2.5 Tri-level Voltage Detector
The tri-level voltage detector of
Figure 13
provides a type of
window comparator function. It detects three different input
voltage ranges: Min-range, Mid-range, and Max-range. The
output voltage (V
O
) is at V
CC
for the Min-range. V
O
is
clamped at GND for the Mid-range. For the Max-range, V
O
is
at V
ee
.
Figure 14
shows a V
O
vs. V
I
oscilloscope photo per
the circuit of
Figure 13.
Its operation is as follows: V
I
deviating from GND, causes
the diode bridge to absorb I
IN
to maintain a clamped condi-
tion (V
O
= 0V). Eventually, I
IN
reaches the bias limit of the di-
ode bridge. When this limit is reached, the clamping effect
stops and the op amp responds open loop. The design equa-
tion directly preceding
Figure 14,
shows how to determine
the clamping range. The equation solves for the input volt-
age band on each side GND. The mid-range is twice this
voltage band.
DS100128-89
|
∆v
|
∆v
|
OV
-Vo
+Vo
-VIN
OV
+VIN
DS100128-35
DS100128-34
FIGURE 14. X, Y Oscilloscope Trace showing V
OUT
vs
V
IN
per the Circuit of
Figure 13
FIGURE 13. Tri-level Voltage Detector
15
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