My intent is to build a simple driver for a laser LED with an operating voltage of 4.6 volts and forward current 1.6 amps. I have some spare LM317s that I would like to use, however they can supply 1.5 amps at most with proper heatsinking. Can I use multiple of them in parallel like this, or should I completely scrap this schematic? I suppose each of those should deliver 500 mA making it 1.5 A total.
Also, if this circuit actually works, how can I calculate the power loss on the LM317 regulators?
Simple Constant Current Regulator for 1.6A Laser LED
laser-diodelaser-driverlm317
Best Answer
I'm not so sure about the wisdom of this circuit.
It may work ok, but I am concerned about the response of the regulators when you switch the MOSFET. That large 100uF capacitor will pull down the right side of the sense resistors to close to zero. If the regulators can respond that fast you will initially have close to 10V across each regulator at a whopping 5W each.
Further, the circuit is terribly inefficient consuming 6W to drive a 2.3W LED.
You would be far better to drive the LED from a 5V switching supply and use a low drop current limiting circuit. Perhaps something like this.
simulate this circuit – Schematic created using CircuitLab
Though this is a better enable method.
simulate this circuit