THRES

GND

C

Output

DISCH

OUT

RESET

TRIG

CONT

Modulation

Input

(see Note A)

Clock

Input

4

8

3

7

6

2

5

1

Time − 0.1 ms/div

Capacitor Voltage

Output Voltage

Input Voltage

21

TLC555

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SLFS043I – SEPTEMBER 1983 – REVISED JULY 2019

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Copyright © 1983–2019, Texas Instruments Incorporated

Typical Applications (continued)

8.2.1.3 Application Curve

C = 0.1 µF

See Figure 18

Figure 19. Timing Waveforms for Missing-Pulse Detector

8.2.2 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 20 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 21 shows the resulting duty cycle versus control voltage transfer function. Attempting to

run under 10% duty cycle could result in inconsistent output pulses. Attempting to run close to 100% duty cycle

will result in frequency division by 2, then 3, then 4.

A.

The modulating signal can be direct or capacitively coupled to CONT. For direct coupling, consider the effects of

modulation source voltage and impedance on the bias of the timer.

Figure 20. Circuit for Pulse-Width Modulation