LM393, LM293, LM2903, LM2903V, NCV2903
APPLICATIONS INFORMATION
These dual comparators feature high gain, wide
bandwidth characteristics. This gives the device oscillation
tendencies if the outputs are capacitively coupled to the
inputs via stray capacitance. This oscillation manifests itself
during output transitions (V
OL
to V
OH
). To alleviate this
situation, input resistors <10 kW should be used.
+15 V
R4
220 k
6.8 k
R2
R5
220 k
*
)
LM393
The addition of positive feedback (<10 mV) is also
recommended. It is good design practice to ground all
unused pins.
Differential input voltages may be larger than supply
voltage without damaging the comparator’s inputs. Voltages
more negative than −0.3 V should not be used.
R1
8.2 k
V
in
R1
D1
10 k
+V
CC
*
10 m
V
in
)
10 k
V
in
V
in(min)
Q
15 k
R3
LM393
V
CC
V
O
− V
EE
DQ
Q
D1 prevents input from going negative by more than 0.6 V.
R1 + R2 = R3
R3
≤
R5
for small error in zero crossing.
10
−V
EE
V
in(min)
[
0.4 V peak for 1% phase distortion (DQ).
Figure 8. Zero Crossing Detector
(Single Supply)
Figure 9. Zero Crossing Detector
(Split Supply)
V
CC
V
CC
R
−
LM393
+
V
C
V
O
+ V
ref
‘‘ON’’ for t
t
O
+
Dt
where:
V
ref
)
Dt
= RC n (
V
CC
V
in
0
V
O
0
V
C
0
t
O
V
ref
V
ref
1.0 mW
V
CC
R
L
10 k
t
R
L
−
LM393
+
V
CC
51 k
−
0.001
mF
LM393
+
C
V
O
51 k
51 k
V
CC
V
O
0
t
t
Figure 10. Free−Running Square−Wave Oscillator
V
CC
Figure 11. Time Delay Generator
R
S
= R1 | | R2
R
S
−
LM393
+
V
ref
R1
R2
R
L
V
th1
= V
ref
+
(V
CC
−V
ref
) R1
R1 + R2 + R
L
(V
ref
−V
O
Low) R1
R1 + R2
V
th2
= V
ref
−
Figure 12. Comparator with Hysteresis
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