# How to identify a SMD diode?

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#### halleffector

##### Member
Two questions.

1: How can I identify a SMD diode just by itself? I ordered a bunch of SMD diodes, and some of them came on rolls that were without labels.

2: What is the voltage of a diode? E.g. if someone says "use a 15 volt diode", what are they talking about? I'm assuming the reverse voltage of the diode? Can someone confirm this?

#### alec_t

##### Well-Known Member
I'm assuming the reverse voltage of the diode?
The reverse breakdown voltage would normally be the case, unless the forward voltage were of interest.

#### dknguyen

##### Well-Known Member
You're probably SOL if you're trying to identify the part number and there is none.

If they're on a roll (i.e. you have more than one and you know they're all the same)...I suppose I would slowly increase the reverse bias voltage on one off them until it blows up. Then use that 70-80% of that voltage as the voltage rating.

Then I'd put the diode into a circuit with a resistor and voltage source to drive about 10mA through the diode and measure the forward voltage drop. ~0.7V is normal and 0.5V is a schottky. Because that's nice to know.

Then you could test the diode's current limit to destruction similar to the voltage test. Blow it up with current and then use 70-80% of that current as your current rating.

Alternatively, at room temperature, slowly turn the current up (so the temperature can stabilize) on a few diodes diodes until they are each 70C, 85C, 125C or 150C. Amongst the ones that didn't die immedietely, record the current and corresponding temperature of each and let it cook for a bit (10 minutes? an hour? I'm not sure tbh) to see which ones fail. That should give your max operating temperature at ambient room temperature as well as a more accurate maximum current than before.

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