Re: Transistors


This is a nice little test to give to applicants for tech or
engineering positions:


+10V
|
|
|
c
+5V--------b
e
|
|
|
1K
|
|
gnd



Am I not seeing something or is this a relatively trivial question? I can
be tricked, but I hate to admit my stupidity so...



It's an average NPN transistor.

Oookay, so beta is somewhere around a hundred or so? Makes the calcs a
little easier, All measurements wrt "gnd".


What's the emitter voltage? Current?

4.4 volts, 4.4 mA.


What's the base voltage?

5 volts


What's the base current?

(assuming b = 100) 44 uA


What's the collector current?

4.4 mA less 44 uA or virtually 4.4 mA


Will anything get hot?

Well, lessee. THere's "about" 6 volts CE at "about" 5 mils, so the
transistor will be dissipating "about"" 30 mW, hardly warm at the
macroscopic case level. Fairly hot on a microscopic junction level.
Resistor dissipating "about" 20 mW, again not warm. Perhaps if the + supply
is being done by toobs...


Any other comments?

Yeah, it'll probably sing like a bird if that 5 volt base supply is AC hard
to ground and there is the slightest unintended (wire) inductance in the
collector supply.

Or did you catch me somewhere? Or did my mental math screw me up again (no
calculator handy).

Jim


.

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