testing diode with mutimeter

[chottu]

Is it possible to test a ld with the diode test function of a multimeter?
If so, can a video or steps be put up as to how to do it?

 

[rog8811]

No picture or video but simple enough, set meter to diode test, touch the probes to the + and - pins of the LD, one way round you will get a reading of 1.4 ish, swap the probes and you will get all zeros.
If you get nothing either way it is likely to be a goner, if you get the readings as above the LD MAY work.

Regards rog8811

 

[sk8er4514]

I would not trust only using a multimeter to test the diode, I've tested many diodes to not register on the diode test function on the DMM but work great when hooking them up to a laser driver.

It never hurts to try out the diode, especially if you think its already dead, can't kill something if its already dead.

-Kendall

 

[icecruncher]

I would not trust only using a multimeter to test the diode, I've tested many diodes to not register on the diode test function on the DMM but work great when hooking them up to a laser driver.

It never hurts to try out the diode, especially if you think its already dead, can't kill something if its already dead.

-Kendall

2/3 of my grab bag diodes did not pass the DMM test. I think the power rating of the diode may also influence whether this will work or not on just a DMM or a cheap DMM, but I'm not the expert.

 

[Flaminpyro]

has anyone ever used an actual diode checker they have different current outputs, seems like one of these mught work very well. if I was at home where mine is I would try it, someont out there get on this !


Pyro...

 

[pseudolobster]

I would not trust only using a multimeter to test the diode, I've tested many diodes to not register on the diode test function on the DMM but work great when hooking them up to a laser driver.

It never hurts to try out the diode, especially if you think its already dead, can't kill something if its already dead.

-Kendall

If you're using lavadrives, that's terrible advice. A dead diode killed both of the flexdrives I ever bought, the very first time I used them. Poof, $60 down the drain.

 

[dr-ebert]

The diode testers on DMMs are designed to deal with the 0.7V drop over common silicium diodes. LEDs and laser diodes, especially BluRay ones, have much higher voltage drops, so the DMM diode testers probably won't work (the voltage they employ can't simply be set to high values, as that may damage a diode if applied in the wrong direction).

I'd be careful with FlexDrives as well.

If you want to test a possibly dead diode, just use a battery or PSU with a series resistor (potentiometer) to limit the current to appropriate (low) values.

 

[Benm]

It depends a bit on the multimeter. Many will in fact send enough voltage to make the diode work like a diode - often its just the meters battery voltage with a large series resistor. The meters usually display the voltage drop in milivolts though, and many have a range limited to 1999 - which may not be sufficient for laser diodes or leds.

You can test your meter for this behaviour by measuring 2 ordinary diodes in series. It should display double the value of 1 diode. If you hook up 3, its likely to be just at or just beyond the 1999 mV maximum reading.

More expensive meters will likely employ a current source limited to a lower voltage for the diode test.

 

[rog8811]

I use a fluke auto range meter which has worked on every LD I have ever connected to it..... I must admit I had not thought that cheaper meters might not work.... sorry.

Regards rog8811

 

[icecruncher]

That's pretty much what I suspected

My harbor freight special doesn't do quite as well as a fluke
But Sam's faqs has a great section on testing unknown diodes. I posted a link in the thread discussing those from the heruusciences grab bag

IIRC, Proper way is with a good regulated adjustable power supply, setting voltage and adjusting cuurent. I'm looking at the mastech 1803d for this.

It depends a bit on the multimeter. Many will in fact send enough voltage to make the diode work like a diode - often its just the meters battery voltage with a large series resistor. The meters usually display the voltage drop in milivolts though, and many have a range limited to 1999 - which may not be sufficient for laser diodes or leds.

You can test your meter for this behaviour by measuring 2 ordinary diodes in series. It should display double the value of 1 diode. If you hook up 3, its likely to be just at or just beyond the 1999 mV maximum reading.

More expensive meters will likely employ a current source limited to a lower voltage for the diode test.

 

[Benm]

The fluke might work because it either goes to 3.999 volts which is plenty, or auto-ranges so that 2.00 or more can be displayed.

I would be careful using lab supplies set at some voltage but with current limiting enabled.. some of them have output caps after the current regulating mechanism, and can give your diode a deadly jolt even when configured to safe current levels... similar to output caps on drivers and dodgy diode connections.

 

[icecruncher]

The fluke might work because it either goes to 3.999 volts which is plenty, or auto-ranges so that 2.00 or more can be displayed.

I would be careful using lab supplies set at some voltage but with current limiting enabled.. some of them have output caps after the current regulating mechanism, and can give your diode a deadly jolt even when configured to safe current levels... similar to output caps on drivers and dodgy diode connections.

Point noted.

Here is the link from Sams FAQ on testing unknown diodes

http://members.misty.com/don/laserdio.htm#diodct0