JP2000287375A - Charging circuit for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the heat generation of a secondary-battery charging circuit by inserting a circuit changing impedance in response to the control signal of a charging control circuit conducting an output in response to the magnitude of a chargung current and/or battery voltage to a resonance circuit. SOLUTION: In a charging circuit for a PHS telephone 1, power supplied to a resonance circuit is reduced and constant-current charging is conducted because a charging-current detector 13 detects a charging current and a constant-voltage constant-current control circuit 15 increases the resistance value of a field-effect transistor Q1 when the charging current intends to exceed a fixed value. When the battery voltage of a non-aqueous electrolytie secondary battery 11 intends to exceed a fixed value, power supplied to the resonance circuit is decreased and constant-voltage charging is conducted because a battery-voltage detector 12 detects the battery voltage and the constant-voltage constant-current control circuit 15 increases the resistance value of the field- effect transistor Q1. When the non-aqueous electrolytic secondary battery 11 is brought to the state of full charging and the charging current is made smaller than the fixed value, a full-charging detector 14 detects full charging, a switching element 16 is interrupted and charging is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charging circuit which can charge a secondary battery such as a portable telephone or a PHS telephone without contact by simply setting it in a charger.

[0002]

2. Description of the Related Art Recent PHS (Personal Handyphone Sy)
stem) In a telephone or the like, a non-contact charging system that can charge a secondary battery built in the telephone or the like by using high-frequency electromagnetic induction without contacting a contact with a charger is adopted. .

FIG. 3 shows a configuration example of a conventional contactless charging system for a PHS telephone. The PHS telephone 1 is configured such that the built-in non-aqueous electrolyte secondary battery 11 is charged by a non-contact simply by being mounted on the mounting table of the charger 2. The charger 2 converts an AC power supply such as a commercial power supply into a direct current by the rectifying and smoothing circuit 21 and then performs switching by the oscillation circuit 22 to supply the switching power to the resonance circuit including the transmission side coil L2 and the resonance capacitor C3. It is designed to produce high frequency power. Also, this feed side coil L2
Is disposed immediately below the mounting table via the plastic case plate of the charger 2.

[0004] The charging circuit of the PHS telephone 1 is provided with a resonance circuit composed of a receiving coil L1 and a resonance capacitor C1. Also, the PHS telephone 1 is connected to the charger 2
The receiving side coil L1 is arranged close to the sending side coil L2 of the charger 2 when placed on the mounting table. When high-frequency power is supplied from the sending-side coil L2 to the receiving-side coil L1 by high-frequency electromagnetic induction, the high-frequency power is converted to direct current through a rectifying diode D1 and a smoothing capacitor C2, and a series pass transistor constituting a dropper circuit The non-aqueous electrolyte secondary battery 11 is charged as a constant voltage and constant current power supply by Q2.

The dropper circuit includes a battery voltage detection circuit 1
A constant-voltage / constant-current power supply is supplied to the nonaqueous electrolyte secondary battery 11 by the constant-voltage / constant-current control circuit 17 controlling the series pass transistor Q2 based on the charge current detection circuit 13 and the full charge detection circuit 14. Is what you do. The battery voltage detection circuit 12 detects the battery voltage from the terminal voltage of the non-aqueous electrolyte secondary battery 11, and the charging current detection circuit 13 detects the charging current from the terminal voltage of the low-resistance current detector RC to fully charge the battery. The detection circuit 14 detects completion of charging based on the charging current detected by the charging current detection circuit 13. When the battery voltage detected by the battery voltage detection circuit 12 exceeds a predetermined value, the constant voltage / constant current control circuit 17 limits the base current of the series pass transistor Q2 to lower the output voltage, and the charging current detection circuit 13 Even when the detected charging current exceeds a predetermined value, the output current is reduced by limiting the base current of the series pass transistor Q2, and the charging current flowing according to the internal resistance of the nonaqueous electrolyte secondary battery 11 is limited. . Also, this charging current detection circuit 1
When the charge current detected by the third pass transistor falls below a predetermined value, the full charge detection circuit detects the completion of the charge, cuts off the base current of the series pass transistor Q2, and turns off the series pass transistor Q2 to charge the battery. To stop. The diode D2 in the circuit of FIG.
Is for preventing the backflow of the charging current.

[0006] The charging circuit of the PHS telephone 1 having the above configuration is as follows.
The constant voltage and constant current charging as shown in FIG. 4 is performed. That is, at the beginning of charging, the charging current is limited to, for example, 100 mA by the charging current detection circuit 13 and constant current charging is performed. During the constant-current charging, the battery voltage of the nonaqueous electrolyte secondary battery 11 increases as the charging proceeds. When the battery voltage of the non-aqueous electrolyte secondary battery 11 reaches, for example, 4.1 V, the battery voltage detection circuit 12 limits the rise of the battery voltage and shifts to constant-voltage charging. The charging current decreases. When the charging current falls below a predetermined value, the charging current is cut off by the full charge detection circuit 14 and charging is completed.

[0007]

However, the above PHS
In the telephone 1, the gap between the sending coil L2 and the receiving coil L1 is not always constant depending on the state of being mounted on the mounting table of the charger 2. Therefore, even if the gap is large, the PHS The setting is made with some allowance so that sufficient power can be supplied to the charging circuit of the telephone 1. However, usually, the PHS telephone 1 is often placed normally, and in this case, the gap between the sending coil L2 and the receiving coil L1 becomes small, so that the charging circuit requires extra power. You will be supplied.
When such extra power is supplied, the potential difference between the voltage supplied to the series pass transistor Q2 of the dropper circuit and the battery voltage of the nonaqueous electrolyte secondary battery 11 increases, and this potential difference and the charging current Is consumed as heat.

For this reason, in the conventional charging circuit of the contactless charging system using the dropper circuit, the heat generated by the series pass transistor Q2 is increased. Therefore, particularly in a small device having a high mounting density such as the PHS telephone 1, etc. However, there has been a problem that it is difficult to take measures against heat radiation.

The present invention has been made to address such circumstances, and provides a charging circuit for a secondary battery that generates less heat by changing the impedance of a resonance circuit to control charging current and voltage. It is intended to be.

[0010]

According to a first aspect of the present invention, there is provided a secondary battery for rectifying and supplying power to a secondary battery by rectifying power in a resonance circuit including a receiving coil for receiving power by electromagnetic induction and a resonance capacitor. And a charge control circuit for detecting a charge current and / or a battery voltage of the secondary battery and outputting a control signal in accordance with the magnitude of the charge current and / or the battery voltage. A variable impedance circuit that changes the impedance according to the control signal output by the control circuit is inserted in the resonance circuit.

According to the first aspect of the present invention, the impedance of the variable impedance circuit is changed by the charge control circuit, so that Q indicating the resonance characteristic of the resonance circuit on the receiving side is changed or the resonance frequency (resonance point) is shifted. By controlling the power received by the resonance circuit, charging control with a constant voltage or a constant current becomes possible. In addition, since the receiving-side resonance circuit does not receive unnecessary power, loss such as when a dropper circuit is used is eliminated, and heat generation of the charging circuit can be reduced.

[0012] According to a second aspect of the present invention, the charge control circuit comprises:
Detects the charging current and battery voltage of the secondary battery, and outputs a control signal that changes the impedance of the variable impedance circuit when the charging current exceeds a predetermined value and when the battery voltage exceeds a predetermined value. Characterized in that:

According to the second aspect of the present invention, since the charging current and the battery voltage of the secondary battery can be controlled, it is possible to perform constant voltage and constant current charging suitable for charging the non-aqueous electrolyte secondary battery.

According to a third aspect of the present invention, the variable impedance circuit is a MOS type field effect transistor inserted in series with a resonance capacitor.

According to the third aspect of the present invention, the MOS type field effect transistor (MOS-F
Since ET) is used, bidirectional impedance can be controlled by a single element, and the circuit can be simplified.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show one embodiment of the present invention. FIG. 1 is a circuit block diagram showing a configuration of a charging circuit of a PHS telephone, and FIG. 2 is a resonance circuit part in the charging circuit of the PHS telephone. And a circuit diagram showing the equivalent circuit.
Components having the same functions as those of the conventional example shown in FIGS. 3 and 4 are denoted by the same reference numerals.

In this embodiment, a charging circuit of the PHS telephone 1 will be described in the same manner as in the conventional example. In addition, the charger 2
The configuration is the same as that of the conventional example shown in FIG.
By simply placing the telephone 1 on the mounting table of the charger 2, the built-in non-aqueous electrolyte secondary battery 11 is charged without contact.

In the charging circuit of the PHS telephone 1 of this embodiment, as shown in FIG. 1, the resonance circuit is constituted by a series resonance circuit including a receiving coil L1, a resonance capacitor C1, and a field effect transistor Q1. Receiving coil L
1 is arranged just above the plastic case plate of the PHS telephone 1 mounted on the mounting table of the charger 2 so as to approach the sending coil L2 of the charger 2 in the related art. Is the same as The receiving coil L1
The resonance capacitor C1 and the resonance capacitor C1 are set so that the resonance frequency when a series resonance circuit is constituted by them alone matches the frequency of the high-frequency electromagnetic induction sent from the sending coil L2 of the charger 2. Field effect transistor Q1
Here, an n-channel MOS-FET is used as a variable resistance element. In the n-channel FET, when the gate voltage VGS is changed in a negative range, the ID-VDS characteristics of the drain current ID and the drain-source voltage VDS change. If the rising portion (unsaturated region) of the ID-VDS characteristic is used, it can be used as a variable resistance element in which the drain-source resistance changes according to the gate voltage VGS. In addition, MOS-FET
Is the same even when a p-channel type is used. Also,
Junction FETs and bipolar transistors can also be used as variable resistance elements, but when MOS-FETs are used, a bidirectional current can flow within the withstand voltage range of the gate oxide film, and the circuit configuration Can be simplified.

The charging circuit of the PHS telephone 1 converts the electric power supplied from the charger 2 to the resonance circuit by high-frequency electromagnetic induction into direct current by the rectifier diode D1 and the smoothing capacitor C2, and sends it to the nonaqueous electrolyte secondary battery 11. It is designed to charge. The charging circuit includes a battery voltage detection circuit 12, a charging current detection circuit 13, and a full charge detection circuit 1.
4 and a constant voltage / current control circuit 15. The battery voltage detection circuit 12 is a circuit that detects the battery voltage from the terminal voltage of the nonaqueous electrolyte secondary battery 11 as in the conventional example,
The charging current detection circuit 13 is also a circuit that detects the charging current from the terminal voltage of the low-resistance current detector RC. The full charge detection circuit 14 is also a circuit for detecting the completion of charging based on the charging current detected by the charging current detection circuit 13 as in the conventional example. The switch element 16 inserted between the battery and the nonaqueous electrolyte secondary battery 11 is shut off to stop charging. Further, the constant voltage / current control circuit 15 includes the battery voltage detection circuit 1.
2 when the battery voltage exceeds a predetermined value, the gate voltage VG of the field effect transistor Q1 is limited to increase the resistance value, and when the charging current detected by the charging current detection circuit 13 exceeds the predetermined value, Also field-effect transistor Q
This is a circuit that limits the gate voltage VG of one and increases the resistance value. Note that the diode D2 is for preventing the backflow of the charging current as in the conventional example.

The charging circuit of the PHS telephone 1 having the above configuration is as follows.
A resonance circuit including the receiving coil L1, the resonance capacitor C1, and the field effect transistor Q1 is represented by an equivalent circuit as shown in FIG. That is, the power induced in the receiving coil L1 is represented by an AC voltage source V, the receiving coil L1 is represented by an inductance L and an internal resistance RL, and the field effect transistor Q1 is represented by a variable impedance Z. Further, the resonance capacitor C1 is represented by the capacitance C as it is.
If the current flowing through the resonance circuit is represented by I, the energy stored in the inductance L is expressed by the following equation 1.

(Equation 1) This current I is expressed by Equation 2.

(Equation 2) Moreover, since the resonance frequency of the inductance L and the capacitance C coincides with the frequency of the high-frequency electromagnetic induction, the inductance L and the capacitance C are expressed by the following equation (3).

(Equation 3) By substituting this into Equation 2, the current I is shown by Equation 4.

(Equation 4) Therefore, the current I flowing through the resonance circuit changes according to the variable impedance Z. Therefore, the energy stored in the inductance L, that is, the power supplied from the charger 2 by high-frequency electromagnetic induction also changes according to the variable impedance Z. Will be.

In this embodiment, since the variable resistance element using the field effect transistor Q1 is used as the variable impedance Z, the change in the current I is caused by a decrease in Q indicating the resonance characteristic of the resonance circuit. However, when the variable impedance Z changes the inductance and the capacitance, the current I changes due to a shift in the resonance frequency (resonance point) of the resonance circuit.

The charging circuit of the PHS telephone 1 having the above configuration is as follows.
When the charging current is going to exceed a predetermined value (for example, 100 mA), the charging current detection circuit 13 detects this and the constant voltage / constant current control circuit 15 increases the resistance value of the field effect transistor Q1. Power to be supplied can be reduced so that constant current charging is performed. When the battery voltage of the non-aqueous electrolyte secondary battery 11 tries to exceed a predetermined value (for example, 4.1 V), the battery voltage detection circuit 1
2 detects this, and the constant voltage / constant current control circuit 15 increases the resistance value of the field effect transistor Q1, so that the power supplied to the resonance circuit can be reduced so that constant voltage charging can be performed. . Further, when the nonaqueous electrolyte secondary battery 11 is fully charged and the charging current becomes smaller than a predetermined value, the full charge detection circuit 14 detects this and shuts off the switch element 16 to complete the charging. Can be.

Therefore, even when the charging circuit of this embodiment is used, constant voltage and constant current charging can be performed as in the conventional example shown in FIG. Moreover, in the case of the present embodiment, the receiving coil L of the resonance circuit is generated by high-frequency electromagnetic induction.
Since the power itself received by 1 can be controlled, there is no need to receive excessive power and consume unnecessary power as heat, so that the heat generation of the charging circuit can be greatly reduced.

In the above embodiment, the receiving coil L
Although the case where the field effect transistor Q1 is inserted into the resonance circuit including the resonance capacitor C1 and the resonance capacitor C1 has been described, any element may be used as long as the variable impedance circuit can change the impedance. It is also possible to insert a variable impedance circuit that changes the impedance by combining a plurality of elements including the above. In addition, this variable impedance circuit may be inserted in series with the resonance capacitor C1 or may be placed at any position as long as it changes Q indicating the resonance characteristics of the resonance circuit or causes a shift in the resonance frequency (resonance point). Can be inserted.

Further, in the above-described embodiment, the charging circuit for performing the constant voltage / constant current charging has been described. However, the present invention can be similarly applied to a charging circuit for performing only the constant voltage charging or the constant current charging. In the above embodiment, the charging circuit of the PHS telephone 1 has been described. However, the present invention can be similarly applied to the charging circuits of other devices using the non-contact charging system. The same can be applied to the charging circuit of the secondary battery.

[0027]

As is clear from the above description, according to the charging circuit for a secondary battery of the present invention, the impedance of the resonance circuit on the receiving side is changed so that unnecessary power is not received. Heat generation of the circuit can be reduced. The reduction in the heat generation of the charging circuit means that the efficiency of the entire non-contact charging system has been improved, and the increased efficiency ultimately increases the power of the charging output.

[Brief description of the drawings]

FIG. 1 illustrates one embodiment of the present invention, wherein PH
FIG. 3 is a circuit block diagram showing a configuration of a charging circuit of the S telephone.

FIG. 2 illustrates one embodiment of the present invention, wherein PH is
FIG. 3 is a circuit diagram showing a resonance circuit portion in a charging circuit of the S telephone and its equivalent circuit.

FIG. 3, which shows a conventional example, is a circuit block diagram illustrating a configuration of a charging circuit of a PHS telephone and a charger of the PHS telephone.

FIG. 4 shows a conventional example and is a diagram for explaining a charging operation of a PHS telephone.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 PHS telephone 11 Non-aqueous electrolyte secondary battery 12 Battery voltage detection circuit 13 Charge current detection circuit 15 Constant voltage constant current control circuit Q1 Field effect transistor L1 Receiving coil C1 Resonant capacitor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G003 AA01 BA01 CA03 CA14 CC02 GA01 GB04 GB08 5H029 AJ02 AJ12 AM01 BJ27 CJ16 HJ17 HJ18 5H030 AA01 AS14 BB01 BB09 DD01 DD05 DD18 FF42 FF43

Claims (3)

[Claims] 1. A charging circuit for a secondary battery, which rectifies power of a resonance circuit composed of a receiving coil for receiving power by electromagnetic induction and a resonance capacitor and supplies the power to the secondary battery, wherein a charging current of the secondary battery is And / or a battery control circuit that detects a battery voltage and outputs a control signal according to the magnitude of the charging current and / or battery voltage, and changes an impedance according to a control signal output by the battery control circuit. A charging circuit for a secondary battery, wherein a variable impedance circuit to be inserted is inserted into a resonance circuit. 2. The charging control circuit detects a charging current and a battery voltage of a secondary battery, and sets a variable impedance when the charging current exceeds a predetermined value and when the battery voltage exceeds a predetermined value. The charging circuit for a secondary battery according to claim 1, wherein the control circuit outputs a control signal that changes the impedance of the circuit. 3. The charging circuit for a secondary battery according to claim 1, wherein the variable impedance circuit is a MOS type field effect transistor inserted in series with a resonance capacitor.