KA555

8

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 monos table 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 an example of pulse width modulation waveform.

5. Pulse Position Modulation

If the modulating signal is applied to the control terminal while the timer is connected for 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

8

4

7

1

2

3

5

6

CONT

GND

Vcc

DISCH

THRES

RESET

TRIG

OUT

+Vcc

Trigger

R

A

C

Output

Input

Figure 9. Circuit for Pulse Width Modulation

Figure 10. Waveforms of Pulse Width Modulation