Re: OT - Archie - I Dare You

On Tue, 16 Jun 2009 12:05:56 -0700 (PDT), George Herold
<ggherold@xxxxxxxxx> wrote:

On Jun 14, 10:05 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 11 Jun 2009 19:03:33 -0500, krw <k...@xxxxxxxxxxxxxxxxx> wrote:
On Thu, 11 Jun 2009 13:00:57 -0700, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Thu, 11 Jun 2009 12:10:51 -0300, YD <ydtech...@xxxxxxxxxx> wrote:

Late at night, by candle light, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> penned this immortal
opus:

On Tue, 9 Jun 2009 16:00:37 -0400, "Tom Del Rosso"
<td...@xxxxxxxxxxxxxxx> wrote:

John Larkin wrote:
On Tue, 09 Jun 2009 03:09:57 GMT, du...@xxxxxxxxxxxx (Richard Cranium)
wrote:

Will you try a very simple electrical puzzle?

John

You're making an On-Topic reply to a purposely Off-Topic post.  That
just seems very, very wrong.

I'll take that for a "no".

Don't let that stop you from posting the puzzle.

I was going to do something really hard like a resistor voltage
divider, but I wouldn't want to damage his "cranium."

But this one has ended a surprising number of "engineer" interviews:

                  +10v
                   |
                   |
                   |
                   |
                   c
+5v----------------b    NPN transistor
                   e
                   |
                   |
                   |
                  1K
                   |
                   |
                   |
                   |
                  gnd

Questions:

1. What is the base voltage?  (yes, they get that wrong!)

2. What is the emitter voltage?

3. What is the collector current?

4. Any other comments?

John

1. 5 V
2. About 4.3 V
3. About 4.3 mA
4. Am I hired?

Well, you didn't mention anything about oscillations.

I don't see any reactive elements.  ;-)

They're there. Emitter followers with stiff base drive often
oscillate.

John- Hide quoted text -

- Show quoted text -

Hmm I slapped this together on some white protoboard. 2n3904. I
didn't see any oscillations. (X10 'scope probe and 200MHz 'scope) But
maybe the proto-board is 'saving' me. Do I need to air wire it?

George H.

Base-emitter capacitance and emitter/ground strays can resonate with
just a short length of wire on the base. Your scope might see it, but
they can start/ stop with the added capacitance of the scope probe, so
it's hard to know. A common 'cure' is 50-100 ohms to the base (more
or less... I've seen upwards of 200 ohms and more.) It softens the
'tank' Q. (And affect the high frequency roll-off.)

Jon
.

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