JP3272104B2 - Battery overcurrent protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A primary battery capable of discharging only and a secondary battery capable of charging / discharging are discharged with a current exceeding a predetermined value, that is, an overcurrent (a secondary battery is also charged with an overcurrent. ), The battery generates heat and the battery performance is reduced, and the battery life is significantly reduced. Therefore, in order to prevent discharge due to overcurrent of the battery, Japanese Patent Application Laid-Open No. 63-15874 has been proposed.
As disclosed in Japanese Unexamined Patent Publication No. 4 (1993) -1994, a breaker or a PTC element (an element whose electric resistance rapidly increases due to heat generated by an electric current) is used, but with these configurations, overcurrent discharge of the battery can be appropriately prevented. Not really. For example, when a PTC element is used, it takes a very long time for the resistance value of the PTC element to increase due to an overcurrent, so that the battery is overcurrently discharged during that time.

[0005] Therefore, if a switch such as a semiconductor switch is provided in order to quickly shut off the discharge when the overcurrent of the battery is detected, it is possible to shut off the switch as soon as it is detected that the battery current has exceeded a predetermined value. it can.

[0004]

As described above, if it is detected that the battery current has exceeded a predetermined value, the switch can be quickly turned off to reliably suppress the heat generation of the battery. For example, even for a momentary short circuit, overcurrent discharge of the battery can be effectively prevented.

[0005] On the other hand, a switch that is cut off by such an instantaneous short-circuit of the battery needs to appropriately return to a dischargeable state when the overcurrent state is released.

Accordingly, the present invention is to prevent the overcurrent of the battery without fail, and to enable the battery to immediately return to the dischargeable state when the overcurrent state is released.

[0007]

According to the present invention, there is provided a battery overcurrent protection circuit comprising: switch means connected in series with a battery; current detection means for detecting a current flowing through the battery;
Control means for controlling on / off of the switch means based on the detection result of the current detection means, and the control means turns off the switch means when a current of a predetermined value or more flows through the battery, The switch means is automatically returned to the on state after a predetermined time has elapsed from the off time.

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

[0009]

In the present invention, when an overcurrent is detected, the switching means is immediately turned off to stop discharging. Thereafter, when a predetermined time has elapsed, the switch means is automatically turned on. At this time, if the overcurrent state still continues, the switch is turned off again, otherwise, the switch is kept on and the battery is returned to the dischargeable state.

[0010]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. Reference numeral 1 denotes a primary battery such as a dry battery, or a chargeable / dischargeable secondary battery such as a lithium ion secondary battery, for example, and 2 denotes a low resistance value connected in series to the battery 1 (for example,
The current detecting means 3 is composed of a resistance element of 100 mΩ) and converts the battery current into a voltage and detects the voltage. The switching means 3 is composed of a MOSFET connected in series to the current detecting means 2.

Reference numeral 4 denotes a first comparator for comparing the detected voltage of the current detecting means 2 with the reference voltage E1, and 5 denotes a flip-flop (hereinafter referred to as FF) set based on the output of the first comparator 4, 6, and Reference numeral 7 denotes a serially connected state, and a constant current source and a MOSFE connected in parallel with the battery 1.
T, and the MOSFET 7 is connected to the FF through the inverter 8.
5 is applied and on / off control is performed. 9 is MOS
The capacitor 10 connected in parallel with the FET 7 is a second comparator that compares the charging voltage of the capacitor 9 with the reference voltage E2 and resets the FF 5 based on the result. The first comparator 4 and the second comparator 10 constitute control means, and the switch means 3 is controlled to be on and off based on the output of the FF 5.

In such a configuration, when the battery 1 is discharged with a normal discharge current (current less than 5 A), the output of the first comparator 4 is at a high level. as a result,
The FF 5 is in a reset state and outputs a low level signal. Therefore, MOSFET 7 is in the ON state,
The capacitor 9 is not charged, and the second comparator 10 outputs a high-level signal. Therefore, FF5
Maintain the reset state, and the switch means 3 is not turned off.

When an overcurrent (for example, an overcurrent of 5 A or more) flows through the battery 1, the output signal of the first comparator 4 becomes low level, and the FF 5 is set. Therefore, the output signal of the inverter 8 becomes a low level signal,
At the same time when the FET 7 is turned off, the switch means 3 is also turned off, and the discharge of the battery 1 is cut off.

Thus, when the MOSFET 7 is turned off, the capacitor 9 is charged at a constant current by the constant current source 6, and exceeds the reference voltage E2 after a lapse of a predetermined time (for example, 0.1 to 10 seconds). At this time, the second comparator 10
Goes low to reset the FF5. Accordingly, the switch means 3 is turned on, and the battery 1 is in a dischargeable state.

On the other hand, the MOSFET 7 is also turned on, the capacitor 9 is discharged, and the output signal of the second comparator 10 becomes high level for a predetermined time (for example, within 10 milliseconds).

Therefore, when the overcurrent discharge state is still continued when the switch means 3 is turned on,
By repeating the above operation, the switch means 3 is again turned off, and the discharge of the battery 1 is interrupted. On the other hand, otherwise, the ON state of the switch means 3 is continued, and the dischargeable state is maintained.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. Reference numeral 20 denotes a detection value of the current detection means 2 and a first reference voltage E.
3, a second comparator 21 for comparing the detection value of the current detecting means 2 with the second reference voltage E4, and a first FF 22 set based on the output of the first comparator 20. The first FF 22 applies a signal to the switch means 3 via the inverter 27, and controls ON / OFF of the signal. 23 is a second FF set based on the output of the second comparator 21. 24, 25, and 26 are connected in series in this order, and the first MOSFET, the first MOSFET,
A constant current source and a second MOSFET. 1st MOSFE
T24 is a normally-off type FET, and the inverter 27
The output of the first FF 22 is applied via the FF and the on / off control is performed. The second MOSFET 26 is a normally-on type FET
And on / off control is performed based on the output of the second FF 23.

Further, reference numeral 28 denotes a first constant current source 25 and a second
A second constant current source connected in parallel to the series circuit of the OSFET 26, a capacitor 29 connected in parallel to the first MOSFET 24, and 30 compares the charged voltage of the capacitor 29 with the third reference voltage E5, based on the result. First FF2
This is a third comparator that resets the second and second FFs 23.

In this configuration, the first reference voltage E
The relationship between E3 and the second reference voltage E4 is E3 <E4,
For example, the first comparator 20 outputs a low level signal when a current of 5 A or more flows, and the second comparator 2
1 outputs a low level signal when a current of 10 A or more flows.

In such a configuration, when the battery 1 is discharged with a normal discharge current (a current of less than 5 A), the output signals of the first comparator 20 and the second comparator 21 are both at a high level, and the first FF 22 And the second FF23
Are both in the reset state. Therefore, the first MOSFET
24 is in the ON state, and the capacitor 29 is not charged. Therefore, the output of the third comparator 30 maintains the high level state, and the first FF 22 and the second FF 23
Are kept reset, and the switch means 3 continues the ON state.

Next, assuming that an overcurrent of 5 A or more and less than 10 A flows through the battery 1, the output signal of the first comparator 20 becomes low level, and the first FF 22 is set.
Therefore, at the same time when the first MOSFET 24 is turned off, the switch means 3 is also turned off, and the discharge of the battery 1 is cut off.

At this time, since the output of the second comparator 21 maintains the high level state, the second MOSFET 26 remains on. Therefore, the capacitor 29 is
Constant current charging is rapidly performed by both the constant current source 25 and the second constant current source 28, and when the predetermined time (for example, 0.1 to 5 seconds) elapses, the voltage exceeds the third reference voltage E5. Then, the output of the third comparator 30 becomes a low level state, and the first F
F22 and the second FF 23 are reset and return to the initial state. That is, the switch means 3 is turned on, and the battery 1 can be discharged.

On the other hand, the first MOSFET 24 is also turned on, the capacitor 29 is discharged, and the output signal of the third comparator 30 becomes high level for a predetermined time (for example, within 10 milliseconds).

In other words, when an overcurrent of 5 A or more and less than 10 A flows through the battery 1, the switching means 3 is turned off, and the discharging of the battery 1 is interrupted. Thereafter, when 0.1 to 5 seconds have elapsed, the switch means 3 is automatically turned on. At this point, if the overcurrent discharge state is still continued, the switch means 3 is turned off again and the battery 1 is turned off.
, The switching means 3 repeats the ON state and the OFF state until the state of the overcurrent discharge is eliminated. On the other hand, when the overcurrent discharge state is resolved, the on state of the switch means 3 is continued, and the discharge means becomes a dischargeable state.

Next, when an overcurrent of 10 A or more flows through the battery 1, the first comparator 20 and the second comparator 21
Are both at a low level, and the first FF 22
And the second FF 23 are set. Therefore, the first MOSF
The ET 24 and the second MOSFET 26 are turned off, and the switch means 3 is also turned off, thereby interrupting the discharge of the battery 1.

After the switch means 3 is turned off, the first MOSFE
Since T24 and the second MOSFET 26 are off, the capacitor 29 is slowly charged at a constant current by only the second constant current source 28 for a predetermined time (for example, 1 to 2).
After 10 seconds, the battery is charged so as to exceed the third reference voltage E5. In this state, the output of the second comparator 30 becomes low level, the first FF 22 and the second FF 23 are reset, returns to the initial state, and the switch unit 3 is turned on, so that the battery 1 can be discharged.

That is, when an overcurrent of 10 A or more flows through the battery 1, the switching means 3 is turned off and the discharging of the battery 1 is interrupted. Is turned on.

As described above, in the second embodiment, the time from when the switch means 3 is turned off to when the switch means 3 automatically returns to the on state in accordance with the battery current of the battery 1 is two times.
Set to stage.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention. Reference numeral 31 denotes a differential amplifier for amplifying the voltage between both ends of the current detecting means 2, and 32 denotes a peak value of the output of the differential amplifier 31. This is a peak hold circuit that holds the peak value by the capacitor 33. 34 is a discharge resistor connected in parallel with the capacitor 33, and 35 is the hold value of the peak hold circuit 32 (that is, the charging voltage of the capacitor 33).
A comparator 36 is a delay circuit for delaying the output of the comparator 35 by a predetermined time (for example, one second) and applying the output to the switch means 3.

When the battery 1 is discharged with a normal current of less than 5 A, the charging voltage of the capacitor 33 becomes
It does not become higher than the reference voltage E6. Therefore, the output of the comparator 35 maintains the high level signal, and the switch means 3 keeps the ON state.

Next, when an overcurrent of, for example, 7 A flows through the battery 1 from the time t0 shown in FIG. 4, the charging voltage Cv of the capacitor 33 of the peak hold circuit 32 becomes as shown by a solid line in FIG. At time t1, the voltage exceeds the reference voltage E6. Therefore, the output of the comparator 35 is in a low level state. This low-level signal is applied to the switch means 3 after being delayed for a predetermined time (that is, time t1 to t2) by the delay circuit 36. As a result, the switch means 3 is turned off, and the battery 1 is discharged. Will be shut off.

When the switch means 3 is cut off, the capacitor 33 is discharged via the discharge resistor 34 and the charge voltage Cv
Falls below the reference voltage E6 at time t3. Therefore,
The output of the comparator 35 becomes the high level state again, and at time t4 after the lapse of the predetermined time (time t3 to t4 is the same as the length of time t1 to t2), the switch means 3 returns to the ON state. .

On the other hand, when an overcurrent of 10 A flows from the time t0 to the battery 1, as shown by the broken line in FIG. 4, the charging voltage Cv of the capacitor 33 becomes the reference voltage at the time t1 as before. When E6 is exceeded, the output of the comparator 35 becomes low level, and at time t2, the switch means 3 is turned off, and the discharge of the battery 1 is cut off.

When the switch means 3 is turned off, the capacitor 33 is discharged through the discharge resistor 34, and the charged voltage Cv reaches the reference voltage E5 at time t5 longer than time t3.
Below 6 Therefore, the output of the comparator 35 becomes the high level state again, and the switch means 3 returns to the ON state at time t6 after the lapse of the predetermined time.

That is, in the third embodiment, the battery 1
The time from when the switch means 3 is turned off to when the switch means 3 returns to the on state changes substantially in proportion to the battery current.

In each of the above embodiments, the current detecting means 2 comprising 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 switching means 3 comprising a MOSFET is provided. May be used as current detecting means, and in this case, the current detecting means 2 including a resistance element is not required.

[0037]

According to the present invention, switch means connected in series with a battery, current detection means for detecting a current flowing through the battery, and control of the switch means based on the detection result of the current detection means Control means for turning off the switch means when a current of a predetermined value or more flows through the battery, and automatically turning off the switch means after a lapse of a predetermined time from the time of turning off the battery. Since the battery is returned to the ON state, overcurrent of the battery can be reliably prevented, and the battery can be appropriately returned to the dischargeable state after the overcurrent discharge state is released.

[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 third embodiment of the present invention.

FIG. 4 is a waveform chart for explaining the operation of the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Current detecting means 3 Switching means 5 Flip-flop

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02H 3/06 H02H 3/08-3/10 H02H 7/18 H02J ⁷ /00-7/00 303

Claims (1)

(57) [Claims] A switch connected in series with the battery; a current detector for detecting a current flowing through the battery;
Control means for controlling on / off of the switch means based on the detection result of the current detection means, and the control means turns off the switch means when a current of a predetermined value or more flows through the battery, The switch means is automatically returned to the on state after a lapse of a predetermined time from the off point, and the predetermined time is equal to the current detection.
Automatically adjusted to be approximately proportional to the current value detected by the output means.
An overcurrent protection circuit for a battery, characterized in that it is regulated .