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3 VOLT LOW BATTERY
VOLTAGE FLASHER This circuit is designed to monitor two alkaline cells (3v) that form the
battery often used in portable electronic equipment. It use an inexpensive IC
from Panasonic that is connected to an efficient LED flashing circuit. When
the battery voltage drops below a certain point the circuit flashes the LED.
In the off state the circuit draws only 1uA, while in the active flashing state it
draws 20uA. Published in EDN, Jan 2, 1997
9v Battery Voltage Monitor uses a
LTC1440 comparator
This circuit turns on a LED whenever the voltage of a standard 9v battery connected
to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also
contains a 1.18v reference diode. In standby mode, the circuit draws only 4uA.
Lead-acid Battery Low Voltage Indicator
Lead-acid batteries should not be discharged below a certain voltage. Discharging
a cell below about 1.8v and can often damage it, which will result in a lower amp-hour
capacity. Large battery banks are critical in off-grid energy storage systems.
One bad cell in a series wired string will weaken the whole bank. The circuits
below are designed to be connected across either a single 2 volt cell or a 6v three cell
battery bank. It will alert the user of a weak cell by turning on a red LED when
the cell voltages drop below 1.8v. The circuit takes advantage of a low voltage
LMP2231 op amp from Nation Semiconductor and a LM385 voltage reference in the first
circuit. In that circuit the red LED must have a forward voltage of about 1.6v at 5ma,
in order to operate properly. In the second three cell bank circuit, a TLV3701
voltage comparator is used. The circuits are simple enough that they could be
placed on a postage stamp size circuit board. [Designed by David A. Johnson]
