Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2002-02-28
2003-06-17
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S136000
Reexamination Certificate
active
06580250
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to a circuit for protecting a battery, and more particularly, to a circuit for protecting a rechargeable battery wherein a control circuit and a FET switch are integrated onto a single integrated circuit device.
(2) Description of the Prior Art
Rechargeable batteries are used in a variety applications of portable electronic devices. In particular, rechargeable batteries are used for portable phones. Several types of batteries are used in the art, most notably those comprising lithium ion or Li
+
. For optimum battery life and performance, the battery must be protected from excessive charging voltage during recharging and from over discharging while supplying the appliance.
Referring now to
FIG. 1
, an exemplary prior art battery protection circuit is shown. A rechargeable battery
10
is configured such that it can source energy to a load
34
or can be recharged by a charger source
38
. Two MOSFET switches N
1
18
and N
2
26
are used to control the flow of current into (charging) and out of (discharging) the battery. The control circuit
14
controls the ON and OFF state of the switches
18
and
26
. Typically, the switches comprise discrete devices. The control circuit
14
typically comprises a separate circuit from the switches. Each switch
18
and
26
contains a parasitic bulk-to-drain diode D
1
22
and D
2
30
. By coupling each switch in an opposite manner, each of the parasitic diodes
22
and
30
conducts current in a different direction.
During normal charging or discharging of the battery
10
, both of the switches are ON. However, if the control circuit
14
detects an over charging voltage from VBATT to GND, then the control circuit turns OFF the switch N
1
. Since the parasitic diode D
1
22
also blocks current flow into the battery, the battery stops charging. In the case of an over discharging condition, the control circuit
14
would detect a too low battery voltage from VBATT to GND. The other switch N
2
26
would be turned OFF. In this case, the parasitic diode D
2
30
blocks current flow out of the battery
10
.
The prior art circuit has at least two disadvantages. First, the use of discrete components
20
and
28
increases the manufacturing cost and space requirements for the protection circuit. Second, the discrete components exhibit a large ON resistance that represents a significant power loss for the circuit.
Several prior art inventions describe battery protection circuits. U.S. Pat. No. 6,037,750 to Von Novak describes a battery pack controller. Von Novak places the battery charging circuits (elements
206
and
208
of
FIG. 2
) inside the battery pack. Such an approach creates at least two significant problems. First, power consumption and heat build up from the charger may cause the connectivity to the external FET devices (
202
and
204
) to fail. Second, if the ground connection to the battery pack is lost, then control of the battery is lost. Battery charging may continue without control and may then result in a battery explosion. U.S. Pat. No. 5,781,390 to Notaro et al teaches an automotive battery protection circuit for protecting against reverse battery and over voltage. U.S. Pat. No. 5,896,025 to Yamaguchi et al describes a battery protection circuit. U.S. Pat. No. 5,789,900 to Hasegawa et al discloses a battery protection circuit showing two MOSFETs back-to-back. U.S. Pat. No. 6,160,381 to Peterzell discloses a battery pack protection circuit. Two MOSFET switches are used.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide an effective and very manufacturable circuit for protecting a battery.
A further object of the present invention is to provide a battery protection circuit with reduced manufacturing cost.
Another further object of the present invention is to provide a battery protection circuit with reduced space requirements.
Another further object of the present invention is to provide a battery protection circuit with reduced ON resistance in the safety circuit.
A still further object of the present invention is to provide a circuit that protects the battery even if the ground connection to the battery pack is lost.
In accordance with the objects of this invention, a battery protection circuit is achieved. The circuit comprises, first, a FET switch. Last, a control circuit determines the ON/OFF state of the FET switch. The FET switch and the control circuit comprise a single integrated circuit device. The control circuit may comprise over charge and over discharge detectors, a voltage reference, and a level shifter.
REFERENCES:
patent: 5781390 (1998-07-01), Notaro et al.
patent: 5789900 (1998-08-01), Hasegawa et al.
patent: 5867008 (1999-02-01), Du et al.
patent: 5890780 (1999-04-01), Tomiyori
patent: 5896025 (1999-04-01), Yamaguchi et al.
patent: 6037750 (2000-03-01), Von Novak
patent: 6160381 (2000-12-01), Peterzell
patent: 6331763 (2001-12-01), Thomas et al.
patent: 0982826 (2000-03-01), None
patent: WO 00/51219 (2000-08-01), None
Fest J-P: “Sauvegarde: Gerer L'Intensite Dams Les Deux Sens,” Electronique, CEP Communication, Paris, FR, No. 91, Apr., 1999, p. 14, XP000896733, ISSN: 1157-1152.
Stockstad et al., “A Micropower Safety IC for Rechargeable Lithium Batteries,” Custom Intergrated Circuits Conf., 1996 Proceedings of the IEEE 1996, San Diego, CA, USA May 5-8, 1996, pp. 127-130.
Hülss Rolt
Keller Michael
Kronmüller Frank
Stellberger Achim
Ackerman Stephen B.
Dialog Semiconductor GmbH
Saile George O.
Schnabel Douglas R.
Tso Edward H.
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