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I need help wiring laser diodes, I made an expensive mistake!

Skept

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Hey guys,

I toasted an expensive laser by connecting it to a Ramps 1.4 board supplying 12V. Apparently, the laser is configured to work with 5V. I wanted to test whether it works and I had no idea it’s very sensitive and would take a fraction of a second to damage it beyond repair (I tested with a cheap laser diode before and it didn’t behave the same way). The Arduino Mega and Ramps boards also seems to have been damaged. I had to replace them.

Here's a diagram of the wiring that damaged the laser:
Laser wiring.jpg

I have one more laser diode of the same type (spec sheet attached). I wired a voltage regulator to the laser diode (to step down voltage from 12V to 5V) and it seems to work fine. My question is, do I need a laser driver instead of the voltage regulator or is the voltage regulator enough? If so, how do I choose a laser driver? I know these are noob questions, I will be surfing the forum and researching but direct insights to my case will help massively!

Laser spec sheet:
Laser spec sheet.jpg
 



Shmackitup

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You must use a current regulator. Never connect laser diodes directly to an unregulated power source. Your datasheet says ≤450mA. You'll likely want a buck driver.
 

ZRaffleticket

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The spec sheet says driver pcb inside, it is already being regulated, and that regulation expects 5V in. Current will be variable, but should not draw more than 450mA in that unit. You should be able to confirm this with the seller. No need to do anything different in this particular scenario -- your step down converter is doing fine.

If you do however use a different module that does not say it has a driver circuit built in, then we'll need that info case by case. Though generally you can look to the driver subforum, pinned thread on how drivers work, you know you have 12v in and can work out which type of driver you should use.
 

Skept

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The spec sheet says driver pcb inside, it is already being regulated, and that regulation expects 5V in. Current will be variable, but should not draw more than 450mA in that unit. You should be able to confirm this with the seller. No need to do anything different in this particular scenario -- your step down converter is doing fine.

If you do however use a different module that does not say it has a driver circuit built in, then we'll need that info case by case. Though generally you can look to the driver subforum, pinned thread on how drivers work, you know you have 12v in and can work out which type of driver you should use.

Thanks for your reply!

Great to hear the step-down converter is sufficient. However, I’m still confused regarding the current and power output. When I measured the current flowing through the laser, I got a 170mA reading. Am I in this case using the maximum power output of the laser (150mW specified in spec sheet) or less?

What knowledge am I missing to calculate the output of the laser given the current (170mA) and voltage (5V)?
 

Skept

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You must use a current regulator. Never connect laser diodes directly to an unregulated power source. Your datasheet says ≤450mA. You'll likely want a buck driver.
Right! the mistake cost me a lot haha.
I wired the other diode using one of those voltage regulators to step-down the voltage to 5V and they both seemed to do the job:
VolrageRegulator.jpg
 

ZRaffleticket

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Thanks for your reply!

Great to hear the step-down converter is sufficient. However, I’m still confused regarding the current and power output. When I measured the current flowing through the laser, I got a 170mA reading. Am I in this case using the maximum power output of the laser (150mW specified in spec sheet) or less?

What knowledge am I missing to calculate the output of the laser given the current (170mA) and voltage (5V)?
170mA @ 5V doesn't sound like it is being driven hard enough to give you 150mW out. Green diodes usually would need a driver supplying around 300-400mA at around 6.5V, assuming it's the PLP520-B1 per DTR's testing. Is the 12V line coming straight from the power supply into the 5V regulator, or is the ramps 1.4 board limiting current to that LD output? What 5v regulator are you using, is there a current it tops out at? If you use some other cheapo 5V power supply, do you get the same current draw?
 

Skept

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170mA @ 5V doesn't sound like it is being driven hard enough to give you 150mW out. Green diodes usually would need a driver supplying around 300-400mA at around 6.5V, assuming it's the PLP520-B1 . Is the 12V line coming straight from the power supply into the 5V regulator, or is the ramps 1.4 board limiting current to that LD output? What 5v regulator are you using, is there a current it tops out at? If you use some other cheapo 5V power supply, do you get the same current draw?
Answering your question, the 170mA current was measured when connecting the laser directly to the 12V power source with a LM2576HV Step-Down Voltage Regulator which has a high current limit (see pic below). The measurement was done without Ramps board. I currently don’t have a cheap 5V power supply to test but I will get my hands on one and test.

LM.png

I was under the impression the diode has an internal driver which automatically draws the required current to supply the maximum power output?

Do I need to connect an external laser driver like the TTL where I manually adjust the voltage to 5V and current to 450mA? Is it safe to assume that 450mA is needed to get the 150mW power output ?

GreenLaser.png

I will forward those questions to the company (A bit tough to get answers since it's done via a sales representative). So i'd love to hear your take on it. I really appreciate your time by the way!

EDIT:
Actually nevermind! I got things mixed up!
The second laser module has different specs (from the tests, the operating current shows 180mA) which is close to what i'm measuring. Last measurement was 176mA.

So basically, I don't need any extra drivers besides the voltage regulator to regulate the voltage down to 5V and the current is managed by the internal driver.

Red.png
 
Last edited:

hakzaw1

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Be sure you have enough heat sink ---overheating has killed a lot of lasers.
 




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