LM555/NE555/SA555

8

8

8

8

4. Pulse Width Modulation

4. Pulse Width Modulation

4. Pulse Width Modulation

4. Pulse Width Modulation

The timer output waveform may be changed by modulating the control voltage applied to the timer's pin 5 and changing the

reference of the timer's internal comparators. Figure 9 illustrates the pulse width modulation circuit.

When the continuous trigger pulse train is applied in the monostable mode, the timer output width is modulated according to

the signal applied to the control terminal. Sine wave as well as other waveforms may be applied as a signal to the control

terminal. Figure 10 shows the example of pulse width modulation waveform.

5. Pulse Position Modulation

5. Pulse Position Modulation

5. Pulse Position Modulation

5. Pulse Position Modulation

If the modulating signal is applied to the control terminal while the timer is connected for the astable operation as in Figure 11,

the timer becomes a pulse position modulator.

In the pulse position modulator, the reference of the timer's internal comparators is modulated which in turn modulates the

timer output according to the modulation signal applied to the control terminal.

Figure 12 illustrates a sine wave for modulation signal and the resulting output pulse position modulation : however, any wave

shape could be used.

Figure 8. Waveforms of Frequency Divider Operation

Figure 8. Waveforms of Frequency Divider Operation

Figure 8. Waveforms of Frequency Divider Operation

Figure 8. Waveforms of Frequency Divider Operation

Figure 9. Circuit for Pulse Width Modulation

Figure 9. Circuit for Pulse Width Modulation

Figure 9. Circuit for Pulse Width Modulation

Figure 9. Circuit for Pulse Width Modulation

Figure 10. Waveforms of Pulse Width Modulation

Figure 10. Waveforms of Pulse Width Modulation

Figure 10. Waveforms of Pulse Width Modulation

Figure 10. Waveforms of Pulse Width Modulation

8

4

7

1

2

3

5

6

CONT

GND

Vcc

DISCH

THRES

RESET

TRIG

OUT

+Vcc

+Vcc

+Vcc

+Vcc

Trigger

Trigger

Trigger

Trigger

R

R

R

R

A

A

A

A

C

C

C

C

Output

Output

Output

Output

Input

Input

Input

Input