JPH06303728A - Overcurrent protective circuit for battery - Google Patents

Abstract

PURPOSE:To suitably protect a battery against an overvoltage without undesirably breaking a switch by detecting a rush current. CONSTITUTION:The covercurrent protective circuit for a battery comprises switch means 3 connected in series with the battery 1, current detecting means 2 for detecting a current flowing to the battery 1, and control means 4, 7 for controlling the means 3 based on a detection result of the means 2, wherein the means 4, 7 break the means 3 when a current of a predetermined value or more flows to the battery 1 for a predetermined time or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery overcurrent protection circuit.

[0002]

2. Description of the Related Art In a primary battery which can only be discharged and a secondary battery which can be charged and discharged, it is discharged with a current of a predetermined value or more, that is, an overcurrent (in a secondary battery, it is also charged with an overcurrent). When the battery is heated, the battery heats up and the battery performance deteriorates, which in turn shortens the battery life significantly. Then, in order to prevent the discharge due to the overcurrent of the battery, Japanese Patent Laid-Open No. 63-15874.
As disclosed in Japanese Patent No. 4 or the like, a breaker or a PTC element (an element whose electric resistance rapidly increases due to heat generated by current) is used.

As described above, even when a breaker or PTC element is used, it is not possible to appropriately prevent overcurrent discharge of the battery. For example, when using a PTC element,
It takes a very long time for the resistance value of the PTC element to increase due to the overcurrent, so that the overcurrent discharge of the battery is performed during that time.

Therefore, if a switch such as a semiconductor switch is provided in order to quickly shut off the discharge when an overcurrent of the battery is detected, the switch can be immediately shut off when it is detected that the battery current exceeds a predetermined value. it can.

[0005]

As described above, when it is detected that the battery current exceeds a predetermined value, the heat generation of the battery can be surely suppressed by quickly turning off the switch. The following problems occur. That is, when the battery is attached to the device and the power switch of the device is turned on, an inrush current larger than the operating current of the normal device flows for a minute time. Therefore, in the configuration in which the switch is quickly shut off when it is detected that the battery current exceeds a predetermined value, the switch is shut off due to the inrush current. In order to prevent the switch from being cut off by such an inrush current, the predetermined value may be increased, but then the battery overcurrent protection cannot be performed.

Therefore, an object of the present invention is to appropriately protect a battery against overcurrent by detecting an inrush current without undesirably shutting off the switch.

[0007]

An overcurrent protection circuit for a battery according to the present invention comprises a switch means connected in series with the battery, a current detection means for detecting a current flowing through the battery,
A control means for controlling the switch means based on the detection result of the current detection means, the control means interrupting the switch means when a current of a predetermined value or more flows in the battery for a predetermined time or more. Characterize.

Further, the predetermined time is substantially inversely proportional to the current value detected by the current detecting means.

[0009]

In the present invention, the switch is cut off only when it is detected that the overcurrent has flowed for a predetermined time or longer. Therefore, the switch is not interrupted by the inrush current that flows for only a minute time.

[0010]

1 is a circuit diagram showing a first embodiment of the present invention. 1 is a primary battery such as a dry battery, or a battery that is a chargeable / dischargeable secondary battery such as a lithium ion secondary battery, and 2 is a low resistance value connected in series to the battery 1 (for example,
100 mΩ) resistance element, current detecting means for converting the battery current into voltage and detecting the voltage, 3 is switch means consisting of MOSFET connected in series to the current detecting means 2, 4
Is a delay circuit composed of a resistance element 5 and a capacitor 6 connected in parallel to the current detection means 2, and 7 is a switch means 3 when the charging voltage of the capacitor 6 is compared with the reference potential E0. The delay circuit 4 and the comparator 7 constitute a control means.

In this structure, when the battery 1 is discharged, the discharge current flows through the current detecting means 2 and the delay circuit 4. In the case of a normal discharge current, the capacitor 6 is charged, but its charging voltage does not exceed the reference voltage E0. Therefore, the output of the comparator 7 maintains the high level signal, and the switch means 3 maintains the ON state.

When an overcurrent flows through the battery 1, the capacitor 6
Is gradually charged and exceeds the reference voltage E0 after a predetermined time. As a result, the output of the comparator 7 becomes a low level signal, the switch means 3 is turned off, and the discharge of the battery 1 is cut off. If the overcurrent flows through the battery 1 for a very short time, the capacitor 6 is not charged until the reference voltage E0 is exceeded. Therefore, the switch means 3 is not shut off.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. 10 is a first comparator for comparing the detected value of the current detecting means 2 with the reference voltage E1, and 11 and 12 are connected in series. Constant current source and M connected in parallel with battery 1 at
The MOSFET 12, which is an OSFET, is on / off controlled by the output of the first comparator 10. 13 is MOS
A capacitor 14 connected in parallel with the FET 12 compares the charging voltage of the capacitor 13 with the reference voltage E2, and on / off controls the switch means 3 based on the result.
It is a comparator.

In such a configuration, when the battery 1 is discharged with a normal discharge current, the output signal of the first comparator 10 is a high level signal, the MOSFET 12 is in the ON state, and the capacitor 13 is charged. There is no.
Therefore, the output of the second comparator 14 maintains the high level signal, and the switch means 3 maintains the ON state.

When an overcurrent flows in the battery 1, the output signal of the first comparator 10 becomes a low level signal and the MOSF
ET12 is turned off. Therefore, the capacitor 13 is charged with a constant current by the constant current source 11 and exceeds the reference voltage E2 after a lapse of a predetermined time. At this time, the output of the second comparator 14 becomes a low level signal, the switch means 3 is turned off, and the discharge of the battery 1 is interrupted.

If the time during which the overcurrent flows through the battery 1 does not exceed the predetermined time, the MOSFET 12 is turned on and the capacitor 13 is discharged before the charging voltage of the capacitor 13 reaches the reference voltage E2. The output signal of the 2 comparator 14 does not change to the low level state but maintains the high level state. Therefore, the switch means 3 is not shut off.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention, in which 20 is a differential amplifier for detecting the voltage across the resistor which is the current detecting means 2, and 21 is proportional to the output of the differential amplifier 20. It is a voltage-controlled constant current source that generates a constant current, and is connected in parallel with the constant current source 11. The same parts as those in the second embodiment shown in FIG. 2 are designated by the same reference numerals.

In such a structure, when the battery 1 is discharged with a normal discharge current, the output signal of the first comparator 10 is a high level signal, the MOSFET 12 is in the ON state, and the capacitor 13 is charged. There is no.
Therefore, the output of the second comparator 14 maintains the high level signal, and the switch means 3 maintains the ON state.

When an overcurrent flows in the battery 1, the output signal of the first comparator 10 becomes a low level signal and the MOSF
ET12 is turned off. Therefore, the capacitor 13 is charged with a constant current by the constant current source 11 and the voltage-controlled constant current source 21. At this time, the voltage-controlled constant current source 21 generates a larger constant current as the voltage output from the differential amplifier 20, in other words, the larger the current of the battery 1. Therefore, the time until the charging voltage of the capacitor 13 exceeds the reference voltage E2 becomes faster as the battery current increases.

When the charging voltage of the capacitor 13 exceeds the reference voltage E2, the output of the second comparator 14 becomes a low level signal, the switch means 3 is turned off, and the discharge of the battery 1 is cut off.

That is, in this embodiment, the larger the battery current of the battery 1, the faster the charging speed of the capacitor 13 and the shorter the time until the switch means 3 is turned off.

If an overcurrent flows through the battery 1 for a very short time, the MOSFET 12 is discharged in place of the ON state before the charging voltage of the capacitor 13 reaches the reference voltage E2. Therefore, the output signal of the second comparator 14 maintains the high level state, and the switch means 3 is not cut off.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention, in which 30 is a detected value of the current detecting means 3 and the first reference voltage E.
3 is a first comparator, 31 is a second comparator for comparing the detected value of the current detection means 3 and the second reference voltage E4, 32, 33 and 34 are connected in this order in series, and are connected to the battery 1. A first MOSFET connected in parallel,
A first constant current source and a second MOSFET. First MOS
The FET 32 is a normally-off type FET and is controlled to be turned on / off by the output of the first comparator 30.
The ET 34 is a normally-on type FET, and is on / off controlled by the output of the second comparator 31. 35 is the first
A second constant current source connected in parallel to the series circuit of the constant current source 33 and the second MOSFET 34, and 36 is the first MOSFET
A capacitor 37 connected in parallel with 32 is a third comparator that compares the charging voltage of the capacitor 36 with the third reference voltage E5, and controls ON / OFF of the switch means 3 based on the result.

In this structure, the first reference voltage E
3 and the second reference voltage E4 is E3 <E4,
In the following description, the first comparator 30 outputs a low level signal when a current of 5 A or more flows, and the second comparator 31 outputs a low level signal when a current of 15 A or more flows.

In such a configuration, when the battery 1 is discharged with a normal discharge current (that is, a current of less than 5 A), the output signals of the first comparator 30 and the second comparator 31 are
Both are high level signals, the first MOSFET 32 is in the ON state (the second MOSFET 34 is in the OFF state), and the capacitor 36 is not charged.
Therefore, the output of the third comparator 37 maintains the high level signal, and the switch means 3 maintains the ON state.

When an overcurrent of 5 A or more and less than 15 A flows in the battery 1, the output signal of the first comparator 30 becomes a low level signal and the first MOSFET 32 is turned off.
On the other hand, the output of the second comparator 31 maintains a high level signal, and the second MOSFET 34 holds the off state.
Therefore, the capacitor 36 is charged with a constant current by the second constant current source 35, and exceeds the third reference voltage E5 after a predetermined time elapses. In this state, the output of the second comparator 37 becomes a low level signal, the switch means 3 is turned off, and the discharge of the battery 1 is cut off.

Further, when an overcurrent of 15 A or more flows in the battery 1, the first comparator 30 and the second comparator 32
Both output signals become low level signals, and the first MOSF
The ET 32 is turned off, and the second MOSFET 34 is turned on. Therefore, the capacitor 36 is charged with a constant current by both the first constant current source 33 and the second constant current source 35, and exceeds the third reference voltage E5 more quickly than the capacitor 36 is charged with only the second constant current source 35. Be charged. In this state, the output of the second comparator 37 becomes a low level signal, the switch means 3 is turned off, and the discharge of the battery 1 is cut off.

That is, in this embodiment, the time until the switch means 3 is turned off is set in two stages according to the battery current of the battery 1.

In the present embodiment as well, as in the above-described embodiments, when the time during which the overcurrent flows through the battery 1 does not exceed the predetermined time, before the charging voltage of the capacitor 36 reaches the third reference voltage E5. , The first MOSFET 32 is turned on, the capacitor 36 is discharged, and the output signal of the second comparator 37 maintains the high level state. Therefore, the switch means 3 is not shut off.

In each of the above embodiments, the current detecting means 2 composed of a resistance element is provided in series with the battery 1 in order to detect the current of the battery 1, but the voltage across the switch means 3 composed of a MOSFET is provided. May be used also as the current detecting means, and in that case, the current detecting means 2 including a resistance element becomes unnecessary.

[0031]

According to the present invention, the switch means connected in series with the battery, the current detecting means for detecting the current flowing through the battery, and the switch means controlled based on the detection result of the current detecting means. In a battery overcurrent protection circuit including a control means for controlling the battery, the control means shuts off the switch means when a current of a predetermined value or more flows for a predetermined time or more, and thus is undesired by detection of an inrush current. It is possible to appropriately protect the battery overcurrent without the switch being cut off.

[Brief description of 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 third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 1 Secondary Battery 2 Current Detecting Means 3 Switching Means 4 Delay Circuit 7 Comparator

Claims (2)

[Claims] 1. A switch means connected in series with a battery; a current detecting means for detecting a current flowing through the battery;
A control means for controlling the switch means based on the detection result of the current detection means, the control means interrupting the switch means when a current of a predetermined value or more flows in the battery for a predetermined time or more. Characteristic battery overcurrent protection circuit. 2. The battery overcurrent protection circuit according to claim 1, wherein the predetermined time is substantially inversely proportional to the current value detected by the current detection means.