Datasheet

WINDOW COMPARATOR
V =
H
R
2
R +R
1 2
´ V
S
(5)
V =
L
R
4
R +R
3 4
´ V
S
(6)
V
S
A1
A2
D1
(2)
D2
(2)
R
5
10kW
R
6
5.1kW
R
7
5.1kW
R
2kW
(1)
IN
V
S
V
S
Q1
(3)
R
1
V
H
V
L
R
2
1/2
OPA2379
1/2
OPA2379
V
S
V
OUT
V
IN
V
S
R
3
R
4
OPA379
OPA2379
OPA4379
www.ti.com ................................................................................................................................................... SBOS347D – NOVEMBER 2005 – REVISED MAY 2008
The window comparator threshold voltages are set as
follows:
Figure 24 shows the OPA2379 used as a window
comparator. The threshold limits are set by V
H
and
V
L
, with V
H
> V
L
. When V
IN
< V
H
, the output of A1 is
low. When V
IN
> V
L
, the output of A2 is low.
Therefore, both op amp outputs are at 0V as long as
V
IN
is between V
H
and V
L
. This architecture results in
no current flowing through either diode, Q1 in cutoff,
with the base voltage at 0V, and V
OUT
forced high.
If V
IN
falls below V
L
, the output of A2 is high, current
flows through D2, and V
OUT
is low. Likewise, if V
IN
rises above V
H
, the output of A1 is high, current flows
through D1, and V
OUT
is low.
(1) R
IN
protects A1 and A2 from possible excess current flow.
(2) IN4446 or equivalent diodes.
(3) 2N2222 or equivalent NPN transistor.
Figure 24. OPA2379 as a Window Comparator
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