Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
2001-11-28
2004-03-23
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S093100
Reexamination Certificate
active
06710995
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to battery circuits, and more particularly, to a battery protection circuit using a sequential blowing fuse circuit.
(2) Description of the Prior Art
Rechargeable batteries are used in a variety of portable electronics devices such as mobile phones. The use of rechargeable batteries brings several challenges to the area of circuit protection. It is necessary to protect both the electronic device and the battery from over current and voltage conditions. Further, it is necessary to protect the battery cell from over current for both the forward, or discharging, direction and for the reverse, or charging, direction. Failure to adequately protect the battery during recharging can result in the battery exploding.
Referring now to
FIG. 1
, a prior art battery protection scheme for a mobile phone battery is illustrated. A battery, VBATT
10
, is rated in this example at about 4.2 Volts. The battery output OUT
52
drives the LOAD
56
through a protection network
20
. The LOAD is coupled to the mobile phone circuit
30
and to a battery charging source I
CHARGE
40
. The protection circuit
20
comprises a fuse F
1
44
and a switch S
1
48
. The protection circuit
20
works by simply turning on the switch S
1
48
to allow current flow. If the current is larger than the rating on the fuse F
1
44
, then the fuse will blow, or be destroyed, to open the circuit connection.
A problem with the prior art circuit is that fuse F
1
44
must have a high rating so that it does not blow inadvertently. However, if there is a fault on the LOAD
56
node, such as a large over voltage condition, the current can be quite large. If the fuse does not blow at a low enough value, the reverse current into the battery may cause the battery to explode.
Several prior art inventions describe battery protection circuits using fuses. U.S. Pat. No. 4,698,736 to Higa teaches a protection circuit for a power converter apparatus. The circuit comprises plural series-parallel connected elements. Fuses are connected in series with semiconductor elements and in parallel with nonlinear resistors. U.S. Pat. No. 5,754,384 to Ashley describes an over discharge current protection circuit for a battery. U.S. Pat. No. 6,049,144 to Frannhagen et al describes a rechargeable battery with a built-in safety circuit. An active device is connected in parallel with the battery cell while the fuse is connected in series. U.S. Pat. No. 6,172,482 to Eguchi describes a battery protection circuit.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide an effective and very manufacturable protection circuit for a battery.
A further object of the present invention is to provide battery protection circuit where the fuse apparatus is tripped at a lower value for a reverse current than for a forward current.
In accordance with the objects of this invention, a battery protection circuit for use between a battery output and a load is achieved. The circuit comprises, first, a plurality of fused cells coupled in parallel between the battery output and the load. Each fused cell comprises, first, a fuse having first and second terminals where the first terminal is coupled to a battery output. Second, a means having zener effect has a p terminal and an n terminal. The p terminal is coupled to the second terminal of the fuse. Finally, a cell switch having first and second terminals completes each fused cell. The cell switch first terminal is coupled to the second terminal of the fuse, and the cell switch second terminal is coupled to the n terminal of the diode to form a cell output. Finally, the battery protection circuit comprises a shorting switch, that may comprise a MOS transistor that exhibits punch through, that is coupled between the load and each fused cell output. The plurality of fused cells forms a large current rating fuse that can be blown at a small current rating during error conditions using a sequential blowing technique.
REFERENCES:
patent: 3882529 (1975-05-01), Warner, Jr.
patent: 4081853 (1978-03-01), Wickson
patent: 4698736 (1987-10-01), Higa
patent: 5631794 (1997-05-01), Yang
patent: 5754384 (1998-05-01), Ashley
patent: 6049144 (2000-04-01), Frannhagen et al.
patent: 6051955 (2000-04-01), Saeki et al.
patent: 6172482 (2001-01-01), Eguchi
patent: 412071 (1966-04-01), None
patent: 13 27202 (1987-07-01), None
R.L. Nailen, “Battery Protection—Where We Stand?”, 1990 IEEE, Industrial & Commercial Power Systems Technical Conference, pp. 69-78.
Ackerman Stephen B.
Demakis James A
Dialog Semiconductor GmbH
Saile George O.
Schnabel Douglas R.
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