LM555/NE555/SA555

5

5

5

5

Figure 1 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls

below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's

internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C1

and setting the flip-flop output at the same time.

When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop,

turning the discharging Tr. on. At this time, C1 begins to discharge and the timer output converts to low.

In this way, the timer operating in the monostable repeats the above process. Figure 2 shows the time constant relationship

It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer

output turns low. That is, although the output remains unaffected even if a different trigger pulse is applied while the output is

high, it may be affected and the waveform does not operate properly if the trigger pulse voltage at the end of the output pulse

remains at below Vcc/3. Figure 4 shows such a timer output abnormality.

2. Astable Operation

2. Astable Operation

2. Astable Operation

2. Astable Operation

Figure 4. Waveforms of Monostable Operation (abnormal)

Figure 4. Waveforms of Monostable Operation (abnormal)

Figure 4. Waveforms of Monostable Operation (abnormal)

Figure 4. Waveforms of Monostable Operation (abnormal)

100m

100m

100m

100m

1

11

110

10

10

10

100

100

100

100

1k

1k

1k

1k

10k

10k

10k

10k

100k

100k

100k

100k

1E-3

1E-3

1E-3

1E-3

0.01

0.01

0.01

0.01

0.1

0.1

0.1

0.1

1

11

1

10

10

10

10

100

100

100

100

(R

(R

(R

(R

A

A

A

+2R

+2R

+2R

B

B

B

)))

Fr equency(Hz)

Fr equency(Hz)

Fr equency(Hz)

Fr equency(Hz)

Figure 5. Astable Circuit

Figure 5. Astable Circuit

Figure 5. Astable Circuit

Figure 5. Astable Circuit

Figure 6. Capacitance and Resistance vs. Frequency

Figure 6. Capacitance and Resistance vs. Frequency

Figure 6. Capacitance and Resistance vs. Frequency

Figure 6. Capacitance and Resistance vs. Frequency

1

5

6

7

8

4

2

3

RESET

Vcc

DISCH

THRES

CONT

GND

OUT

TRIG

+Vcc

C1

C2