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555

PRECISION TIMERS

Diodes Incorporated. 

NE555/SA555/NA555

PRECISION TIMERS

Typical Applications Characteristics (cont.)

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 10 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 11 shows the

resulting output pulse-width modulation. While a sine-wave modulation signal is shown, any wave shape could be used.

Fig 10. Circuit for Pulse width modulation

Fig 11. Pulse width modulation timing diagrams

Pulse Position Modulation

As shown in Figure 12, 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 13 shows a triangular-wave modulation

signal for such a circuit; however, any wave shape could be used.

Fig 12. Circuit for pulse position modulation

Fig 13. Pulse position modulation timing diagrams

NE555/SA555/NA555

Document number: DS35112 Rev. 4 - 2

10 of 14

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February 2012

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