Npn transistor puzzle

  • Thread starter donpacino
  • Start date

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
 

meBigGuy

Gold Member
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Cool problem. Amazing effect.
 

phyzguy

Science Advisor
4,101
1,118
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.
 

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