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Lista de partido

IC555

Single Timer

Fairchild Semiconductor 

5. Pulse Position Modulation

If the modulating signal is applied to the control terminal while the timer is connected for the astable operation, as in

Figure 12, the timer becomes a pulse position modulator.

In the pulse position modulator, the reference of the timer's internal comparators is modulated, which modulates the

timer output according to the modulation signal applied to the control terminal.

Figure 13 illustrates a sine wave for modulation signal and the resulting output pulse position modulation; however, any

wave shape be used.

+Vcc

RA

4

8

RESET

Vcc 7

DISCH

2 TRIG

RB

6

Output

THRES

3 OUT

Modulation

GND CONT 5

C

1

Figure 12. Circuit for Pulse Position Modluation

Figure 13. Wafeforms of pulse position modulation

6. Linear Ramp

When the pull-up resistor RA in the monostable circuit shown in Figure 2 is replaced with constant current source, the

VC1 increases linearly, generating a linear ramp. Figure 14 shows the linear ramp generating circuit and Figure 15 illus-

trates the generated linear ramp waveforms.

+Vcc

4

RESET

2 TRIG

8

Vcc

DISCH 7

Output

3 OUT

THRES 6

GND

1

CONT 5

RE R1

Q1

R2

C1

C2

Figure 14. Circuit for Linear Ramp

Figure 15. Waveforms of Linear Ramp

© 2002 Fairchild Semiconductor Corporation

LM555 Rev. 1.1.0

9

www.fairchildsemi.com

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