Calculating Current in a Diode Circuit with Given Voltages

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Discussion Overview

The discussion revolves around calculating the current through a resistor in a diode circuit given specific voltages at two points. Participants explore the implications of diode characteristics, including barrier voltage, and how these affect circuit behavior.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant requests help calculating the current through a resistor with given voltages, VA=5V and VB=3V.
  • Another participant expresses difficulty understanding the provided circuit image and questions the clarity of the information.
  • Assuming a barrier voltage of 0.7V for the diodes is suggested as a starting point, leading to a discussion about the behavior of the diodes in the circuit.
  • One participant calculates that if VA=VB=5V and the diodes have a barrier voltage of 0.7V, the voltage across the resistor would be 4.3V.
  • It is noted that with the given conditions, only diode A conducts while diode B is reverse biased, resulting in a current of 4.3 mA through the resistor.
  • Another participant connects the circuit's behavior to logic gates, suggesting it functions like an OR gate based on the voltage levels defined.

Areas of Agreement / Disagreement

There is no consensus on the initial conditions, as participants propose different scenarios for the voltages at VA and VB. Some participants agree on the calculations involving the barrier voltage of the diodes, while others express uncertainty about the clarity of the circuit image and its implications.

Contextual Notes

Participants mention the potential for contradictions in diode behavior based on the assumed conditions, indicating that the discussion may be limited by the clarity of the circuit diagram and the assumptions made about the diode characteristics.

Who May Find This Useful

This discussion may be useful for students learning about diode circuits, those interested in circuit analysis, and individuals exploring the relationship between electronic components and logic gates.

Proff Young
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http://img545.imageshack.us/img545/7113/diodeq.jpg
In the circuit shown in the figure (c) above if VA=5V and VB=3V, calculate the current through RL.

Please explain.
Thank you
 
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I just finished a unit on circuits in class so I wanted to try this out, but the picture you have provided isn't working.
 
hope the image works now :)
 
Here you go:

yhowKZh.png
 
Thank you but pardon me. I cannot grasp what is written on the image. It's not clear. And what if the diodes have a Barrier voltage of 0.7V each.
Thank you.
 
I'm sorry, but I thought you preferred really really poor picture quality. Anyway, assuming a diode voltage drop of 0.7V is a good start because by doing that you'll soon enough run into a contradiction (of sorts) and see that one of the diodes is reversed biased. Think about it some more and you'll see it, I'm sure.

EDIT: SchemeIt is a good alternative for drawing circuits. It's free and very easy to use. Check it out!
 
Last edited:
I got the idea thank you. If VA=VB=5V and if the diodes have a barrier voltage of 0.7V each then voltage across the resistor will be 4.3V. Am I right?
 
Assuming you're using standard silicon diodes (voltage drop about 0.7 V), the current that flows through RL is 4.3 mA, only diode A conducts and diode B is reverse biased.
 
Proff Young said:
If VA= VB= 5V and if the diodes have a barrier voltage of 0.7V each then voltage across the resistor will be 4.3V. Am I right?
Yes. By the way, your circuit is also functionally equal to a _____ gate. Do you know which one?

Logic_gate.gif


P.S Let a logic '1' be any voltage > 4.3V and a logic '0' be any voltage < 4.3V. The gate output 'F' from the figure above would be the node between the diodes and load resistor.
 
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  • #10
Gordianus said:
Assuming you're using standard silicon diodes (voltage drop about 0.7 V), the current that flows through RL is 4.3 mA, only diode A conducts and diode B is reverse biased.

Thank you.
 
  • #11
gnurf said:
Yes. By the way, your circuit is also functionally equal to a _____ gate. Do you know which one?

Logic_gate.gif


P.S Let a logic '1' be any voltage > 4.3V and a logic '0' be any voltage < 4.3V. The gate output 'F' from the figure above would be the node between the diodes and load resistor.

I hope it is the OR gate. Thank you for helping, I have a better idea now.
 

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