NE555, SA555, SE555, SE555C
PRECISION TIMERS
SLFS022 – D1669, SEPTEMBER 1973—REVISED FEBRUARY 1992
APPLICATION INFORMATION
VCC (5 V to 15 V)
4
RESET
Clock
Input
2
TRIG
8
VCC
OUT
3
RL
RA
DISCH
Modulation
Input
(see Note B)
5
CONT
GND
1
7
Voltage – 2 V/div
Output
THRES
6
C
Pin numbers shown are for the D, JG, and P packages only.
NOTE B: The modulating signal may 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
pulse-position modulation
As shown in Figure 20, any of these timers may be used as a pulse-position modulator. This application
modulates the threshold voltage, and thereby the time delay, of a free-running oscillator. Figure 21 illustrates
a triangular-wave modulation signal for such a circuit; however, any wave shape could be used.
VCC (5 V to 15 V)
4
RESET
2
TRIG
8
VCC
OUT
RL
3
RA
Output
Voltage – 2 V/div
DISCH
Modulation 5
Input
(see Note B)
CONT
GND
THRES
7
6
RB
C
Pin numbers shown are for the D, JG, and P packages only.
NOTE B: The modulating signal may 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
Figure 20. Circuit for Pulse-Position Modulation
Figure 21. Pulse Position-Modulation Waveforms
POST OFFICE BOX 655303
•
DALLAS, TEXAS 75265
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RA = 3 kΩ
C = 0.02
µF
RL = 1 kΩ
See Figure 18
Modulation Input Voltage
Clock Input Voltage
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Output Voltage
Capacitor Voltage
Time – 0.5 ms/div
RA = 3 kΩ
RB = 500
Ω
RL = 1 kΩ
See Figure 20
Modulation Input Voltage
Output Voltage
Time – 0.1 ms/div
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13
TI [ TEXAS INSTRUMENTS ]
