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Diode Help Answered

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Hi, i have a bunch of diodes laying around, can somebody explain the diode function on multimeter? sure, there's numbers on the multimeter, but what do they mean? maybe give me a formula? Thank You!

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guyfrom7up (author)2008-05-19

The diode function of a multi meter tells weather a diode is good (working) or not. It should conduct one way, and be highly resistive the other way.

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tech-king (author)guyfrom7up2008-05-19

By highly resistive, he mean nearly infinity ohms.

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Sandisk1duo (author)tech-king2008-05-19

i understand that part ; ) but i read that you can figure out how much current/volts it will lower, kind of like a resistor and voltage ragulator

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tech-king (author)Sandisk1duo2008-05-20

ohh. all diodes, when properly biased, lower the voltage by about 0.6 volts. they do not lower current.

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Sandisk1duo (author)tech-king2008-05-20

so even the specialty zener diodes lower voltage by 0.6?

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gmoon (author)Sandisk1duo2008-05-20

Actually, there's a lot of variance in voltage drop between diode types.

-General silicon diodes are around 0.6 or 0.7, as TK wrote.
-Germanium diodes (as the diodes in the photo look to be) are closer to ~0.3.
-And Schottky diodes can be lower still (as low 0.15, but they vary widely)

The forward voltage drop of zener is similar to other silicon types (of course, there's variance within all these types.)

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gmoon (author)gmoon2008-05-20

Oh--and just connect the diode to your voltage source and compare the output to the known voltage. The difference is the voltage drop. Also, I forgot to add LEDs to that list--their voltage drop is anywhere from 1.5 to 4V...

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tech-king (author)gmoon2008-05-20

good call, i forgot about how germanium and schottky diodes have a different voltage drop than silicone ones.

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Sandisk1duo (author)gmoon2008-05-21

so can i use diodes to make a basic regulator?

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gmoon (author)Sandisk1duo2008-05-21

You can use typical diodes to drop voltage, but that's not really regulation, per se. Zeners are the type useful for regulating voltage. Tech-king will elaborate (that's one of his favorite subjects...;-)

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Sandisk1duo (author)gmoon2008-06-27

so they lower voltage, no matter the current?

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forgesmith (author)Sandisk1duo2008-06-28

Well in theory there's some tiny minimal current below which a diode won't conduct at all, but otherwise yeah, they'll drop voltage, provided the voltage is there. Can't drive a LED with a 1.8V drop with a 1.3V rechargeable AA, for example. And I won't say "no matter the current" since too much will blow a diode, then they won't lower the voltage since none will get thru!

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westfw (author)2008-05-20

analyzing a zener diode will take more than a multimeter. I don't think there is any way to figure out a diode's current or wattage rating with a meter (though you can make a pretty good guess based on physical size.)

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tech-king (author)westfw2008-05-20

you could measure a zener diodes breakdown voltage with two meters; one to measure applied voltage, and one to detect the voltage once the diode hits breakdown voltage. or you can replace the second meter with a Vreg and an led/resistor combination.

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