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Test load or high wattage resistor?

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I saw it mentioned in another thread that you don't need a test load made of diodes and whatnot to test driver output. One of the people in the thread said that he just used a high-wattage resistor as the test load and claimed that he never had a problem with it.

The logic put forth was that the laser diode drops 100% of the voltage put to it, and that the driver is going to apply whatever voltage it needs to in order to deliver its set current through the load. With that in mind, a high-wattage resistance that will keep the driver within its safe voltage limits should function as a test load.

Can I then put the DMM in series with the circuit for a direct current measurement? Or will it introduce oscillations and/or otherwise give a bad reading?

Curious about it; I have a dead 650nm diode here from a Lazerer LZCS, looks like an LPC-826 or similar. The driver seems ok, it will light up the LED'd diode. I'm guessing it's some kind of buck driver, or maybe a linear... it has a transistor and an IC, a resistor, some caps. No coil. Would like to see what current it's set to and whether I could use it for something else. If I put 8.2 ohms across it the driver should be fine because unless it's a boost driver (red diode, so it's not) then max v-out 3.7 volts, which would be at most 451mA with an 8.2 ohm load. Right?

I just wanted to find out ahead of time if I can use a power resistor and be fine with that, or if I do need to put together a test load with diodes and the like. I would hate to try it later, on a driver that I do care about, and have it die. Thanks for any clarification on the matter!
 
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Cyparagon

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A power resistor will work fine as a load. But the characteristics are linear, where a diode is exponential, so you need to change your resistor when you change the current or when you change the type of diode you want to simulate. I think it's easier to use diodes, myself.

DMM in ammeter mode acts as a very low inductance in series with a very low resistance. It will have no effect on the current regulation in the vast majority of cases, and will give you the average* current through it.

If there's no inductor, it's a linear driver. As such, it will be okay if you use only the DMM as the load. Don't have it active this way for too long though, since the IC may overheat if you're not paying attention.
 

Benm

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On an ideal driver it should not matter at all. That would output the same amount of current across a resistor, bank of diodes or a monkey wernch.

Test loads comprised of several silicon diodes and a bit of a resistance in series approximate the behaviour of real laser diodes best though, making them preferable for testing.

A multimeter on amperage range could be a poor choice since it has very low resistance in this configuration. A perfect driver would manage just fine, but don't epxect boost drivers to behave with a load like that.
 




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