Diodes. Silicon vs Germanium. Specs

Thread Starter

RAMBO999

Joined Feb 26, 2018
259
Hello

I bought an assortment of diodes on ebay some time ago. They are described as germanium. They all look the same apart from their markings.
I have read a few articles now that say that the threshold voltage of germanium diodes is 0.3V. I have been sampling these diodes and some of them appear to have a threshold voltage of 0.6V (1N4002), which is more like a silicon diode, and some have a threshold voltage of 0.2V (1N5819), which seems a bit low. Can anyone explain these findings? Is this normal is it just a matter of them being crap?

These are the diodes I bought.

https://www.ebay.co.uk/itm/303029116321

Also, I am looking for a regular diode with a threshold value of 3V or 5V. I have had a look around and I tend to keep coming across zener diodes. That's not what I want. Can anyone suggest a source? Or a type.

Thanks
 

AlbertHall

Joined Jun 4, 2014
12,345
Neither of the ones you mention is germanium. 1N4002 is a 100V, 1A silicon rectifer diode. The 1N5819 is a schottky diode. The voltages you quote are normal for those diodes.
The only diodes around with those threshold voltages are zener diodes.
 

Thread Starter

RAMBO999

Joined Feb 26, 2018
259
Neither of the ones you mention is germanium. 1N4002 is a 100V, 1A silicon rectifer diode. The 1N5819 is a schottky diode. The voltages you quote are normal for those diodes.
The only diodes around with those threshold voltages are zener diodes.
Thanks for that. Here's the spec from the ebay advert (attached). I guess it's bs then. And Zener it is. It's the threshold I mean to utilise rather than the bias so I guess they will be ok.
 

Attachments

AlbertHall

Joined Jun 4, 2014
12,345
All those inthat list are silicon. The 1N4xxx are 1A rectiifer diodes with various reverse voltage ratings. The 1N5xxx are schottky diodes with a forward voltage similar to germanium but they are silicon.
 

Thread Starter

RAMBO999

Joined Feb 26, 2018
259
Your link takes me here:
100pcs 10 Values Rectifier Diode Assortment Electronic Kit 1N4001~1N5819 UK and the kit spells out 10 each os 1N4001 through 1N4007 (all standard silicon) and 1N5817, 1N5818 and 1N5819 Schottky Barrier Rectifiers.

Nothing about Germanium? Not a bad kit but not germanium either.

Ron
Check out the screen dump I sent to Albert a couple of posts back. Probably a mistake but nevertheless it says Material : Germanium. You need to scroll down to the bottom of the ebay page to see it.
 

Reloadron

Joined Jan 15, 2015
7,501
Check out the screen dump I sent to Albert a couple of posts back. Probably a mistake but nevertheless it says Material : Germanium. You need to scroll down to the bottom of the ebay page to see it.
I also saw that. I guess we write it off as incorrect. :(

Ron
 

bertus

Joined Apr 5, 2008
22,270
Hello,

Next to the mentioning of Germanium, there is something else incorrect.
They are mentioning bridge rectifier.

Bertus
 

MisterBill2

Joined Jan 23, 2018
18,169
Thanks for that. Here's the spec from the ebay advert (attached). I guess it's bs then. And Zener it is. It's the threshold I mean to utilise rather than the bias so I guess they will be ok.
If you are seeking a diode that is not a zener but has a specific forward drop, one option is a string of silicon diodes in series, using the forward drop of the whole string to achieve your desired voltage. A bit cumbersome but it would be effective and work well.
 

Analog Ground

Joined Apr 24, 2019
460
If you are seeking a diode that is not a zener but has a specific forward drop, one option is a string of silicon diodes in series, using the forward drop of the whole string to achieve your desired voltage. A bit cumbersome but it would be effective and work well.
You can also stack LEDs. Fewer devices since they have a larger forward voltage.
 

Thread Starter

RAMBO999

Joined Feb 26, 2018
259
If you are seeking a diode that is not a zener but has a specific forward drop, one option is a string of silicon diodes in series, using the forward drop of the whole string to achieve your desired voltage. A bit cumbersome but it would be effective and work well.
That's interesting. But you say "forward drop". I am talking about threshold voltage. Are we on the same page? Are we talking about the same thing.
 

Reloadron

Joined Jan 15, 2015
7,501
That's interesting. But you say "forward drop". I am talking about threshold voltage. Are we on the same page? Are we talking about the same thing.
You are on the same page. The threshold or forward voltage is the voltage where the diode, when forward biased, begins to conduct current.
Also, I am looking for a regular diode with a threshold value of 3V or 5V. I have had a look around and I tend to keep coming across zener diodes. That's not what I want. Can anyone suggest a source? Or a type.
That lends to a little confusion because 3-5 volts is not common and the reason you keep getting directed to Zener Diodes is those numbers would be typical for a zener diode. That said as mentioned:
If you are seeking a diode that is not a zener but has a specific forward drop, one option is a string of silicon diodes in series, using the forward drop of the whole string to achieve your desired voltage. A bit cumbersome but it would be effective and work well.
So you can see if you look at the data sheet for the 1N400X family the Vf (Forward Voltage Drop) which for a silicon diode is about 0.65 to 0.70 volt. You would be stringing a whole bunch and those numbers are approximate and based on a given temperature. A Germanium diode is typically 0.3 volt, so less than a typical silicon.

This would go much better if you simply state your objective. Exactly what are you trying to do?

Ron
 

MisterBill2

Joined Jan 23, 2018
18,169
That's interesting. But you say "forward drop". I am talking about threshold voltage. Are we on the same page? Are we talking about the same thing.
Forward drop is the voltage across the diode after the curve turns to the part where the voltage increases very little as the current increases quite a bit. And the "threshold' is also referred to as the diode knee. Diodes have a little current flowing below that point, thus "threshold" is not the best term,
 
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