At 09:43 PM 1/30/2003 -0600, you wrote:
>I know that many of you have the book, The Art of Electronics,
>this question deals with the circuit from fig 2.75 on page 105.
>
>a zener diode and two transistors, along with 3 1K resistors.
>
>I rekon if these transistors are just variations of the ones called for
>in this circuit, then the resistors are the same, the diode must be
>the deciding factor?  but the circuit claims to regulate 12 to 25 v input
>to 10 v output, so my 5.5v out is way off from this, so does a difference
>of a 5.1V zener versus a 4.3V zener make this much of a difference?

No, maybe something else is wrong. Is it possible you've got the
'3055 connected wrong?

   .---.
  |  O  |
  .-----.
  |     |
  |1 2 3| TIP3055
   -----
   | | |
   B C E

That's about the output voltage you'd get if you swapped B
and C. (this can permanently reduce the beta of the transistor).

To a first approximation, the base of Q2 draws no current, so
the voltage there is just half the output voltage. In your case, it
should be about 5.7VDC. The voltage on the emitter of Q2 should
be about 5.1V. And the output voltage should be about 11.5V.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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