JPH10290530A - Secondary battery protective circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery protective circuit which enables a secondary battery to accurately output its voltage to a battery charger or used equipment without receiving any influence from the voltage drops of diodes connected in parallel with overvoltage and over-discharge preventing switching elements. SOLUTION: In a protective circuit, switching elements 11 and 12, which are respectively connected in parallel with diodes D1 and D2 so that the forward directions of the diodes D1 and D2 may become coincident with the charging and discharging directions of a secondary battery 10, are connected to the charging and discharging circuit of the battery 10. The protective circuit prevents the over-charge of the battery 10 by turning the element 11 off by means of a charge inhibiting circuit 14 when the terminal voltage of the battery 10 reaches a charge inhibiting voltage and over- discharge of the battery 10 by turning the element 12 off by means of a discharge inhibiting circuit 15 when the terminal voltage of the battery 10 reaches a discharge inhibiting voltage. The protective circuit is provided with a discharge detecting circuit 16 which turns the element 11 on when the circuit 16 detects the discharge of the battery 10 and a charge detecting circuit 17 which turns the element 12 on when the circuit 17 detects the charge of the battery 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for protecting a secondary battery from overcharging and overdischarging, and more particularly to eliminating the effect of a voltage drop in a diode connected in parallel with a protection switch. And a protection circuit.

[0002]

2. Description of the Related Art In general, in a non-aqueous solvent secondary battery such as a lithium secondary battery or a lead storage battery, if the battery voltage becomes too high during charging, the battery performance deteriorates and safety is impaired. A voltage higher than a predetermined value is not generated on the device side. However, if the charger is broken, the voltage of the secondary battery is monitored in consideration of the fact that a voltage higher than a predetermined value is applied to the secondary battery during charging, and charging is controlled so that the battery voltage is within a predetermined range. I needed to. In particular, in the case of a lithium secondary battery, for example, when the battery voltage becomes 4.5 V or more, gas is generated due to decomposition of the electrolytic solution, and as a result, the internal pressure of the battery rises, the safety valve operates, and liquid leakage occurs. There was also.

Therefore, when a lithium secondary battery is used, it is general that the battery is charged via a protection circuit having a function of interrupting charging when the battery voltage rises and reaches a charging prohibition voltage. The charge prohibition voltage is set to a voltage (for example, 4.35 V) slightly lower than the voltage at which the decomposition of the electrolytic solution starts.

[0004] Further, non-aqueous solvent secondary batteries such as lithium secondary batteries and lead-acid batteries deteriorate battery performance and impair safety even if the battery voltage becomes too low during discharging. A voltage lower than a predetermined value is prevented from being generated on the used device side as a load. However, if the equipment used is broken, the discharge of the secondary battery is controlled so that the battery voltage is within a predetermined range by monitoring the voltage of the secondary battery in consideration of the fact that the voltage of the secondary battery will be lower than a predetermined value at the time of discharging. I needed to. In particular, in the case of a lithium secondary battery, if the battery voltage is discharged to a non-recovery voltage (for example, 1 V), it may not be used at all even if subsequently charged.

Therefore, when a lithium secondary battery is used, it is general that the battery is discharged through a protection circuit having a function of interrupting the discharge when the battery voltage decreases and reaches a discharge inhibition voltage. The discharge prohibition voltage is slightly higher (for example, 2.3 V) than the voltage (about 2 V) at which the negative electrode copper begins to melt.
V).

Conventional protection circuits having such a function include, for example, a voltage detection circuit for detecting a battery voltage and a FET for interrupting a charging current or a discharging current based on an output of the voltage detection circuit. When the battery voltage reaches the charging prohibition voltage, the first and second switch elements
The switching current of the switch element is turned off to interrupt the charging current,
When the battery voltage reaches the discharge prohibition voltage, the second switch element is turned off to cut off the discharge current,
It is configured to prevent overcharge and overdischarge.

[0007]

In the above-described conventional protection circuit for a secondary battery, when the battery voltage reaches a charging inhibition voltage, the first switch element is turned off to stop charging the secondary battery, When the battery voltage drops to the charge prohibition release voltage, the first switch element becomes conductive, and charging of the secondary battery is restarted. Here, when the secondary battery is discharged when the first switch element is in the cut-off state, the discharge is performed via the first diode connected in parallel to the first switch element. Has a problem that the battery voltage is not accurately output due to the voltage drop of the first diode.

In the above-described conventional protection circuit for a secondary battery, when the battery voltage reaches the discharge prohibition voltage, the second switch element is turned off to stop discharging the secondary battery.
When the battery voltage rises to the discharge prohibition release voltage, the second switch element becomes conductive, and the discharge of the secondary battery is restarted. Here, when charging the secondary battery when the second switch element is in the cut-off state, the charging is performed via the second diode connected in parallel to the second switch element. Has a problem that the battery voltage is not accurately output due to the voltage drop of the second diode. As a result, when performing charging control by performing full charge detection or the like from the battery voltage with a charger, it is difficult to perform appropriate charging control.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem of the prior art, and has been described in connection with the effect of a voltage drop of a switch element for preventing overcharge and a diode connected in parallel to the switch element for preventing overdischarge. It is an object of the present invention to provide a protection circuit for a secondary battery capable of accurately outputting a battery voltage to a charger or a device to be used without receiving the same.

[0010]

In order to solve the above problems, a protection circuit for a secondary battery according to the present invention includes a switch element inserted in series in a charge / discharge circuit of the secondary battery, A diode connected in parallel with the switch element so that the forward direction matches the discharge direction and a terminal voltage of the secondary battery are detected, and the switch element is turned off when the terminal voltage reaches a charging prohibition voltage. Overcharge prevention means and discharge detection means for detecting the presence or absence of discharge of the secondary battery and maintaining the switch element in a conductive state at the time of discharge are provided.

[0011] Another secondary battery protection circuit according to the present invention includes:
Detects the switch element inserted in series in the charge / discharge circuit of the secondary battery, the diode connected in parallel with the switch element so that the forward direction matches the charging direction of the secondary battery, and the terminal voltage of the secondary battery An overdischarge preventing means for turning off the switch element when the terminal voltage reaches the discharge prohibition voltage;
Charge detecting means for detecting the presence or absence of charging of the secondary battery and turning on the switch element at the time of charging.

[0012] Still another secondary battery protection circuit according to the present invention is a first secondary battery protection circuit that is inserted in series into a secondary battery charge / discharge circuit.
The second switch element, the first diode connected in parallel to the first switch element so that the forward direction matches the discharge direction of the secondary battery, and the forward direction matches the charge direction of the secondary battery The second diode connected in parallel with the second switch element and the terminal voltage of the secondary battery are detected, and when the terminal voltage reaches the charging prohibition voltage, the first switch element is turned off. Overcharge prevention means for detecting the discharge of the secondary battery, discharge detection means for turning on the first switch element at the time of discharge, and detecting the terminal voltage of the secondary battery to discharge the terminal voltage. Overdischarge prevention means for turning off the second switch element when the prohibition voltage is reached, charge detection means for detecting the presence or absence of charging of the secondary battery and turning on the second switch element during charging; It is characterized by having.

As described above, in the protection circuit according to the present invention, when the discharge detection means detects the discharge of the secondary battery, the switch element (first switch element) for preventing overcharge is forcibly made conductive. As a result, a voltage drop due to a diode (first diode) connected in parallel with the switch element so that the forward direction coincides with the discharge direction does not occur, and an accurate value of the battery voltage is output to the device to be used. can do.

Further, in the protection circuit of the present invention, when charging of the secondary battery is detected by the charging detecting means, the switch element (second switch element) for preventing overdischarge is forcibly made conductive. An accurate value of the battery voltage is output to the charger side by preventing a voltage drop due to a diode (second diode) connected in parallel with the switch element so that the forward direction matches the charging direction. be able to.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a configuration of a protection circuit for a secondary battery according to a first embodiment of the present invention. A secondary battery (hereinafter simply referred to as a battery) 10 to be protected by the protection circuit is a non-aqueous solvent-based secondary battery such as a lithium battery or a battery charged at a constant voltage such as a lead storage battery. Is a lithium secondary battery as an example.

As shown in FIG. 1, NPN type first and second field effect transistors (hereinafter, referred to as FETs) 11, 1 constituting a switch element are provided in a charge / discharge circuit of a battery 10.
2 are inserted in series. That is, the positive terminal of the battery 10 is connected to the positive terminal (+) which is an external connection terminal, and the source terminal of the first FET 11 is connected to the negative terminal (-) which is an external connection terminal. A charger or a device to be used is connected to the plus terminal (+) and the minus terminal (-). The drain terminal of the first FET 11 is connected to the drain terminal of the second FET 12,
The source terminal of the FET 12 is connected to the negative pole of the battery 10. Here, the first FET 11 is a switch element for preventing overcharge, and the second FET 12 is a switch element for preventing overdischarge.

A first diode D1 is connected in parallel to the first FET 11 so that the forward direction coincides with the discharge direction as shown in FIG. 1, that is, the first diode D1 becomes forward during discharge. The second diode D2 is connected to the second FET 12 in parallel so that the forward direction coincides with the charging direction as shown in FIG. 1, that is, the second diode D2 becomes forward when charging. As these diodes D1 and D2,
The respective parasitic diodes of the FETs 11 and 12 may be used, or a dedicated element different from the FET may be used.

The overcharge / discharge prevention circuit 13 includes first and second F
A circuit for controlling the ETs 11 and 12 to prevent overcharging and overdischarging of the battery 10, the input terminal a of which is the positive pole of the battery 10, the input terminal b is the negative pole of the battery 10, and the input terminal e is the negative pole of the battery 10. The drain terminal of the first FET 11 and the second F
The input terminal f is the first FET at the drain terminal of ET12.
Twelve source terminals and a negative terminal (-), which is an external connection terminal, respectively. The overcharge / discharge prevention circuit 13 includes a charge prohibition detection circuit 14, a discharge prohibition detection circuit 15, a discharge detection circuit 16, a charge detection circuit 17, and an OR
It is composed of circuits 18 and 19.

The charge inhibition detection circuit 14 monitors the terminal voltage of the battery 10 and generates a charge inhibition output when the terminal voltage exceeds a predetermined charge inhibition voltage during charging. Is a circuit that monitors a terminal voltage of the terminal and generates a discharge inhibition output when the terminal voltage falls below a predetermined discharge inhibition voltage during discharging. The discharge detection circuit 16
Is a circuit for detecting the presence or absence of discharge of the battery 10 from the voltage between both ends of the FET 12.
11 is a circuit for detecting the presence or absence of charging of the battery 10 from the voltage between both ends of the battery 11.

The output of the charge inhibition detection circuit 14 and the output of the discharge detection circuit 16 are input to an OR circuit 18,
Is supplied to the gate of the first FET 11. The output of the discharge prohibition detection circuit 15 and the output of the charge detection circuit 17 are O
The input to the R circuit 19, the output of the OR circuit 19 is the second F
It is supplied to the gate of ET12.

When the terminal voltage of the battery 10 reaches a predetermined charge inhibition voltage, the charge inhibition detection circuit 14 generates a charge inhibition output, and the output g of the charge inhibition detection circuit 14 changes from a high level to a low level. On the other hand, when the terminal voltage of the second FET 12 reaches a predetermined discharge detection voltage in the discharge direction, the discharge detection circuit 16 generates a discharge detection output, and the discharge detection circuit 16
Changes from a low level to a high level. The output g of the charge inhibition detection circuit 14 and the output i of the discharge detection circuit 16 are O
When the signal is input to the R circuit 18 and the output c of the OR circuit 18 changes from a high level to a low level, the first FET 11 is turned off.

When the terminal voltage of the battery 10 reaches a predetermined discharge prohibition voltage, the discharge prohibition detection circuit 15 generates a discharge prohibition output, and the output h of the discharge prohibition detection circuit 15 changes from a high level to a low level. I do. On the other hand, when the terminal voltage of the first FET 11 reaches a predetermined charge detection voltage in the charging direction,
The charge detection circuit 17 generates a charge detection output, and the output of the charge detection circuit 17 changes from a low level to a high level. The output h of the discharge prohibition detection circuit 15 and the output j of the charge detection circuit 17 are input to an OR circuit 19, and when the output d of the OR circuit 19 changes from a high level to a low level, the second FET 12 is turned off. It is configured.

Next, the operation of the protection circuit for a secondary battery according to this embodiment will be described. When the terminal voltage of the battery 10 is between the charge prohibition voltage and the discharge prohibition voltage, the outputs g and h of the charge prohibition detection circuit 14 and the discharge prohibition detection circuit 15 both generate high level signals, and the OR circuit 18 Since both the outputs c and d of the OR circuit 19 generate high-level signals, the first and second FETs 11 and 12 are turned on, and charging and discharging are performed normally.

In general, the charger performs charging so that the charging voltage per battery is lower than a predetermined charging prohibition voltage set in the overcharge / discharge prevention circuit 13, so that a positive terminal as an external connection terminal is used. When charging is performed by connecting a charger to the (+) and the minus terminal (-), the terminal voltage of the battery 10 is lower than the charge prohibition voltage, and the charge prohibition detection circuit 1
4 is at a high level, and the output c of the OR circuit 18 is also at a high level, so that the first FET 11 maintains a conductive state.

On the other hand, when the charging voltage of the battery 10 increases due to a failure of the charger and exceeds a predetermined charging prohibition voltage, the output g of the charging prohibition detecting circuit 14 becomes low. In addition, when a current flows in the battery 10 in the charging direction and when charging is stopped, the output i of the discharge detection circuit 16 is also at a low level, so that the first FET 11 is in a non-conductive state. The charging of the battery 10 is stopped, and overcharging is prevented.

Next, when the battery 10 is discharged by connecting the equipment used to the plus terminal (+) and the minus terminal (-) which are the external connection terminals in the above state, the terminal voltage of the battery 10 is released from the charging inhibition. Until the voltage drops below the voltage, the output g of the charge prohibition detection circuit 14 is at a low level, but when a current flows in the discharge direction, the output i of the discharge detection circuit 16 is at a high level, and the output c of the OR circuit 18 is output. Is also at a high level, so that the first FET 11 becomes conductive. Therefore, the first
Since the voltage drop at the diode D1 connected in parallel to the FET 11 does not occur, an accurate value of the battery voltage can be output to the device to be used.

On the other hand, the equipment used discharges so that the discharge voltage per battery becomes higher than a predetermined discharge prohibition voltage set in the overdischarge prevention circuit 13, so that a positive terminal (external connection terminal) is used. +) And minus terminal (-)
When a device to be used is connected to perform discharge, the terminal voltage of the battery 10 is higher than a predetermined discharge prohibition voltage, the output h of the discharge prohibition detection circuit 15 becomes high level, and the output d of the OR circuit 19
Becomes high level, the second FET 12 maintains the conductive state.

On the other hand, when the discharge voltage of the battery 10 decreases due to a failure of the equipment used and drops to a predetermined discharge inhibition voltage, the output h of the discharge inhibition detection circuit 15 becomes low. When a current is flowing in the battery 10 in the discharge direction and when the discharge is stopped, the charge detection circuit 1
Since the output j of 7 is at a low level, the second FET 12 is turned off, so that the discharging of the battery 10 is stopped and overdischarge is prevented.

Next, when charging is performed by connecting a charger to the plus terminal (+) and the minus terminal (-) which are external connection terminals in the above state, the terminal voltage of the battery 10 is equal to or higher than the discharge inhibition release voltage. Until the discharge prohibition detection circuit 15
Is low, but when a current flows in the charging direction, the output j of the charging detection circuit 17 becomes high,
Since the output d of the OR circuit 19 also becomes high level, the second F
ET12 becomes conductive. Therefore, the second FET 12
The voltage drop at the diode D2 connected in parallel to the power supply can be eliminated, and an accurate value of the battery voltage can be output to the charger.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a protection circuit for a secondary battery according to the embodiment. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and only the differences from the first embodiment will be described.

In this embodiment, the discharge detection circuit 16 and the charge detection circuit 17 in FIG.
The equipment connection terminal 21 and the charger connection terminal 22 are connected to one of the input terminals 8 and 19, respectively. That is, in the present embodiment, the presence / absence of discharge is directly detected by the presence / absence of the use equipment connected to the use equipment connection terminal 21, and the presence / absence of charge is directly detected by the presence / absence of the charger connected to the charger connection terminal 22. This is different from the first embodiment. Needless to say, the same effect as in the first embodiment can be obtained by such a configuration.

The present invention is not limited to the above embodiment, but can be implemented with various modifications as follows. (1) In the embodiment, a non-aqueous solvent battery has been described as an example of a battery charged at a constant voltage. However, a lead storage battery or another battery may be used.

(2) In the embodiment, one battery is connected in series. However, a plurality of batteries may be connected in series, or a plurality of cell blocks connected in parallel may be connected in series. (3) In the embodiment, the example in which the FET as the switch element is connected to the minus side of the battery 10 has been described.
May be connected in series to the charging / discharging path of the battery 10.

(4) In the embodiment, the presence / absence of a current flowing through the FETs 11 and 12 is detected as the discharge detection circuit 16 and the charge detection circuit 17, but it may be detected by a shunt resistor for current detection. (5) In the embodiment, the example on both the charging side and the discharging side is shown, but either one may be used.

[0035]

As described above, according to the secondary battery protection circuit of the present invention, when the discharge of the secondary battery is detected, the switch element (first switch element) for preventing overcharge is forcibly applied. To prevent the voltage drop due to the diode (first diode) connected in parallel with the switch element so that the forward direction coincides with the discharge direction. Can be output, and when the charging of the secondary battery is detected, the switch element (second switch element) for preventing overdischarge is forcibly turned on, so that this switch element To output an accurate value of the battery voltage to the charger side without causing a voltage drop by a diode (second diode) connected in parallel so that the forward direction coincides with the charging direction. It can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a protection circuit for a secondary battery according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a protection circuit for a secondary battery according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Secondary battery 11, 12 ... 1st, 2nd FET (switch element) D1, D2 ... Diode 13 ... Overcharge / discharge prevention circuit 14 ... Charge inhibition detection circuit 15 ... Discharge inhibition detection circuit 16 ... Discharge detection circuit 17 ... Charge detection circuit 18, 19 ... OR circuit 21 ... Device connection terminal 22 ... Charger connection terminal

Claims (3)

[Claims] 1. A switch element inserted in series in a charge / discharge circuit of a secondary battery, a diode connected in parallel to the switch element so that a forward direction matches a discharge direction of the secondary battery, An overcharge prevention unit that detects a terminal voltage of the secondary battery and turns off the switch element when the terminal voltage reaches a charging prohibition voltage; and detects discharge of the secondary battery to detect discharge. And a discharge detecting means for keeping the switch element conductive at times. 2. A switch element inserted in series in a charge / discharge circuit of a secondary battery, a diode connected in parallel to the switch element so that a forward direction matches a charging direction of the secondary battery, Over-discharge prevention means for detecting the terminal voltage of the secondary battery and turning off the switch element when the terminal voltage reaches the discharge prohibiting voltage, detecting the presence or absence of charging of the secondary battery, and detecting the charge A protection circuit for a secondary battery, comprising: charge detection means for making the switch element conductive. 3. A first and a second switch element inserted in series in a charge / discharge circuit of a secondary battery, and the first switch element is connected to the first switch element so that a forward direction of the secondary battery coincides with a discharge direction of the secondary battery. A first diode connected in parallel; a second diode connected in parallel to the second switch element such that a forward direction matches a charging direction of the secondary battery; and a terminal of the secondary battery. Detecting a voltage, and when the terminal voltage reaches a charging prohibition voltage, an overcharge prevention unit that sets the first switch element to a non-conductive state; and detects whether or not the secondary battery is discharged. Discharging detection means for turning on the first switch element; detecting a terminal voltage of the secondary battery and turning off the second switch element when the terminal voltage reaches a discharge prohibiting voltage; Discharge prevention means, and charging of the secondary battery Detecting a no-protection circuit of a secondary battery characterized by comprising a charging detecting means for conducting state the second switching element during charging detection.