Easy zener diode circuit questions

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Discussion Overview

The discussion revolves around calculating the current through a zener diode and load in a circuit with varying supply voltages of 10V and 15V. Participants explore the implications of using the correct zener voltage in their calculations and the conditions under which the zener diode operates effectively.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Initial calculations for the zener and load currents at 10V and 15V supply voltages are presented, but the participant expresses confusion about their correctness.
  • Some participants assert that the calculations appear correct, while others suggest that the zener voltage should be 5.1V instead of 5V, which affects the results.
  • A participant explains that if the voltage after the resistor is less than the zener voltage, the zener will not conduct, effectively behaving as if it is removed from the circuit.
  • There is a discussion about whether to use 5V or 5.1V in calculations, with a consensus emerging that 5.1V should be used.
  • Revised calculations using 5.1V lead to a negative current through the zener for the 10V supply, prompting questions about the interpretation of this result.
  • Some participants clarify that a negative current indicates the zener is not conducting, and suggest checking the potential at the zener's node to confirm its operational status.
  • There is a debate about whether calculations should be shown in a test to demonstrate understanding, even if the zener does not conduct.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of using 5.1V for the zener voltage in calculations. However, there is disagreement regarding the interpretation of results, particularly concerning the implications of negative current and the necessity of showing calculations in a test scenario.

Contextual Notes

Participants note that the calculations depend on the assumption that the zener will conduct, which is not the case for the 10V supply scenario. The discussion highlights the importance of verifying the operational conditions of the zener diode before proceeding with calculations.

  • #31
nothing909 said:
I don't understand what you mean. :/
If your load current is 5 mA, what is the voltage V1 in the following diagram?
upload_2016-11-5_16-45-18.png


nothing909 said:
Can I ask one more question about this circuit. What is zener voltage supposed to be? 9.1?
Yes.
 
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  • #32
gneill said:
If your load current is 5 mA, what is the voltage V1 in the following diagram?
View attachment 108524Yes.
The voltage is 5V.

And just quickly about that second circuit, just so I know this is correct. The reading on the voltmeter would be 9.1V and the reading on the ammeter would be:

Voltage across resistor = 20 - 9.1 = 10.9V

Reading on ammeter = 10.9/10000 = 1.09mA
 
  • #33
nothing909 said:
The voltage is 5V.
Correct. Which is less that the zener voltage of 5.1 V. So the zener placed there would not conduct. That's the test I was urging you to carry out.
And just quickly about that second circuit, just so I know this is correct. The reading on the voltmeter would be 9.1V and the reading on the ammeter would be:

Voltage across resistor = 20 - 9.1 = 10.9V

Reading on ammeter = 10.9/10000 = 1.09mA
Yes, that looks good.
 
  • #34
gneill said:
Correct. Which is less that the zener voltage of 5.1 V. So the zener placed there would not conduct. That's the test I was urging you to carry out.

Yes, that looks good.
okay, great, thanks very much for all your help. :)
 

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