LM555 datasheet(9/12 Pages) NSC

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Applications Information (Continued)

PULSE POSITION MODULATOR

This application uses the timer connected for astable opera-

tion, as in Figure 10, with a modulating signal again applied

to the control voltage terminal. The pulse position varies with

the modulating signal, since the threshold voltage and hence

the time delay is varied. Figure 11 shows the waveforms

generated for a triangle wave modulation signal.

LINEAR RAMP

When the pullup resistor, R

A, in the monostable circuit is

replaced by a constant current source, a linear ramp is

generated. Figure 12 shows a circuit configuration that will

perform this function.

Figure 13 shows waveforms generated by the linear ramp.

The time interval is given by:

BE . 0.6V

00785113

VCC = 5V

Top Trace: Modulation 1V/Div.

TIME = 0.2 ms/DIV.

Bottom Trace: Output Voltage 2V/Div.

RA = 9.1kΩ

C = 0.01µF

FIGURE 9. Pulse Width Modulator

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FIGURE 10. Pulse Position Modulator

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VCC = 5V

Top Trace: Modulation Input 1V/Div.

TIME = 0.1 ms/DIV.

Bottom Trace: Output 2V/Div.

RA = 3.9kΩ

RB =3kΩ

C = 0.01µF

FIGURE 11. Pulse Position Modulator

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FIGURE 12.

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