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參數(shù)資料
| 型號： | SA555 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Precision Timers(精密定時器) |
| 中文描述： | 精密計時器（精密定時器） |
| 文件頁數(shù)： | 6/10頁 |
| 文件大?。?/td> | 110K |
| 代理商： | SA555 |
CAPACITOR VOLTAGE = 2.0V/div
R1 = 9.1k
, C1 = 0.01
μ
F, R = 1k
t = 0.1 ms / div
INPUT = 2.0V/div
OUTPUT VOLTAGE = 5.0V/div
Figure 11
Reset
Trigger
Output
R1
C1
Control Voltage
0.01
μ
F
NE555
= 5 to 15V
V
CC
4
2
3
1
5
6
7
8
Figure10
C
(
μ
F)
10
1.0
0.1
0.01
0.001
10
s
100
s
1.0
ms
10
ms
100
ms
10
s
(t )
10M
1M
100
10k
R1=1
Figure 12
APPLICATION INFORMATION
MONOSTABLEOPERATION
In the monostable mode, the timer functions as a
one-shot.Referring tofigure10 theexternalcapaci-
tor is initially held discharged by a transistorinside
thetimer.
Thecircuit triggerson a negative-goinginput signal
whenthelevelreaches1/3Vcc. Oncetriggered,the
circuit remains in this state until the set time has
elapsed, even if it is triggered again during this in-
terval.ThedurationoftheoutputHIGHstateisgiven
by t = 1.1 R
1
C
1
andis easilydeterminedby
figure 12.
Notice that since the chargerate and the threshold
levelofthecomparatorarebothdirectlyproportional
to supply voltage,the timing intervalis independent
ofsupply.Applyinganegativepulsesimultaneously
to the reset terminal (pin 4) and the trigger terminal
(pin 2) during the timing cycle discharges theexter-
nalcapacitorandcausesthecycleto startover.The
timing cycle now starts on the positive edge of the
reset pulse. During the time the reset pulse in ap-
plied, theoutput is driven to its LOW state.
Whenanegativetriggerpulseisappliedtopin2, the
flip-flop is set, releasingthe short circuit across the
externalcapacitor anddrivingtheoutputHIGH.The
voltage across the capacitor increases exponen-
tiallywith thetimeconstant
τ
=R
1
C
1
. Whenthe volt-
ageacrossthecapacitorequals2/3V
cc
,thecompa-
ratorresetstheflip-flopwhichthendischargetheca-
pacitor rapidly and drivers the output to its LOW
state.
Figure11showstheactualwaveformsgeneratedin
thismode of operation.
When Reset is not used, it should be tied high to
avoidany possiblyor false triggering.
ASTABLEOPERATION
Whenthe circuit is connectedasshownin figure13
(pin2and6connected)ittriggersitself andfreeruns
as a multivibrator. The external capacitor charges
throughR
1
andR
2
and discharges throughR
2
only.
Thusthedutycyclemay bepreciselyset bytheratio
of thesetwo resistors.
In the astable mode of operation, C
1
charges and
dischargesbetween 1/3 V
cc
and 2/3 Vcc. Asin the
triggeredmode,thechargeanddischargetimesand
therefore frequency are independentof the supply
voltage.
NE555/SA555/SE555
6/10
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