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Grounding the base of an NPN BJt

Meta_Alchemy

New Member
Hello,
I made a simple circuit connecting an LED to the collector of an npn transistor. After I applied some 3V, I noticed the LED lit up and very dim of course.

I simply grounded the base and the LED turned off.
When I removed the ground, suddenly the LED turns nice and bright but not to the point of burning and then after a bit it will go back the previous dimly lit LED.

When I hooked up the base to the positive side, I could see amperage increase on the power source and the led will get bright but not as much as when I unhooked it from the ground.



In terms of electron mobility conduction and charge distribution, i.e. capacitance.....What takes places at each of the two junctions base-emitter and base-collector.
1. When the base is floating.
2. When grounding the base
3. When ungrounding the base.
4. Hooking up the base to positive supply.

5. One last question. Why does the LED becomes bright when touching the base or the emitter ( I think ) as I am not remotely part of the circuit. In fact even I move too fast or even get close to these points.

Thank you in advance for your response and especially responses that are put together using simple clear terminologies. It removes all the back and forth.
 

danadak

Well-Known Member
Most Helpful Member
Do you have current limiting R in the base and in the collector/led
branch ?

An ungrounded base is subject to pickup via capacitive coupling. A base grounded
results in a small leakage in collector - base circuit.


Regards, Dana.
 

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