HELP WITH LASER DIODE DRIVER

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icarus1
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Posted by icarus1: Thu. Jun 13, 2019 - 07:52 AM
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Hi there,

 

I already built a constant current source (using a NPN BJT, a N-MOSFET and some resistors, 30mA) that drives a red laser diode (I bought it from ebay for 1$). I also placed a N-Mosfet switch that disconnects the whole circuit from the GND. So I can on and off the Laser output in high frequency (I m gonna measure it and post it).

 

My problem is that after some minutes the Laser output brightness decreases.

 

Does anybody have the experiense on laser diodes driving to help me understand and solve the problem?

Also is there any Laser Diode driver ic ?

 

Thank you in advance.

Michael.

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Learning and Information, General Electronics
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andrewm1973
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Posted by andrewm1973: Thu. Jun 13, 2019 - 09:35 AM
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is this bread boarded.  Is there enough inductance in your leads to have ringing or oscillations  that exceeds the diodes rating?

 

I assume you have checked you CC driver does not overshoot on turn on.

 

There are lots of laser driver ICs but they are all for a lot more complex tasks than a simple red diode doing square waves.

 

Also - if you want to on/off at high frequency (you have not defined what high is BTW) then you often want to modulate the current between two levels.  "Off" being a low current that is around the lase threshold and "on" being the higher current that is - well on obviosuyl.

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ki0bk
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Posted by ki0bk: Thu. Jun 13, 2019 - 12:33 PM
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icarus1 wrote:
My problem is that after some minutes the Laser output brightness decreases.

So how hot is your diode?   Does it have a heat sink? 

Do you have a part number for your diode?   and a datasheet?

 

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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Paulvdh
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Posted by Paulvdh: Thu. Jun 13, 2019 - 03:42 PM
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d

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Mon. Jun 24, 2019 - 08:51 AM
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gchapman
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Posted by gchapman: Thu. Jun 13, 2019 - 03:57 PM
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icarus1 wrote:
Also is there any Laser Diode driver ic ?
modules

Laser Drivers/Laser Controllers/Laser Diode Drivers| Analogtechnologies.com

 

"Dare to be naïve." - Buckminster Fuller

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avrcandies
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Posted by avrcandies: Fri. Jun 14, 2019 - 02:30 AM
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Where is your schematic??!!!

 

Make sure you keep the laser diode cool!!

 

It will have very low tolerance for overdriving...once you do, can blow apart the internal mirror facets from too high of  an energy density and/or will run dim...forever

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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