Diodes & Rectifiers: Homework Solutions

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SUMMARY

The discussion centers on solving homework problems related to diodes and rectifiers, specifically analyzing a circuit with a DC voltage source of 10V and a resistor of 2k ohms. Participants clarify the importance of the diode's forward voltage drop of 0.7V and how it affects the transfer characteristics and output waveform. The conversation emphasizes the need to distinguish between AC and DC sources when plotting voltage characteristics and understanding the behavior of the diode in the circuit.

PREREQUISITES
  • Understanding of diode characteristics, specifically the forward voltage drop (VD=0.7V).
  • Knowledge of basic circuit analysis involving resistors and voltage sources.
  • Familiarity with transfer characteristics in electronic circuits.
  • Ability to differentiate between AC and DC voltage sources.
NEXT STEPS
  • Learn how to sketch transfer characteristics for diode circuits.
  • Study the behavior of ideal diodes in forward and reverse bias conditions.
  • Explore the concept of voltage across resistors in series with diodes.
  • Investigate the differences between AC and DC waveforms in circuit analysis.
USEFUL FOR

Students studying electronics, electrical engineers, and anyone seeking to understand diode behavior in circuits, particularly in relation to rectification and waveform analysis.

Cocoleia
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Homework Statement


I am practicing problems like this:
upload_2017-1-21_15-45-27.png

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)

Homework Equations

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?
upload_2017-1-21_15-49-10.png

I am also unsure of how to draw the waveform, but I think it could be something like:
upload_2017-1-21_15-50-17.png

Is this correct?

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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
 
  • #10
Cocoleia said:
they say it is like a battery + ideal diode with VD=0.7V
images (4).jpg

Now for input voltage Vs≤0.7V, what is the diode voltage? For Vs>0.7V, what is the diode voltage?
 
  • #11
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?
 
  • #12
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:
  • #13
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.
 
  • #14
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.

You are right about Vs>0.7V.
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?
 
  • #15
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.
 
  • #16
cnh1995 said:
Ok. We can work that out here. We will take the voltage source as AC, with magnitude 10V.

You are right about Vs>0.7V.
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.
 

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