From: jl@glen--canyon.com   
      
   On Fri, 12 Dec 2025 22:03:14 +0000, Cursitor Doom    
   wrote:   
      
   >Gentlemen,   
   >   
   >I have a bunch of red lasers I bought a while ago which perform best   
   >at 45mA. So I initially thought I'd knock up a current source for that   
   >much to keep them happy. However, I then remembered the temperature   
   >issue and wondered how best to compensate for that effect. There was   
   >some app note I found on the Mouser site which suggested that by far   
   >the best way to operate such laser LEDs is to drop the constant   
   >current approach and go for constant power instead, sampling the   
   >laser's output with a photodiode and rigging up a feedback loop, so   
   >whatever light level I get from 45mA at 20 degrees C can be kept   
   >stable regardless of the ambient temp or the device's junction temp.   
   >However, the app note didn't go into the practicalities. How is one   
   >supposed to sample the light output without interrupting the beam?   
   >There's just no appreciable spread within the confines of a housing to   
   >get any light from the edge region so how could this be done?   
   >   
   >CD   
      
   I doubt that $2 laser pointers have an optical feedback loop.   
   Constant-current should be fine.   
      
   Do you need a super stable light level?   
      
   I suspect that constant electrical power does not result in constant   
   optical output over temperature.   
      
   Try blasting a laser pointer (or an LED) with a heat gun and freeze   
   spray. They are dramatically more efficient when cold.   
      
      
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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