# Diodes & Rectifiers: Homework Solutions

• Cocoleia
In summary, the homework asks for V0(t), not VD(t). I found a graph in the textbook that had Vs and VI on the same axis, but I don't know what a transfer characteristics is. I think if it is forward then you put a short circuit and if it is reverse you put an open circuit? But I don't know how that translates on the graph.
Cocoleia

## Homework Statement

I am practicing problems like this:

where Vs=10V, R=2kohm, they say it is like a battery + ideal diode with VD=0.7V
I have to sketch the transfer characteristic Vo=f(Vs) and draw the waveform of Vo(t)

## The Attempt at a Solution

I am really unsure how to go about these problems. I have the answer, I just don't know they got to it. Can someone explain please?

I am also unsure of how to draw the waveform, but I think it could be something like:

Is this correct?

[/B]

VI = Vs?

Where did you take the voltage drop at the diode into account?

The problem statement asks for V0(t), not VD(t).

mfb said:
VI = Vs?

Where did you take the voltage drop at the diode into account?

The problem statement asks for V0(t), not VD(t).
I do not understand, I just found this graph in my textbook. Can you explain even the first part, since it too is just a drawing from the book.

Your first plot has an axis label VI. What is that?
Where did you find that graph? The symbols should be introduced somewhere.

The diode won't conduct until there is a 0.7 V potential difference between its sides.

mfb said:
Your first plot has an axis label VI. What is that?
Where did you find that graph? The symbols should be introduced somewhere.

The diode won't conduct until there is a 0.7 V potential difference between its sides.
VI is supposed to be Vs, sorry the example in the book had different variables than my question. I don't understand what a transfer characteristics is. I think if it is forward then you put a short circuit and if it is reverse you put an open circuit? But I don't know how that translates on the graph

Cocoleia said:
VI is supposed to be Vs, sorry the example in the book had different variables than my question. I don't understand what a transfer characteristics is. I think if it is forward then you put a short circuit and if it is reverse you put an open circuit? But I don't know how that translates on the graph
Is your voltage source ac or dc? You have shown it as dc but you have drawn the waveforms assuming it to be ac.

cnh1995 said:
Is your voltage source ac or dc? You have shown it as dc but you have drawn the waveforms assuming it to be ac.
I don't know, I guess it is DC?

Cocoleia said:
I don't know, I guess it is DC?
Well, go with dc since you have shown it that way.
So, your dc source is variable, say from 0V to 10V. The diode drop is assumed to be 0.7V. What can you say about the i-v characteristic of the diode from this? Can you plot the diode voltage first, as a function of the input dc voltage?

cnh1995 said:
Well, go with dc since you have shown it that way.
So, your dc source is variable, say from 0V to 10V. The diode drop is assumed to be 0.7V. What can you say about the i-v characteristic of the diode from this? Can you plot the diode voltage first, as a function of the input dc voltage?
Would it be forward biased and therefore a short circuit ? I'm not sure about the plot

Cocoleia said:
they say it is like a battery + ideal diode with VD=0.7V

Now for input voltage Vs≤0.7V, what is the diode voltage? For Vs>0.7V, what is the diode voltage?

cnh1995 said:
View attachment 111968
Now for input voltage Vs≤0.7V, what is the diode voltage? For Vs>0.7V, what is the diode voltage?
When it is less, it is 0. When it is more it is 0.7?

Cocoleia said:
When it is less, it is 0. When it is more it is 0.7?
We are talking about "voltage" across the diode. If Vs=0.5V, what is the voltage across the diode? Use the above graph. You are right about Vs>0.7V.
Cocoleia said:
I don't know, I guess it is DC?
Cocoleia said:
draw the waveform of Vo(t)
It seems that the input is supposed to be ac, since the output voltage is a function of time. With dc input, you can draw the transfer characteristic but I don't think they are expecting you to draw Vo(t) for dc input.

Last edited:
cnh1995 said:
We are talking about "voltage" across the diode. If Vs=0.5V, what is the voltage across the diode? Use the above graph. You are right about Vs>0.7V.It seems that the input is supposed to be ac, since the output voltage is a function of time. With dc input, you can draw the transfer characteristic but I don't think they are expecting you to draw Vo(t) for dc input.
I am unsure on how to draw transfer characteristics and the Vo(t), it was never explained to me in class.

Cocoleia said:
I am unsure on how to draw transfer characteristics and the Vo(t), it was never explained to me in class.
Ok. We can work that out here. We will take the voltage source as AC, with magnitude 10V.

What is the volage across the diode when Vs<=0.7V? Refer the graph in #10. Once you know that, you can draw the transfer characteristic easliy.

Or answer this: If Vs<=0.7V, what is the voltage across the 2k resistor?

Cocoleia said:
VI is supposed to be Vs, sorry the example in the book had different variables than my question. I don't understand what a transfer characteristics is. I think if it is forward then you put a short circuit and if it is reverse you put an open circuit? But I don't know how that translates on the graph
There is still the resistor.

At V0=-10 V, analyze the circuit. What is the voltage at the resistor?
At V0=-5 V, analyze the circuit. What is the voltage at the resistor?
At V0=0 V, analyze the circuit. What is the voltage at the resistor?
At V0=+5 V, analyze the circuit. What is the voltage at the resistor?
At V0=+10 V, analyze the circuit. What is the voltage at the resistor?
With those values (and suitable intermediate values), you can plot the voltage at the resistor as function of the source voltage. That is the curve you need in the first part.

I would expect your voltage source to be AC, otherwise plotting things as function of time is useless.

cnh1995 said:
Ok. We can work that out here. We will take the voltage source as AC, with magnitude 10V.

What is the volage across the diode when Vs<=0.7V? Refer the graph in #10. Once you know that, you can draw the transfer characteristic easliy.

Or answer this: If Vs<=0.7V, what is the voltage across the 2k resistor?
mfb said:
There is still the resistor.

At V0=-10 V, analyze the circuit. What is the voltage at the resistor?
At V0=-5 V, analyze the circuit. What is the voltage at the resistor?
At V0=0 V, analyze the circuit. What is the voltage at the resistor?
At V0=+5 V, analyze the circuit. What is the voltage at the resistor?
At V0=+10 V, analyze the circuit. What is the voltage at the resistor?
With those values (and suitable intermediate values), you can plot the voltage at the resistor as function of the source voltage. That is the curve you need in the first part.

I would expect your voltage source to be AC, otherwise plotting things as function of time is useless.
Ok thank you, I understand now.

## 1. What is the difference between a diode and a rectifier?

A diode is a two-terminal electronic component that allows current to flow in one direction while blocking it in the other direction. A rectifier is a circuit that converts AC (alternating current) to DC (direct current) by using one or more diodes.

## 2. How does a diode work?

A diode works by having a P-N junction, which is the interface between a P-type semiconductor (with positively charged carriers) and an N-type semiconductor (with negatively charged carriers). When a voltage is applied, the P-N junction allows current to flow in one direction and blocks it in the other direction due to the built-in potential barrier.

## 3. What is the purpose of a rectifier?

The purpose of a rectifier is to convert AC (alternating current) to DC (direct current). This is important for many electronic devices that require DC to function properly, such as computers, televisions, and phones.

## 4. What are the different types of rectifiers?

There are three main types of rectifiers: half-wave, full-wave, and bridge. Half-wave rectifiers use only one diode and are the simplest type, but they have a lower efficiency. Full-wave rectifiers use four diodes and have a higher efficiency. Bridge rectifiers use four diodes as well, but they are arranged in a different configuration for better efficiency.

## 5. What are some common applications of diodes and rectifiers?

Diodes and rectifiers have a wide range of applications, including power supplies, battery charging, voltage regulation, signal demodulation, and LED lighting. They are also used in electronic circuits to protect against reverse polarity and voltage spikes.

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