JPH1094188A - Charging circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge the existence of a recharge able battery without providing a mechanical switch. SOLUTION: This circuit 20 charges a recharge able battery 30 with constant currents, and then, charges it with constant voltage. In the period of performing charging with constant currents, the existence of the recharge able battery 30 is judged from the magnitude of the charging current. The period of performing charging with a constant voltage includes the period of performing charging by its constant voltage intermittently in specified cycles. In the period of performing the constant-voltage charging intermittently, the differential voltage between the terminal voltage of the battery 30 at the time of being supplied with constant voltage and the terminal voltage of the battery 30 at the time of being not supplied with constant voltage is obtained. The existence of the recharge able battery 30 is judged from the magnitude of this differential voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a charging circuit.

[0002]

2. Description of the Related Art In general, portable electronic devices such as a headphone stereo and a portable CD player can use a rechargeable battery (secondary battery) as a power source. Some devices have a built-in charging circuit so that they can be charged without removing the rechargeable battery from the device.

As a rechargeable battery, there is a lithium-ion battery. Since the lithium-ion battery has a large change in terminal voltage, if charging is performed at a constant voltage, an extremely large charging current flows at the start of charging. Would. However, if charging is performed with a constant current, complete constant current charging may not be possible, so that the charging current decreases as charging proceeds, and charging does not proceed.

Therefore, when charging a lithium-ion battery, as shown in FIG. 4, the battery is charged with a constant current from the start of charging to a predetermined time t1, and is charged with a constant voltage after the time t1. I have to. Then, when a predetermined time has elapsed, the charging is determined to be completed.

[0005]

However, when charging a rechargeable battery, before charging is completed, the currently charged battery is taken out and the next battery is set.
Charging is performed only for the remaining time until charging is completed, and charging is incomplete. Therefore, if a battery is removed during charging, it is necessary to detect this.

For this reason, some chargers are provided with a switch that is turned on / off mechanically depending on the presence or absence of a battery, and when a battery is removed during charging, this is detected by the switch, and the next battery is charged. It starts from 0.

[0007] However, when such a switch is provided, the cost is increased correspondingly, and the design is restricted by the physical arrangement of the switch and the wiring layout.

The present invention is to solve such a problem.

[0009]

According to the present invention, in a charging circuit configured to charge a rechargeable battery with a constant current and then charge the battery with a constant voltage, the charge circuit is charged during the period of charging with the constant current. The presence or absence of the rechargeable battery is determined from the magnitude of the current, and a period in which charging at the constant voltage is performed intermittently at a predetermined cycle is provided during the period of charging at the constant voltage. In the period during which the constant voltage is supplied, a terminal voltage of the rechargeable battery when the constant voltage is supplied and a terminal voltage of the rechargeable battery when the constant voltage is not supplied are obtained. The charging circuit is configured to determine the presence or absence of the rechargeable battery from the magnitude of the voltage. Therefore, if the rechargeable battery is removed during charging, it is determined from the change in the magnitude of the charging current or the magnitude of the difference voltage.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10 indicates an external DC power supply, reference numeral 20 indicates a charging circuit according to the present invention, and reference numeral 30.
Indicates a rechargeable battery.

The external DC power supply 10 is, for example, an AC adapter. The AC adapter 10 converts a commercial AC voltage into a DC voltage having a predetermined value and takes out the DC voltage. It is supplied to the external power supply terminals 21P and 21N. Also, the battery 30
Is, for example, a lithium-ion battery. In the example shown in FIG.
With a capacity of During charging, the positive and negative poles of battery 30 are connected to charging terminals 29P and 29N of charging circuit 20, respectively.

The charging circuit 20 has an FET 22, a control circuit 23, and a microcomputer 24 for controlling charging.

In this case, the FET 22 controls the magnitude of the charging current or the charging voltage in accordance with the control signal from the control circuit 23. Therefore, the source is connected to the terminal 21P and the drain is connected to the terminal 27P. Connected to. Note that the terminal 21N is connected to the ground.

The control circuit 23 is composed of one chip I
It is configured so as to be able to control the magnitude of the charging current and the charging voltage to a characteristic as shown in FIG. 4 by itself, for example. Therefore, the control circuit 23 includes, as external connection terminals, a power supply terminal T1, a control terminal T2 of the FET 22, a charge voltage detection terminal T3, a charge current detection terminal T4, a charge inhibition / permission control terminal T5, and a ground terminal T6. Having.

The power supply terminal T1 and the ground terminal T6 are connected to the terminals 21P and 21N, and a voltage between these terminals is supplied as an operating voltage. Furthermore, terminals T3 and T4 are connected to terminals 27P and 27N, a capacitor 25 is connected between terminals 27P and 27N, and a small value for current detection, for example, between terminal 27N and ground.
A resistor 26 of 0.2Ω is connected. The control circuit 23
Is connected to the gate of the FET 22.

Accordingly, the charging current of the battery 30 is converted into a voltage by the resistor 26, and this voltage is supplied to the terminal T4 of the control circuit 23, so that the control circuit 23 reduces the magnitude of the charging current of the battery 30. You can also know. Further, the control circuit 23 can know the magnitude of the voltage (charging voltage or terminal voltage) of the battery 30 through the terminal T3.

When the charging circuit 20 is built in an electronic device such as a CD player, the microcomputer 24 performs system control and the like. It also does. For this reason, although not shown, the microcomputer 24 includes a CPU and an RO in which a program is written.
M, RAM for work area, input / output port, etc.
For example, a charging routine 30 shown in FIG. 2 is prepared as a part of the program written therein.

The microcomputer 24 has:
The voltages of the terminals 21P and 21N are supplied as operating voltages,
The voltage of the terminals 27P and 27N is applied to the analog input port (A
/ D converters) A1 and A2, and a control signal for prohibiting / permitting charging is supplied from an output port Q to a control terminal T5 of the control circuit 23. Therefore, the microcomputer 24 can also know the magnitude of the charging voltage and the charging current of the battery 30. The difference between the input voltage of the port A1 and the input voltage of the port A2 indicates that the battery 30
Can be calculated.

In such a configuration, first, a case where the microcomputer 24 always permits charging by the control circuit 23 (a case where the control circuit 23 controls charging alone) will be described as follows.

That is, when charging is permitted, a charging current flows to the battery 30 through the FET 22, and the magnitude of the charging current is detected by the charging circuit 23 through the terminal T4. The resistance between the drains is controlled, and the magnitude of the charging current is controlled to be constant. Therefore, battery 30 is charged with a constant current.

At this time, the charging voltage of the battery 30 is detected by the control circuit 23 through the terminal T3, and the detected voltage is a predetermined voltage (the voltage at the time t1 in FIG. 4).
If it is smaller than the threshold voltage, the detection voltage at the terminal T4 has priority over the detection voltage at the terminal T3, and the constant current charging is performed as described above.

As the charging proceeds, the terminal voltage of the battery 30 rises. However, when the voltage of the battery 30 reaches a certain value at time t1, the voltage of the FET 22 becomes constant thereafter so that the voltage of the terminal 27P becomes constant. The resistance between the source and the drain is controlled. That is, the battery 30 is charged at a constant voltage.

In this manner, the battery 30 is charged by a constant current before the time t1, and is charged by a constant voltage after the time t1, by the function of the control circuit 23.

The charging operation of the control circuit 23 is as follows.
Further, it is controlled by the microcomputer 24 as follows.

That is, the battery 30 is connected to the terminals 27P and 27N.
Is connected, the voltage of the terminal 27P changes at this time.
4 judges that the battery 30 has been connected to the charging circuit 20.

Then, in the microcomputer 23, the processing of the routine 30 starts, and first, the mode 0
In, the timer by software is cleared.
At this point, the FET 22 is still off by the microcomputer 24.

Subsequently, the processing of the CPU proceeds to mode 1,
In this mode 1, the terminal voltage of the battery 30 is checked through the port A1. This check is performed using a timer for, for example, one second. If the voltage of the battery 30 does not decrease to, for example, 2.2 V or less during this check period, the battery 30 is considered to be normal, and the process proceeds to mode 2. . When the voltage of the battery 30 has dropped to 2.2 V, the routine 30 ends as it is.

In the mode 2, a predetermined control signal is supplied from the port Q of the microcomputer 24 to the terminal T5.
The ET 22 is turned on to start charging, and then, for example, a wait of 0.5 seconds is executed. In this case, this waiting time is performed in order to wait for the voltages at the terminals T3 and T4 to stabilize. When the waiting time is over, the timer is cleared, and the process proceeds to mode 3.

In this mode 3, for example, the charging with the characteristics shown in FIG. 4 is formally started, and the charging of the battery 30 is executed from the constant current charging. During this charging, (1) Mode 3 was started, for example, 4 hours had elapsed. (2) The charging current is, for example, 200 mA or less. Is checked, and when both the conditions (1) and (2) are not satisfied, the mode 3 is continuously executed.

When charging proceeds and one or both of the items (1) and (2) are established, the process proceeds from mode 3 to mode 4, in which the microcomputer 24 sends the signal from the microcomputer 24 to the terminal T5. The supplied control signal is made to change at a predetermined cycle, so that FE
At T22, for example, an ON period of 1.8 seconds and an OFF period of 0.8 seconds are alternately repeated. Therefore, from the start of mode 4, the battery 30 has been charged for 1.8 seconds,
The charge stop for 2 seconds is alternately repeated, and the battery 3
The charge of 0 is changed to intermittent charge.

In this mode 4, (3) for example, four hours have passed since the start of mode 3. (4) The voltage difference ΔV is, for example, 0.2 V or more. It is checked whether or not. In this case, as shown in FIG. 3, the voltage difference ΔV is ΔV = VH−VL VH: terminal voltage of the battery 30 at the start of the charging period VL: terminal voltage of the battery 30 at the end of the charging stop period. .

FIG. 3A shows that the battery 30 has a terminal 27P,
This shows a voltage change when connected to 27N, and the voltage difference ΔV at this time is about 0.4 V at the beginning of charging, and is almost 0 when charging is completed. Further, FIG. 3B shows that the battery 30 is connected to the terminal 2
7B shows a voltage change when not connected to 7P and 27N, and the voltage difference ΔV at this time becomes 1 V or more. However,
The voltage difference ΔV varies depending on the value of the capacitor 25, and can be set to a required value by connecting a resistor to the capacitor 25 in parallel.

When both the conditions (3) and (4) are not satisfied, the mode 4 is continuously executed. However, when item (3) is established, the process proceeds from mode 4 to mode 5, and when item (4) is established, it is considered that the battery 30 has been removed, and the process ends.

Further, in mode 4, (5) the charging current is, for example, 200 mA or more, and the terminal voltage of the battery 30 is, for example, 3.9 V or more. (6) The charging current is, for example, 200 mA or more, and the terminal voltage of the battery 30 is, for example, 3.9 V or less. It is checked whether or not is satisfied. When the condition (5) is satisfied, the process returns to the mode 3, and when the condition (6) is satisfied, the process returns to the mode 2.

In the mode 5, similarly to the mode 4, the FET 22 is turned on for 1.8 seconds,
The off period of seconds is alternately repeated. Therefore, the charging for 1.8 seconds and the charging stop for 0.8 seconds are alternately repeated, and the battery 30 is intermittently charged following the mode 4.

Further, in this mode 5, (7) for example, 6 hours have passed since the start of mode 3. (8) The voltage difference ΔV is, for example, 0.2 V or more. It is checked whether or not. And (7),
When both of the conditions (8) are not satisfied, this mode 5
Is continuously executed, and when one or both of the items (7) and (8) are established, it is considered that the charging is completed, and the charging is terminated.

As described above, according to the charging circuit 20, the charging of the battery 30 is executed. When the battery 30 is removed during the charging, if the battery 30 is in the mode 3, the charging current Becomes 0, so that the process proceeds to mode 4. In this mode 4, the voltage difference ΔV is equal to or more than the specified value. Charging ends. Also, when the battery 30 being charged is removed in the mode 4 or the mode 5, the charging is similarly terminated in the mode 5. That is, when the battery 30 is removed, this is detected, and the charging is completed.

As described above, according to the charging circuit 20, the presence or absence of the battery 30 can be detected without providing a mechanical switch, so that an increase in cost can be suppressed, and the physical It is possible to remove restrictions on the design surface caused by the arrangement and the routing of the wiring.

During a period in which the charging current is large, the presence or absence of the battery 30 is determined from a change in the charging current.
Is determined, the determination of the presence or absence of the battery 30 is reliable.

[0040]

According to the present invention, it is possible to determine the presence or absence of a rechargeable battery without providing a mechanical switch, thereby suppressing an increase in cost and eliminating design restrictions. be able to.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating one embodiment of the present invention.

FIG. 2 is a flowchart illustrating one embodiment of the present invention.

FIG. 3 is a waveform chart for explaining the present invention.

FIG. 4 is a characteristic diagram for explaining the present invention.

[Explanation of symbols]

10: external DC power supply, 20: charging circuit, 22: FET,
23 ... control circuit, 24 ... microcomputer, 25 ...
Capacitor, 26: resistor, 30: rechargeable battery

Claims (3)

[Claims] In a charging circuit for charging a rechargeable battery with a constant current and thereafter charging with a constant voltage, during the period of charging with the constant current, the rechargeable battery is charged based on the magnitude of the charging current. In the period in which charging at the constant voltage is performed, a period in which charging at the constant voltage is performed intermittently at a predetermined cycle is provided. The difference voltage between the terminal voltage of the rechargeable battery when supplied and the terminal voltage of the rechargeable battery when the constant voltage is not supplied is determined, and the rechargeable battery is determined from the magnitude of the difference voltage. Charging circuit that determines the presence or absence of a battery. 2. The charging circuit according to claim 1, wherein a transistor is connected in series between a power supply terminal and the rechargeable battery, and a small-value resistor is connected in series to the rechargeable battery. While detecting the magnitude of the current, the transistor is controlled from the detected voltage and the charging voltage supplied to the rechargeable battery to perform the constant current charging and the constant voltage charging. Charging circuit. 3. The charging circuit according to claim 2, wherein said rechargeable battery is a lithium-ion battery.