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PRECISION TIMERS
SLFS022F – SEPTEMBER 1973 – REVISED JUNE 2006
APPLICATION INFORMATION (continued)
Pulse-Width Modulation
The operation of the timer can be modified by modulating the internal threshold and trigger voltages, which is
accomplished by applying an external voltage (or current) to CONT.
shows a circuit for pulse-width
modulation. A continuous input pulse train triggers the monostable circuit, and a control signal modulates the
threshold voltage.
shows the resulting output pulse-width modulation. While a sine-wave modulation
signal is shown, any wave shape could be used.
V
CC
(5 V to 15 V)
4
RESET
Clock
Input
2
TRIG
8
V
CC
OUT
3
R
L
R
A
Output
7
DISCH
Modulation
5
Input
(see Note A)
CONT
THRES
GND
1
C
6
Pin numbers shown are for the D, JG, P, PS, and PW packages.
NOTE A: The modulating signal can be direct or capacitively coupled
to CONT. For direct coupling, the effects of modulation source
voltage and impedance on the bias of the timer should be
considered.
Figure 18. Circuit for Pulse-Width Modulation
Figure 19. Pulse-Width-Modulation Waveforms
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ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
ÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏÏÏÏÏÏÏÏ
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R
A
= 3 kΩ
C = 0.02 µF
R
L
= 1 kΩ
See Figure 18
Modulation Input Voltage
Clock Input Voltage
Output Voltage
Capacitor Voltage
Time − 0.5 ms/div
Voltage − 2 V/div
13
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