EVERYTHING FOR ELECTRONICS
DIGGIN’ THE DIOS
The Dios microcomputer articles
are very worthwhile, and Michael
Simpson does a good job of putting out
info that can be really used and things
that can be built. I find this stuff more
interesting than articles based on a
preprogrammed micro and board type
project that you have to buy from one
supplier. Anyway, keep up the real
Nuts & Volts!
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I would just like to say I have enjoyed Nuts & Volts magazine very much.
I have been an electronics technician
for about 15 years. I was introduced to
Mike Simpson through your articles. It
was through an advertisement in this
magazine that I learned about his
Athena microcontrollers and used his
free software to write my first program.
It was because of his products that I was
able to start using the PICs that I read
about for years. I would be interested
in seeing more articles using the Athena
and various other microcontrollers
available from the Kronos website.
His articles take you through diverse
paths in the microcontroller world.
They range from health and fitness to
building your own test equipment. I
would like to see more.
series regulators is about 4%. Unless the
7805’s are matched, it appears that the
7805 with the highest output voltage
will supply most of the output current,
and will be overloaded. Assume three
7805s — A, B, and C — connected in
parallel. Their outputs are 4. 97 volts,
5.00 volts, and 5.02 volts, respectively.
C will output 5.02 volts, which is
above the output voltage of A and B.
Therefore, A and B will shut down in an
attempt to bring the output voltage
down to their internal “setting,” and all
the output current will be from A.
His other suggestion, using two or
three pass transistors, also has problems.
When pass transistors are paralleled, it
is usually necessary to connect a small
resistor in series with the emitter of each
transistor to equalize the current in
the transistors. These resistors result in
slightly lower output voltage and
slightly poorer regulation. Also, there is
a voltage drop in the base/emitter
junction of the transistor, usually about
0.6 volts, and 5.6 volt regulators (for a
final output of five volts) are hard to find.
(This last problem can be solved by
placing a forward-biased silicon diode
between the GND terminal of the
7805 and the actual circuit ground; the
voltage drop in the diode is about
the same as the voltage drop in the
However, the worst problem with
pass transistors is that you lose the over-current, over-heating, and short circuit
protection that is built into the 7805.
To me, using a heatsink is the best
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Michael Simpson will be doing an
upcoming series using X10, along with
other cool Control-Your-World projects,
so stay tuned! — Ed.
HEATSINKS STILL HOT
Thomas Ernst’s letter paralleling
7805 regulators in the August Reader
Feedback is interesting, but I see
problems. According to the data sheet,
the output voltage tolerance of the 78xx
HAPPY WITH LIFE (SUB)
Many years ago, I picked up a copy
of Nuts & Volts at Hatry's in Hartford,
CT. The offer was a lifetime subscription
and I got to place an ad. Well I did, and
offered a two-meter ham transceiver. So,
for all these years you have kept up your
end of the bargain. I am thankful and
impressed that you kept your word.
Martin De Filippo
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