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5
Logic Level Translators
The HA-4900 series comparators can be used as versatile logic
interface devices as shown in the circuits above. Negative logic
devices may also be interfaced with appropriate supply
connections. If separate supplies are used for V- and VLOGIC-,
these logic level translators will tolerate several volts of ground
line differential noise.
RS-232 To CMOS Line Receiver
This RS-232 type line receiver to drive CMOS logic uses a Schmitt
trigger feedback network to give about 1V input hysteresis for
added noise immunity. A possible problem in an interface which
connects two equipments, each plugged into a different AC
receptacle, is that the power line voltage may appear at the receiver
input when the interface connection is made or broken. The two
diodes and a 3W input resistor will protect the inputs under these
conditions.
Window Detector
The high switching speed, low offset current and low offset
voltage of the HA-4900 series makes this window detector circuit
extremely well suited to applications requiring fast, accurate,
decision-making. The circuit above is ideal for industrial process
system feedback controllers or “out-of-limit” alarm indicators.
Oscillator/Clock Generator
This self-starting fixed frequency oscillator circuit gives excellent
frequency stability. R1 and C1 comprise the frequency determining
network while R2 provides the regenerative feedback. Diode D1
enhances the stability by compensating for the difference between
VOH and VSUPPLY. In applications where a precision clock
generator up to 100kHz is required, such as in automatic test
equipment, C1 may be replaced by a crystal.
Schmitt Trigger (Zero Crossing Detector With Hysteresis)
This circuit has a 100mV hysteresis which can be used in
applications where very fast transition times are required at the
output even though the signal input is very slow. The hysteresis
loop also reduces false triggering due to noise on the input. The
waveforms below show the trip points developed by the hysteresis
loop.
MEMORY
MICRO-
PROCESSOR
IN
TE
RF
ACE
IN
T
E
RF
ACE
D/A
COMPARATORS
PROCESSOR
LA
T
C
H
ANALOG
INPUT
S
ANALOG INPUT MODULE
1/4
HA-4900
+
-
4.7k
Ω
VL+
1N914s
+5.0V
1/4
HA-4900
+
-
TTL TO CMOS
1/4
HA-4900
+
-
10k
Ω
V+
+5.0V
1/4
HA-4900
+
-
CMOS TO TTL
+5V TO +15V
10k
Ω
1/4
HA-4900
+
-
+10V
4.7k
Ω
3W
1k
Ω
1N4001s
56k
Ω
51k
Ω
1k
Ω
+
-
VL+
+15V
+
-
-15V
1/2 HA-4900
INPUT
LOW REF
HIGH REF
HIGH
LOW
IN
WINDOW
+5.0V
1/4 HD-74C02
1/4
HA-4900
+
-
V+
150k
Ω
150k
Ω
R2
150k
Ω
V+
R1
50k
Ω
C1
f
1
2.1R
1C1
----------------------
≈
D1
1N914
HA-4900, HA-4902, HA-4905