NE555/SA555/NA555

Document number: DS35112 Rev. 5 - 2

9 of 14

www.diodes.com

February 2021

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NE555

Missing Pulse Detector

The circuit shown in Figure 7 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 8.

0.01µF

THRES

TRIG

DISCH

RESET

CONT

GND

OUT

Output

2

5

1

3

8

4

(5V to 15V)

C

Input

7

6

Fig. 7 Circuit for Missing Pulse Detector

Fig. 8 Timing Waveforms for Missing Pulse

Detector

Frequency Divider

By adjusting the length of the timing cycle, the basic circuit of Figure 1 can be made to operate as a frequency divider. Figure 9 shows a

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

Fig. 9 Divide by Three Circuit Waveforms