4
QR-D-IV-0016A3(A)
A
A3
Edition
Date
Approved By
Checked By
Drawing By
Drawing
Number
Name
File
Material
5
F
1
E
D
3
2
C
B
A
1
2
3
4
7
6
F
E
D
5
6
7
C
B
8
PELLENC
BT-001 Trigger Test Board
2 rows 8 channels 2.54MM
2012-02-11
ASTABLEOPERATION
When the circuit is connected as shown in figure 13
(pin 2and 6 connected)it triggers itself andfree runs
as a multivibrator. The external capacitor charges
throughR1 and R2 and discharges throughR2 only.
Thus the duty cyclemay beprecisely set by the ratio
of these two resistors.
In the astable mode of operation, C1 charges and
discharges between 1/3 Vcc and 2/3 Vcc. As in the
triggeredmode, thechargeanddischarge timesand
therefore frequency are independent of the supply
voltage.
Figure 14showsactualwaveforms generatedin this
mode of operation.
The charge time (output HIGH) is given by :
t1 = 0.693 (R1 +R2) C1
and the discharge time (outputLOW) by :
t2 = 0.693 (R2) C1
Thus the total period T is given by :
T = t1 + t2 = 0.693 (R1 + 2R2) C1
The frequency ofoscillation is them :
·ÇÎÈ̬¶àгÕñµ´Æ÷
1
GND
2
TRIGGER
3
OUTPUT
4
RESET
8
VCC
7
DISCHARGE
6
THRESHOLD
5
CONTROL
U2
NE555DT STMicroelectronics
C1
104
R2
100K
1
GND
2
TRIGGER
3
OUTPUT
4
RESET
8
VCC
7
DISCHARGE
6
THRESHOLD
5
CONTROL
U1
NE555DT STMicroelectronics
1
GND
2
OUT1
3
OUT2
4
VCC12V
5
NC1
6
NC2
7
NC3
8
NC4
J1
TE CONNECTIVITY / AMP - 215307-4 ¨C Straight case
1
D
3
S
2
G
Q2
2N7002
1
D
3
S
2
G
Q1
2N7002
R1
1K
C2
33UF/20V
R3
1K
R4
100K
C3
22UF/20V
C4
104
GND
+12V
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