參數(shù)資料
型號： AN1872
廠商： Maxim Integrated Products, Inc.
英文描述： Low-Battery Indicator Has Low Cost and High Efficiency
中文描述： 低電池指標，低成本，高效率
文件頁數(shù)： 2/2頁
文件大?。?/td> 223K
代理商： AN1872
www.maxim-ic.com/an1872 Page 2 of 2
Note that LBO (active high) is usable as shown, but an active-low warning (LBO-bar) requires
the optional circuitry shown in the box. IC1 then turns on, causing the LED to flash in
accordance with the following analysis:
First, keep the duty cycle low:
DC = t
ON
/(t
ON
+ t
OFF
).
On-time is derived from the equation for time-varying voltage across a charging capacitor:
V(t) = V(1 - e
-t/RC
).
t
ON
= -R
5
Cln(1 - V
TRIPHI
/V
OUT
).
Off-time is derived from the equation for time-varying voltage across a discharging capacitor:
V(t) = Ve
-t/RC
.
t
OFF
= -R
4
Cln(V
TRIPLO
/V
OUT
).
The comparator's high and low trip levels are found using Kirchoff's current laws:
V
TRIPHI
= V
OUT
[R
3
(R
1
+ R
2
)] / [R
3
(R
1
+ R
2
) + R
1
R
2
].
V
TRIPLO
= V
OUT
[R
3
R
2
] / [R
3
(R
1
+ R
2
) + R
1
R
2
].
The typical V
OUT
for a comparator is V
DD
. Assuming a 2.5% duty cycle, and assuming that
LBO trips the comparator on when battery voltage equals 3V, the resulting trip levels are 1V
for low and 2V for high. The standard component values corresponding to this performance
are:
C1 = 0.1μF
R1 = R2 = R3 = 1M
R4 = 3.6M
R5 = 91k .
The circuit accommodates any type of LBO output (active high or active low). Supply current
drawn by IC1 is typically 35μA when active and only 0.05μA while in shutdown. The circuit's
small size, low power consumption, and low cost are ideal for battery-powered systems.
A similar version of this article appeared in the May 3, 2001 issue of
EDN
magazine.
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