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Have i made this circuit correctly?

GhostDog98

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So i've made this circuit to drive a Mitsubishi ML101U29-25 at a working voltage (The diode represents the laser diode); Is this going to work?

The first part of the circuit is a simple voltage divider to reduce 3v down to 2.5v, then it goes through the lm317 in constant current mode to produce140ma worth of power which means a total of 350 mw thru the laser. Is this correct?
 



paul1598419

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Those diodes tend to peak around 230 mW at best. The voltage divider is unnecessary as this is a constant current driver. Didn't do the math to check your current, but the rest looks right.
 

Anthony P

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Don't take my word for it, and someone please correct me if I am wrong.
Like Paul said... lose the divider. The spec on diode data sheets that say "max operating voltage" is actually the voltage drop accross the diode. This spec can be used to configure your test load, but input voltage can and should be a bit higher ( too high just creates heat). Also, LM317 1.25/8.9Ohm=140mA... not 350mA.
 

paul1598419

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Yeah these diodes have a forward voltage ~2.3 volts and you need some headroom for the LM317 of ~1.5 volts, IIRC. I'd use a 5 volt supply as every volt over gets converted to heat. Or rather, the current that voltage causes to flow is converted to heat.
 




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