as it gets hotter it will require a little more voltage correct?