Power supply circuit

Electricity: battery or capacitor charging or discharging – Capacitor charging or discharging

Reexamination Certificate

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Details

C320S164000

Reexamination Certificate

active

06798175

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply circuit provided with a capacitor for accommodating the voltage regulation (voltage variation) of a battery.
2. Description of the Related Art
In recent years, power supply circuits having a capacitor which is connected (in parallel) to a battery to suppress the voltage regulations of a battery have been proposed. Since a capacitor whose ESR (equivalent series resistance) is low, and whose accumulate capacitance is large, is suitable for such power supply circuits, an electric double layer capacitor is mainly used.
However, in the case where the electric double layer capacitor is connected in parallel to a secondary (or rechargeable) battery (e.g., a rechargeable lithium-ion battery) provided with an overcurrent protective circuit, a large (heavy) electric current is drawn from the battery when the electric double layer capacitor is charged, which may actuate the overcurrent protective circuit to interrupt the output current of the battery to the electric double layer capacitor. Accordingly, if the overcurrent protective circuit is actuated to interrupt the output current of the battery to the electric double layer capacitor, since the operator cannot determine whether the overcurrent protective circuit has been actuated, in most cases an operator mistakenly determines that the battery is empty (‘flat’) even though the battery is not, or mistakenly determines that the electronic device to which the power supply circuit is connected has broken down. If the operator mistakenly determines that the battery is empty, the battery ends up being replaced by a new one even though the battery still has enough power, and the remaining power of the battery is wasted.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a power supply circuit provided with a capacitor for accommodating the voltage regulations(voltage variations) of a battery, wherein the overcurrent protective circuit of the battery can be prevented from being actuated while the capacitor is being charged.
To achieve the object mentioned above, according to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a capacitor which is connected in parallel to the battery to be charged by the battery, and a restricting device which restricts an output current of the battery so that the output current of the battery is not interrupted by the overcurrent protective device while the capacitor is being charged with the battery.
Preferably, the power supply circuit further includes a voltage detector which detects a terminal voltage across the capacitor, wherein the restricting device restricts the output current of the battery in accordance with the terminal voltage detected by the voltage detector.
Preferably, the restricting device restricts the output current of the battery in accordance with the terminal voltage detected by the voltage detector so that a the output current of the battery becomes maximum within a range in which the overcurrent protective device is not actuated to interrupt the output current of the battery to the power supply circuit.
In an embodiment, the restricting device includes a variable resistor via which the battery is connected to the capacitor, and a controller which controls the output current of the battery by varying a resistance value of the variable resistor in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a plurality of resistors connected in parallel via which the battery is connected to the capacitor; a plurality of switches with which each of the plurality of resistors can be connected to and disconnected from one of the battery and the capacitor; and a controller which controls the plurality of switches independently of one another in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a plurality of field effect transistors connected in parallel via which the battery is connected to the capacitor, and a controller which controls an ON/OFF state of each of the plurality of field effect transistors in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a field effect transistor via which the battery is connected to the capacitor; and a controller which controls the output current of the battery by controlling a voltage across a gate and a source of the field effect transistor in accordance with the terminal voltage detected by the voltage detector.
In an embodiment, the restricting device includes a transistor, wherein a collector of the transistor is connected to a gate of the field effect transistor while an emitter of the transistor is connected to ground, and the controller controls the voltage across the gate and a source of the field effect transistor by controlling a base voltage of the transistor.
In an embodiment, the power supply circuit further includes a plurality of resistors and a plurality of switches which are turned ON and OFF so that a base of the transistor is connected to and disconnected from the ground via the plurality of resistors, respectively. The controller controls the base voltage of the transistor by changing ON/OFF states of the plurality of switches.
According to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a capacitor, a first switch provided in a primary path for connecting the battery with the capacitor, a second switch provided in an alternative path for connecting the battery with the capacitor, a voltage detector which detects a terminal voltage across the capacitor, and a charge control device which controls a switching operation of the first switch to intermittently charge the capacitor with the battery via the primary path in the case where the terminal voltage Vc across the capacitor is smaller than a predetermined threshold value. The charge control device switches the primary path to the alternative path to continuously charge the capacitor with the battery via the alternative path in the case where the terminal voltage across the capacitor exceeds the predetermined threshold value.
In an embodiment, a duration of an ON state of the first switch in an intermittent charging operation, in which the capacitor is charged intermittently, is shorter than a time necessary for the overcurrent protective device to detect an overcurrent of the battery.
In an embodiment, a duration of an ON state of the to first switch in an intermittent charging operation, in which the capacitor is charged intermittently, is shorter than a duration from the moment the battery is connected to the capacitor to the moment an output current of the battery exceeds an overcurrent detection value of the overcurrent protective device.
According to an aspect of the present invention, a power supply circuit is provided, which is connected to a battery having an overcurrent protective device, the power supply circuit including a capacitor, an adjusting condenser connected in parallel with the battery, the adjusting condenser having a capacitance so that when the capacitor is charged with the battery, the overcurrent protective device is not actuated to interrupt an output current of the battery to the power supply circuit; a switching element with which the adjusting condenser can be connected to and disconnected from the capacitor; and a charge control device which controls a switching operation of the switching element to intermittently charge the capacitor with power output from the battery and the adjusting condenser.
In an embodiment, the capacitor is charged with power output from the battery and the adjusting condenser when the switching element is ON, and the capacitor is charged with power o

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