# Voltage Across Diode Pair: Ideal Source | Vin Positive Half

• anhnha
In summary, I think you are saying that when you short an ideal voltage source, you don't get a paradox.
anhnha

If the diodes are ideal, there is no reverse leakage current, & no forward voltage drop. If the ac source is an ideal current source, the voltage across the diode pair is always zero, since 1 of the 2 diodes is forward biased.

If the ac source is an ideal voltage source, you get a paradox. A zero resistance perfect voltage source is loaded by a perfect diode with zero voltage drop, resulting in the current ramping up towards infinity.

Claude
I want to ask about the bold part. In the case, what is the voltage across the diode pair, zero or voltage source (Vin) when it is in positive half?

I=E/R and division by zero is undefined. That's the cop-out that I'd use.

Basically, you are asking what happens when you short an ideal voltage source. No need for a diode.

How about an ideal current source in series with an ideal voltage source?

The answer is : sorry, does not compute! Qualifies as a paradox.

Thank you.
Basically, you are asking what happens when you short an ideal voltage source. No need for a diode.
Yup.
Consider a circuit including an ideal voltage source, V and an ideal wire is connected across two ends of the source.
Let's call the voltage between two ends of the ideal wire v.
$$v = \lim_{R \rightarrow 0} i.R = \lim_{R \rightarrow 0} \frac{V}{R} . R = V$$

(by apply L'Hospital's Rule for 0/0)
How about an ideal current source in series with an ideal voltage source?

The answer is : sorry, does not compute! Qualifies as a paradox.
Can you tell me why this is a paradox?

Last edited:
anhnha said:
Can you tell me why this is a paradox?
No idea how I came to that conclusion. I should go back and edit it out. LOL

Applying limits is the only valid approach for dealing with infinity, but I can't help you with whether this is a valid application of L'Hospital's Rule.

Actually, thinking about it a bit, I think you nailed it. In the limit it makes sense.

A current source connected to a voltage source is no paradoxat all. One will deliver power to the other. Connect a 1 volt source to a 1 amp source in a loop. The relative polarity determines which which one delivers and which one receives power.
Claude

didn't I just say that I was wrong? Which doesn't seem to be something you are capable of.

## 1. What is the purpose of a diode pair in an ideal source for a positive Vin half?

In an ideal source, a diode pair is used to prevent any reverse current from flowing through the circuit, ensuring that the voltage remains constant in the positive Vin half. This allows for a more stable and accurate voltage output.

## 2. How does a diode pair affect the overall voltage across the circuit?

A diode pair has a voltage drop of approximately 0.7 volts, so it will decrease the overall voltage across the circuit by this amount. However, this decrease is necessary to prevent any reverse current and maintain a stable voltage output.

## 3. Can a diode pair be used with any type of ideal source?

Yes, a diode pair can be used with any type of ideal source as long as the voltage polarity is correct. It is a common component in many electronic circuits and can be easily incorporated into the design.

## 4. What happens if the diode pair is connected in reverse polarity?

If the diode pair is connected in reverse polarity, it will not function properly and may cause damage to the circuit. The diodes will not be able to prevent reverse current and the voltage output may become unstable.

## 5. Are there any limitations to using a diode pair in an ideal source?

One limitation of using a diode pair in an ideal source is that it can only prevent reverse current up to a certain threshold. If the reverse current exceeds this threshold, the diodes will not be able to protect the circuit and may fail. Additionally, the diode pair may introduce a small voltage drop, which may affect the overall accuracy of the voltage output.

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