All About Circuits Forum Diode Formula (Equation)
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#1
03-05-2008, 06:03 PM
 Livingwaters Junior Member Join Date: Mar 2008 Posts: 16
Diode Formula (Equation)

Hello Group,

What is the standard formula for determining the diode value of any given circuit? (Using Volts @amps to determine values needed)

Please make this as simple as possible to determine. I'm on this site to seek expert advoce. My electronics is pretty basic.

Thanks In Advance for the help!

Livingwaters
#2
03-05-2008, 06:12 PM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

Diodes are selected for a circuit by their voltage, current, power dissipation and speed ratings.
#3
03-05-2008, 09:58 PM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

You should look at the Ebers-Moll/Shockley equations. They are pretty much the same equations expressed in different terms describing current-voltage relationship of a diode.

Dave
#4
03-05-2008, 10:11 PM
 Ron H E-book Developer Join Date: Apr 2005 Location: Idaho, USA (GMT-7) Posts: 7,050

Quote:
 Originally Posted by Dave You should look at the Ebers-Moll/Shockley equations. They are pretty much the same equations expressed in different terms describing current-voltage relationship of a diode. Dave
Dave, I think you need to reread his question.

Livingwaters, diodes don't have values, like resistors do. They have part numbers, and each part has a set of specifications such as current rating, breakdown voltage, recovery time, etc.
#5
03-05-2008, 10:26 PM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

Quote:
 Originally Posted by Ron H Dave, I think you need to reread his question. Livingwaters, diodes don't have values, like resistors do. They have part numbers, and each part has a set of specifications such as current rating, breakdown voltage, recovery time, etc.
The notion of "values" is ambiguous and the OP states merely I and V, where Ebers-Moll defines the I-V characteristic.

The differential of Ebers-Moll is ∂I/∂V - the reciprocal of which at a given voltage will give a resistance at that voltage. Naturally the resistance changes with voltage.

Dave
#6
03-05-2008, 10:35 PM
 scubasteve_911 Senior Member Join Date: Dec 2007 Posts: 1,202

Quote:
 Originally Posted by Ron H Dave, I think you need to reread his question. Livingwaters, diodes don't have values, like resistors do. They have part numbers, and each part has a set of specifications such as current rating, breakdown voltage, recovery time, etc.
I suppose if you want to be picky, everything has a part number and you cannot associate anything to an exact value. Ie. A resistor isn't just a component with a value of resistance, it has an associated power dissipation, inductance, thermal noise voltage characteristic, tolerance, and thermal coefficient.

Steve
#7
03-05-2008, 10:56 PM
 Ron H E-book Developer Join Date: Apr 2005 Location: Idaho, USA (GMT-7) Posts: 7,050

Quote:
 Originally Posted by Dave The notion of "values" is ambiguous and the OP states merely I and V, where Ebers-Moll defines the I-V characteristic. The differential of Ebers-Moll is ∂I/∂V - the reciprocal of which at a given voltage will give a resistance at that voltage. Naturally the resistance changes with voltage. Dave
I guess it is ambiguous, but his statement,
Quote:
 My electronics is pretty basic.
led me to believe that Ebers-Moll is probably not what he is looking for. If you're correct, I will apologiz(s)e profusely.
#8
03-05-2008, 11:00 PM
 Dave Senior Member Join Date: Nov 2003 Posts: 6,961 Blog Entries: 17

Quote:
 Originally Posted by Ron H I guess it is ambiguous, but his statement,led me to believe that Ebers-Moll is probably not what he is looking for. If you're correct, I will apologiz(s)e profusely.
Seems a fair assessment, perhaps clarity is required from the OP. Apologies not required

And its apologise!! (As the lonesome Brit I'd be out-numbered on this one!)

Dave
#9
03-05-2008, 11:02 PM
 Ron H E-book Developer Join Date: Apr 2005 Location: Idaho, USA (GMT-7) Posts: 7,050

Quote:
 Originally Posted by scubasteve_911 I suppose if you want to be picky, everything has a part number and you cannot associate anything to an exact value. Ie. A resistor isn't just a component with a value of resistance, it has an associated power dissipation, inductance, thermal noise voltage characteristic, tolerance, and thermal coefficient. Steve
OK, Mr. Spock.
#10
03-05-2008, 11:11 PM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

Hi Dave,
You are a Brit?

I was in London one time. I remember Picadilly Circus, a foreign language called Cockney and cars driving on the "wrong" side of the road.

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