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參數(shù)資料
| 型號： | UPC1555G2 |
| 廠商： | NEC Corp. |
| 英文描述： | TIMER CIRCUIT |
| 中文描述： | 定時器電路 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 103K |
| 代理商： | UPC1555G2 |
8
μ
PC1555
When the
μ
PC1555 is used in a circuit configuration
shown in Fig. d, the circuit is triggered by itself to
operate as an astable multivibrator, because pin 2
(trigger pin) and pin 6 (threshold pin) are connected to
each other. When the output voltage is high, capacitor
C
1
is charged through R
1
and R
2
. When C
1
is charged
up to a voltage two-thirds as high as V
CC
, the threshold
pin is turned on, and the output pin becomes low. At
this point C
1
starts discharging through R
2
. When C
1
discharges, and the voltage across C
1
decreases to a
voltage one-third as high as V
CC
, the trigger pin is turned
on, and the output voltage becomes high, causing the
charge current to flow into C
1
through R
1
and R
2
again.
This operation is shown in Fig. e. Because C
1
repeats
charging and discharging between one-third as high as
V
CC
and two-thirds as high as V
CC
, the oscillation
frequency is not affected by the supply voltage.
Oscillation is represented theoretically using the
following expressions.
When the output voltage is high, the charge time is
When the output voltage is low, the discharge time is :
Adding expressions (1) and (2) determines period T
Therefore, the oscillation frequency is
(see Fig. f for reference)
......................................
:
t
1
= 0.693 (R
1
+ R
2
) C
1
..........................................(1)
t
2
= 0.693
R
2
C
1
.................................................(2)
T = t
1
+ t
2
= 0.693 (R
1
+ 2R
2
) C
1
..........................(3)
:
:
f =1
=
1.44
(4)
T
(R
1
+ 2R
2
) C
1
R
2
R
1
+ 2R
2
The duty cycle is determined by the equation (5)
:
D =
(5)
The values obtained this way are approximate values, however. If it is necessary to obtain an accurate oscillation
frequency, determine R
1
, R
2
, and C
1
through actual measurement and confirmation; a trimmer should be used as
required. Moreover, R
1
and R
2
should be 300
or higher.
Note 10.
If the load is connected across the output and GND pins, a “staircase” occurs in the output waveform.
........................................................
(2) Astable multivibrator example
Fig. d Astable Multivibrator Example
Fig. e Astable Multivibrator Response Waveform
Fig. f Interrelationships among Oscillation
Frequency, R1, R2, and C1
(approximate value obtained by
calculation)
3
5
4
8
7
6
2
1
V
CC
= 5 to 15 V
C
1
OUTPUT
0.01 F
R
L
R
1
R
2
PC1555
μ
Control voltage
Note 10
(Free running frequency)
t = 0.5 ms/DIV
(R
1
= R
2
= 4.8 k
, C1 = 0.1 F, R
L
= 1 k
)
"H"
"H"
"H"
"L"
"L"
Output voltage: 5 V/DIV
Capacitor (C
1
) voltage: 1.7 V/DIV
100
10
0.1
1.0
10
100 1.0 k
10 k 100 k
1.0
0.1
0.01
0.001
1 M
10M
10k
1
1
(R
1
+ 2R
2
)
Oscillation frequency f (Hz)
C
μ
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