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filtered for the microprocessor. This has not been built, so some tweaking may
be necessary, but the micro can handle the scale factor.
Russell Kincaid
Milford, NH
#3 Avago Technologies (a spin-off of Agilent, which was spun off of HP)
makes an "analog" optocoupler, the HCNR200. This is an optocoupler with
an LED and two well matched photodiodes, which is designed for isolation of
analog signals, primarily for industrial and measurement purposes (scope input
isolation). You can find all the necessary information on their website (check for
their Optocoupler Designer's Guide and the HCNR200 datasheet). Available at
Digi-Key and not expensive.
Walter Heissenberger
Hancock, NH
I had requested ideas for an
aquarium light timer/controller and
had received a couple inventive
responses in the last issue. I just
wanted to express my appreciation
to those who sent in their ideas.
Phil Daniels
Figure 3
instability. If you are charging a
battery, you will not need as large an
input filter capacitor. The battery does
not care about ripple current. You wil
have to make L1 using a transformer
core, about 500 VA. 800 mH is the
minimum. You can make it larger for
even better performance.
PARTS LIST
All Mouser parts.
Part Part number
D1 583-MP3505
R1, R2, R3 284-HS15-0.1
R4 284-HS200-5.0F
R5, R6 71-RH10-0.03
R7 660-MF1/2CC6192F
R8 660-MF1/2CC7151F
Q1, Q2, Q3 511-MJ2955
Q4 511-TIP112
Q5 511-2N3055
C1, C2 75-36DY104F040DC2A
C3 80-C317C472K1R
IC1 511-LM723CN
ohms at 40 watts (use two 20 watt
resistors), and change Q1 through
Q10 to 2N5885 or add a third string
of 2N3055s and emitter resistors.
Your transformer will need to be
able to deliver at least 1.5 times the
current drawn from the supply. To
understand that, recognize that when
the input voltage (rectified AC) drops
below 24 volts, the capacitor provides
the difference between the input and
the 24 volts delivered to the load.
When the input rises above 24 volts, it
must re-charge the capacitor and
supply current to the load.
Therefore, the current required
from the transformer is greater than
the amount the load draws. You also
want the AC output from the transformer to be fairly "stiff." If it sags too
much under load, regulation will be
lost; 5% sag would be acceptable.
Regarding dissipating less heat
with MOSFETs vs. bipolar — that is
irrelevant in a linear supply. The linear
regulates by "throwing away" excess
energy as heat. The same amount of
excess energy must be dissipated,
regardless of the type of transistors
used.
Russell Kincaid
Milford, NH
Ed Schick
Harrison, NY
#2 The LM723 is
so old (nearly 40
years), why do you
want to use it? A
MOSFET will not
save any power
unless you use a
switching supply. I
think you are
considering a linear
regulator, using the
2N3055 (another
ancient device!).
This circuit (Figure
4) will supply 30
amps to a 24 volt
load. I don’t know if
you will need an
output filter or not,
but I think a large
value may cause
Figure 4
l
104
September 2006
