Has anyone used drivers for normal LEDs for laser diodes? I had an idea of building many small low power units without scanners when I saw some neat rgb led drivers with integrated dmx.
How much is different between led and laser diode drivers?
Junior Member
Led driver for Laser diode
Has anyone used drivers for normal LEDs for laser diodes? I had an idea of building many small low power units without scanners when I saw some neat rgb led drivers with integrated dmx.
How much is different between led and laser diode drivers?
Senior Member
LED drivers probably wouldn't be a good match for laser diodes. The main reason being, that LED drivers, especially the ones controlled via DMX normally depend on the LED's to have their own current limiting as most LED strips do. The second draw back is that DMX LED drivers are Pulse Width Modulation. PWM normally isn't a good choice for laser diodes. Peak currents could kill diodes pretty fast, not to mention very undesirable laser effects.
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PWM usually sucks for LD driving. As we have learned in the past, the only way you can find out is to buy two or three of the drivers, hook up some sacrificial laser diodes, and watch the output (while lasing) for spikes on a very fast oscilloscope. Then let it run for a week at various modulation levels as a test, with frequent turn on/turn off cycles for the DC power supply.
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Typically a 100 Mhz scope would be a good start, but you could get by with a sensitive, high quality. 20 Mhz scope. If the spikes are there, they will occur on each and very PWM cycle or transition, resulting in a very short LD lifetime... The spikes from the PWM buck inductor are very fast and narrow. They can be hard to see on low cost test gear.
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Then test both open circuit, and with a LED as a load.
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LEDs are far more tolerant of large spikes, they act somewhat like large Zener diodes... Laser diodes blow if you sneeze, especially diodes with very small junctions such as single-mode devices.
Steve
Last edited by mixedgas; 03-20-2016 at 13:35.
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Senior Member
... yes, my experiences are similar -- I've bought one of this >20A PWM LED-drivers as potential laserdiode-driver, but didn't test it for this until now :-/
My first designed LD-drivers are built with 5x LM317 configured for current-regulating to 0.5A to 1A per IC (or LM338 for 2A to 2.5A) and "parallelized" with jumpers, so I can select any stable current from 0.5A to 8.5A in 0.5A- or 1A-steps for my IR-LD's with 9A max. current. Switching the LM-groups with a MOSFET works like a charm (no spikes, super stable), but was limited in the predefined 'current-steps'.
Then I've developed a simple analogue current driver with OP-AMPs and sense-resistors capable of up to 20A (or more with parallelizing), that works too pretty stable, but generates much more excessive heat than this high current LED-drivers.
Actually my company is developing a more 'proffessional' driver module with an embedded PIC as intelligent controller, which is much more energy efficient (nearly no heat) with a DC-DC converter, but it's generating spikes at some specific (reproducible) conditions.
So for me and my private gear it's OK to use my own 'old-stylish' drivers with the big coolers ... but in the company we have to finish or redesign the DC-DC-modules, so they will work stable ...
Viktor
Senior Member
the first linked led driver is NOT suitable for laser diodes, i have tried and failed with that listed driver and lost a good diode in less then a week with one(that was one of the reasons i found this forumOriginally Posted by ghosttrain
, for what a laser diode driver costs these days it's just not worth the risk in my humble view, they work great for LED though and i use one for some UV leds that i have on hand, i don't have experience with the second one but i would be wary of that device as well, i would not be surprised if it has the LD deadly PWM spikes, this things are not a clean source of power for a LD
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Junior Member
This forum is great!
So much info and interesting discussions. Thanks for all the answers.
What I found interesting with DMX led drivers were how easy they are to come by and that they are premade with logic and everything.
Why isn't PWM suitable for laser diodes? Is it the overshoot of the drivers or something else?
Every one seems to agree on that LED drivers wont work well out of the box, has anyone tried adding filtering Caps to get rid of the overshoot?
Senior Member
I have used the cheap dmx three channel led drivers with MM diodes. The have been used for many thousands of hours with no ill effects. I used a ballast resistor and regulated power supply. The PWM output of the drivers is about 5kHz. As long as the overhead voltage is at least equal to or greater than the diode Vf you shouldn't have a problem. This is not a solution for scanned beams due to the "on off" nature of PWM.
Senior Member
... I'm driving all my diode lasers with PWM - Pulse lengths down to 500ns, frequencies up to 1 MHz. For this I'm selecting high-speed OP-Amps for current regulating and optocouplers with >4 MHz bandwith.
I'm avoiding filtering caps to get the 'edges' sharp at higher frequencies, but for 'slow' PWM they could be helpfull ...
Viktor
Senior Member
That begs the question what are you doing with them? Just curiosity talking
Senior Member
PWM works fine on a Laser Driver, something that is made to run a laser diode, over shoot and noise are a problem with drivers not designed to work with laser diodes, they just wont tolerate even a little overshoot unlike an led will, the drivers that where listed are buck converters with an inductor and these hit the inductor with the PWM drive and adjust that drive to change the voltage output, the can work in reverse as well as boost converters in a different configuration. This is used in laser drivers as well but they are better designed as the laser diode will not tolerate noise or overshoot.
I my self use both PWM and Liner laser drivers and have built them my self as well but there is a lot more to consider then when just using it to charge a battery or run LEDs. In electronics a Laser diode is the most sensitive device most of us run into and even a 20 watt laser diode bar can be killed by a reverse bias of only a few volts and people are not kidding when they say sneezing at one can damage it.
out of curiosity what is an MM diode?
Remember Remember The 8th of November, When No One Stood, but Kneel, In Surrender
In a popular government when the laws have ceased to be executed, as this can come only from the corruption of the republic, the state is already lost. Montesquieu
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