How strict is the voltage rating on laser diodes?

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Discussion Overview

The discussion revolves around the voltage ratings of laser diodes, specifically the implications of operating slightly above the maximum voltage rating. Participants explore the risks associated with exceeding the specified voltage, the importance of current regulation, and the design considerations for driving laser diodes.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant questions the strictness of the voltage rating for a laser diode rated at 1.9 - 2.2 volts, expressing concern about operating at 2.22 volts.
  • Another participant suggests that manufacturers often include a margin of error in specifications, but warns that exceeding the voltage may lead to premature failure of the diode.
  • Some participants emphasize the importance of current regulation over voltage regulation when driving laser diodes, noting that even small increases in voltage can lead to significant increases in current.
  • A suggestion is made to check for a datasheet for the diode, as some may include features for temperature sensing and current regulation.
  • One participant mentions the potential for modifying the circuit to regulate current instead of voltage, indicating that this could mitigate risks associated with overvoltage.
  • Another participant provides links to resources for understanding laser diodes and emphasizes the need for careful driving electronics to prevent damage.
  • Concerns are raised about the participant's initial approach of using a voltage source, with multiple participants advising against this method.

Areas of Agreement / Disagreement

Participants generally agree that driving a laser diode requires careful consideration of current regulation, but there is no consensus on the exact implications of exceeding the voltage rating. Multiple competing views on the best practices for driving laser diodes remain present in the discussion.

Contextual Notes

Some participants note the lack of detailed information available for the specific laser diode in question, which may affect the ability to make informed decisions regarding its operation.

Ravenous Travis
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Hey everyone, this is semi-related to electrical engineering and a quick search didn't appear to turn anything up regarding this question specifically so I figured this is an appropriate place to ask this. I've bought this laser diode rated for 1.9 - 2.2 volts for a project I'm working on. I've built a driver circuit that's ended up being a few percent over the maximum voltage. It clocks in at about 2.22 volts according to my free harbor freight multimeter, so I know I'm close to the recommended voltage... probably. How set in stone are those ratings? Am I going to fry this diode if I'm just a few fractions of a volt over the top end? I'd wire it up and find out myself but I spent 20 U.S. dollars on this diode so I would rather have a little patience and get some advice.
 
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Typically manufacturers try to build in some margin of error with the specs, so it might be OK. But a good designer will design the circuit such that normal operating conditions falls well within the specs of the components. So what I'm saying, it may not fry today, but it most likely will fry much faster than you want it to.

Have you considered that the diode will draw some current? How will that affect the voltage at the output of your circuit? Multimeters are typically designed to draw almost no current, unless your multimeter has a "battery tester" mode. If it is still above range, can you add or swap out a resistor, which will bring the voltage down some?
 
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scottdave said:
Typically manufacturers try to build in some margin of error with the specs, so it might be OK. But a good designer will design the circuit such that normal operating conditions falls well within the specs of the components. So what I'm saying, it may not fry today, but it most likely will fry much faster than you want it to.

Can you add or swap out a resistor, which will bring the voltage down some?

Hmm alright, that's what I was afraid of. I can probably find something to replace one of my resistors with if I dig around enough, maybe it's about time I just order an assortment of some shiny new resistors. Thanks for the advice.
 
Have you a datasheet for your laser diode?
Some of them have an extra wire to sense temperature. It's used to regulate current so you won't fry it.
 
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The problem with diodes/LEDs is that once they are open even a tiny increase in voltage can mean a far greater increase in current => not good for the dissipation.
That is why it is better to give them constant current instead of constant voltage.

My opinion is, that with good cooling this 0.02V won't mean much harm.
My suggestion is to check and/or modify the circuit if possible, because if that supply unit is sensitive to anything, then...
 
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jim hardy said:
Have you a datasheet for your laser diode?
Some of them have an extra wire to sense temperature. It's used to regulate current so you won't fry it.
I don't, the best I could find is the pinout posted in a review on the site I purchased it from which claims that the third pin isn't used. Lack of information seems to be the trend when buying cheap laser diodes.
 
Rive said:
The problem with diodes/LEDs is that once they are open even a tiny increase in voltage can mean a far greater increase in current => not good for the dissipation.
That is why it is better to give them constant current instead of constant voltage.

My opinion is, that with good cooling this 0.02V won't mean much harm.
My suggestion is to check and/or modify the circuit if possible.
I wasn't entirely sure how to go about making the driving circuit, and I saw a lot of people using voltage regulating circuits to drive their diodes so I just went with that. It looks like I could convert my circuit relatively easily to regulate current instead of voltage.
 
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Ravenous Travis said:
It looks like I could convert my circuit relatively easily to regulate current instead of voltage.

Rive said:
My suggestion is to check and/or modify the circuit if possible, because if that supply unit is sensitive to anything, then...

I'll Second that .
 
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I'll do that then. Thanks for all the help guys!
 
  • #10
Why are you using a voltage source to drive a laser diode? The voltage that is listed is provably Vf (forward voltage drop) versus current. You don't put a voltage across an LED or laser diode -- you drive a current through it. That can either be from a current source, or a voltage source with a series resistor to set the diode current based on the diode's Vf and desired current.

The exception would be if the laser diode package includes its own current-setting resistor. But then the drive voltage listed would be more like 5V, not the 2.2V that is a typical Vf for a red laser diode.

Look at datasheets for other laser diodes...
 
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  • #12
berkeman said:
Why are you using a voltage source to drive a laser diode? The voltage that is listed is provably Vf (forward voltage drop) versus current. You don't put a voltage across an LED or laser diode -- you drive a current through it. That can either be from a current source, or a voltage source with a series resistor to set the diode current based on the diode's Vf and desired current.

The exception would be if the laser diode package includes its own current-setting resistor. But then the drive voltage listed would be more like 5V, not the 2.2V that is a typical Vf for a red laser diode.

Look at datasheets for other laser diodes...
My knowledge of electronics is fairly limited, so I've been approaching this project with google in one hand and community help in the other. The information given about the diode stated it had a "working voltage" of 1.9-2.2 so I had assumed applying that potential across the pins would be sufficient so long as I used a voltage regulator. That's my excuse for my initial approach. I've since converted my circuit to limit current to the listed operating current.
 
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  • #13
Ravenous Travis said:
I've since converted my circuit to limit current to the listed operating current.
Good. Have a read through that reference link that I posted. It looks to be a pretty good introductory reference. :smile:
 
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  • #14
berkeman said:
Good. Have a read through that reference link that I posted. It looks to be a pretty good introductory reference. :smile:
Will do!
 
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  • #15
Under no circumstances should any diode, laser or otherwise, be directly connected to a voltage source. Drive it with a constant current driver. Search for a laser diode driver. I have one I thought about publishing. I used it years ago with great results.
Again, do not even attempt to drive a diode with voltage, never can that work. Look up "thermal runaway".
 
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