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− Output Pulse Duration − s
C − Capacitance − µF
10
1
10
−1
10
−2
10
−3
10
−4
1001010.10.01
10
−5
0.001
t
w
R
A
= 10 MΩ
R
A
= 10 kΩ
R
A
= 1 kΩ
R
A
= 100 kΩ
R
A
= 1 MΩ
Voltage − 2 V/div
Time − 0.1 ms/div
Capacitor Voltage
Output Voltage
Input Voltage
R
A
= 9.1 kΩ
C
L
= 0.01 µF
R
L
= 1 kΩ
See Figure 9
Astable Operation
Voltage − 1 V/div
Time − 0.5 ms/div
t
H
Capacitor Voltage
Output Voltage
t
L
R
A
= 5 kW R
L
= 1 kW
R
B
= 3 kW See Figure 12
C = 0.15 µF
GND
OUT
V
CC
CONT
RESET
DISCH
THRES
TRIG
C
R
B
R
A
Output
R
L
0.01 µF
V
CC
(5 V to 15 V)
(see Note A)
NOTE A: Decoupling CONT voltage to ground with a capacitor can
improve operation. This should be evaluated for individual
applications.
Open
5 8
4
7
6
2
3
1
Pin numbers shown are for the D, JG, P, PS, and PW packages.
NA555 , NE555 , SA555 , SE555
PRECISION TIMERS
SLFS022F – SEPTEMBER 1973 – REVISED JUNE 2006
APPLICATION INFORMATION (continued)
Figure 10. Typical Monostable Waveforms Figure 11. Output Pulse Duration vs Capacitance
As shown in Figure 12 , adding a second resistor, R
B
, to the circuit of Figure 9 and connecting the trigger input to
the threshold input causes the timer to self-trigger and run as a multivibrator. The capacitor C charges through
R
A
and R
B
and then discharges through R
B
only. Therefore, the duty cycle is controlled by the values of R
A
and
R
B
.
This astable connection results in capacitor C charging and discharging between the threshold-voltage level
( ≈ 0.67 × V
CC
) and the trigger-voltage level ( ≈ 0.33 × V
CC
). As in the monostable circuit, charge and discharge
times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.
Figure 12. Circuit for Astable Operation Figure 13. Typical Astable Waveforms
10
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