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參數資料
| 型號： | LMC555 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | CMOS Timer |
| 中文描述： | 的CMOS定時器 |
| 文件頁數： | 6/12頁 |
| 文件大小： | 318K |
| 代理商： | LMC555 |
Application Info
(Continued)
The charge time (output high) is given by
t
1
= Ln2 (R
A
+ R
B
)C
And the discharge time (output low) by:
t
2
= Ln2 (R
B
)C
Thus the total period is:
T = t
1
+ t
2
= Ln2 (R
A
+ R
B
)C
The frequency of oscillation is:
Figure 6 may be used for quick determination of these RC
Values. The duty cycle, as a fraction of total period that the
output is low, 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 7shows the waveforms generated in a divide by three
circuit.
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 the Control
Voltage Terminal. Figure 8 shows the circuit, and in Figure 9
are some waveform examples.
PULSE POSITION MODULATOR
This application uses the timer connected for astable opera-
tion, as in Figure 10 with a modulating signal again applied
to the control voltage terminal. The pulse position varies with
DS008669-12
V
= 5V
TIME = 20 μs/Div.
R
A
= 3.9k
R
= 9k
C = 0.01μF
Top Trace: Output 5V/Div.
Bottom Trace: Capacitor Voltage 1V/Div.
FIGURE 5. Astable Waveforms
DS008669-13
FIGURE 6. Free Running Frequency
DS008669-14
V
CC
= 5V
TIME = 20 μs/Div.
R
= 9.1 k
C = 0.01μF
Top Trace: Input 4V/Div.
Middle Trace: Output 2V/Div.
Bottom Trace: Capacitor 2V/Div.
FIGURE 7. Frequency Divider Waveforms
DS008669-20
FIGURE 8. Pulse Width Modulator
DS008669-15
V
CC
= 5V
TIME = 0.2 ms/Div.
R
A
= 9.1 k
C = 0.01μF
FIGURE 9. Pulse Width Modulator Waveforms
Top Trace: Modulation 1V/Div.
Bottom Trace: Output Voltage 2V/Div.
L
www.national.com
6
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