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ID diode help

bigone5500

Apr 9, 2014
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I have a bunch of these diodes that have no markings. They are small, about the size of a 1/4 watt resistor. I put one on my meter on diode mode and I get .510 volts. Whatever that means. How can I test these to find the values?

tmp_4227-20140907_114752-1-1669988596.jpg
 

Harald Kapp

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Sorry, bad luck. Without markings I don't think you stand any chance of identifiying these diodes.
 

KJ6EAD

Aug 13, 2011
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That voltage, if accurate, suggests it may be a schottky diode.
 

KrisBlueNZ

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Yeah, either throw them out or send them to Guangdong Market so they can get a street urchin to paint "MBR340" on them. Then you can buy them back on eBay and your marking problem will be solved!
 

Arouse1973

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Yeah, either throw them out or send them to Guangdong Market so they can get a street urchin to paint "MBR340" on them. Then you can buy them back on eBay and your marking problem will be solved!

Class Kris PSML.
 

KrisBlueNZ

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Alternative spelling of PMSL - "P*ss(ing) myself laughing"
 

Colin Mitchell

Aug 31, 2014
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The only thing to do is put them in tester and see if they break down below say 100v.
The tester is generally called a zener tester.
Then you put them in a power supply and draw about 700mA to 1,00mA and see if they work for a few hours.
If they do, you can use them for a 1 amp power supply.

That's about all they are good for.
They are NOT Schottkey diodes.
 

Arouse1973

Adam
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The only thing to do is put them in tester and see if they break down below say 100v.
The tester is generally called a zener tester.
Then you put them in a power supply and draw about 700mA to 1,00mA and see if they work for a few hours.
If they do, you can use them for a 1 amp power supply.

That's about all they are good for.
They are NOT Schottkey diodes.

It could be a Schottky diode they will usually have a lower forward voltage drop than the silicon diode. This depends on forward current obviously, or more accurately the current is dependant on applied voltage.

Only one problem I can see with this is if you have a low reverse breakdown diode that is not a zener how would you know? Are the zener testers clever enough to determine between zener breakdown and avalanche breakdown? I don't know.

It could be a silicon diode a 1N4001 with 100 uA of current give approx. 0.5 V but I would hope the DMM would pass enough current through the diode to bring it in to full conduction, but I am not going to assume anything here.

Pass 5 mA through the diode and measure it's voltage drop. If it's greater than 0.6 V then it's either a zener or silicon diode if the voltage stays at 0.5 V then it could be a Schottky diode.

So to determine if it is a Schottky or a zener then do as Colin has said and see where it breaks down. If it breaks down 5.6 Volts or bellow then pretty sure it will be a zener. If it breaks down up to 20 V then I think it's going to be difficult because after 5.6 Volts the zener has a positive temperature coefficient just like the avalanche effect. So using heating to see if the reverse current increases is going to be pointless.

One other method is say it has a breakdown of 20 V and you want to know if it's a zener or a Schottky, then apply 10 Volts to it limited by a 1K resistor and measure the current you get through the diode. If it's around 1 uA then it's more likely a Schlocky as they have terrible reverse leakage current. If it's say 200pA then it's more likely a zener.

This is only a rough guide but should help in trying to work out what diode it is.

Thanks
Adam
 
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bigone5500

Apr 9, 2014
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Anyone want them? I will send them to you free. Just pay the postage...

First come first serve...
 

KrisBlueNZ

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Pass 5 mA through the diode and measure it's voltage drop. If it's greater than 0.6 V then it's either a zener or silicon diode if the voltage stays at 0.5 V then it could be a Schottky diode. So to determine if it is a Schottky or a zener then do as Colin has said and see where it breaks down. If it breaks down 5.6 Volts or bellow then pretty sure it will be a zener. If it breaks down up to 20 V then I think it's going to be difficult because after 5.6 Volts the zener has a positive temperature coefficient just like the avalanche effect. So using heating to see if the reverse current increases is going to be pointless. One other method is say it has a breakdown of 20 V and you want to know if it's a zener or a Schottky, then apply 10 Volts to it limited by a 1K resistor and measure the current you get through the diode. If it's around 1 uA then it's more likely a Schlocky as they have terrible reverse leakage current. If it's say 200pA then it's more likely a zener.
Or, just throw them away! Then if you need a diode in future, spend ten cents and get a diode whose characteristics you know about!
 

davenn

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A better idea yet ... get out the soldering iron and use a bit creativity and construct a component sculpture :)
use those diodes and a few other old components
an example ....

r1.jpg
 
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