Steve Baldwin wrote:
> You may find that you learn better using experiments. Some do, some
> don't.

That's a good point.  I think it would be quite instructional to build this
little circuit on a breadboard and make some measurements under different
conditions.

All you need is R2, D3, Q1, and a basic power supply in the 7-15V range or
so.  12V would do fine.  Use the power supply to provide the "8.2V" rail,
hook up R2, D3, and Q1 as shown.  Leave the emitter of Q1 open but allow for
connecting different resistors between there and ground.

Put around 50Kohms between the emitter and ground.  Measure the voltage on
the emitter.  Based on that, how much current is flowing thru the test
resistor.  Repeat the experiment for resistors around 5Kohms and 500ohms.
Roughly what was the ratio of highest to lowest test resistor current
accross the tests?  What wsa the ratio of highest to lowest emitter voltage
accross the tests?  What conclusion can you draw from that about the
stability of the emitter voltage as a function of the emitter current?  In
what application might this property be useful?

You don't have to use a MMTB4401 transistor.  Just about any jellybean NPN
will work here.  The zener voltage doesn't have to be exactly 5.6V either,
but should be at least a 2.5V or so less than your supply voltage.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist