JPH0898427A - Charger - Google Patents

Abstract

PURPOSE: To obtain a charger in which a battery is not overcharged even if the battery undergoes boosting charge after a short time use. CONSTITUTION: A charging current/battery voltage operating means 8 commands a charging circuit control means 9 to turn a switching means 6 to the side of a constant current charging circuit 2 thus starting the boosting charge. Means 7 measures the time of constant current charging. When the battery voltage is settled, a constant voltage charging circuit 3 for turning the switching means 6 to the side of a constant voltage charging circuit 3 is connected with a lithium ion battery 10. If the time measured by the means 7 is shorter than a predetermined time, operation of the constant voltage charging circuit 3 is stopped to finish the charging operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device.

[0002]

2. Description of the Related Art In recent years, in devices using a battery as a power source, non-rechargeable primary batteries typified by manganese batteries are gradually replaced by nickel cadmium storage batteries and small sealed batteries, and they are repeatedly charged many times. Rechargeable batteries that can be used are becoming popular.

Further, in order to shorten the charging time, a charging device for performing rapid charging has been used. Compared to normal charging, quick charging requires more voltage and current, but if charging is started at a constant voltage when the secondary battery to be charged has a low remaining capacity, the current value becomes too large and the load on the secondary battery is increased. Therefore, after charging is started, constant current charging is performed until the terminal voltage of the storage battery reaches a constant voltage, and then rapid charging is performed by performing constant voltage charging.

Conventionally, nickel-cadmium storage batteries and small lead-sealed storage batteries have been used as the secondary batteries, but lithium-ion storage batteries that have a much higher capacity than these have been introduced. This battery uses lithium cobalt oxide for the anode and various carbons for the cathode, and a battery capacity that is 250 to 300% higher than that of the conventional nickel-cadmium storage battery can be obtained.

However, the performance of a lithium ion storage battery deteriorates faster than that of a nickel-cadmium storage battery when overcharged, and in the worst case, lithium ions inside the battery take a needle-like crystal structure called dendrite to form metallic lithium. As a result, there is a possibility of breaking through the separator separating the battery's anode and cathode, causing a short circuit inside the battery, and causing ignition and smoking.

For this reason, it is necessary to take measures to prevent overcharge, but due to the nature of the nickel-cadmium storage battery, the battery voltage slightly decreases when it is near full charge (normally-
It was possible to accurately detect full charge due to the occurrence of (ΔV)). However, in a lithium ion storage battery, these phenomena are small and difficult to detect.
Conventionally, at the time of charging by constant voltage charging, the value of the current flowing through the lithium ion storage battery was measured, and if the current value was below a certain value, charging was stopped.

A conventional charging device for a lithium storage battery will be described below. FIG. 5 is a block diagram showing a configuration of a conventional charging device, 1 is a power supply circuit for supplying power to the charging device, 2 is a constant current charging circuit for performing constant current charging, and 3 is constant voltage charging for performing constant voltage charging. A circuit 4 is a charging current detection circuit for detecting a charging current, 5 is a battery voltage detection circuit for detecting the voltage of a battery, and 6 is a lithium-ion battery 10 for either one of the constant current charging circuit 2 and the constant voltage charging circuit 3. Switching means connected to the control means, 12 is a control means for receiving the signals from the charging current detection circuit 4 and the battery voltage detection circuit 5, and controlling the operations of the constant current charging circuit 2 and the constant voltage charging circuit 3, and 10 is a lithium ion storage battery , 11 are fixed resistors for detecting the charging current.

The operation of the charging device configured as described above will be described below with reference to FIG.

In FIG. 6, i is the charging current, v
Is the battery voltage, Tf1 is the time for constant current charging in the first rapid charge, Tv1 is the constant voltage charge in the first rapid charge, and Td is a lithium ion storage battery. (Discharging) time, Tf2 indicates the time during constant current charging in the first rapid charging, and Tv2 indicates the time during constant voltage charging in the second rapid charging.

In this charging device, when the power supply circuit 1 is powered on, the control means 12 reads the voltage of the lithium-ion battery 10, and if the voltage allows rapid charging, the switching means 6 is moved to the constant current charging circuit 2 side. Switch to start rapid charging (T
f1). When the battery voltage reaches a constant value, the control means 12 switches the switching means 6 to the constant voltage charging circuit 3 side to perform constant voltage charging (Tv1). Normally, the rapid charging is ended when the charging current becomes a certain value or less. Then, it is discharged by using the lithium-ion battery 10 (T
d). When charging is started again after using the battery, constant current charging (Tf2) and constant voltage charging (Tv2) are performed in the same procedure.

[0011]

However, when the charging time is short, that is, when charging is performed in a state close to full charge, the battery may be fully charged before the charging current falls below the specified value. , If the control of the end of charging was performed based on the value of the charging current during constant voltage charging, regardless of the amount of discharge of the battery as in the past, there was a case where overcharging was performed by the amount of constant voltage charging. .

[0012] In particular, overcharging due to this phenomenon, like a secondary battery mounted in a cordless telephone, causes the battery to be discharged only during a call, and after the call, it is placed on a charging stand and charged. However, it has been a problem for devices that always maintain a fully charged state.

An object of the present invention is to solve the above problems and to provide a power storage device which charges a lithium ion storage battery safely and reliably even in a short charge / discharge cycle.

[0014]

In order to solve the above-mentioned conventional problems, the present invention is directed to a case where the output of the battery voltage detecting means reaches a predetermined value while charging by a constant current charging circuit, If the time from the start of charging to reaching the predetermined value is equal to or longer than the predetermined value, the switching circuit is controlled to perform charging by the constant voltage charging circuit.

Further, the differential value of the charging current is obtained from the output of the charging current detecting means, and the constant voltage charging is terminated when the calculation result is a certain value or more.

Further, the differential value of the battery voltage is obtained from the output of the battery voltage detecting means, and the time for switching to constant voltage charging is controlled according to the calculation result.

[0017]

With the above-described structure, the present invention can terminate charging before overcharging even after a short period of use.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a charging device according to an embodiment of the present invention. In FIG. 1, 1 is a power supply circuit that supplies power, 2 is a constant current charging circuit that performs constant current charging, 3 is a constant voltage charging circuit that performs constant voltage charging, and 4 is a voltage of a battery that is being charged. A charging current detection circuit, 5 is a battery voltage detection circuit for detecting the charging current, 7 is a time measuring means for measuring the time during which the charging current is flowing, 8 is a charging current / battery voltage calculation for calculating changes in the charging current / battery voltage Means, 9 is a charging circuit control means for controlling the operation of the constant current / constant voltage charging circuit by receiving a signal from the battery voltage / charging current calculation means, and 6 is for switching the connection between the constant current / constant voltage charging circuit and the battery. Switching means, 10 is a lithium ion storage battery, and 11 is a charging current detecting resistor.

The operation of the charging device configured as described above will be described below with reference to the drawings.

2 is a graph showing a change curve of the terminal voltage / charging current of the battery when the lithium ion storage battery 10 is charged by the same charging device, where v is a change curve of the terminal voltage of the battery, and i is a curve. A change curve of the charging current, ij indicates a change curve of the conventional charging current, and Tf indicates the time during constant current charging.

In the charging device, when the power supply circuit 1 is turned on, the battery voltage detection circuit 5 reads the voltage of the lithium-ion battery 10 and transmits it to the charging current / battery voltage calculating means 8. If the voltage allows rapid charging, the charging current / battery voltage calculation means 8 instructs the charging circuit control means 9 to switch the switching means 6 to the constant current charging circuit 2 side to start rapid charging. The time during which the constant current charging is performed is measured by the time measuring means 7. When the battery voltage reaches a certain value, the charging circuit control means 9 connects the constant voltage charging circuit 3 for switching the switching means 6 to the constant voltage charging circuit 3 side to the lithium ion storage battery 10. At this time, the time Tf during which the time measured by the time measuring means 7 has been a fixed time is equal to or shorter than the fixed time (meaning that the discharge time of the lithium ion storage battery 10 is short and the discharge amount is small). If it is found, the charging circuit control means 9 sends a signal to the effect that charging is terminated.
To stop the operation of the constant voltage charging circuit 3 (T
s). On the contrary, when the time Tf measured by the time measuring means 7 is a fixed time and is longer than the fixed time,
Constant voltage charging is continued until the charging current falls below a certain value.

As described above, in the present embodiment, overcharging of the lithium-ion storage battery 10, which is represented by the conventional charging current change curve ij, is not performed, and charging is performed without impairing the battery life. It becomes possible to do.

Next, a second embodiment will be described with reference to FIG. Note that the configuration of the second embodiment is the same as that of the first embodiment, so description will be omitted.

FIG. 3 is a graph showing a change curve of the terminal voltage / charging current of a battery when a lithium ion storage battery is charged by the charging device according to the second embodiment of the present invention, and v is the battery. Terminal voltage change curve, is
Is a change curve of charging current when charging after short-time discharging, il is a change curve of charging current when performing charging after long-time discharging, ij is a change curve of conventional charging current, and Tf is constant current charging Indicates the time you are doing.

In the charging device, when the power supply circuit 1 is turned on, the battery voltage detection circuit 5 reads the voltage of the lithium-ion battery 10 and transmits it to the charging current / battery voltage calculating means 8. If the voltage allows rapid charging, the charging current / battery voltage calculation means 8 instructs the charging circuit control means 9 to switch the switching means 6 to the constant current charging circuit 2 side to start rapid charging. The time during which the constant current charging is performed is measured by the time measuring means 7. When the battery voltage reaches a constant value, the charging circuit control means 9 switches the switching means 6 to the constant voltage charging circuit 3 side to perform constant voltage charging. After that, the charging current / battery voltage calculating means 8 and the time measuring means 7 measure the change amount di of the charging current for a short time dT.

Here, in the constant voltage charging of the lithium ion storage battery 10, in the case of charging when the discharge time is short and the discharge amount is small, the terminal voltage rapidly increases as the lithium ion storage battery 10 approaches the fully charged state. Therefore, as shown in the charging current curve is, the change amount of the charging current in a short time becomes large, and its differential value di /
dT becomes large. On the other hand, in the case of charging when the discharge time is long and the discharge amount is large, the lithium ion storage battery 10
Takes a long time to approach the full charge state and the terminal voltage rises sharply. Therefore, the change amount of the charging current in a short time becomes small as shown in the charging current curve il, and the differential value di / dT is Get smaller.

Therefore, when di / dT is a certain value or more, the charging current / battery voltage calculating means 8 judges that the discharge time of the lithium ion storage battery 10 is short and the discharge amount is small, and terminates the charging. The signal is transmitted to the charging circuit control means 9 and the operation of the constant voltage charging circuit 3 is stopped, whereby the charging is completed. Therefore, the lithium-ion storage battery 10 is not overcharged, and can be charged without impairing the life of the battery.

Next, a third embodiment will be described with reference to FIG. Since the structure of this embodiment is similar to that of the first embodiment, its explanation is omitted.

FIG. 4 is a graph showing a change curve of the terminal voltage / charging current of the battery when the lithium ion storage battery 10 is charged by the charging device according to the third embodiment of the present invention, where vs is short. The terminal voltage change curve of the battery when power is received after time discharge, vl is the terminal voltage change curve of the battery when power is received after long time discharge,
i Charge current change curve, ij is conventional charge current change curve, Tf is time for constant current charge, dT is preliminary charge time for determining time for constant current charge, Tf1 is short time The constant current charging time after discharging, Tf2 indicates the constant current charging time after discharging for a long time.

In the charging device, when the power supply circuit 1 is turned on, the battery voltage detection circuit 5 reads the voltage of the lithium-ion battery 10 and transmits it to the charging current / battery voltage calculating means 8. If the voltage allows rapid charging, the charging current / battery voltage calculation means 8 instructs the charging circuit control means 9 to switch the switching means 6 to the constant current charging circuit 2 side, and determines the time for constant current charging. To start the pre-constant current charging for a short time to do. The short time dT during the preliminary constant current charging is clocked by the clock means 7. The change in the battery voltage during this short time is taken into the charging current / battery voltage calculation means 8 through the battery voltage detection circuit 5. Charging current
The battery voltage calculation means 8 calculates the degree of increase of the battery voltage, that is, the differential value (dV / dT), from the amount of change dV of the battery voltage in a short time dT.

Here, in the constant current charging of the lithium ion storage battery 10, in the case of charging when the discharge time is short and the discharge amount is small, the battery voltage rises rapidly as shown by the voltage change curve vs. Therefore, the change amount (dV / dT) of the battery voltage in a short time becomes large. On the other hand, in the case of charging when the discharge time is long and the discharge amount is large, as shown in the voltage change curve vl, it takes a long time for the battery voltage to rise, so the battery voltage in a short time Change amount (dV / dT) becomes smaller.

Therefore, the charging current / battery voltage calculating means 8 and the clocking means 7 judge that the discharge time of the lithium ion storage battery 10 is short when the dV / dT is large and the discharge amount is small, and the constant current charging time Tf1. Is shortened to dV
When / dT is small, it is determined that the discharge time of the lithium ion storage battery 10 is long and the discharge amount is large, and the constant current charging time Tf2 is lengthened. That is, the charging current / battery voltage calculation means 8 and the time counting means 7 transmit a signal to the charging circuit control means 9 so as to perform constant current charging for a time inversely proportional to dV / dT.

Therefore, the lithium-ion storage battery 10 is not overcharged and can be charged without impairing the life of the battery.

In this embodiment, the lithium ion storage battery is taken as a charging target, but it goes without saying that it can be applied to the charging of a metallic lithium storage battery, a lead storage battery, a secondary battery using another organic solvent, and the like.

[0036]

The present invention does not perform constant voltage charging when the time during which constant current charging is performed is below a certain value, or
If the rate of decrease of the differential value of the charging current during constant voltage charging after constant current charging is above a certain level, constant voltage charging is terminated, or constant current charging is performed for a short time, and the degree of increase in battery voltage during that period ( By measuring (differential value of voltage change) and performing constant current charging only for a time proportional to that value, it is possible to perform rapid charging that is safe and reliable even after using the lithium-ion storage battery for a short time without damaging battery life. It is possible to provide a practically effective charging device.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a charging device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a graph showing a change curve of a terminal voltage / charge current of a battery when a lithium ion storage battery is charged by the same charging device.

FIG. 3 is a diagram showing a graph showing a change curve of a terminal voltage / charge current of a battery when a lithium ion storage battery is charged by the charging device according to the second embodiment of the present invention.

FIG. 4 is a diagram showing a graph showing a change curve of a terminal voltage / charging current of a battery when a lithium ion storage battery is charged by a charging device according to a third embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional charging device.

FIG. 6 is a diagram showing a graph showing a change curve of a terminal voltage / charging current of a battery when a lithium ion storage battery is charged by the charging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 power supply circuit 2 constant current charging circuit 3 constant voltage charging circuit 4 charging current detection circuit 5 battery voltage detection circuit 6 switching means 7 timing means 8 charging current / battery voltage calculation means 9 charging circuit control means 10 lithium ion storage battery 11 charging current detection Resistor 12 control means

Claims (10)

[Claims] 1. A battery voltage detecting means for detecting a terminal voltage of a battery, a constant current charging circuit for performing constant current charging, a constant voltage charging circuit for performing constant voltage charging, and a time measuring means for starting time counting at the start of charging. Switching means for switching between a first connection state in which the constant current charging circuit is connected to a battery and a second connection state in which the constant voltage charging circuit is connected to a battery, and charging in the first connection state When the output of the battery voltage detecting means reaches a predetermined value during the time, the switching circuit is controlled to switch to the second connection state if the time measured by the time measuring means is equal to or more than the predetermined value, A charging device provided with a control circuit that terminates charging if the output from the battery voltage detection means has not reached a predetermined value. 2. A charging current detecting means for detecting a charging current of a battery is provided, and when the control circuit is charging by the constant voltage charging circuit, an output from the charging current detecting means is below a predetermined value. The charging device according to claim 1, wherein the charging is terminated when the battery charge is reached. 3. The charging device according to claim 1, wherein the control means controls the switching circuit at the start of charging to switch to the first connection state. 4. A constant voltage charging circuit for performing constant voltage charging, a charging current detecting means for detecting a charging current of a battery, an arithmetic means for obtaining a differential value of the charging current from an output of the charging current detecting means, and the arithmetic operation. A charging device provided with a control circuit for terminating constant voltage charging when the calculation result of the means is equal to or greater than a certain value. 5. The charging according to claim 4, wherein the control circuit terminates the charging when the output from the charging current detecting means becomes equal to or less than a predetermined value during the charging by the constant voltage charging circuit. apparatus. 6. A constant current charging circuit for performing constant current charging, a battery voltage detecting means for detecting a terminal voltage of a battery, a first connection state in which the constant current charging circuit is connected to a battery, and the constant voltage charging. Switching means for switching the circuit to a second connection state in which the circuit is connected to the battery, and the computing means outputs the differential value of the charging current from the output of the charging current detection means in the second connection state. At the same time, the control circuit controls the switching circuit to control the switching circuit when the output of the battery voltage detection means reaches a predetermined value while charging is performed in the first connection state.
The charging device according to claim 4, wherein the charging device is switched to the connection state. 7. The charging device according to claim 6, wherein the control means controls the switching circuit at the start of charging to switch to the first connection state. 8. A charging current detecting means for detecting a charging current of a battery, a battery voltage detecting means for detecting a voltage of the battery, a constant current charging circuit for performing constant current charging, and a constant voltage charging circuit for performing constant voltage charging. Calculating means for obtaining a differential value of the battery voltage from the output of the battery voltage detecting means, a first connection state in which the constant current charging circuit is connected to the battery, and a first connection state in which the constant voltage charging circuit is connected to the battery. Switching means for switching between the second connection state and the second connection state, control means for controlling the switching from the first connection state to the second connection state according to the magnitude of the output of the arithmetic means, the battery and the constant current charging. A charging device provided with switching means for switching connection between a circuit and a constant voltage charging circuit. 9. A charging current detecting means for detecting a charging current of a battery is provided, and when the control circuit is charging by the constant voltage charging circuit, an output from the charging current detecting means is below a predetermined value. 9. The charging device according to claim 8, wherein the charging is terminated when it becomes. 10. The charging apparatus according to claim 8, wherein the control means controls the switching circuit at the start of charging to switch to the first connection state.