ICL8211 Datasheet, PDF (14/14 Pages) Intersil Corporation – Programmable Voltage Detectors

ICL8211, ICL8212
application shown, the first ICL8212 is used as a zero cross-
ing detector. The output circuit consisting of R₃, R₄ and C₂
results in a slow output positive ramp. The negative range is
much faster than the positive range. R₅ and R₆ provide hys-
teresis so that under all circumstances the second ICL8212
is turned on for sufficient time to discharge C₃. The time con-
stant of R₇ C₃ Is much greater than R₄ C₂. Depending upon
the desired output polarities for low and high input frequen-
cies, either an ICL8211 or an ICL8212 may be used as the
output driver.
This circuit is sensitive to supply voltage variations and
should be used with a stabilized power supply. At very low
frequencies the output will switch at the input frequency.
Switch Bounce Filter (Figure 37)
Single pole single throw (SPST) switches are less costly and
more available than single pole double throw (SPDT) switches.
SPST switches range from push button and slide types to cal-
culator keyboards. A major problem with the use of switches is
the mechanical bounce of the electrical contacts on closure.
Contact bounce times can range from a fraction of a millisecond
to several tens of milliseconds depending upon the switch type.
During this contact bounce time the switch may make and
break contact several times. The circuit shown in Figure 37 pro-
vides a rapid charge up of C₁ to close to the positive supply
V+
C₁
INPUT
R₂
R₁
1
8
R₄
2
ICL8212 ⁷
3
6
R₅
A
4
5
1
R₆
8
R₇
2
ICL8212
7
3
6
B
4
5
1
8
ICL8211
2
OR
ICL8212
7
3
#3
6
4
5
R₃
C₂
C₃
TIME CONSTANT R₃C₂ < R₄C₂ ≤ R₇C₃
VARY R₁ FOR OPTION ZERO CROSSING DETECTION
VARY R₄ TO SET DETECTION FREQUENCY
R₆
OUTPUT
INPUT
1.15V
A
1.15V
B
R₄ 100Ω
R₂
R₃
R_{1 C1}
ON TIME #2
OFF
INDETERMINATE
BELOW F_O
ON
F_O FREQUENCY
FIGURE 36. FREQUENCY LIMIT DETECTOR
1
8
2
ICL8211 ₇
OR
3 ICL8212 6
4
5
V+
500k
R_L
56k
V_O
1
2
ICL8212
3
4
4.7k
8
7
6
3.9k
5
ON
OFF
V-
OUTPUT
REFERENCE
LM199
FIGURE 37. SWITCH BOUNCE FILTER
FIGURE 38. LOW VOLTAGE POWER SUPPLY DISCONNECT
7-174