JPH10208779A - Protective circuit for pack battery and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress voltage decrease as much as possible at the time of discharging. SOLUTION: A circuit 15 exclusively for charging through which charging current Ic to a secondary battery 11 flows and a circuit 13 exclusively for discharging through which discharging current Id flows are installed. A FET 16 for preventing overcharging is installed at least in the circuit 15 exclusively for charging of them and the discharging current Id is made to run only in one FET 14 at the time of charging, so that the voltage decease due to the inner resistance of FET is lowered to a half as compared with that in a conventional battery. Consequently, since the discharging current does not flow in a switching element of the circuit exclusively for charging due to installation of the circuit exclusively for charging, vain voltage decrease by the switching element can be avoided and as a result, high output voltage can be reliably retained even in the case a secondary battery as same as a conventional one is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery pack containing a secondary battery and a protection circuit for the secondary battery.

[0002]

2. Description of the Related Art For example, a configuration shown in FIG. 3 is known as a battery pack containing a lithium ion battery and a protection circuit therefor. This is because, for example, P
TC2 is provided, and the FET3, 4
And the control circuit 5 controls the FETs 3 and 4 to be turned on and off.

[0003] In this configuration, at the time of discharging, FET3,
When the terminal voltage of the secondary battery 1 falls below a predetermined value, the control circuit 5 detects this and the FET 3 is turned off, thereby preventing overdischarge. During charging, the charging current Ic flows through the FETs 3 and 4, and when the battery is fully charged, this is detected by the control circuit 5 and the FET 4 is turned off to prevent overcharging.

[0004]

By the way, in the field of portable telephones, for example, a digital communication system called GSM system has recently been developed. According to this method, a pulse current of about 2 A flows through the power supply circuit, and a voltage drop in the power supply circuit cannot be ignored. However, in the above-described conventional structure, since the discharge current Id flows from the secondary battery 1 through the two FETs 3 and 4, there is a problem that the voltage drop due to the internal resistance of each of the FETs 3 and 4 becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a protection circuit for a battery pack and a secondary battery capable of minimizing a voltage drop during discharging.

[0006]

The battery pack of the present invention comprises:
A dedicated charging circuit in which a secondary battery is housed in a case and a switching element is provided in the charging / discharging circuit of the secondary battery to protect the secondary battery, in which a charging current to the secondary battery flows. And a dedicated discharge circuit through which a discharge current flows, and at least a switching element is provided in the dedicated charge circuit.

A secondary battery protection circuit according to the present invention includes a secondary battery charge / discharge circuit provided with a switching element to protect the secondary battery, wherein a charge current to the secondary battery flows. It is characterized in that a dedicated circuit and a dedicated discharge circuit through which a discharge current flows are provided, and at least a switching element is provided in the dedicated charge circuit.

[0008]

According to the first and second aspects of the present invention, since a discharge-only circuit is provided and its discharge current does not flow through the switching element of the charging-only circuit, useless voltage drop by the switching element is avoided. Therefore, a large output voltage can be ensured even when a secondary battery equivalent to a conventional one is used.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment> A first embodiment of the present invention will be described below with reference to FIG. A pack (not shown) contains, for example, a lithium ion secondary battery 11, and three side terminals of a common anode terminal 11A, a discharge cathode terminal 11B, and a charge cathode terminal 11C are provided on the side wall of the pack. ing. The PTC 12 is disposed between the anode common terminal 11A and the anode of the secondary battery 11, and has a function of suppressing overcurrent by increasing resistance due to self-heating when an overcurrent flows.

On the other hand, the discharge cathode terminal 11B and the secondary battery 1
A discharge-only circuit 13 is provided between the first cathode and the first cathode, and a discharge switch 14 is interposed therebetween. The discharge switch 14 is composed of, for example, a power N-channel MOS-FET, and its source terminal is connected to the cathode of the secondary battery 11 and its drain terminal is connected to the discharge cathode terminal 11B. Note that the diode D1 in the figure is FE
2 shows a body diode (parasitic diode) existing between the source and drain of T.

A charging cathode terminal 11C and a secondary battery 11
A dedicated charging circuit 15 is provided between the negative electrode and the negative electrode, and a charging switch 16 is interposed here. The charging switch 16 is also formed of a power N-channel MOS-FET, and has a drain terminal connected to the cathode of the secondary battery 11 and a source terminal connected to the charging cathode terminal 11C. The diode D2 in the figure is also a body diode (parasitic diode) existing between the source and the drain of this FET.
It is.

The gate terminal of each FET is connected to a control circuit 17 to control the on / off of the discharge switch 14 and the charge switch 16.
When the battery voltage decreases to a predetermined overdischarge detection voltage, the discharge switch 14 is switched from the on state to the off state, and when the battery voltage increases to the predetermined overcharge detection voltage, the charge switch is switched from the on state to the off state. I have to.

Next, the operation of this embodiment will be described. To charge the battery pack, the output terminal of the charger 20 is connected between the common anode terminal 11A and the charging cathode terminal 11C. Then, when the secondary battery 11 is not in the fully charged state, the charge switch 16 is turned on by the gate signal from the control circuit 17, so that the charge dedicated circuit 15
, A charging current of the charger 20 flows, and the secondary battery 11 is charged. When the secondary battery 11 is fully charged, this is detected by the control circuit 17, and the charge switch 16 is opened to prevent overcharging.

The load 30 is connected between the common anode terminal 11A and the discharge cathode terminal 11B. Secondary battery 11
When the battery voltage exceeds the overdischarge detection voltage, the discharge switch 14 of the dedicated discharge circuit 13 is in the ON state, so that the load current flows through the dedicated discharge circuit 13. As described above, the load current flows through the common circuit on the anode side of the secondary battery 11 and the dedicated discharge circuit 13, and does not flow through two FETs in series at the time of discharging unlike the conventional configuration shown in FIG. (Discharge switch 14) only. As a result, even if a voltage drop due to the internal resistance of the FET occurs, it can be suppressed to a half of the conventional value. This means, for example, that even in a GSM digital mobile phone in which a large pulse current flows, a voltage drop can be effectively suppressed. Can be taken out.

<Second Embodiment>

FIG. 2 shows a second embodiment of the present invention. The difference from the first embodiment is that the secondary battery 11 uses a type that is not damaged by overdischarge,
The discharge switch 14 is omitted from the discharge circuit 13. The other components are the same as those in the first embodiment, and the same portions are denoted by the same reference numerals and overlapping description will be omitted.

According to the above configuration, the discharge switch 14 is not provided in the dedicated discharge circuit 13, so that the voltage drop at the time of discharge can be further suppressed. Moreover,
Since only one FET is required, there is also obtained an effect that the parts cost and the assembly cost of the battery pack can be reduced and the battery pack can be manufactured inexpensively and lightly.

<Other Embodiments>

The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention. Various changes can be made without departing from the scope of the present invention.

(1) In each of the above embodiments, an example is shown in which the present invention is applied to a battery pack that is configured to be detachable from the device body. However, the present invention is not limited to this, and a secondary battery is irremovably built into the device body. The protection circuit of the present invention can be applied to the configuration. In this case, in FIG. 1 or FIG.
The load 30 is composed of the anode common terminal 11A and the discharge cathode terminal 11
B, and the charger 20 is connected to the terminals 11A,
11C. When the charger 20 is also built in the device body, the load 30 and the charger 20 may be always directly connected to the terminals 11A, 11B, and 11C. The effect is obtained.

(2) In each of the above embodiments, the PTC 12 is provided for overcurrent protection. However, the present invention is not limited to this, and another overcurrent protection element such as a current fuse or a temperature fuse may be used. When the possibility of short-circuit between terminals is small, the overcurrent protection element can be omitted.

(3) In the above embodiments, the secondary battery 11
However, the present invention is not limited to this. For example, a nickel cadmium type or a nickel hydride type may be used, and an element other than the FET can be used as a switching element.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional protection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Secondary battery 13 ... Discharge circuit 14 ... Discharge switch 15 ... Charge circuit 16 ... Charge switch 17 ... Control circuit 20 ... Charger 30 ... Load

Claims (2)

[Claims] 1. A battery pack in which a secondary battery is housed in a case and a switching element is provided in a charge / discharge circuit of the secondary battery to protect the secondary battery.
A battery pack comprising: a dedicated charging circuit through which a charging current flows to the secondary battery; and a dedicated discharging circuit through which a discharging current flows, and at least the switching element is provided in at least the dedicated charging circuit. 2. A method for protecting a secondary battery by providing a switching element in a charging / discharging circuit of the secondary battery, wherein a dedicated charging circuit through which a charging current flows to the secondary battery and a dedicated discharging circuit through which a discharging current flows. A protection circuit for a secondary battery, wherein the switching element is provided at least in the dedicated charging circuit.