Understanding Reverse Bias Diode Output Voltage

In summary, when the AC source voltage swings negative, the forward bias diode allows current to flow in both directions, resulting in a negative output.
  • #1
Petrucciowns
74
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The link provided shows two cases of reverse bias Diodes. From my understanding a reverse bias diode is supposed to block the voltage from reaching the output. So from the following picture wouldn't both of the outputs be 0v. I know that the answers in the diagram are correct because I did them in class, but I don't understand why the voltage across the output on the second picture is - 4.3 volts. I understand the voltage drop across the diode is .7 and the output of a circuit with a forward bias diode would be source-.7 ,but I just don't understand this.


http://img268.imageshack.us/img268/5602/reversebias.jpg
 
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  • #2
Petrucciowns said:
The link provided shows two cases of reverse bias Diodes. From my understanding a reverse bias diode is supposed to block the voltage from reaching the output. So from the following picture wouldn't both of the outputs be 0v. I know that the answers in the diagram are correct because I did them in class, but I don't understand why the voltage across the output on the second picture is - 4.3 volts. I understand the voltage drop across the diode is .7 and the output of a circuit with a forward bias diode would be source-.7 ,but I just don't understand this.


http://img268.imageshack.us/img268/5602/reversebias.jpg

In the diagram with the AC source, the diode is not always reverse biased, right?
 
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  • #3
I think you're right, because the current flows in both directions does that make the output negative if its in the reverse bias position? If so what's the reasoning for this?
 
  • #4
Petrucciowns said:
I think you're right, because the current flows in both directions does that make the output negative if its in the reverse bias position? If so what's the reasoning for this?

When the AC source voltage swings negative, that forward biases the diode for VAC < -0.7V.

Write the equation for the output voltage as a function of time for the AC source, and figure out where the forward and reverse bias regions are for the diode. That will leave some voltage on the resistor.

However, this problem is a bit too simplified. There will only be -4.3V on the output resistor load at what point in the AC source waveform drive?
 
  • #5
I see, when the source switches to negative the diode becomes forward bias. The .7 volts across the diode becomes negative because of the negative source, and -5 volts peak - .7 volts peak = -4.3v across the resistor.

Is this correct?
 
  • #6
Petrucciowns said:
I see, when the source switches to negative the diode becomes forward bias. The .7 volts across the diode becomes negative because of the negative source, and -5 volts peak - .7 volts peak = -4.3v across the resistor.

Is this correct?

Very good. And you see that is only true at the peak negative excursion of the AC supply, right? So plot the voltage across the resistor as a function of time, versus the output of the AC source. That will help to cement the concepts in your mind.
 
  • #7
Yes, I understand that now. I hope to see you on some of my future posts, because I will definitely have more!
 

FAQ: Understanding Reverse Bias Diode Output Voltage

What is a reverse bias diode?

A reverse bias diode is a type of diode where the external voltage is applied in the opposite direction to the normal flow of current. This results in a depletion region forming within the diode, preventing the flow of current through it.

How does reverse bias affect the output voltage of a diode?

When a diode is reverse biased, the output voltage will be equal to the breakdown voltage of the diode. This is the voltage at which the diode will start to conduct in the reverse direction. Therefore, the output voltage of a reverse biased diode will remain constant until the breakdown voltage is exceeded.

What factors affect the reverse bias output voltage of a diode?

The reverse breakdown voltage of a diode is determined by the doping concentration and width of the depletion region. A higher doping concentration and narrower depletion region will result in a higher breakdown voltage. Temperature also plays a role, as an increase in temperature can lower the breakdown voltage.

How is reverse bias diode output voltage measured?

Reverse bias diode output voltage can be measured using a voltmeter connected in parallel with the diode. The voltmeter should be set to measure DC voltage, and the negative lead should be connected to the anode of the diode and the positive lead to the cathode.

What are the applications of reverse bias diode output voltage?

Reverse bias diode output voltage is commonly used in voltage regulation circuits, surge protection, and in the generation of high voltage signals. It is also used in photodiodes and solar cells to convert light energy into electrical energy.

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