# V-I Characteristics of Forward/Reverse Bias Diodes

• TyErd
In summary, circuit 2 would be used to measure the V-I characteristics of a forward biased diode, as the voltmeter has a higher resistance compared to the component in the circuit. For a reverse biased diode, circuit 1 would be more suitable as the voltmeter has a lower resistance, allowing for accurate measurement of the V-I characteristics. The resistance of a diode depends on the direction of the applied potential difference, with a higher resistance in reverse bias and a lower resistance in forward bias.

## Homework Statement

Which of the following circuits in the diagram provided would you use to measure the V-I characteristics of a:
a. Forward biased diode i.e Vx>Vy? Explain.
b. Reverse biased diode i.e Vx<Vy? Explain.

## Homework Equations

None required I think.

## The Attempt at a Solution

There is no working out I believe, just one of those theory type problems.

#### Attachments

• circuit4.JPG
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If you have to choose between the two, then the 2 important points you need to consider in answering this are
1. A voltmeter should have a very much higher resistance than the component it is placed across
2. How does the resistance of a forward biased diode compare with the resistance of a reverse biased diode?

okay well there's no resistance in a diode correct? there the voltmeter will have a higher resistance. In a reversed biased diode there is no current flowing thus also no resistance anywhere in the circuit right? whereas in a forward biased diode there will be a current thus resistance along its components.

TyErd said:
okay well there's no resistance in a diode correct?
There is resistance: but the resistance of a diode depends on the direction of the applied pd.
In a reversed biased diode there is no current flowing thus also no resistance anywhere in the circuit right?
Why do you say that if no current flows there is no resistance?
If you connect a battery across a component and no current flows through it, would you conclude that the component has no resistance or a very high resistance?
whereas in a forward biased diode there will be a current thus resistance along its components.
There will be some resistance, but how does this compare with the resistance in reverse bias?

Stonebridge said:
Why do you say that if no current flows there is no resistance?
If you connect a battery across a component and no current flows through it, would you conclude that the component has no resistance or a very high resistance?

Oh I see, so there would be a very high resistance in a reversed biased diode because no current would pass through it. Okay I understand that bit.
And the resistance in a forward biased diode is far less than a reversed biased diode because current is actually passing through.
Anyway getting back to the question, if the didoe is forward biased, then circuit 2 is the only one wherethe voltmeter would be greater than what it is placed across because it has the least resistance, and if it is reversed biased then voltmeter would be below the resistane of the diode. Is this correct? or is there more than I should look at?

You are correct.
In circuit 2 the voltmeter would be fine in that position for a forward biased diode. The V-meter will have a much greater resistance than the component it is placed across.
Circuit 1 is better for the reverse bias diode.

## 1. What is the purpose of studying the V-I characteristics of forward/reverse bias diodes?

The V-I characteristics of a diode refer to the relationship between the voltage applied across the diode and the resulting current flow through it. This is important to study because it helps us understand how the diode behaves under different bias conditions and how it can be used in electronic circuits.

## 2. What is the difference between forward and reverse bias in a diode?

In forward bias, the diode is connected in such a way that the positive terminal of the voltage source is connected to the anode (positive end) of the diode, and the negative terminal of the voltage source is connected to the cathode (negative end) of the diode. This allows current to flow through the diode. In reverse bias, the polarity of the voltage source is reversed, causing very little to no current to flow through the diode.

## 3. How does the V-I curve of a forward-biased diode differ from that of a reverse-biased diode?

In a forward-biased diode, the V-I curve shows a gradual increase in current as the voltage increases. Once a certain threshold voltage is reached, the current increases rapidly. In a reverse-biased diode, the V-I curve shows very little current flow until a certain breakdown voltage is reached, after which the current increases rapidly.

## 4. Why does the current in a diode increase rapidly once the threshold voltage is reached in forward bias?

Once the threshold voltage is reached in a forward-biased diode, the majority carriers (electrons in an N-type semiconductor or holes in a P-type semiconductor) are able to overcome the potential barrier at the junction and start to flow through the diode, resulting in a rapid increase in current.

## 5. What is the significance of the reverse breakdown voltage in a diode?

The reverse breakdown voltage is the voltage at which the diode experiences a sudden increase in current flow in the reverse direction. This is an important parameter to consider when designing electronic circuits, as exceeding this voltage can damage the diode and affect the circuit's functionality.

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