NA555, NE555, SA555, SE555
PRECISION TIMERS
www.ti.com
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. 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.
V
CC
(5 V to 15 V)
R
A
= 3 kΩ
C = 0.02 µF
= 1 kΩ
R
L
See Figure 18
R
L
R
A
4
8
RESET
V
Modulation Input Voltage
Clock Input Voltage
CC
3
2
5
OUT
Clock
Input
Output
TRIG
7
6
DISCH
THRES
Modulation
Input
(see Note A)
CONT
GND
1
C
Output Voltage
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.
Capacitor Voltage
Time − 0.5 ms/div
Figure 18. Circuit for Pulse-Width Modulation
Figure 19. Pulse-Width-Modulation Waveforms
13
Submit Documentation Feedback
TI [ TEXAS INSTRUMENTS ]
