JPH11178224A - Battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the chip size of a switch element disposed between a secondary battery positive electrode side and a (positive) terminal. SOLUTION: When a battery pack is connected to a load device, the voltage of a secondary battery 13 is hoosted by a charge pump 21, and N-channel type MOSFETS 14, 15 connected to the positive electrode side of the secondary battery 13 are driven by the boost voltage, so that the secondary battery 13 turns into discharge state. When discharging is accelerated to become lower than over-discharge detection voltage, the MOSFET 15 turns into an off state, the discharging is stopped, a power supply switching circuit 26 is switched, the voltage from the secondary battery 13 to a control part 16 is interrupted, and the charge pump 21 and the MOSFET 14 turns into an off state. The secondary battery 13 having a voltage lower than the over-discharge detection voltage is connected to a charging device, voltage from the charging device is applied to the charge pump 21 via the parasitic diode of the MOSFET 15 and the MOSFET 29 of the power supply switching circuit 26, from a (+) terminal 11, the MOSFET 14 is driven by its boosting voltage, and the secondary battery 13 turns into the charging condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery pack comprising a secondary battery and a protection circuit therefor.
The present invention relates to a battery pack that is a lithium ion secondary battery.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional battery pack has a positive terminal 1 and a negative terminal 2 for inputting / outputting a charge / discharge voltage, and a negative terminal of a secondary battery 3 is connected to a negative terminal 2. , Two P-channel MOSFETs 4 and 5 for turning on / off the charging / discharging voltage are connected in series between the + terminal 1 and the positive electrode side of the secondary battery 3, and between the positive electrode side and the negative electrode side of the secondary battery. MOSFE
A control unit 6 for controlling T4 and T5 is connected by input terminals V + and V-. The MOSFETs 4 and 5 are connected in series on the source side, the connection point is connected to the current detection terminal OC of the control unit 6, and the gates of the MOSFETs 4 and 5 are connected to the control terminals QC and QD of the control unit 6, respectively. . M
The OSFETs 4 and 5 and the control unit 6 constitute a protection circuit 7 for the secondary battery 3.

Next, the operation of this battery pack will be described. Secondary battery 3 detected from input terminals V +, V− of control unit 6
Is higher than the overdischarge detection voltage set in the control unit 6 and equal to or lower than the overcharge detection voltage, and the voltage of the current detection terminal OC is equal to or lower than the overcurrent detection voltage set in the control unit 6. MOSFET from terminal QC, QD
4 and 5 are turned on so that the secondary battery 3 can be charged and discharged. (Hereinafter, this state is referred to as chargeable / dischargeable state.) If the voltage of the secondary battery 3 exceeds the overcharge detection voltage during charging in this chargeable / dischargeable state, the MOSFET 4 is turned off by a signal from the control terminal QC. Then, charging of the secondary battery 3 is stopped, and the secondary battery 3 is protected from overcharge. (Less than,
This state is called an overcharge protection state. ) When the voltage of the secondary battery 3 drops below the overcharge release voltage in the overcharge protection state,
It returns to a chargeable / dischargeable state. When the voltage of the secondary battery 3 falls below the overdischarge detection voltage during discharging in the chargeable / dischargeable state,
The MOSFET 5 is turned off by the signal from the control terminal QD to stop the discharge of the secondary battery 3, thereby protecting the secondary battery 3 from overdischarge. (Hereinafter, this state is referred to as an overdischarge protection state.) When the voltage of the secondary battery 3 becomes equal to or higher than the overdischarge release voltage in the overdischarge protection state, the state returns to the chargeable / dischargeable state. If the voltage of the current detection terminal exceeds the overcurrent detection value during discharge in the chargeable / dischargeable state, the signal from the control terminal QD will
The SFET 5 is turned off to stop discharging the secondary battery 3 and protect the secondary battery 3 from overcurrent. (Hereinafter, this state is referred to as an overcurrent protection state.) When the load is disconnected from the terminals 1 and 2 in the overcurrent protection state, the state returns to the chargeable / dischargeable state.

[0004]

By the way, the above-mentioned conventional battery pack has a P-channel MOSFET 4 as a switch element connected between the positive terminal of the secondary battery 3 and the + terminal 1.
5, the on-resistance of the P-channel type MOSFET is several times higher than that of the N-channel type MOSFET with the same chip size. Therefore, if a low on-resistance is to be obtained, the chip size becomes large and the cost increases. In order to reduce the size and weight of portable devices such as notebook computers and mobile phones, it is necessary to reduce the size of the battery pack, which is a problem. SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a battery pack in which an N-channel MOSFET that can reduce the chip size can be arranged between the positive terminal of the secondary battery and the + terminal. With the goal.

[0005]

A battery pack according to the present invention comprises a pair of terminals to which a charge / discharge voltage is connected, a secondary battery having one of the terminals connected to a negative electrode, and a positive electrode of the secondary battery. N-channel MOS connected in series between the other terminal
A battery pack including an FET and a control unit including a charge pump for controlling a MOSFET, the control unit including a power supply line and a ground line connected to one terminal, and connected to the power supply line. The positive side of the secondary battery and the MOSFET
, The voltage of the power supply line is boosted, and the boosted voltage drives the gate of the MOSFET. According to the above means, the switch element of the battery pack in which the switch element for controlling charging / discharging is arranged between the positive electrode side of the secondary battery and the other terminal can be constituted by an N-channel MOSFET, and thus includes the switch element or the switch element. The chip size of the protection circuit can be reduced. in this case,
When the secondary battery drops below the overdischarge detection voltage during discharging, the electrical connection between the positive electrode side of the secondary battery and the power supply line is cut off. The pump is turned off and the MOSF
The ET is also turned off, and enters the overdischarge protection state. Also,
When charging the rechargeable battery, when the rechargeable battery is below the overdischarge release voltage, the power supply line is electrically connected between the series connection point of the MOSFET and the power supply line.
The charging voltage is supplied through the parasitic diode of the SFET, and therefore, the charge pump is turned on, and the charging MOSFET is turned on to start charging.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A battery pack according to an embodiment of the present invention will be described below with reference to FIG. As shown in the figure, the battery pack has terminals 11 and 12 to which a charging voltage is input from a charging device (not shown) or a discharging voltage is output from a load device (not shown). The negative electrode side of the secondary battery 13 is connected to a certain-terminal 12 and the secondary battery 1
3, two series-connected N-channel MOSFETs 14 and 15 for turning on / off the charging / discharging voltage between the positive terminal of the power supply 3 and the + terminal 11 which is the other terminal.
And a protection circuit 17 including a control unit 16 for controlling the control circuit 15.

The control unit 16 is formed of an integrated IC, and a power supply line 19 to which a power supply voltage for operating a circuit inside the control unit 16 is supplied from the outside of the control unit 16, and a ground line connected to the negative terminal 12. And a charge pump 2 connected between a power supply line 19 and a ground line 20 for boosting a voltage therebetween.
1 and the boosted voltage of the charge pump 21
P-channel type MOSFETs 22 and 23 applied to respective gates of FETs 14 and 15;
N-channel MOSFETs 24 and 25 for setting the respective gates of the gates 4 and 15 to the potential of the ground line 20, and a power supply switching circuit connected between the power supply line 19 and the positive side of the secondary battery 13 and the series connection point of the MOSFETs 14 and 15. 26. The charge pump 21 has a capacitor built in an IC. MOSFET22,24 and MOSFET
The gates of 23 and 25 are commonly connected to each other,
Are connected to an internal circuit (not shown). The power supply switching circuit 26 includes a P-channel MOSFET 28 connected between the positive electrode side of the secondary battery 13 and the power supply line 19, and a MOSFE.
A P-channel MOSFET 29 connected between the series connection point of T14 and T15 and the power supply line 19;
8 and an inverter 27 for inverting the gate input of
The gate of the OSFET 28 via the inverter 27 and the MO
The gate of the SFET 29 is connected in common and connected to an internal circuit (not shown).
One of the FETs 28 and 29 is turned on, and the voltage supply to the power supply line 19 can be switched from the secondary battery 13 or the + terminal 11.

Next, the operation of the battery pack will be described. (1) When the battery pack is connected to a charging device that is not built in the load device When the voltage value of the secondary battery 13 falls below the overdischarge release voltage set inside the control unit 16, the MOSFET 28 of the power supply switching circuit 26 is turned off. State, M
The OSFET 29 is controlled to be turned on, and the MOSFET 1
The voltage from the charging device is applied to the power supply line 19 via the parasitic diode 5 and the MOSFET 29, and the voltage is boosted by the charge pump 21. The MOSFET 22 is turned on and the MOSFET 24 is turned off. Is applied to the gate of
The SFET 14 is turned on, and the secondary battery 13 starts charging. When the voltage of the secondary battery 13 is lower than the overdischarge release voltage, the voltage to the power supply line 19 during charging is MOSFE
It is supplied from the charging device via T29. If the voltage of the secondary battery 13 becomes higher than the overdischarge release voltage during charging,
The same operation as described below is performed.

When the voltage value of the secondary battery 13 is equal to or higher than the overdischarge release voltage set within the control unit 16 and equal to or lower than the overcharge release voltage, the MOSFET 28 of the power supply switching circuit 26 is in the on state.
The OSFET 29 is controlled to be turned off, a voltage from the secondary battery 13 is applied to the power supply line 19, and the charge pump 21
The voltage is boosted, and the MOSFETs 22 and 23 are turned on and the MOSFETs 24 and 25 are turned off. The boosted voltage is applied to the gates of the MOSFETs 14 and 15 to turn on the MOSFETs 14 and 15 and turn on the Start charging. The voltage to the power supply line 19 during charging is supplied from the secondary battery 13 and from the charging device via the MOSFETs 14 and 15. When the voltage of the secondary battery 13 exceeds the overcharge detection voltage during charging, the same operation as described below is performed.

When the voltage value of the secondary battery 13 exceeds the overcharge detection voltage set inside the control unit 16, the MOSFET 22 is controlled to be off and the MOSFET 24 is controlled to be on, and the gate of the MOSFET 14 is connected to the ground line 2.
The potential becomes the same as 0, the MOSFET 14 is turned off, the charging of the secondary battery 13 is stopped, and the secondary battery 13 is protected from overcharging. In this state, M of the power supply switching circuit 26
The OSFET 28 is turned on, the MOSFET 29 is turned off, and the voltage to the power supply line 19 is supplied from the secondary battery 13. In this state, when the voltage of the secondary battery 13 falls to or below the overcharge release voltage, charging is started again.

(3) When the battery pack is connected to a load device that does not have a built-in charging device The voltage of the secondary battery 13 is equal to or higher than the overdischarge detection voltage set inside the control unit 16 and When the voltage between the drain and the source is equal to or lower than the overcurrent detection voltage set inside the control unit 16, the power supply switching circuit 26 turns on the MOSFET 28,
The OSFET 29 is controlled to be off, and the power line 19
The voltage of the secondary battery 11 is applied via the OSFET 28, the voltage is boosted by the charge pump 21, and M
OSFETs 22 and 23 are on, MOSFET 24
25 is controlled to an off state, and the boosted voltage is
The voltage is applied to the gates of T14 and T15,
15 is turned on, and the discharge of the secondary battery 13 is started.
If the voltage of the secondary battery 13 falls below the overdischarge detection voltage during this discharge, the same operation as described below is performed.

When the voltage value of the secondary battery 13 is lower than the overdischarge detection voltage set in the control unit 16, the MOSFET 23 is controlled to be in an off state, the MOSFET 25 is controlled to be in an on state, and the gate of the MOSFET 15 is connected to the ground line 2.
The potential becomes the same as 0, the MOSFET 15 is turned off, the discharge of the secondary battery 13 is stopped, and the secondary battery 13 is protected from overdischarge. At this time, the MOSFE of the power supply switching circuit 26
Although T28 is off and MOSFET 29 is on, no voltage is applied to the power supply line 19 because no charging device is connected to the + terminal 11, so that the charge pump 21 is also off and the MOSFET 14 is also off. State, and the protection circuit 17 enters the power saving state.

During the discharge of the above (3), the MOSFET 1
In the case where the voltage between the drain and the source of the MOSFET 4 exceeds the overcurrent detection voltage set inside the control unit 16, the MOSFET 23 is controlled to be in an off state, the MOSFET 25 is controlled to be in an on state, and the gate of the MOSFET 15 is connected to the ground line 2
The potential becomes equal to 0, the MOSFET 15 is turned off to stop discharging the secondary battery 13, and the secondary battery 13 is protected from overcurrent.

(4) When the battery pack is set in a load device having a built-in charging device, the charging device is operated, and the load device is not operated. The same operation as in the above item (1) is performed. (5) When the battery pack is set in the load device having the built-in charging device and the load device is operated without operating the charging device. The same operation as in the above item (2) is performed. (6) When the battery pack is set in the load device having the built-in charging device and both the charging device and the load device are operated. The same operation as in the above (1) is performed. At this time, the load device is supplied with a voltage from the charging device.

In the above embodiment, the protection circuit is described as including the control unit formed as an IC and the MOSFET externally attached to the IC. However, the protection circuit may be formed as a single-chip IC. As described above, the control unit 16 controls the secondary battery 1 in the overdischarge protection state while the battery pack is connected to the load device.
3 is turned off by the power supply switching circuit 26 to turn off the charge pump 21, and when a charging device is connected to the battery pack in the overdischarge protection state, charging is performed by the power supply switching circuit 26 built in the control unit 16. By supplying a voltage to the charge pump 21 from the device,
An N-channel type MO that allows the protection circuit 17 to have a smaller chip area with the same on-resistance than a P-channel type MOSFET
Since the SFETs 14 and 15 can be driven on the high side, the size of the protection circuit 17 can be reduced even if the protection circuit 17 is formed as an IC or only the control unit 16 of the protection circuit 17 is formed as an IC.

[0017]

According to the present invention, when the protection circuit is disposed between the positive terminal and the + terminal of the secondary battery, N
Because it can be composed of channel type MOSFET, MOSFE
By reducing the size of the chip including T, the cost of the chip can be reduced, and the size and weight of the battery pack can be reduced. Therefore, the size and weight of portable devices such as a notebook computer, a mobile phone, a PHS, and a camcorder can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a battery pack according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional battery pack.

[Explanation of symbols]

 Reference Signs List 11 + terminal 12-terminal 13 rechargeable battery 14 N-channel first MOSFET 15 N-channel second MOSFET 16 control unit 17 protection circuit 19 power supply line 20 ground line 21 charge pump 26 power supply switching circuit

Claims (3)

[Claims] 1. A pair of terminals to which a charge / discharge voltage is connected, a secondary battery having one of the terminals connected to a negative electrode side, and a series connected between a positive electrode side of the secondary battery and the other of the terminals. A battery pack comprising: a connected N-channel type MOSFET; and a control unit including a charge pump for controlling the MOSFET, wherein the control unit includes a power supply line and a ground line connected to the one terminal. The connection to the power supply line is switched between the positive electrode side of the secondary battery and the series connection point of the MOSFET, and the voltage of the power supply line is boosted.
A battery pack characterized by driving a gate of an FET. 2. The battery pack according to claim 1, wherein when the secondary battery falls below an overdischarge detection voltage during discharging, an electrical connection between a positive electrode side of the secondary battery and a power supply line is cut off. 3. The battery pack according to claim 1, wherein when the secondary battery is charged, when the voltage is lower than an overdischarge release voltage, a series connection point of the MOSFET and the power supply line are electrically connected.