Will a NPN transistor conduct emitter - collector

Thread Starter

dandy1

Joined Sep 30, 2017
73
I have a circuit where I got the collector - emitter mixed up. Will the transistor work reversed?
MMBT3904 - 4.3v@ emitter (should have been collector).

Implemented as a signal switch, best thing is i got i right on a high side driver right next to the switch, cant believe i ballsed it up!
 

crutschow

Joined Mar 14, 2008
23,292
A BJT will usually work inverted but with very low gain.
Also beware that the max reverse Vbe is typically about 5V.
 

Thread Starter

dandy1

Joined Sep 30, 2017
73
Yes, but very poorly.
Is that in all respects? mainly im only concerned about switching speed and as long as theres enough voltage for the micro to read the signal. stated switching is about 0.1ms rise and fall, theoretically i only need 15.0ms
 

Thread Starter

dandy1

Joined Sep 30, 2017
73
A BJT will usually work inverted but with very low gain.
Also beware that the max reverse Vbe is typically about 5V.
Thanks crutschow, i think ill bite the bullet and give her a shot.
I've got 4.3v on the emitter so the reverse Vbe is 1.3v under the stated 6v
 

Berzerker

Joined Jul 29, 2018
541
Why would you use it inverted is my question.
Why not just wire it up correctly. Did it blow something? Did what your trying to get to work , Not work?
just replace it and it will work as normal.
Maybe I need more knowledge but I didn't understand that's how they were suppose to work.
 

Thread Starter

dandy1

Joined Sep 30, 2017
73
Why would you use it inverted is my question.
Why not just wire it up correctly. Did it blow something? Did what your trying to get to work , Not work?
just replace it and it will work as normal.
Maybe I need more knowledge but I didn't understand that's how they were suppose to work.
It wasn't intended to be used inverted, i made a mistake (or rather the software made a mistake);)when I designed a PCB.
I Can not change the traces on a PCB, although id like to find one
I asked the question before blowing something up - trust me I'm No1 at that.

I read some posts that indicated some transistors are actually designed for inverse operation, so as usual came to the right place for the right info.

thanks all
 

Berzerker

Joined Jul 29, 2018
541
From my fixing to put together my first project Transistors have very long connections. you can't just remove it and place another with the legs crossed so they're right? now not all of them but most. I couldn't fix my IC if I were to make a mistake on my PCB traces but transistors are different.
Just asking.
 

dl324

Joined Mar 30, 2015
8,849
I have a circuit where I got the collector - emitter mixed up. Will the transistor work reversed?
MMBT3904 - 4.3v@ emitter (should have been collector).
Unless you grossly over designed the circuit, no. Beta for inverted mode is very low.
 
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