Why Isn't the Drain Voltage in a MOSFET Circuit Equal to 1.8V?

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Discussion Overview

The discussion revolves around understanding why the drain voltage in a MOSFET circuit is not equal to 1.8V, despite the expectation that the resistor should receive the entire voltage. The scope includes conceptual clarification and technical reasoning related to MOSFET operation and circuit analysis.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question why the drain voltage is not simply equal to 1.8V, suggesting that the resistor should receive the entire voltage.
  • One participant notes that the drain voltage would be 1.8V only if the FET were completely non-conducting (cut off), prompting a query about the operating state of the FET.
  • Another participant reflects on their misunderstanding, indicating that they were considering the terminals of the MOSFET independently and did not account for the influence of the gate terminal on the voltage.
  • A later reply emphasizes the importance of using given parameters to determine the operating mode of the FET and to find its DC operating point.
  • One participant points out a contradiction in the reasoning presented regarding the voltage assumption.

Areas of Agreement / Disagreement

Participants express differing views on the assumptions regarding the drain voltage and the operational state of the MOSFET. No consensus is reached on the correct interpretation of the circuit behavior.

Contextual Notes

Limitations include potential misunderstandings of circuit diagrams and the need for specific parameters to accurately determine the MOSFET's operating mode and drain voltage.

CoolDude420
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Homework Statement


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Homework Equations

The Attempt at a Solution



We have been given this question along with some parameters.
It asks for find drain votltage, my question is why isn't the drain voltage just equal to 1.8? I mean the resistor should be getting the entire 1.8V so?
 
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CoolDude420 said:
We have been given this question along with some parameters.
It asks for find drain votltage, my question is why isn't the drain voltage just equal to 1.8? I mean the resistor should be getting the entire 1.8V so?
It would be 1.8 V if the FET were cut off (completely non-conducting). Do you have reason to believe that this is the case?
 
gneill said:
It would be 1.8 V if the FET were cut off (completely non-conducting). Do you have reason to believe that this is the case?
no. Ah, I keep considering the branches of the terminals of the MOSFET independent due to the gap in the circuit diagram of it. So basically because of the gate terminal I can't just assume its 1.8V
 
CoolDude420 said:
no. Ah, I keep considering the branches of the terminals of the MOSFET independent due to the gap in the circuit diagram of it. So basically because of the gate terminal I can't just assume its 1.8V
Schematic diagram symbols often offer a stylized hint as to the underlying construction of the components they represent, but really they can't do more than jog your memory about how they actually function.

You hinted at being given some parameters. You'll have to use them to work out what operating mode the FET is in and then find its DC operating point.
 
CoolDude420 said:
It asks for find drain votltage, my question is why isn't the drain voltage just equal to 1.8? I mean the resistor should be getting the entire 1.8V so?
You're contradicting yourself here.
 

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