NE556D Ver la hoja de datos (PDF) - ON Semiconductor
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NE556D Datasheet PDF : 10 Pages
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Figure 15. Monostable Circuit
+VCC (5.0 V to 15 V)
MC3456
RL
Reset
4 (10)
5 (9)
VCC
RA
14 Discharge
1 (13)
Output
6 (8)
RL
Trigger
1/2
MC3456
7 Gnd
2 (12)
C
Threshold
3 (11)
Control
Voltage
0.01 µF
Pin numbers in parenthesis ( ) indicate B–Channel
Figure 16. Monostable Waveforms
t = 50 µs/cm
(RA = 10 kΩ, C = 0.01 µF, RL = 1.0 kΩ, VCC = 15 V)
Figure 17. Astable Circuit
+VCC (5.0 to 15 V)
RL
Reset
VCC
RA
4 (10)
14
Output
1 (13) Discharge
5 (9)
1/2
MC3456
2 (12) Threshold
RB
Trigger
RL
6 (8)
3 (11)
Control
7 Gnd
Voltage
0.01 µF C
Figure 18. Astable Waveforms
t = 20 µs/cm
(RA = 5.1 kΩ, C = 0.0 1 µF, RL = 1.0 kΩ, RB = 3.9 kΩ, VCC = 15 V)
Astable Mode
In the astable mode the timer is connected so that it will
retrigger itself and cause the capacitor voltage to oscillate
between 1/3 VCC and 2/3 VCC (see Figure 17).
The external capacitor charges to 2/3 VCC through RA and
RB and discharges to 1/3 VCC through RB. By varying the
ratio of these resistors the duty cycle can be varied. The
charge and discharge times are independent of the supply
voltage.
The charge time (output high) is given by:
t1 = 0.695 (RA+RB) C
The discharge time (output low) by:
t2 = 0.695 (RB) C
Thus the total period is given by:
T = t1 + t2 = 0.695 (RA + 2RB) C
The frequency of oscillation is then: f =
1
T
=
1.44
(RA +2RB) C
and may be easily found as shown in Figure 19.
The duty cycle is given by: DC =
RB
RA +2RB
To obtain the maximum duty cycle, RA must be as small as
possible; but it must also be large enough to limit the
discharge current (Pin 7 current) within the maximum rating
of the discharge transistor (200 mA).
The minimum value of RA is given by:
RA ≥
VCC (Vdc) ≥
I7 (A)
VCC (Vdc)
0.2
Figure 19. Free Running Frequency
100
10
1.0
0.1
0.01
0.001
0.1
(RA + 2 RB)
1.0
10
100 1.0 k
10 k
f, FREE RUNNING FREQUENCY (Hz)
100 k
6
MOTOROLA ANALOG IC DEVICE DATA
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