# Potential difference across a diode

anigeo
Why is the potential difference across a conducting diode zero?

## Answers and Replies

Gold Member
If the potential difference across a diode in zero, it's not conducting.

Looks like there's a nonzero voltage everywhere except when the current is zero.

Unless of course it's shorted internally. But even then, you'll see a potential difference, albeit kinda small.

anigeo
but then in explaining the working of the signal circuits of the OR and AND gates , i found the book assuming that there can be no potential difference across a diode

Pls refer to this youtube video from one of the best EEC professors in india(He says the same)

Thank you.

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Staff Emeritus
Why is the potential difference across a conducting diode zero?
The PD is small and approximately constant over a range of forward currents. In comparison with other voltages around the circuit, it is often convenient to think of it as 0 volts. (We may approximate 0.6V to 0 volts, especially when discussing applications where the difference does not matter. Alternatively, you can picture the discussion as involving idealized diodes.)

It is usually convenient to think of a mechanical switch as having zero volts across it when it is in the ON position, though we all recognize that no practical switch can have 0.000000V across its contacts while conducting useful lighting current in the home.

Gold Member
but then in explaining the working of the signal circuits of the OR and AND gates , i found the book assuming that there can be no potential difference across a diode

Pls refer to this youtube video from one of the best EEC professors in india(He says the same)

Thank you.

This is the world of Real Engineering, in which insignificant quantities can be validly regarded as zero. If the circuitry that follows a diode is not 'aware' that it isn't zero (when it is near zero) then it IS zero. In digital circuitry, we use 0 and 1 quite happily when neither of those voltage levels is actually 0 or 1.

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Gold Member
This is the world of Real Engineering, in which insignificant quantities can be validly regarded as zero. ... In digital circuitry, we use 0 and 1 quite happily when neither of those voltage levels is actually 0 or 1.

I'm thinking that since this is a "Lecture Series on Electronics For Analog Signal Processing", the OP will need to understand the diode curve sooner or later.