voltage drop across ideal diode

Both diodes are ideal, can we find what is potential drop acoss each diode in this situation, if yes what is potential difference across each diode

• What have you done to solve it? Commented Jul 12, 2020 at 17:52
• Diode D1 will be obviously reverse biased, even if we know D1 reverse biased it does not give any idea about what will be the potential drop across it, all we can say here is the combined potential drop across the diodes will be 10V. That is all I understand , if anyone can tell me if I am missing something then that will be helpful Commented Jul 12, 2020 at 17:59
• What do you understand by 'ideal'?
– Chu
Commented Jul 12, 2020 at 18:02
• It behaves like a switch in FB short circuit and RB open circuit Commented Jul 12, 2020 at 18:07
• OK, so draw the diagram with two switches. Now what can you see?
– Chu
Commented Jul 12, 2020 at 18:08

If these are ideal semiconductor diodes (e.g. a pn junction diode), then the current follows the equation I = I0(exp(q.V/kT) -1). As with most electronics there are some approximations here. When reverse biased as D1 is, the reverse current is I0. Typically this is very small (nA). This flows through D2, and using the equation above results in q.V/kT = ln(2) = 0.69. At room temperature this means that the voltage across D2 is 0.69*kT/q, or about 18 mV. The voltage drop across the 1k resistor will be negligible (uV).

Yes, once you clarify what you mean by "ideal diode" then the voltages can be found easily using KVL and Ohm's Law.

I think every definition of an "ideal" diode says that there is no current flow through a reverse-biased diode. So, if one of the diodes is reverse biased you should be able to easily determine the voltage across the other diode using KVL and Ohm's Law.

Unfortunately, the forward bias behavior of an "ideal diode" is not something that is universally defined. Some people say that the forward voltage across an ideal diode is 0V, others like to say that it is 0.7V or so.

You might also need to think about what your ideal diode does under zero bias. How much current flows if the voltage across the diode is zero? What is the voltage across the diode if zero current flows through it?

• Ideal diode means zero voltage drop across diode in FB ,if you are talking about 0.7V drop across diode that is in the case of constant voltage drop model of a diode, So, if D1 is RB voltage drop across it will be 10V and across D2 zero Commented Jul 12, 2020 at 18:54
• @user204283 your instructor might have defined things that way, but you can’t expect everybody on the internet to be using the same definitions you are in this case. Commented Jul 12, 2020 at 20:19
• We use different models of diode for different situations, you can search for diode models, anywhere it's not about my instructor Commented Jul 12, 2020 at 20:23
• Yes, we use different models of the diode for different situations, and the phrase "ideal diode" can mean at least two of those models, as well as two different practical circuits used for different purposes. If you don't specify which of those things you mean by "ideal diode", it is not possible to answer you. :-) Commented Jul 13, 2020 at 0:56