Solve NPN Transistor Puzzle: -0.4V?

AI Thread Summary
The discussion revolves around a puzzling scenario involving an NPN transistor where the base is grounded, and +12 volts is applied to the emitter through a 1k resistor, resulting in a collector voltage of approximately -0.4 volts. Participants express confusion over how this negative voltage occurs, particularly with the collector left open. It is noted that applying such reverse bias can damage most NPN transistors, especially with high voltages. Links to further reading on the topic are shared, highlighting the phenomenon's complexity and the potential for interesting effects. The conversation emphasizes the intriguing nature of the problem while cautioning about the risks to the transistor's functionality.
donpacino
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I was just sent an email with the following text.
""
Here is a puzzle I just encountered.

Take any NPN transistor and ground the base. Now apply +12 volts to the emitter through a series resistor of 1k. Yes, it is a Zener diode of about 6 volts so about 6 ma of current flows.What is the voltage between the collector and ground? I couldn't guess. Well I could guess it was zero volts, but then, that would not have been a puzzle. So I gave up.Answer: about -0.4 volts ! (Yes negative.) Why?
""I am at a loss for understanding where they are getting this supposed -0.4V. Any takers?

edit: it is important to note my interpretation of the problem is the the collector is left open
 
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Cool problem. Amazing effect.
 
Note that most NPN transistors will be damaged by reverse biasing the E-B junction, especially with such large voltages. I'm not discouraging you from doing the experiment (these things are cheap, after all), but don't expect the transistor to function properly afterward.
 
meBigGuy said:
Cool problem. Amazing effect.
My thoughts exactly. Thanks for the links everyone. Great reads!
 

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