LM555CMX_12 FAIRCHILD [Fairchild Semiconductor], LM555CMX_12 Datasheet - Page 8

• Manufacturer Part Number: LM555CMX_12
• Description: Single Timer
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

LM555
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
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.
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Figure 9. Circuit for Pulse Width Modulation
Trigger
Output
2
3
TRIG
OUT
RESET
4
GND
1
Vcc
THRES
DISCH
8
CONT
Figure 8. Waveforms of Frequency Divider Operation
7
6
5
Input
C
R
A
+Vcc
Figure 10. Waveforms of Pulse Width Modulation