Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-03-01
2001-04-17
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06218810
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an output circuit and a battery pack.
The demand for batteries that last longer in portable electronic equipment, such as notebook computers, has grown in recent years. The life of such a battery can be prolonged by increasing the capacity of the battery and decreasing power consumption in each circuit. Thus, decreasing the power consumed by output circuits of portable electronic equipment will help to prolong the life of the battery.
A notebook computer is provided with a rechargeable battery pack. The notebook computer may also be provided with a backup battery pack, which has a large capacity and can be used for a long period of time. A typical battery pack includes an output circuit for generating a control signal used to indicate whether power can be supplied properly. The output circuit generates the control signal when the battery pack is electrically connected to the computer.
A conventional output circuit employs a bipolar transistor to form an open collector circuit. An output circuit employing a MOSFET, which output loss is small, to form an open drain circuit has also been proposed. The drain of the MOSFET sends control signals to circuits in the computer that are concerned with the processing of electric power.
The battery pack may be disconnected from the computer. When the battery pack is disconnected and then reconnected to the computer, the circuits or semiconductor devices within the computer must be activated immediately. Thus, the MOSFET is always in an on state.
FIG. 10
shows an example of a prior art output circuit, which includes a p-channel output MOSFET
51
. The source of the MOSFET
51
is connected to a power supply line via a current detecting resistor Rs. A lithium ion battery (not shown) incorporated in the battery pack supplies a power supply voltage Vdd to the power supply line. The drain of the MOSFET
51
is connected to an external output terminal of the battery pack. The gate of the MOSFET
51
is connected to the collector of a drive bipolar transistor
52
via a resistor R
2
, which forms a bias circuit with a resistor R
1
. The power supply line, which provides the power supply voltage Vdd, is connected to one end of the resistor R
1
.
The bipolar transistor
52
goes on when a high drive control signal SG
1
is input to the base of the bipolar transistor
52
via a resistor R
3
. This decreases the gate voltage of the MOSFET
51
to the voltage determined by the bias circuit (formed by the resistors R
1
, R
2
) and causes the MOSFET
51
to go on. An output voltage Vout, or control signal, is output from an external output terminal and sent to the semiconductor devices in the computer that are related with the processing of power.
The bipolar transistor
52
goes off when the drive control signal SG
1
falls. This increases the gate voltage of the MOSFET
51
to the power supply voltage Vdd and causes the MOSFET
51
to go off.
The current detecting resistor Rs is connected between the source of the MOSFET
51
and the power supply line. The source of the MOSFET
51
is connected to the base of a current restricting bipolar transistor
53
. The collector of the bipolar transistor
53
is connected to the gate of the MOSFET
51
. The emitter of the bipolar transistor
53
is connected to the power supply line.
When the MOSFET
51
is on, a large output current Iout flows into the MOSFET
51
if a short circuit occurs between the external output terminals for some reason. This increases the voltage between the terminals of the current detecting resistor Rs (Iout×Rs). More specifically, the base emitter voltage Vbe of the current restricting bipolar transistor
53
increases and the collector current of the bipolar transistor
53
flows into the resistor R
2
of the bias circuit. This increases the gate voltage of the MOSFET
51
, or decreases the voltage between the gate and source of the MOSFET
51
, and causes the MOSFET
51
to go on, thereby suppressing the increase of the output current Iout.
However, current constantly flows in the output circuit because the bipolar transistor
52
is on when the MOSFET
51
is on. In other words, current flows through the bipolar transistor
52
since the MOSFET
51
is on, even if the battery pack is detached from the computer, when there is no short circuit. Thus, current is consumed by the bipolar transistor
52
, which drives the MOSFET
51
, even when the battery pack is not being used.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an output circuit and a battery pack that prolongs the life of a battery by not consuming power in an unnecessary manner.
To achieve the above object, the present invention provides an output circuit including an output MOSFET having a gate and forming an open drain circuit and a CMOS drive transistor, which has a PMOS transistor, an NMOS transistor, an input terminal, and an output terminal. The input terminal receives a drive control signal and the output terminal is connected to the gate of the output MOSFET. When the drive control signal is active, the PMOS transistor is turned off and the output MOSFET is turned on.
A further aspect of the present invention provides a battery pack including a battery and an output circuit connected to the battery. The output circuit includes an output MOSFET having a gate and forming an open drain circuit, and a CMOS drive transistor having a PMOS transistor, an NMOS transistor, an input terminal, and an output terminal. The input terminal receives a drive control signal and the output terminal is connected to the gate of the output MOSFET. When the drive control signal is active, the PMOS transistor is turned off and the output MOSFET is turned on, thereby delivering power from the battery to an output terminal.
A further aspect of the present invention provides an output circuit including an output MOSFET having a gate and forming an open drain circuit. The circuit also includes a CMOS drive transistor having a PMOS transistor, an NMOS transistor, an input terminal, and an output terminal. The input terminal receives a drive control signal and the output terminal is connected to the gate of the output MOSFET. When the drive control signal is active, the PMOS transistor is turned off and the output MOSFET is turned on. A detection means detects the current flowing through the output MOSFET and generates a detection signal therefrom. A current control means is connected to the detection means for controlling the gate voltage of the output MOSFET based on the detection signal from the detection means.
A further aspect of the present invention provides an output circuit having an output terminal including a first output MOSFET having a source connected to a power supply and a drain connected to the output terminal and a CMOS drive transistor connected between the power supply and a ground. The CMOS drive transistor has a PMOS transistor, an NMOS transistor, an input terminal and an output terminal. The input terminal receives a drive control signal and the CMOS drive transistor output terminal is connected to the gate of the first output MOSFET. When the drive control signal is active, the PMOS transistor is turned off, the first output MOSFET is turned on, and power from the power supply is provided at the output terminal by way of the first output MOSFET.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 5764028 (1998-06-01), Freiman et al.
patent: 5867008 (1999-02-01), Du et al.
patent: 5-268724 (1993-10-01), None
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Tibbits Pia
Wong Peter S.
LandOfFree
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