MC3456
Pulse Width Modulation
Test Sequences
If the timer is triggered with a continuous pulse train in the
monostable mode of operation, the charge time of the
capacitor can be varied by changing the control voltage at
Pin 3. In this manner, the output pulse width can be
modulated by applying a modulating signal that controls the
threshold voltage.
Several timers can be connected to drive each other for
sequential timing. An example is shown in Figure 24 where
the sequence is started by triggering the first timer which
runs for 10 ms. The output then switches low momentarily
and starts the second timer which runs for 50 ms and so forth.
+V (5.0 V to 15 V)
CC
Modulation Input Voltage 5.0 V/cm
R
L
R
A
4 (10)
Reset
V
14
CC
Clock Input Voltage
5.0 V/cm
Discharge
Output
5 (9)
1 (13)
Output
Threshold
1/2
C
Output Voltage
5.0 V/cm
MC3456
2 (12)
Trigger
6 (8)
Control
Capacitor Voltage
5.0 V/cm
3 (11)
Clock
Input
Modulation
Input
Gnd
7
t = 0.5 ms/cm
(R = 10 kW, C = 0.02 mF, V = 15 V)
A
CC
Figure 22. Pulse Width Modulation Waveforms
Figure 23. Pulse Width Modulation Circuit
V
(5.0 V to 15 V)
CC
9.1 k
27 k
9.1 k
27 k
50 k
Reset
V
Reset
V
Reset
V
CC
CC
CC
0.01 μF
0.01 μF
0.01 μF
Threshold
Threshold
Discharge
Trigger
Threshold
Discharge
Control
Control
Control
Discharge
Trigger
1/2
1/2
1/2
MC3456
MC3456
MC3456
Output
Output
Output
0.001 μF
0.001 μF
Trigger
Gnd
Gnd
Gnd
1.0 μF
5.0 μF
5.0 μF
Load
Load
Load
Figure 24. Sequential Timing Circuit
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