Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-10-19
2003-07-01
Patel, Rajnikant B. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C320S145000
Reexamination Certificate
active
06586917
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to shunt regulators. More particularly, the present invention is related to a shunt regulator that controls the charging current for a battery cell using two feedback control loops.
BACKGROUND OF THE INVENTION
Rechargeable lithium bases batteries, including Lithium-Ion batteries and Lithium-Polymer batteries, are used in portable applications such as cellular telephones. Lithium batteries are sensitive to excessive voltages. Without a suitable safety circuit overcharging may compromise the batteries reliability. A shunt regulator is often employed to regulate the charging voltage to the lithium battery.
An example shunt regulator charging system for a lithium battery is shown in FIG.
1
. As shown in
FIG. 1
, the shunt regulator charging system includes a power source (PS), a NMOS transistor (MN), a PMOS transistor (MP), an amplifier (AMP), three resistors (R
1
-R
3
), and a lithium battery (BATT). The power source (PS) includes a voltage source (VS) and a source resistance (RS).
In operation the power source provides a charging current (I) to the lithium battery through source resistance RS, PMOS. transistor MP, and resistor R
3
. Resistor R
3
converts the charging current (I) into a voltage (VSNS), which is used by other circuitry (not shown) to control the activation of transistor MP. PMOS transistor MP is activated during normal charging operations. Resistors R
1
and R
2
form a voltage divider that provide a feedback signal to amplifier AMP. Amplifier AMP compares the feedback signal to a reference voltage (VREF) and provides a control signal to transistor MN. Transistor MN provides, amplifier AMP, and resistors R
1
-R
2
together operate as a shunt regulator that regulates the input voltage (VIN). The shunt regulator provides safe charging of lithium battery BATT by limiting the charging voltage (input voltage) similar to a zener diode.
SUMMARY OF THE INVENTION
Briefly stated, an apparatus and method is related to a shunt regulator that includes two feedback control loops. The shunt regulator provides a charging current to a battery cell from a power source. The input voltage from the power source is limited by the first feedback control loop to ensure that the input voltage does not exceed the breakdown voltage of the shunt regulator. The output voltage from the shunt regulator is limited by the second feedback control loop to ensure that the output voltage does not exceed the maximum rated voltage of the battery. The dual feedback control loops provide maximum charging current to the battery, while protecting the shunt regulator and the battery from damage. The shunt regulator is suitable for implementation in an integrated circuit.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, to the following detailed description of illustrative embodiments of the invention, and to the appended claims.
REFERENCES:
patent: 4472672 (1984-09-01), Pacholok
patent: 5161097 (1992-11-01), Ikeda
patent: 5708348 (1998-01-01), Frey et al.
patent: 5777457 (1998-07-01), Lee
Hertzberg Brett A.
Merchant & Gould
National Semiconductor Corporation
Patel Rajnikant B.
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