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From: email@example.com (N. Thornton)
Subject: Re: Transistor Switching
Date: 13 Sep 2002 04:40:05 -0700
NNTP-Posting-Date: 13 Sep 2002 11:40:05 GMT
Chuck Simmons wrote in message news:<3D7ECB70.F12B0DDD@webaccess.net>...
> Tim wrote:
> > My electronics instructor demonstrated a transistor amplifier
> > that had a small gain. He used a signal generator to apply
> > a ac signal to the base. Later he mentioned something about
> > a transistor oscillator than had a frequency of 20 KHz. He totally
> > lost me. How can a bipolar transistor be configured to self
> > oscillate at 20 KHz.
> You only really need a gain of one or slightly more to make an
> oscillator. Then the output is connected to the input with a circuit
> that selects the desired frquency. You would be surprised at how often
> this happens by accident. I don't know how much you know about AC
> circuits so I can't detail an example. Except for a very unusual case, a
> single transistor oscillator will require at least an inductor and a
> capacitor in addition to bias resistors. (Unless someone knows about
> another exception not involving mechanical resonators.)
Ah, you're asking for trouble there :)
One tr, one R, one cap: connect the tr backwards so it functions as a
breakdwn device, R in series, cap across tr. And if you solder the tr
badly enough, you could omit the R :)
There are also impractical circuits that don't require that.
1. Carbon arc: carbon arc runs off battery, the batteries internal
resistance being sufficient to permit it to oscillate. A tr in series
with it (c connected to b) will enable it to be at a push called a 1
2. Neon: similar setup.
3. and of course, who could forget the tr soldered to a bimetallic
switch? A standard bimetal oscillator, aranged so the current flows
thru the tr.
4. And if you want to be a bit sillier still, how about stretching a
rubber band out in the wind, and gluing a transistor to the middle of
it lol. Now you have a wind powered one transistor oscillator.
Ever practical :)
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