MC1455, MC1455B, NCV1455B
http://onsemi.com
7
APPLICATIONS INFORMATION
Linear Voltage Ramp
In the monostable mode, the resistor can be replaced by a
constant current source to provide a linear ramp voltage. The
capacitor still charges from 0 V
CC
to 2/3 V
CC
. The linear
ramp time is given by:
t =
2
3
V
CC
1
, where I =
V
CC
− V
B
− V
BE
R
E
If V
B
is much larger than V
BE
, then t can be made
independent of V
CC
.
Missing Pulse Detector
The timer can be used to produce an output when an input
pulse fails to occur within the delay of the timer. To
accomplish this, set the time delay to be slightly longer than
the time between successive input pulses. The timing cycle
is then continuously reset by the input pulse train until a
change in frequency or a missing pulse allows completion of
the timing cycle, causing a change in the output level.
Figure 20. Linear Voltage Sweep Circuit Figure 21. Missing Pulse Detector
Figure 22. Linear Voltage Ramp Waveforms Figure 23. Missing Pulse Detector Waveforms
Discharge
Threshold
V
CC
Reset 4
3
Digital
Output
2
Trigger
1
MC1455
8V
CC
R
E
R1
2N4403
or Equiv
V
B
R2
C
7
6
5
Sweep
Output
0.01 mF
Control
Voltage
+V
CC
(5.0 V to 15 V)
Reset
R
L
V
CC
R
A
7
6
5
Control
Voltage
0.01 mF
1
Trigger
Input
Output
48
C
2N4403
or Equiv
MC1455
t = 100 ms/cm
V
E
3
2
t = 500 ms/cm
(R
E
= 10 kW, R2 = 100 kW, R1 = 39 kW, C = 0.01 mF, V
CC
= 15 V) (R
A
= 2.0 kW, R
L
= 1.0 kW, C = 0.01 mF, V
CC
= 15 V)
I
