5. Almost all of the bulb current will be
carried by the relay, so the additional
IN4001 diode should not reduce bulb
brightness and can be eliminated if
you trust the relay contacts.
roresonants is that they
can be audibly noisy, so
sitting in the same room
as one can become irritating.
Total Recoil Magnetics
I have just read the question
about ferroresonant transformers in
the Dec. 2003 issue and wish to add
that Sola also supplies ferroresonant
transformers that are "Harmonically
Neutralized" to minimize the impact
of the third harmonics on the waveform. This technology requires that
part of the capacitor winding be separated from the rest of the capacitor
winding by a set of silicon steel
shunts. This additional winding comprises approximately one-third of the
total capacitor winding. A visual
inspection will reveal three coils, separated by two sets of shunts.
The output waveform looks pretty close to a sine wave, with none of
the flattening out that you mentioned.
I have measured harmonic distortion
values in the range of 1.5%- 3.0%,
which is not bad for ancient technology. However, I have noticed some
"clipping or apparent commutating"
distortion when using dynamic loads,
such as switch-mode power supplies.
Even this distortion does not seem to
Another potential problem for fer-
In the December
issue's schematic for a
+ 5 to - 5 converter (Figure
10), is the 10 uF cap
between - 5 volts out and
ground reversed — or am
I missing something?
No, I missed it when
I drew the schematic.
Q & A Editor
R a d ioShack
(12V, 1050 ohm coil,
1A contact rating)
10W Reader Circuit
12V 275-233 Relay
SPST (12V, 1050 ohm coil,
1A contact rating)
Your articles are usually accurate
and informative. However, in the
December 2003 issue, page 24, you
state that the circuit illustrated in
Figure 5 features a bandpass filter, of
which you show the frequency
response in Figure 6. In fact, the net-
work composed of the series 100-
ohm resistor and 1-uF capacitor to
ground, at pin 3 of the second 555, is
a low-pass filter which, as you correctly state, attenuates the off harmonics.
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