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Came across a circuit with current flowing from Low to High potential across a resistor (electrons moving from high to low potential)

Physics Asked by Ayosh Maitra on February 10, 2021

This is the circuit of small signal analysis for a BJT amplifier.

The current shouldn’t flow at all. How is it even flowing ?

I’m attaching the snap shot of this particular moment from the video lecture.
enter image description here

According to this video, the current gm*Vin is flowing out of the circuit, from low to high potential points ( given they are moving from the grounded points to the collector point )

One Answer

What you have drawn is the equivalent circuit for a small signal response.

enter image description here

I can only guess what the original circuit looks like but it might well be that the bottom end of the load resistor $R_{rm L}$ is connected to the positive terminal of the voltage source $+V_{rm S}$ which provides the bias voltages/currents.

This means that the actual current is the bias current (flowing from a positive to a negative potential) minus a small signal current due to the small signal input voltage to the device $v_{rm in}$ with $V_{rm s} gg v_{rm in}$ and flowing from a high potential to a lower potential..

Answered by Farcher on February 10, 2021

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