![](http://datasheet.mmic.net.cn/120000/540-MK216_datasheet_3270055/540-MK216_3.png)
A
3
CALEX
FaxFACTS:
323
1997
Model 540 Voltsensor
http://www.calex.com
2401 Stanwell Drive
Concord, CA 94520-4841
(925) 687-4411 Fax (925) 687-3333
Operation
The Model 540 consists of a protected IC input stage and a
power transistor output stage. The set-point input, or
comparison voltage, can be applied to either input (pin 8 or pin
9). The varying input signal is applied to the other input. When
the voltage at pin 9 is more positive than the voltage at pin 8,
the IC comparator output switches to the high logic state and
applies a positive drive to the output power transistor Q1.
When the voltage at pin 9 is negative with respect to the
voltage at pin 8, the IC comparator will switch to the low logic
state, which is near zero volts. If the output is connected as
a current sink, (pin 16 connected to common and the load
connected between pin 1 and a positive voltage), then
positive drive from the output of the IC comparator will cause
Q1 to saturate. With Q1 switched on, the output sink can
accept up to +100 mA. A relay or lamp load at the output will
be switched to the energized condition when Q1 saturates.
When the IC comparator goes to the low state, Q1 is cut off
and no current will flow. The Voltsensor output will then rise
FIGURE 3.
FIGURE 2.
to the positive supply lead. A relay or lamp load would then be
de-energized.
If the output is connected as a current source (pin 1 connected
to +VS and the output load connected between pin 16 and
common), then positive drive from the output of the IC
comparator will cause Q1 to go to a high output state. In this
mode of operation, Q1 is used as an emitter follower and it will
essentially follow the voltage output of the IC comparator.
When the IC comparator switches to the low state, the
Voltsensor output (output source, pin 16) will drop to nearly
zero volts (+50 mV maximum).
The input diodes protect the IC comparator for a maximum
input voltage of ±100V. The output stage is current limited to
140 mA in the event of a short circuit. The diode between
output source and common offers transient protection when
a relay is used as a load in the current-source mode.
External connections for the two modes of operation current
sinking and current sourcing, are shown below.