Question about Diode potential of anode with respect to cathode

Thread Starter

skyline1397

Joined Sep 13, 2017
13
If I have an ideal diode and I apply -9 V in the anode (P-type junction) and -10 V at the cathode (P-type junction) would the diode become forward biased??
I get that the current-voltage relationship of an ideal diode shows that as long as the voltage across the ideal diode is non-negative i.e. V≥0, the ideal diode looks like a short circuit but the graphs refer to V. Is this V equal to V(anode)-V(cathode)?
Where V potential of anode with respect to cathode
 

JUNELER

Joined Jul 13, 2015
183
Hi,
A diode is called a P-N junction ,where the anode is supplied a positive voltage and the cathode is negative ,it will be called
a forward bias, a current flow . A voltage drop of at least 0.7v across the junction.

When you reverse the polarity across it ,it will be called reverse bias and no current flow ,no voltage drop.
 

WBahn

Joined Mar 31, 2012
29,930
If I have an ideal diode and I apply -9 V in the anode (P-type junction) and -10 V at the cathode (P-type junction) would the diode become forward biased??
I get that the current-voltage relationship of an ideal diode shows that as long as the voltage across the ideal diode is non-negative i.e. V≥0, the ideal diode looks like a short circuit but the graphs refer to V. Is this V equal to V(anode)-V(cathode)?
Where V potential of anode with respect to cathode
If the diode is ideal and if it looks like a short circuit circuit when forward biased, then it is not possible to get any positive voltage across it (where, as you surmised, V is the voltage of the anode relative to the cathode). Look at the I-V characteristic for an ideal diode. It is a flat line at zero current for all voltages less than or equal to zero and it is a vertical line at zero voltage for all currents greater than or equal to zero. If you look at the graph and try to find the current for a voltage of +1 V across it, you will see that the characteristic is undefined there.
 

WBahn

Joined Mar 31, 2012
29,930
Hi,
A diode is called a P-N junction ,where the anode is supplied a positive voltage and the cathode is negative ,it will be called
a forward bias, a current flow . A voltage drop of at least 0.7v across the junction.
What if it is a germanium diode?

Or, as explicitly stated by the TS, what if it is an ideal diode?

Even if it is a real silicon diode, you will have current flowing at less than 0.7 V, possibly a significant amount.

When you reverse the polarity across it ,it will be called reverse bias and no current flow ,no voltage drop.
No voltage drop? Are you sure about that?
 

JUNELER

Joined Jul 13, 2015
183
Hi,
just for info.....

measured the diode using the digital multimeter and select the diode function.
At forward bias the readings is 0.4v to max 0.7v , it depends on the diode specs(generic part number) While at reverse OL is shown.
This is a simple test .
 

WBahn

Joined Mar 31, 2012
29,930
Hi,
just for info.....

measured the diode using the digital multimeter and select the diode function.
At forward bias the readings is 0.4v to max 0.7v , it depends on the diode specs(generic part number) While at reverse OL is shown.
This is a simple test .
Now repeat the test using an ideal diode.

Not such a simple test.
 
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