Voltage
sensing
is
performed
by a solid state electronic
circuit.
This
circuit requires very little
power
in order to
perform
its function
of
sensing
and
control. The series regulating
element
consists
of
a
semi-
conductor
switch; this
switch
is
controlled
by
the voltage
sensing element,
eg:
Theoretically,
when
a
perfect switch is
connected into
a series circuit, it
will
exhibit the following
characteristics
(1)
When
open, the switch will
have
infinite resistance and will pass zero
current. (2)
When
closed,
the
switch
will have zero resistance and
will
be
capable of passing infinite
current.
In both
cases,
the
switch will
dissipate zero power.
The
Model
20138 regulator controls the state
of
charge
of the battery
by
controlling the
average
field current. This is achieved by
varying the
"On" time
to the
"Off"
time of
the series switch.
The
duty
cycle
can vary
from 0%
to 100%
but will
typically be less
than
50%.
: Fast
switching
produces
maximum
efficiency
and
minimum
heat. However,
excessive
switching
speeds produce high
order
harmonics and
the
possibility of radio frequency interference
(RFI). The
Model
20138
is specially
designed
for optimum
switching
speed,
resulting
in
high efficiency with negligible
RFI
generation. This circuit is fully
covered in paragraph
3-3.
3-3
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