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Pulse-Width Modulation
THRES
GND
C
R
A
R
L
V
CC
(5 V to 15 V)
Output
DISCH
OUT
V
CC
RESET
TRIG
CONT
Modulation
Input
(see Note A)
Clock
Input
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.
4 8
3
7
6
2
5
Pin numbers shown are for the D, JG, P, PS, and PW packages.
1
Voltage − 2 V/div
Time − 0.5 ms/div
Capacitor Voltage
Output Voltage
Clock Input Voltage
R
A
= 3 kΩ
C = 0.02 µF
R
L
= 1 kΩ
See Figure 18
Modulation Input Voltage
NA555 , NE555 , SA555 , SE555
PRECISION TIMERS
SLFS022F – SEPTEMBER 1973 – REVISED JUNE 2006
APPLICATION INFORMATION (continued)
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. Figure 18 shows a circuit for pulse-width
modulation. A continuous input pulse train triggers the monostable circuit, and a control signal modulates the
threshold voltage. Figure 19 shows the resulting output pulse-width modulation. While a sine-wave modulation
signal is shown, any wave shape could be used.
Figure 18. Circuit for Pulse-Width Modulation Figure 19. Pulse-Width-Modulation Waveforms
13
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