NE555,SA555,SE555

PRECISION TIMERS

www.artschip.com

8

APPLICATION INFORMATION

Missing-pulse detector

The circuit shown in Figure 15 can be used to detect a missing pulse or abnormally long spacing between consecutive pulses in a

train of pulses. The timing interval of the monostable circuit is retriggered continuously by the input pulse train as long as the pulse

spacing is less than the timing interval. A longer pulse spacing, missing pulse, or terminated pulse train permits the timing interval

to be completed, thereby generating an output pulse as shown in Figure 16.

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

Figure 15. Circuit for Missing-Pulse Detector

Time – 0.1ms/div

Figure 16. Completed-Timing Waveforms

For Missing-Pulse Detector

Frequency divider

By adjusting the length of the timing cycle, the basic circuit of Figure 9 can be made to operate as a frequency divider. Figure 17

shows a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle.

Time – 0.1 ms/div

Figure 17. Divide-by-Three Circuit Waveforms

Pulse-width modulation

The operation of the timer can be modified by modulating the internal threshold and trigger voltages, which is accomplished by

applying and external voltage (or current) to CONT. Figure 18 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 19 shows the resulting output

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