Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2002-02-14
2003-08-12
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06605925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power source circuit which is capable of monitoring a voltage of a secondary battery to control charge and discharge.
2. Description of the Related Art
FIG. 3
is a block diagram, partly in circuit diagram, showing schematically a configuration of a conventional power source circuit.
A negative external terminal
313
to which either a battery charger
310
or a load
311
is to be connected, is connected to a negative electrode of a secondary battery
301
. A positive external terminal
312
to which the battery charger
310
or the load
311
is to be connected, is connected to a positive electrode of the secondary battery
301
through a switching device (P-channel MOS FET)
302
and a switching device (P-channel MOS FET)
303
connected in series. In addition, a charge and discharge controlling circuit
316
is connected in parallel with the secondary battery
301
. The charge and discharge controlling circuit
316
has the function of detecting a voltage of the second battery
301
and a voltage developed across the switching devices
302
and
303
.
That is, the charge and discharge controlling circuit
316
has the function of detecting the state in which the battery voltage of the secondary battery
301
is lower than a predetermined voltage value to turn OFF the switching device
302
. Then, this state is referred to as “the over-discharge detection state” when applicable. In addition, the circuit
316
has the function of detecting the state in which the voltage developed across a VDD terminal
314
and a terminal
309
for detecting the battery charger connection and the over-current, is larger than a predetermined voltage value to turn OFF the switching device
302
. Then, this state is referred to as “the over-current detection state” when applicable. Also, the circuit
316
has the function of detecting the state in which the battery voltage of the secondary battery
301
is higher than a predetermined voltage value to turn OFF the switching device
303
. Then, this state is referred to as “the over-charge detection state” when applicable.
Now, the description will hereinbelow be given with respect to the operation in the case of the over-charge state. The battery charger
310
is connected between the positive external terminal
312
and the negative external terminal
313
to charge the secondary battery
301
with the electric charges, thereby providing the state in which the voltage developed across the VDD terminal
314
and a VSS terminal
315
is higher than a predetermined voltage value. At the time when this state has been provided, an over-charge and over-discharge detecting circuit
317
sends an over-charge detection signal to a logic circuit
318
for controlling switching devices. In response to the over-charge detection signal, the logic circuit
318
for controlling switching devices sends a signal to turn OFF the switching device
302
through a charge control terminal
304
.
Next, the description will hereinbelow be given with respect to the operation in the case of the over-discharge state. The load
311
is connected between the positive external terminal
312
and the negative external terminal
313
to discharge the secondary battery
301
, thereby providing the state in which the voltage developed across the VDD terminal
314
and the VSS terminal
315
is lower than the predetermined voltage value. At the time when this state has been provided, the over-charge and over-discharge detecting circuit
317
sends an over-discharge detection signal to the logic circuit
318
for controlling switching devices. In response to the over-discharge detection signal, the logic circuit
318
for controlling switching devices sends a signal to turn OFF the switching device
303
through a discharge control terminal
305
.
Finally, the description will hereinbelow be given with respect to the operation in the case of the over-current state. At the time when the terminal voltage developed across the VDD terminal
314
and the terminal
309
for detecting the battery charger connection and the over-current, has become larger than a predetermined voltage value, a circuit
319
for detecting the battery charger connection and the over-current sends an over-current detection signal to the logic circuit
318
for controlling switching devices. In response to the over-current detection signal, the logic circuit
318
for controlling switching devices sends a signal to turn OFF the switching device
303
through the discharge control terminal
305
. In addition, when the load
311
is connected to provide the over-current state, the terminal
309
for detecting the battery charger connection and the over-current is pulled down. However, at the time when the load
311
between the positive external terminal
312
and the negative external terminal
313
is released, a signal to turn ON the P-channel MOS FET
306
is sent from the logic circuit
318
for controlling switching devices to pull up the terminal
309
for detecting the battery charger connection and the over-current to VDD, thereby carrying out the release of the over-current state.
Here, when the battery charger
310
is connected in the over-charge detection state, even if the switching device
303
is turned OFF, the current is caused to flow from the battery charger
310
to the secondary battery
301
through a current path
320
passing through the positive external terminal
312
, the terminal
309
for detecting the battery charger connection and the over-current, and a parasitic diode
308
of the P-channel MOS FET
306
so that the battery
301
is charged with the electric charges. For this reason, a resistor
307
is provided in order to limit an amount of current which is caused to flow from the battery charger
310
to the secondary battery
301
.
As described above, in the conventional power source circuit, the resistor
307
is provided in order to limit an amount of current which is caused to flow from the battery charger
310
to the secondary battery
301
. However, since the current is caused to flow through the resistor, it is impossible to cut off perfectly the current path.
SUMMARY OF THE INVENTION
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to prevent a current from being caused to flow into a secondary battery by providing a diode instead of employing a resistor having a fixed magnitude of resistance.
Another object of the present invention is to provide a power source circuit having a current limit function of adjusting an amount of current of a secondary battery, the power source circuit comprising: a negative external terminal through which one of a battery charger and a load is connected to a negative electrode side of the secondary battery; a positive external terminal through which one of the battery charger and the load is connected to a positive electrode side of the secondary battery via a switching device connected in series with the positive electrode side of the secondary battery; and a charge and discharge controlling circuit connected in parallel with the secondary battery, wherein the charge and discharge controlling circuit includes: a voltage detecting circuit for detecting a voltage of the secondary battery to output a signal; a switching-device-controlling logic circuit for in response to the signal from the voltage detecting circuit, controlling the switching device; a current detecting circuit for outputting a signal to control the switching-device-controlling logic circuit on the basis of a value of the electric potential difference between a voltage of the positive electrode of the secondary battery and a voltage of the positive external terminal; a transistor having a gate electrode to which a signal having the information that exhibits the over-current state is inputted from the switching-device-controlling logic
Ando Tsutomu
Tange Yoshihisa
Adams & Wilks
Seiko Instruments Inc.
Tibbits Pia
Tso Edward H.
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