JP2004357440A - Battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely cut off a current, when an overcurrent flows to an FET and a temperature rises, and to surely protect the FET from the temperature rise, without installing a temperature sensor. <P>SOLUTION: This battery pack comprises the FET 2 for protection connected between a battery 1 and an output terminal 5, and a control circuit 3 that switches the FET 2 to on/off states. The control circuit 3 comprises a voltage detection circuit 6, that detects the voltage between a drain and a source of the FET 2 and a current detection circuit 7, that detects the current flowing between the drain and the source of the FET 2. The control circuit cuts off an FET voltage detected by the voltage detection circuit 6, and also cuts off a current flowing to the FET 2 from an FET current detected by the current detection circuit 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a battery pack having a protective FET connected in series with the battery.
[0002]
[Prior art]
The characteristics of a battery pack deteriorate when an overcurrent flows. Also, if an excessive current flows through the battery pack, heat is generated by Joule heat and the battery cannot be used safely. In order to prevent this problem, a battery pack having a built-in circuit for detecting an overcurrent and interrupting the current has been developed (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-2000-340267
In the battery pack described in this publication, a fuse 23 having a heating resistor 22 is connected in series with a battery 21 as shown in FIG. In this battery pack, when an overcurrent flows through the battery 21, the heating resistor 22 is energized to blow the fuse 23 and cut off the current. The battery pack can protect the battery 21 and the circuit from overcurrent, but it is difficult to cut off the current promptly because the fuse 23 has a time delay in blowing. Further, it is difficult to make the relative positional relationship between the heating resistor 22 and the fuse 23, the temperature characteristic of the fuse 23, and the like uniform, and it is difficult to quickly cut off the current under accurate conditions.
[0005]
In order to cut off the overcurrent promptly, it is possible to connect an FET that cuts off the current in series with the battery, detect the overcurrent, and switch the FET from on to off. In this battery pack, an FET is connected between the battery and an output terminal. The FET is turned on and off by a control circuit that detects an overcurrent. The control circuit switches the FET from on to off when an excessive current flows through the battery. This battery pack is normally used with the FET turned on. This is because the FET in the ON state electrically connects the battery and the output terminal. When the FET is turned off, the battery and the output terminal are not substantially electrically connected, and charging and discharging of the battery are stopped.
[0006]
[Problems to be solved by the invention]
In a battery pack in which an FET is switched on and off by a control circuit, an excessive current may flow through the FET and be destroyed by heat. The destruction of the FET can be protected by placing a thermal fuse connected in series with the FET close to the FET. In this battery pack, the high-temperature FET blows the thermal fuse to cut off the current. However, in this battery pack, since the temperature difference between the thermal fuse and the FET becomes large, it is difficult to accurately cut off the current with an overcurrent. This battery pack also has a disadvantage that the heated FET heats the thermal fuse and deteriorates the thermal fuse.
[0007]
The present invention has been developed to solve such disadvantages. An important object of the present invention is to provide a battery pack that can reliably shut off current when the temperature rises due to an overcurrent flowing through the FET.
Another important object of the present invention is to provide a battery pack that can reliably protect a FET from a rise in temperature without providing a temperature sensor for detecting the temperature of the FET.
[0008]
[Means for Solving the Problems]
The battery pack of the present invention includes a protection FET 2 connected between the battery 1 and the output terminal 5, and a control circuit 3 for switching the FET 2 on and off. The control circuit 3 includes a voltage detection circuit 6 for detecting a voltage between the drain and the source of the FET 2 and a current detection circuit 7 for detecting a current flowing between the drain and the source of the FET 2. Then, the current flowing through the FET 2 from the FET current detected by the current detection circuit 7 is cut off. In order to cut off the current of FET2 from the FET voltage and the FET current, the on-resistance is detected from the FET voltage and the FET current, the junction temperature is detected from the on-resistance, and the current is cut off when the FET temperature becomes higher than the set temperature. Because.
[0009]
In the battery pack according to the second aspect of the present invention, the control circuit 3 is provided with a timer. The battery pack calculates the on-resistance of the FET 2 from the FET voltage and the FET current, detects the FET temperature from the on-resistance, and cuts off the current when the FET temperature becomes longer than the set temperature of the timer and becomes higher than the set temperature.
[0010]
The battery pack according to claim 3 of the present invention includes the communication circuit 10. In this battery pack, the control circuit 3 calculates the on-resistance of the FET 2 from the FET voltage and the FET current, detects the FET temperature from the calculated on-resistance, and uses the detected FET temperature by the communication Output to
[0011]
In the battery pack according to the fourth aspect of the present invention, the current cutoff element 4 is connected in series with the FET 2. When the ON resistance of the FET 2 becomes larger than the set value and the FET temperature becomes higher than the set temperature, the control circuit 3 cuts off the current by the current cutoff element 4.
[0012]
In the battery pack according to claim 5 of the present invention, when the on-resistance of the FET 2 becomes higher than the set value and the FET temperature becomes higher than the set temperature, the FET 2 is switched from on to off to cut off the current of the FET 2.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the following examples illustrate a battery pack for embodying the technical idea of the present invention, and the present invention does not specify a battery pack as follows.
[0014]
Further, in this specification, in order to make it easy to understand the claims, the numbers corresponding to the members shown in the embodiments are referred to as “claims” and “means for solving the problems”. Are added to the members indicated by "." However, the members described in the claims are not limited to the members of the embodiments.
[0015]
The battery pack shown in the circuit diagram of FIG. 2 has a protection FET 2 connected between the battery 1 and the output terminal 5, a control circuit 3 for switching the FET 2 on and off, and a series connection with the battery 1. And a current interrupting element 4. Battery 1 is a lithium ion battery. However, the battery may be a secondary battery other than the lithium ion battery, for example, a nickel-hydrogen battery or a nickel-cadmium battery. In the illustrated battery pack, a plurality of batteries 1 are connected in series, but the battery pack may include a single battery.
[0016]
The battery pack shown in the figure has a charging FET 2A for interrupting the charging current to protect the battery 1 and the circuit from overcurrent during charging, and the battery 1 and the circuit from interrupting the discharging current and overcurrent during discharging. A discharge FET 2B is provided for protection. This battery pack can protect the battery 1 and the circuit from overcurrent both during charging and during discharging. However, the battery pack of the present invention does not necessarily need to include the charging and discharging FETs. For example, only the discharging FET or only the charging FET may be provided.
[0017]
FET2 is a power MOSFET. However, the FET need not necessarily be a power MOSFET, and any FET that can switch the battery current on and off can be used. The power MOSFET has a parasitic diode connected in parallel. The parasitic diode is connected in a direction that allows current to flow in the reverse direction when the FET is off. Therefore, the battery can be charged even when the discharging diode is turned off, and can be discharged even when the charging diode is turned off.
[0018]
In the FET, the on-resistance between the drain and the source changes depending on the temperature. The on-resistance between the drain and the source with respect to the temperature of the FET changes depending on the type of the FET, and FIG. 3 shows an example thereof. This figure shows the on-resistance between the drain and the source with respect to the temperature of the power MOSFET. The on-resistance of the FET changes not only with the temperature but also with the voltage between the gate and the source. The voltage between the gate and the source that keeps the FET on can be constant. When the voltage between the gate and the source is fixed, the on-resistance is specified by the temperature. In this figure, since the pulse measurement is 250 μsec, the junction temperature is in thermal equilibrium with the ambient temperature, and the ambient temperature can be treated as the junction temperature. Therefore, FIG. 3 shows the characteristics of the on-resistance with respect to the junction temperature of the FET, in other words, the characteristics of the junction temperature of the FET with respect to the on-resistance. From this characteristic, the FET can determine the junction temperature by detecting the on-resistance. An FET is destroyed by heat when the junction temperature becomes abnormally high. Therefore, when the junction temperature of the FET becomes higher than the set temperature, the current of the FET can be cut off to protect the FET. Since the junction temperature of the FET is specified by the on-resistance, when the on-resistance of the FET reaches a set value, the current is cut off, and the FET can be prevented from being thermally damaged.
[0019]
In order to detect the on-resistance of the FET 2, the control circuit 3 includes a voltage detection circuit 6 for detecting a drain-source voltage of the FET 2, and a current detection circuit 7 for detecting a current flowing between the drain and the source of the FET 2. The current detection circuit 7 includes a current detection resistor 7A connected in series with the battery 1, and a current measurement circuit 7B for detecting a current from a voltage induced across the current detection resistor 7A. The control circuit 3 detects the on-resistance of the FET 2 from the FET voltage detected by the voltage detection circuit 6 and the FET current detected by the current detection circuit 7, detects the junction temperature of the FET 2 from the on-resistance, When a certain junction temperature becomes higher than the set temperature, the current flowing through the FET 2 is cut off. The control circuit 3 of FIG. 2 includes an arithmetic circuit 8 that calculates the on-resistance and controls the interruption of the current.
[0020]
The arithmetic circuit 8 controls the current cutoff element 4 to cut off the current of the FET 2. The current interrupting element 4 includes a fuse 4A with a heater and a fuse blowing switch 4B for blowing the fuse 12 by energizing the heater 11 of the fuse 4A with the heater. When the junction temperature, which is the FET temperature, becomes higher than the set temperature, the arithmetic circuit 8 turns on the fuse blowing switch 4B to energize the heater 11. The heater 11 that is energized is heated to thermally blow the fuse 12. In the battery pack of FIG. 2, when the FET temperature becomes higher than the set temperature, the arithmetic circuit 8 incorporated in the control circuit 3 blows the fuse 12 of the heater-equipped fuse 4A as the current interrupting element 4 to interrupt the current. .
[0021]
In the battery pack of the present invention, the current interrupting element is not limited to a circuit that blows a fuse with a heater. A breaker or the like controlled by an arithmetic circuit can be used as the current interrupting element. Further, as shown by a chain line in the figure, when the FET temperature becomes higher than the set temperature, the protection circuit 9 can switch the FET 2 from on to off to cut off the current. As shown in FIG. 2, in the battery pack in which the charging and discharging FETs are connected in series, when the FET temperature becomes higher than the set temperature, the arithmetic circuit 8 turns on both the FETs 2 via the protection circuit 9. To switch off to cut off the current.
[0022]
The arithmetic circuit 8 includes an arithmetic circuit 8 that calculates an on-resistance from the FET voltage and the FET current, detects a junction temperature from the calculated on-resistance, and cuts off the current at the junction temperature. The operation circuit 8 calculates the ON resistance of the FET 2 by calculating Ohm's law, that is, FET voltage / FET current. Further, the arithmetic circuit 8 stores the characteristics of the junction temperature with respect to the on-resistance of the FET 2 in a storage circuit (not shown). The arithmetic circuit 8 calculates the junction temperature from the characteristics stored in the storage circuit and the calculated on-resistance. When the junction temperature becomes higher than the set temperature, the arithmetic circuit 8 controls the current cutoff element 4 or the FET 2 through the protection circuit 9. To cut off the current.
[0023]
Further, the control circuit 3 includes a timer (not shown). The control circuit 3 calculates the on-resistance of the FET 2 from the FET voltage and the FET current, detects the junction temperature, which is the FET temperature, from the on-resistance, and determines that the time when the FET temperature becomes higher than the set temperature is longer than the set time of the timer. Cut off current when longer. The control circuit 3 cuts off the current only when the FET temperature becomes higher than the set temperature for a longer time than the set time.
[0024]
Further, the battery pack of FIG. 2 also includes a communication circuit 10 for transmitting the FET temperature to a battery-using device (not shown). The communication circuit 10 outputs the detected FET temperature to the device using the battery. The communication circuit 10 always transmits the FET temperature to the battery-powered device at a constant cycle, or when the FET temperature becomes higher than the set temperature, the FET 2 becomes higher than the set temperature. Output to the battery-powered device. The battery-powered device to which the current cutoff signal is transmitted processes the current until the current is cut off. For example, in a laptop microcomputer using a battery pack as a power supply, when a current cutoff signal is input from the battery pack, a process for shutting off the electrodes can be performed. After outputting the current cutoff signal, the control circuit 3 cuts off the current after a predetermined time.
[0025]
The illustrated control circuit 3 has a built-in protection circuit 9 for the battery 1. The control circuit 3 does not control the charging FET 2A and the discharging FET 2B to be turned on / off only when an overcurrent flows. Instead, the charged battery 1 becomes fully charged or the discharged battery 1 Is completely discharged, or the protection circuit 9 detects that the battery temperature becomes abnormally high, and controls the FET 2 to be turned on and off. When the charged battery 1 is fully charged and becomes overcharged, this is detected by the protection circuit 9 and the charging FET 2A is switched from on to off by the protection circuit 9 to reduce the charging current. Cut off. When the discharging FET 2B is in an overdischarged state during discharging, it is switched from on to off and cuts off the discharging current.
[0026]
As shown in FIG. 4, the battery pack performs the following operations to cut off the current.
[Steps for n = 1]
The voltage detection circuit 6 detects an FET voltage which is a drain-source voltage of the FET 2.
[Steps for n = 2]
The current detection circuit 7 detects a passing current of the FET 2, that is, an FET current that is a current flowing between the drain and the source.
[Steps for n = 3]
The arithmetic circuit 8 calculates the FET voltage / FET current to detect the ON resistance of the FET 2.
[Steps for n = 4]
The arithmetic circuit 8 converts the detected on-resistance of the FET 2 into a junction temperature based on the stored on-resistance and junction temperature.
[Steps for n = 5]
The arithmetic circuit 8 compares the FET temperature, which is the junction temperature, with the set temperature, and determines whether the temperature is abnormal. If the FET temperature is higher than the set temperature, it is determined that the temperature is abnormal. If the FET temperature is not higher than the set temperature and is not an abnormal temperature, a loop of n = 1 steps is performed.
[Steps for n = 6]
It is determined whether the time during which the FET temperature becomes abnormal is longer than the set time, and if shorter than the set time, the process loops to the step of n = 1.
[Steps for n = 7]
When the time during which the FET temperature becomes abnormal becomes longer than the set time, the fuse blowing switch 4B is turned on, the heater 11 is energized, and the heater 11 is heated to thermally blow the fuse 12 of the fuse 4A with heater.
[0027]
【The invention's effect】
The battery pack of the present invention has a feature that when an overcurrent flows through the FET and the temperature rises, the current is reliably cut off to effectively prevent the FET from being thermally destroyed. Further, the battery pack of the present invention has a feature that the FET can be reliably protected from temperature rise without providing a temperature sensor for detecting the temperature of the FET. This is because the battery pack of the present invention detects the on-resistance from the voltage and current of the FET, detects the FET temperature from the on-resistance, and cuts off the current when the FET temperature becomes abnormally high.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a conventional battery pack. FIG. 2 is a circuit diagram of a battery pack according to one embodiment of the present invention. FIG. 3 is a graph showing the relationship between the on-resistance between the drain and source of an FET and the ambient temperature. FIG. 4 is a flowchart for interrupting a current by the battery pack shown in FIG. 2;
1: Battery 2: FET 2A: Charge FET
2B: FET for discharge
3 ... Control circuit 4 ... Current interrupting element 4A ... Fuse with heater 4B ... Fuse blowing switch 5 ... Output terminal 6 ... Voltage detecting circuit 7 ... Current detecting circuit 7A ... Current detecting resistor 7B ... Current measuring circuit 8 ... Operation circuit 9 ... Protection Circuit 10 Communication circuit 11 Heater 12 Fuse 21 Battery 22 Heating resistor 23 Fuse

Claims (5)

A battery pack comprising: a protection FET (2) connected between a battery (1) and an output terminal (5); and a control circuit (3) for turning the FET (2) on and off.
The control circuit (3) includes a voltage detection circuit (6) for detecting a drain-source voltage of the FET (2) and a current detection circuit (7) for detecting a current flowing between the drain and source of the FET (2). A battery pack comprising a FET voltage detected by a voltage detection circuit (6) and a current flowing through the FET (2) from an FET current detected by a current detection circuit (7). The control circuit (3) includes a timer, calculates the on-resistance of the FET (2) from the FET voltage and the FET current, detects the FET temperature from the on-resistance, and the FET temperature is longer than the set time of the timer. 2. The battery pack according to claim 1, wherein the current is cut off when the temperature of the battery pack becomes high. A communication circuit for calculating an on-resistance of the FET from the FET voltage and the FET current, detecting a FET temperature from the calculated on-resistance, and outputting the detected FET temperature; The battery pack according to claim 1, wherein the communication circuit (10) outputs the FET temperature to the battery-powered device. The current interrupting element (4) is connected in series with the FET (2). When the on-resistance of the FET (2) becomes larger than the set value and the FET temperature becomes higher than the set temperature, the control circuit (3). 2. The battery pack according to claim 1, wherein the current is interrupted by the current interrupting element (4). The control circuit (3) switches the FET (2) from on to off and cuts off current when the on-resistance of the FET (2) becomes higher than a set value and the FET temperature becomes higher than the set temperature. The battery pack described in 1.

Images