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  #1  
Old 03-05-2008, 06:03 PM
Livingwaters Livingwaters is offline
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Question 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
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Old 03-05-2008, 06:12 PM
Audioguru Audioguru is offline
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Diodes are selected for a circuit by their voltage, current, power dissipation and speed ratings.
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Old 03-05-2008, 09:58 PM
Dave Dave is offline
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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
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Old 03-05-2008, 10:11 PM
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Ron H Ron H is offline
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Quote:
Originally Posted by Dave View Post
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.
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Old 03-05-2008, 10:26 PM
Dave Dave is offline
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Quote:
Originally Posted by Ron H View Post
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
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Old 03-05-2008, 10:35 PM
scubasteve_911 scubasteve_911 is offline
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Quote:
Originally Posted by Ron H View Post
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
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Old 03-05-2008, 10:56 PM
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Quote:
Originally Posted by Dave View Post
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.
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Old 03-05-2008, 11:00 PM
Dave Dave is offline
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Quote:
Originally Posted by Ron H View Post
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
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Old 03-05-2008, 11:02 PM
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Quote:
Originally Posted by scubasteve_911 View Post
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.
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Old 03-05-2008, 11:11 PM
Audioguru Audioguru is offline
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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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