Datasheet

NE555, NE555Y, SA555, SE555, SE555C
PRECISION TIMERS
SLFS022A – SEPTEMBER 1973 – REVISED SEPTEMBER 2000
12
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
frequency divider
By adjusting the length of the timing cycle, the basic circuit of Figure 9 can be made to operate as a frequency
divider. Figure 17 shows a divide-by-three circuit that makes use of the fact that retriggering cannot occur during
the timing cycle.
Voltage – 2 V/div
Time – 0.1 ms/div
Capacitor Voltage
Output Voltage
Input Voltage
V
CC
= 5 V
R
A
= 1250 Ω
C = 0.02 µF
See Figure 9
Figure 17. Divide-By-Three Circuit Waveforms
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 illustrated, any wave shape could be used.