LM555J/883 National Semiconductor, LM555J/883 Datasheet - Page 8

• Manufacturer Part Number: LM555J/883
• Description: IC,TIMER,BIPOLAR,DIP,8PIN,CERAMIC
• Manufacturer: National Semiconductor

www.national.com
Applications Information
Figure 5 shows the waveforms generated in this mode of
operation.
V
TIME = 20µs/DIV.
R
R
C = 0.01µF
The charge time (output high) is given by:
And the discharge time (output low) by:
Thus the total period is:
The frequency of oscillation is:
Figure 6 may be used for quick determination of these RC
values.
The duty cycle is:
FREQUENCY DIVIDER
The monostable circuit of Figure 1 can be used as a fre-
quency divider by adjusting the length of the timing cycle.
Figure 7 shows the waveforms generated in a divide by three
circuit.
CC
A
B
= 3.9k
= 3k
= 5V
FIGURE 6. Free Running Frequency
FIGURE 5. Astable Waveforms
T = t
Bottom Trace: Capacitor Voltage 1V/Div.
t
Top Trace: Output 5V/Div.
1
1
+ t
= 0.693 (R
t
2
2
= 0.693 (R
= 0.693 (R
A
+ R
B
) C
A
B
+2R
) C
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B
(Continued)
) C
8
V
TIME = 20µs/DIV. Middle Trace: Output 2V/Div.
R
C = 0.01µF
PULSE WIDTH MODULATOR
When the timer is connected in the monostable mode and
triggered with a continuous pulse train, the output pulse
width can be modulated by a signal applied to pin 5. Figure
8 shows the circuit, and in Figure 9 are some waveform
examples.
V
TIME = 0.2 ms/DIV. Bottom Trace: Output Voltage 2V/Div.
R
C = 0.01µF
CC
CC
A
A
= 9.1k
= 9.1k
= 5V
= 5V
FIGURE 8. Pulse Width Modulator
FIGURE 9. Pulse Width Modulator
FIGURE 7. Frequency Divider
Bottom Trace: Capacitor 2V/Div.
Top Trace: Input 4V/Div.
Top Trace: Modulation 1V/Div.
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