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Limiting Only Voltage When Driving Blue Diode..

BrilliantLasers

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I had a question with regard to driving a high amp blue diode. I've noticed that blue laser diodes(And other diodes) only take in a set amount of amperage if the voltage is low enough. Is it unsafe to limit only the voltage when driving a diode? I can't see anything wrong with this since the diode simply will not take more than a certain amount of amperage if the voltage is set low enough? My point is, limiting voltage to the right level, in turn limits amperage with the given behavior of the diode. Isn't that all that really matters in the end? Will the diode ever draw unpredictable amounts of current once stable? It sure looks stable to me.


Ps, I am an armature in electronics, but I do have a good grasp of amperage vs voltage.
 



Encap

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Assuming forward steady current. There must be enough Voltage to overcome the forward voltage of the diode.
The forward Voltage will vary with temperature and change slightly for each laser at the same current.
That's why constant current drive is recommended.
If you drive it with constant Voltage, the voltage needs to vary with die temperature which is not easy.
Laser diodes require careful control of forward current for optimal performance.
They are easily damaged or destroyed by brief over-current or reverse high-voltage transients.

See "Why Shouldn't You Voltage Drive a Laser Diode?" https://blog.rpmclasers.com/why-shouldnt-you-voltage-drive-a-laser-diode
See RP Photonics Laser Diode Drivers explaination here: https://www.rp-photonics.com/laser_diode_drivers.html

See: https://www.laserdiodecontrol.com/l...undamentals#what-is-a-laser-diode-driver-link
also have a look at pdf by WaVelength Electronic here: https://www.teamwavelength.com/download/applicationtechnotes/an-ld13.pdf

Do you not have a thread and 19 posts in it about running a blue diode wihtout a driver already?
https://laserpointerforums.com/thre...run-time-power-increased.104596/#post-1563345


 
Last edited:

FireMyLaser

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Laser diodes become more conductive and pass more current as they heat up. If you were to perfectly fine tune the voltage until it draws the desired current at room temperature, the diode will soon after start drawing more current and get in thermal runaway situation.
With current regulation, the voltage drop of the diode will automatically drop to maintain the current as it heats, while at the same time reducing the output.
 

BrilliantLasers

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Alright makes sense. Thanks! I guess I wasn't pushing them hard enough in the test to see increase in current over time.
 




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