Battery fuel gauge using safety circuit

Details Battery fuel gauge using safety circuit Battery fuel gauge using safety circuit

2005-11-29

2005-11-29

Tibbits, Pia (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

With charging

C320SDIG021, C340S636120

Reexamination Certificate

active

06969974

ABSTRACT:
A safety circuit for a rechargeable cell is employed as a simple, low cost, fuel gauging circuit. The safety circuit includes an undervoltage circuit having a reference voltage. The input of the safety circuit is selectively coupled between the voltage of a rechargeable cell and a scaled down voltage of the rechargeable cell. The scaled down voltage corresponds to a predetermined capacity threshold. A user or electronic device actuates a switch that couples the scaled down voltage to the safety circuit. The safety circuit compares this scaled down voltage to the reference voltage of it's under voltage circuit. If the scaled down voltage is above the reference voltage, the safety circuit causes a transistor coupled serially with the cell to be on, or in a conductive state, so as to allow current to flow through a capacity indicator like a LED. If the scaled down voltage is below the reference voltage the safety circuit causes the transistor to enter a high impedance state, thereby turning the indicator off. The state of the indicator provides the user with an approximation of the cell's remaining capacity. In a battery pack, two or more safety circuits with different reference voltages may be employed for increased resolution.

REFERENCES:
patent: 5767657 (1998-06-01), Oglesbee
patent: 6304063 (2001-10-01), Maloizel et al.
patent: 6879133 (2005-04-01), Geren
patent: 2004/0036620 (2004-02-01), Herrmann et al.

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