Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-04-07
2001-10-09
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06300750
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to battery protection circuits and, more specifically, to a voltage regulator for regulating charging to a battery.
2. Description of the Prior Art
Overcharging is a universal issue that must be addressed when designing battery protection circuits. Lithium based batteries, including Lithium-Ion batteries and Lithium-Polymer batteries tend to be sensitive to excessive voltage. Without a suitable safety circuit overcharging could compromise battery reliability.
To improve reliability, several chargers and battery packs include devices that bypass the battery charging current when charging becomes excessive. Such devices detect excessive charging and, when detected, reroute the charging current through a shunt circuit. One such device is a “Zener-fuse” circuit, as shown in FIG.
1
. In this circuit, a zener diode
106
begins conducting in the reverse-biased, or “avalanche,” mode when the voltage from the power supply/charger
102
exceeds the normal charging voltage of the battery cells
104
. Once the zener diode
106
is in avalanche mode, it acts somewhat like a short circuit relative to the power supply/charger
102
. The avalanche condition causes current to increase rapidly which, in turn, causes the fuse
108
to clear, isolating the battery cells
104
from the power supply/charger
102
.
The problem with this circuit is that, in reality, the zener diode
106
is not a pure short. In avalanche mode, there is actually a voltage across the zener diode
106
, causing it to dissipate power. The high current required to clear the fuse also rapidly heats the zener diode
106
. Thus, a “thermal race” condition exists between the zener diode
106
and the fuse
108
. As both the fuse
108
and the zener diode
106
being degraded by excess heat, the zener diode
106
must experience degradation slower than the fuse
108
in order for the fuse
108
to safely clear. Therefore a zener diode
106
with a high power rating must be used to ensure that the fuse
108
clears before the zener diode
106
reaches a temperature high enough to cause it to fail. These high power zener diodes are often big, bulky and expensive.
There is therefore a need for a small, reliable, inexpensive circuit to protect against overcharging in battery cells.
REFERENCES:
patent: 4544876 (1985-10-01), Bailey et al.
patent: 4862013 (1989-08-01), Konopka
patent: 5844399 (1998-12-01), Stuart
patent: 5898296 (1999-04-01), Maddox et al.
patent: 5932938 (1999-08-01), Shimamori
patent: 6046575 (2000-04-01), Demuro
patent: WO 99/39421 (1999-08-01), None
Oglesbee John W.
Smith Greg J.
National Semiconductor Corporation
Needle & Rosenberg P.C.
Nguyen Matthew
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