NPN Transistor Biasing with polarity inversion

Thread Starter

pll_check

Joined May 28, 2017
23
Hi,

I am learning NPN transistor characteristics by changing the supply polarities.

There are two circuits below.

1. I forward biased the BE and reverse biased the CB junctions. I see the following VBE vs IC Char. (also I don't understand the slope, please explain?)
Circuit 2.png

2. I reverse biasing the BE and forward bias the CB junctions, I still see similar amount of current (-ve)
Circuit 1.png


What is happening in these circuits, what is the slope in first plot, which one is right, when to use what? More details. Please.
 

MrChips

Joined Oct 2, 2009
21,052
What is right for what purpose?

The base-emitter conjunction looks like a normal p-n diode junction. When it is reversed biased, there is very little B-E current.
The base-emitter conjunction needs to be forward bias. When that happens you get collector-emitter current flow.
 

crutschow

Joined Mar 14, 2008
24,914
A BJT will operate as a transistor with the emitter and collector connections reversed, just with a much lower gain.
That's what you see in the second simulation.
 

Thread Starter

pll_check

Joined May 28, 2017
23
The slope is because of the resistor value I used. But in my simulation here where I am stepping the rc resistor from 10 to 100 Ohms. How is there a -ve voltage at the collector (vc) when my VCC supply is positive.

Circuit 3.png
 
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