Hi everyone.

I have a theorical question about using a diode in series with a resistor.

Let's say I have a AC source of 100V and connected to it I have a string of 10 resistors in series, each one of 1k. In each resistor there would be a voltage drop of 10 volts. Now I add one diode In series. What should be the max reverse voltage of that diode?

I mean, if it is just the diode connected to the AC source should be at least 100v. But since it is a diode with a string of resistors I'm not sure. It is just a theorical question, I'm not looking to apply to anything, I'm just curious about that.

Thank you. Best regards

 

Hi everyone.

I have a theorical question about using a diode in series with a resistor.

Let's say I have a AC source of 100V and connected to it I have a string of 10 resistors in series, each one of 1k. In each resistor there would be a voltage drop of 10 volts. Now I add one diode In series. What should be the max reverse voltage of that diode?

I mean, if it is just the diode connected to the AC source should be at least 100v. But since it is a diode with a string of resistors I'm not sure. It is just a theorical question, I'm not looking to apply to anything, I'm just curious about that.

Thank you. Best regards

That's a very good question.
The answer is 140 V.

 

Let's say I have a AC source of 100V and connected to it I have a string of 10 resistors in series, each one of 1k. In each resistor there would be a voltage drop of 10 volts. Now I add one diode In series. What should be the max reverse voltage of that diode?

The 10V is only dropped across each resistor when the diode is conducing current in the forward direction.
In the reverse direction there is no significant current so no voltage drop and the full AC peak voltage appears across the diode.

 

Thank you for your answers.

Yes, I forgot to mention it is was peak voltage or RMS.

In any case, now is clear. But a new question came to my mind. Lets say is a DC power source of 100V and it is connected just in foward direction, what should beparamters of that diode?

Thank you

 

Thank you for your answers.

Yes, I forgot to mention it is was peak voltage or RMS.

In any case, now is clear. But a new question came to my mind. Lets say is a DC power source of 100V and it is connected just in foward direction, what should beparamters of that diode?

Thank you

If the diode is always forward biased, the maximum reverse voltage of the diode does not matter.

 

Lets say is a DC power source of 100V and it is connected just in foward direction, what should beparamters of that diode?

If it's never reverse biased, then what's the purpose of the diode?

 

Hi everyone.

I have a theorical question about using a diode in series with a resistor.

Let's say I have a AC source of 100V and connected to it I have a string of 10 resistors in series, each one of 1k. In each resistor there would be a voltage drop of 10 volts. Now I add one diode In series. What should be the max reverse voltage of that diode?

I mean, if it is just the diode connected to the AC source should be at least 100v. But since it is a diode with a string of resistors I'm not sure. It is just a theorical question, I'm not looking to apply to anything, I'm just curious about that.

Thank you. Best regards

In "theory", a diode has no max reverse voltage -- it is a theoretical component which conducts current when forward biased and blocks current when reverse biased. So the question has to be considered from the "practical" side of the house. So there are two questions -- what is the maximum reverse voltage that the diode sees, and what is the minimum reverse voltage that the diode should be rated for.

If the diode has negligible reverse leakage current, then when reverse biased there will be negligible current in the resistors and, hence, negligible voltage drop across them. Therefore, all of the voltage will be dropped across the diode. If 100 V is the amplitude of the AC source, then the peak reverse voltage seen by the diode would be 100 V. On paper, you need a diode that has a minimum reverse voltage rating of 100 V. In practice, using such a diode would be risky. A common rule of thumb for many things is to use a safety factor of at least two wherever practicable, so use a minimum reverse rating of at least 200 V. Where a factor of two isn't practical, proceed carefully.

 

Thank you all.

No real purpose crutschow , I just was curious, I´m learning electronics and I like to understand everything. But now everything is clear. As always in this great forum