CA555, CA555C, LM555C
Figure 2 shows the typical waveforms generated during this
mode of operation, and Figure 3 gives the family of time
delay curves with variations in R and C .
Repeat Cycle Timer (Astable Operation)
Figure 4 shows the CA555 connected as a repeat cycle
timer. In this mode of operation, the total period is a function
1
T
of both R and R
2.
1
SWITCH S “OPEN”
1
3V
INPUT
VOLTAGE (TERMINAL 2)
V+
5V
SWITCH S “CLOSED”
1
0
R
1
2
4
3.3V
7
8
5
CAPACITOR
VOLTAGE (TERMINALS 6, 7)
EO
3
R
CA555
0
6
t
RELAY
COIL
D
1
2
5V
OUTPUT
VOLTAGE
C
0.01µF
T
(TERMINAL 3)
0
FIGURE 4. REPEAT CYCLE TIMER (ASTABLE OPERATION)
FIGURE 2. TYPICAL WAVEFORMS FOR RESET TIMER
T = 0.693 (R + 2R ) C = t + t
2
1
2
T
1
100
where t = 0.693 (R + R ) C
T
1
1
2
o
= 25 C
T
A
and t = 0.693 (R ) C
V+ = 5V
2
2
T
10
1
the duty cycle is:
R
= 1kΩ
1
t
R + R
1 2
R + 2R
1 2
1
10kΩ
--------------- ------------------------
=
t
+ t
100kΩ
1
2
1MΩ
0.1
10MΩ
Typical waveforms generated during this mode of operation
are shown in Figure 5. Figure 6 gives the family of curves of
free running frequency with variations in the value of
0.01
0.001
(R + 2R ) and C .
1
2
T
-5
10
-4
10
-3
10
-2
-1
10
10
1
10
TIME DELAY(s)
FIGURE 3. TIME DELAY vs RESISTANCE AND CAPACITANCE
4
INTERSIL [ Intersil ]
