From: cd@notformail.com   
      
   On Fri, 26 Dec 2025 18:36:57 -0500, ehsjr  wrote:   
      
   >On 12/26/2025 12:56 PM, Cursitor Doom wrote:   
   >> Gentlemen (IOW not you, Bill),   
   >>   
   >> I've got a bunch of green laser diodes which are specified for 370mA   
   >> current draw. I've been using a straight 5 ohm WW resistor rated at   
   >> 10W as a dummy load, but it's crude and inaccurate. Is there something   
   >> better I should be using? I've got some 2W blue ones to do later on as   
   >> well so something which could be adapted for those would be a plus.   
   >> Ideally something which mimics the knee you get as it starts to   
   >> conduct.   
   >>   
   >> Cheers,   
   >>   
   >> CD   
   >   
   >If you want something better than a 5 ohm resistor dummy   
   >load, see the LM317 datasheet figure 8.8   
   >   
   >As you did not specify your supply voltage, I don't know   
   >how close your 5 ohm resistor dummy load is to drawing   
   >370 mA when connected directly across the supply.   
   >   
   >If you put the LM317 circuit in series with your 5 ohm resistor,   
   >you compute the current drawn by by  1.2/R1.  So, for example,   
   >if R1 is 3.25 ohms the current drawn will be ~369 mA.  This of   
   >course assumes a supply of enough "grunt" and within Vmax   
   >for the 317.   
   >   
   >Some more detail:   
   >R1, at 3.25 ohms, will dissipate around half a watt. Use   
   >at least 1 watt. I don't know what you have on hand - I'd   
   >use power resistors - a 3 ohm in series with a .25 ohm.   
   >   
   >Ed   
      
   Okay, many thanks. Yes, I know there were scant details provided but I   
   only wanted vague suggestions I could maybe develop myself. The other   
   idea I had was four diodes in series with a one ohm resistor so as to   
   mimic the Vf of the laser diode. Fortunately I have a good selection   
   of WW power resistors in my stash here.   
      
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