Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2001-12-26
2003-09-02
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06614205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a charge/discharge control circuit for controlling the charge and discharge of a secondary battery and to a rechargeable or charging-type power-supply unit with a secondary battery that includes the charge/discharge control circuit.
2. Related Background Art
A power-supply unit as shown in a circuit block diagram in
FIG. 4
is known as a conventional charging-type power-supply unit including a secondary battery. Such a configuration is disclosed in, for instance, Japanese Patent Application Laid-open No. Hei 4-75430 “A Charging-Type Power-Supply Unit”. That is, a secondary battery
101
is connected to an external terminal −V0 or +V0 through a switching circuit
102
. In addition, a charge/discharge control circuit
110
is connected to the secondary battery
101
in parallel. This charge/discharge control circuit
110
has a function of detecting the Voltage of the secondary battery
101
.
When the secondary battery
101
is either in an overcharged state (the state where the battery has a higher voltage than a predetermined voltage: hereinafter referred to as an “overcharge protective state”) or in an overdischarged state (the state where the battery has a lower voltage than a predetermined voltage: hereinafter referred to as an “overdischarge protective state”), a signal is outputted from the charge/discharge control circuit
110
so that the switching circuit
102
is turned off. Further, the switching circuit
102
is set to be turned off to stop discharge when the external terminal +V0 reaches a certain voltage, so that a current flowing through the switching circuit
102
can be limited. In other words, discharge can be stopped (overcurrent can be controlled) when an excessive current flows. Hereinafter, this state is referred to as an “overcurrent protective state”. The charge/discharge control circuit serves to protect the battery from such states.
It is necessary for this charge/discharge control circuit
110
to output a control signal for turning the switching circuit
102
on when a load
103
is disconnected from between the terminals +V0 and −V0 after the overcurrent protective state is realized.
FIG. 2
is a block diagram showing a charging-type power-supply unit including a conventional charge/discharge control circuit. When the load
103
is connected and the Voltage of an overcurrent detecting terminal exceeds that of a reference Voltage source
122
, the charge/discharge control circuit detects overcurrent. When the overcurrent is detected, an overcurrent detecting comparator
120
outputs a high-level Voltage which serves as an overcurrent detecting signal. The output signal from this overcurrent detecting comparator
120
serves as an input signal to an internal control circuit
210
. The internal control circuit outputs a signal for turning the switching circuit
102
off. At this time, the internal control circuit
210
outputs a signal to a gate of an N-channel transistor
201
so that the overcurrent detecting terminal can be connected to a VSS terminal on a lower Voltage side of the secondary battery
101
through a resistor
123
. Afterward, when the load
103
is disconnected from terminals +V0 and −V0, the voltage of the overcurrent detecting terminal drops to the same electric potential as the voltage of the VSS terminal since the overcurrent detecting terminal is connected to the VSS terminal through the resistor
123
. In this case, the output signal from the overcurrent detecting comparator
120
is reversed, and the internal control circuit
210
outputs a signal for turning the switching circuit
102
on to cancel the overcurrent state.
In the case of employing the above-mentioned circuit configuration, however, there has been a problem when a charger
104
is connected, the secondary battery
101
is brought into an overcharged state, and thus the switching circuit
102
is turned off. In the overcharged state, the switching circuit
102
is turned off, so that the charging of the secondary battery
101
is prohibited. In the circuit configuration shown in
FIG. 2
, however, although the switching circuit
102
is turned off, a parasitic diode
202
is present in the N-channel transistor
201
. Therefore, there has been a problem in that a charging current may flow into the secondary battery
101
through the resistor
123
and the parasitic diode
202
.
SUMMARY OF THE INVENTION
In order to solve the above problem, in the present invention, it is detected that a charger is connected, and then a resistor is disconnected from an overcurrent detecting terminal, so that a charging current is prevented from flowing into a secondary battery through a parasitic diode even when a switching circuit is turned off and thus the charger is connected.
REFERENCES:
patent: 5547775 (1996-08-01), Eguchi et al.
patent: 6060185 (2000-05-01), Okutoh
Adams & Wilks
Seiko Instruments Inc.
Tibbits Pia
Tso Edward H.
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