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Pulse-Width Modulation

THRES

GND

C

Output

DISCH

OUT

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

Time − 0.5 ms/div

Capacitor Voltage

Output Voltage

Clock Input Voltage

C = 0.02

µF

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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