Old 10-15-2010, 05:25 PM #1
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Default ld driver current measurement

Hello everyone, i just recently started getting into lasers and have built a couple powering them up with daedal's driver (http://laserpointerforums.com/f42/di...ver-26339.html)

I didn't post this question to the driver thread because i believe it doesn't have anything to do with that specific drive (which is excellent by the way) but with my own ignorance.

I am using a benchtop regulated power supply with lcd displays for both current and voltage.

The thing is when i measure current on a test load (4diodes + 10ohm res) by measuring voltage on the resistor and using ohm's law to get current the reading i get is the same as the one on the power supply.
When i measure current by having the multimeter just before the diodes, to measure amps directly (without the resistor), or when i am actually powering a LD, then the reading on the multimeter and the power source are slightly different. For instance i would get 160ma on the multimeter and 140ma on the power source. Its always more on the multimeter and the difference increases with higher current from 10ma to 40ma

Now my questions are, why does this happen? Is having a multimeter just before the ld a good way to measure the actual current going through?

Thanks


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