I have a few questions about Vce(sat) and static resistance

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Discussion Overview

The discussion revolves around the static resistance of semiconductors, particularly in the context of transistors and their voltage drop characteristics when saturated. Participants explore the relationship between doping levels, voltage drops, and the nature of transistor operation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that static resistance in semiconductors decreases with heavier doping.
  • One participant suggests that the typical 0.2V voltage drop between the emitter and collector in saturated transistors is due to static resistance.
  • Another participant questions the 0.2V figure, stating that for silicon junction transistors, the drop is about 0.7V, and asks for clarification on the type of transistor being referenced.
  • Some participants argue that the minimum voltage drop is not solely due to resistance but is necessary for forward polarization of one of the junctions.
  • There are references to external resources, such as Wikipedia, to provide additional context on sheet resistance in semiconductors.

Areas of Agreement / Disagreement

Participants express differing views on the cause of the voltage drop in saturated transistors, with no consensus reached on the exact values or the underlying reasons for the observed behavior.

Contextual Notes

There are unresolved questions regarding the definitions and conditions under which the voltage drop occurs, as well as the types of transistors being discussed.

Genji Shimada
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I think this is the place to ask these questions about static resistance of semiconductors:
The static resistance in semiconductors is that kind of resistance that will decrease if the semiconductor is more heavily doped, right?

In transistors, and especialy saturated transistors the usual 0,2V voltage drop between the emitter and the collector is the inevitable loss of energy duo to the static resistance of the semiconductor. Is that right?

If so, that voltage drop will slightly increase with the increase of the collector current, right?
 
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anorlunda said:
Ah! And so because of this resistance, the transistor will drop some voltage between the emitter and the collector even though it is expected to act like a short circuit when saturated. My point is that it is that sheet resistance that causes that Vce(sat) right?
 
This minimum voltage drop is not due to the resistance but to the need to forward polarize one of the junctions.
I don't understand though where do you get the 0.2 V. For silicon transistors (junction type) is about 0.7 V.
Maybe you are talking about a different type of transistor? What kind of transistor do you mean?
 
nasu said:
This minimum voltage drop is not due to the resistance but to the need to forward polarize one of the junctions.
I don't understand though where do you get the 0.2 V. For silicon transistors (junction type) is about 0.7 V.
Maybe you are talking about a different type of transistor? What kind of transistor do you mean?
I don't speak about the minimum turn on voltage you need to apply across a diode in a forward dirrection to turn it on. I am talking about the voltage difference between the emitter and the collector when a transistor is saturated:
latest-topic-4-bipolarjunctiontransistors-21-638.jpg
 

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