NE555,SA555,SE555

PRECISION TIMERS

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9

APPLICATION INFORMATION

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

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.

Figure 18. Circuit for Pulse-Width Modulation

Time – 0.5ms/div

Figure 19. Pulse-Width-Modulation Waveforms

Pulse-position modulation

As shown in Figure 20, any of these timers can 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 shows a triangular-wave modulation signal for such a

circuit; however, any wave shape could be used.

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

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.

Figure 20. Circuit for Pulse-Position Modulation

Time – 0.1 ms/div

Figure 21. Pulse – Position – Modulation Waveforms