SLFS022 – D1669, SEPTEMBER 1973—REVISED FEBRUARY 1992

NE555, SA555, SE555, SE555C

PRECISION TIMERS

POST OFFICE BOX 655303

13

APPLICATION INFORMATION

THRES

GND

C

RA

RL

VCC (5 V to 15 V)

Output

DISCH

OUT

VCC

RESET

TRIG

CONT

Modulation

Input

(see Note B)

Clock

Input

Time – 0.5 ms/div

Capacitor Voltage

Output Voltage

Clock Input Voltage

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.

RA = 3 kΩ

C = 0.02

µF

RL = 1 kΩ

See Figure 18

Modulation Input Voltage

48

3

7

6

2

5

Pin numbers shown are for the D, JG, and P packages only.

1

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.

RB

Modulation

Input

(see Note B)

CONT

TRIG

RESET

VCC

OUT

DISCH

Output

VCC (5 V to 15 V)

RL

RA

C

GND

THRES

RA = 3 kΩ

RB = 500 Ω

RL = 1 kΩ

See Figure 20

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

Output Voltage

Modulation Input Voltage

Time – 0.1 ms/div

Pin numbers shown are for the D, JG, and P packages only.

48

3

7

6

2

5

Figure 20. Circuit for Pulse-Position Modulation

Figure 21. Pulse Position-Modulation Waveforms