JP3597618B2 - Secondary battery protection circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery protection circuit, and more particularly to a technique effective for use as a protection circuit for overcharge and overdischarge in a battery mounted together with a lithium (Li) ion battery in a battery pack.
[0002]
[Prior art]
As a secondary battery used for portable electronic devices, there is a Li-ion secondary battery. In this Li-ion secondary battery, when overcharged, metallic Li precipitates, leading to an accident. Further, when overdischarge is performed, the number of times of repeated charge / discharge use becomes extremely poor. For this reason, when overcharge or overdischarge is detected, a protection switch including a power MOSFET or the like for separating the battery from the device body is provided. Such a Li-ion secondary battery is described in Nikkei McGraw-Hill, “Nikkei Electronics,” November 20, 1995, pp. 100-117.
[0003]
[Problems to be solved by the invention]
When the Li-ion secondary battery is discharged to a predetermined voltage or lower, the number of times of repeated charging and discharging becomes extremely poor. In determining such an overdischarge, as shown in FIG. 2, when the battery voltage VCC approaches the end voltage at which the discharging operation should be stopped, the voltage margin decreases, and a sudden load change, in other words, the load When an overcurrent flows, the internal voltage of the battery causes the battery voltage VCC to temporarily fall below the cut-off voltage, and it is erroneously determined that the discharge voltage itself has fallen below the cut-off voltage. Would.
[0004]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a secondary battery protection circuit having improved usability and safety, and improved usability. The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
[0005]
[Means for Solving the Problems]
The outline of a representative one of the inventions disclosed in the present application will be briefly described as follows. That is, in the protection circuit of the secondary battery, overvoltage or overdischarge of the battery voltage is detected by the voltage detection circuit, and counting is performed while the detection signal is at one level corresponding to the overcharge or overdischarge state. A timer circuit having a frequency dividing counter for performing an operation is provided, and when the count output reaches a count value corresponding to a predetermined time setting, an output signal is formed, and the latch circuit is stabilized at one level by the output signal. When the other level of the detection signal of the voltage detection circuit is output, the latch circuit is inverted to the other level, and the overdischarge protection switch is turned off by the output signal in a stable state at one level of the latch circuit. The over-discharge protection switch is turned on by the output signal in the stable state at the other level.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a circuit diagram of an embodiment of the secondary battery protection circuit according to the present invention, which is directed to overdischarge protection. Each circuit element shown in FIG. 1 is formed on a single semiconductor substrate by a known semiconductor integrated circuit manufacturing technique together with another protection circuit described later. Although not particularly limited, a battery to be protected is a Li-ion secondary battery.
[0007]
The switch MOSFET Q1 is for inhibiting overdischarge. In determining such an overdischarge as to whether or not to stop the discharging operation by turning off the switch MOSFET Q1, as described with reference to FIG. 2 above, the battery voltage VCC is the final voltage at which the discharging operation should be stopped. , The voltage margin becomes smaller, and if the load fluctuates rapidly, in other words, if an overcurrent to the load flows, the battery voltage VCC temporarily drops below the cutoff voltage due to the internal impedance of the battery, and the discharge voltage itself becomes erroneously. Is determined to be equal to or lower than the end voltage.
[0008]
The following timer circuit is provided in order to prevent such a malfunction and continue the discharging operation up to the end voltage of the battery, in other words, to extend the battery life substantially. The voltage comparison circuit COMP4 compares a divided voltage VCC / N formed by a resistor circuit as described later with a reference voltage V4 corresponding to the end voltage in relation to the divided voltage, and a battery voltage VCC. Is lower than the end voltage, a low-level detection signal is formed. This detection signal is formed in response to the temporary overcurrent as described above.
[0009]
The detection signal is not used to immediately turn off the overdischarge protection switch MOSFET Q1, but it is determined whether or not the detection signal is continuously generated for a predetermined period set by the timer circuit. The timer circuit forms a time signal by supplying an oscillation pulse generated by a built-in oscillation circuit to a frequency division counter. The output signal of the voltage comparison circuit is supplied to a reset terminal of the frequency division counter, and is normally reset in a normal state.
[0010]
If it is determined by the voltage comparison circuit COMP4 that the battery voltage VCC has become equal to or lower than the end voltage, the detection signal is set to the low level during that time, the reset of the frequency division counter is released, and the counting operation of the oscillation pulse is performed. The count output of the frequency division counter is supplied to the gate circuit G3 constituting the decoder, and the counting operation corresponding to the set time is determined here. If the battery voltage VCC returns to the original state before the count value is reached, a reset signal is generated and the frequency division counter is reset during the counting. Therefore, if the count setting in the decoder is set to a relatively long time after completing the load fluctuation, even if the battery voltage VCC is temporarily reduced to the end voltage or less in response to the load fluctuation, it is ignored.
[0011]
The above-described load fluctuations are various in accordance with various electronic circuits mounted on an electronic device using the battery pack. For example, in an electronic device equipped with a motor driver, the time required for starting the motor is known in accordance with the performance of the motor. Set for a long time. As described above, since the time during which the battery voltage temporarily drops varies depending on the load, there is no particular limitation between the input of the gate circuit G3 constituting the decoder and the output of the frequency dividing counter. It can be set programmably according to the load by the master slice method, in other words, according to the use of the battery pack.
[0012]
In order to increase the degree of freedom in time setting as described above, in other words, in order to enable setting even after forming a protection IC, a current is selectively passed through a fuse made of a polysilicon layer or the like. May be mounted, and the time may be set by selectively disconnecting the circuit. Alternatively, an external terminal for time setting may be provided, and the time may be set by supplying a high level / low level to the external terminal.
[0013]
The timer circuit may be a circuit that supplies the output signal of the voltage comparison circuit COMP4 and a delay signal thereof to a logic circuit and invalidates the output signal within the delay time. However, in such a circuit, a relatively large time constant circuit must be formed in the semiconductor integrated circuit in order to form a delay signal, and the number of external parts such as capacitors increases. is there. When a capacitor is built-in, the set time is fixed, and a plurality of types of protection ICs must be prepared.
[0014]
The output signal of the decoder is supplied to the clock terminal CK of the latch circuit LT2, although not particularly limited. A high-level power supply voltage VCC is constantly supplied to the input of the latch circuit LT2, and the latch circuit LT2 is set when the clock CK is input. The output signal Q of the latch circuit LT2 changes to high level according to the set state, the gate of the overdischarge protection switch MOSFET Q1 is set to low level via the inverter circuit IV1 as a driver and the external terminal T3, and the switch MOSFET Q1 is turned off. Let it be in a state. The output signal of the voltage comparison circuit COMP4 is supplied to the reset terminal R of the latch circuit LT2, and when the VCC recovers to the end voltage or more by the charging operation, the reset state is set. The charging current until the latch circuit LT2 is reset flows through the parasitic diode D1 between the drain and the source while the MOSFET Q1 is off.
[0015]
In order to reduce the current consumption of the frequency division counter, the gate signal G2 provided at the input unit is controlled by the carry signal of the frequency division counter to close the gate. Thus, the input of the oscillation pulse to the frequency division counter is stopped. That is, when the battery voltage VCC becomes equal to or lower than the end voltage and the frequency dividing counter performs the maximum counting operation, the unnecessary counting operation thereafter is stopped, so that the current consumption can be reduced.
[0016]
FIG. 3 is a circuit diagram of another embodiment of the secondary battery protection circuit according to the present invention. The voltage at both ends of the Li-ion battery is supplied to terminals T1 and T2 of the semiconductor integrated circuit device IC constituting the protection circuit, and is also used as the operating voltage VCC. The positive electrode of the secondary battery is directly connected to the positive battery pack terminal +.
[0017]
Between the negative electrode of the secondary battery and the negative battery pack terminal-, protection switch MOSFETs Q1 and Q2 are connected in series. The switch MOSFET Q1 is a switch for discharge protection described with reference to FIG. 1, and the switch MOSFET Q2 is a switch for charge protection. The sources of the switch MOSFETs Q1 and Q2 are connected to a substrate (channel). Therefore, the PN junction between the drain and the channel is provided as the parasitic diodes D1 and D2 in parallel with the switch MOSFETs Q1 and Q2, respectively.
[0018]
In the above-mentioned semiconductor integrated circuit device IC, the battery voltage VCC across the terminals T1 and T2 is divided by the series resistors R1 to R6 and is not particularly limited, but the divided voltage at the connection point between the resistors R1 and R2 is a voltage comparison. It is supplied to one input terminal + of the circuit COMP1. A reference voltage V1 formed by a reference voltage generation circuit (not shown) is supplied to the other input terminal-of the voltage comparison circuit COMP1. This voltage detection circuit COMP1 constitutes a first voltage detection circuit. The detection signal of the first voltage detection circuit is supplied to the reset terminal R of the latch circuit LT1. The output signal Q of the latch circuit LT1 is at a high level in the set state, and is at a low level in the reset state. This output signal Q is supplied to the gate of the MOSFET Q2, which is the charge protection switch, via the terminal T4.
[0019]
Although not particularly limited, the divided voltage at the connection point between the resistors R4 and R5 is supplied to one input terminal-of the voltage comparison circuit COMP2. The other input terminal + of the voltage comparison circuit COMP2 is supplied with a reference voltage V2 formed by a reference voltage generation circuit (not shown). The output signal of the voltage comparison circuit COMP2 is supplied to the set terminal S of the latch circuit LT1 through the OR (logical sum) gate circuit G1. The reference voltage V2 corresponds to a specified voltage that instructs a battery charging operation. That is, when the divided voltage (battery voltage) drops below the prescribed reference voltage V2, the output signal of the voltage comparison circuit COMP2 changes to a high level, sets the latch circuit LT1, and sets the output signal Q of the latch circuit LT1. As a result, the switch MOSFET Q2 for overcharge protection is turned on.
[0020]
In this embodiment, when an overvoltage is erroneously made, the voltage comparison circuit COMP1 detects this and resets the latch circuit LT1 to turn off the overcharge protection switch MOSFET Q2. In the present invention, the switch MOSFET Q2 is used to prevent accidents due to heat generation due to the deposition of Li due to overcharging. Focusing on the fact that it is desirable to return to a normal state, the following function of detecting a load connection is added.
[0021]
The potential of the output side of the switch MOSFET Q2, in other words, the potential of the battery pack terminal-is taken into the semiconductor integrated circuit IC through the terminal T5, and supplied to the input terminal + of the voltage comparison circuit COMP3. A reference voltage V3 is supplied to the other input terminal-of the voltage comparison circuit COMP3. The reference voltage V3 is set to a relatively low potential for detecting the forward voltage Vf of the parasitic diode D2. The voltage comparison circuit COMP3 constitutes a second voltage detection circuit.
[0022]
If a load (electric device) is connected between the battery pack terminals + and-in a state where the latch circuit LT1 is reset by the overcharge and the MOSFET Q2 is turned off as a result, the overvoltage as described above occurs. In this state, the over-discharge protection switch connected in series with the MOSFET Q2 is connected to the negative side of the battery via the parasitic diode D2 with respect to the ground potential of the circuit with respect to the terminal T2 because the switch MOSFET Q1 is in the ON state. The current flows, and the potential of the battery pack terminal-rises by the forward voltage Vf of the parasitic diode D2.
[0023]
In the voltage comparison circuit COMP3, when the above-described discharge path is formed, in other words, an electronic device as a load is connected between the battery pack terminals + and-, and the potential of the battery pack terminal- The rising is detected by the voltage VM from the terminal T5, and the output signal is changed from the low level to the high level. As a result, the latch circuit LT1 in the reset state is inverted to the set state via the OR gate circuit G1, so that the output signal Q changes from low level to high level, and the MOSFET Q2 is turned on again, and the load Can be supplied with current. By the discharging operation by the connection of the load, the overcharge state is automatically released, and the output of the voltage comparison circuit COMP1 returns to the low level. The resistor R7 is added for preventing electrostatic breakdown at the terminal T5, but may be omitted.
[0024]
The operational effects obtained from the above embodiment are as follows. That is,
(1) In the protection circuit of the secondary battery, overvoltage or overdischarge of the battery voltage is detected by the voltage detection circuit, and while the detection signal is at one level corresponding to the overcharge or overdischarge state, A timer circuit having a frequency division counter for performing a counting operation is provided, and when the count output reaches a count value corresponding to a predetermined time setting, an output signal is formed, and the latch circuit is stabilized at one level by the output signal. When the detection signal of the voltage detection circuit outputs the other level, the latch circuit is inverted to the other level, and the overdischarge protection switch is turned off by the output signal in a stable state at one level of the latch circuit. And the overdischarge protection switch is turned on by the output signal in the stable state at the other level, thereby preventing a transient drop in the discharge voltage. There is an effect that the discharge capacity can be substantially improved without responding.
[0025]
(2) The frequency division counter is reset by the voltage detection circuit based on the other level, and the counting operation is stopped by controlling the overflow signal of the counting operation to close the gate provided at the input portion of the counting pulse. As a result, an effect that unnecessary current consumption in the frequency division counter can be suppressed can be obtained.
[0026]
(3) Since the protection circuit is integrated with the lithium ion battery as a battery pack, it is possible to obtain an effect that the usability can be improved while the discharge performance is substantially improved.
[0027]
(4) The protection circuit and the switch are for over-discharge protection, and a switch for over-charge protection is connected to the switch in series, and the switch for over-charge protection is connected to a protection circuit corresponding thereto. By performing the switch control, it is possible to obtain an effect that the usability can be improved while the substantial discharge capacity is improved and safety is secured.
[0028]
Although the invention made by the inventor has been specifically described based on the embodiments, the invention of the present application is not limited to the embodiments, and it is needless to say that various modifications can be made without departing from the gist of the invention. Nor. For example, a bipolar transistor or another switch element may be used as the switch element in addition to the MOSFET. In the case of the above-mentioned MOSFET, a parasitic diode between the drain and the source can be used. However, when there is no such a parasitic diode, a diode that allows a current equivalent to that to flow is provided in each switch in parallel. do it.
[0029]
In addition to the voltage detection circuit using the voltage comparison circuit as described above, the voltage detection circuit that detects the floating of the negative terminal-of the battery pack corresponding to the forward voltage of the parasitic diode D2 uses the threshold voltage of the MOSFET. It may be used. That is, the voltage VM of the terminal 5 is supplied to the gate of the N-channel MOSFET having a threshold voltage lower than the forward voltage of the parasitic diode D2, and the ground potential of the circuit corresponding to the negative electrode potential of the battery is supplied to the source. And a low-level / high-level detection signal corresponding to the on / off state may be formed from the drain of the MOSFET, and the detection signal may be inverted by an inverter circuit and used for the set signal.
[0030]
The reference voltage supplied to the voltage comparison circuit may be one common constant voltage. Based on this, the battery voltage VCC is divided by a voltage dividing resistor circuit, and the voltage dividing ratio is set to correspond to each of the specified voltage for setting the overcharge and latch circuits and the termination voltage for stopping the discharging operation. What is necessary is just to form a divided voltage. INDUSTRIAL APPLICABILITY The present invention can be widely used as various secondary battery protection circuits that need to perform overcharge protection.
[0031]
【The invention's effect】
The following is a brief description of an effect obtained by a representative one of the inventions disclosed in the present application. That is, in the protection circuit of the secondary battery, overvoltage or overdischarge of the battery voltage is detected by the voltage detection circuit, and counting is performed while the detection signal is at one level corresponding to the overcharge or overdischarge state. A timer circuit having a frequency dividing counter for performing an operation is provided, and when the count output reaches a count value corresponding to a predetermined time setting, an output signal is formed, and the latch circuit is stabilized at one level by the output signal. When the other level of the detection signal of the voltage detection circuit is output, the latch circuit is inverted to the other level, and the overdischarge protection switch is turned off by the output signal in a stable state at one level of the latch circuit. The over-discharge protection switch is turned on by the output signal in the stable state at the other level, so that the transient discharge voltage is reduced. It is possible to improve the substantial discharge capacity not respond to.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing one embodiment of a secondary battery protection circuit according to the present invention directed to overdischarge protection.
FIG. 2 is a characteristic diagram for explaining an operation of a protection circuit that controls the switch MOSFET Q1.
FIG. 3 is a circuit diagram showing an embodiment of another protection circuit for overcharge protection in the secondary battery protection circuit according to the present invention.
[Explanation of symbols]
R1 to R7 resistors, LT1 and LT2 latch circuits, G1 to G3 logic gate circuits, IV1 inverter circuits, COMP1 to CPMP4 voltage comparison circuits, Q1 to Q2 MOSFETs, D1, D2 diodes.

Claims (4)

A secondary battery protection circuit that receives a voltage between both ends of the secondary battery and is operated at the battery voltage,
A voltage detection circuit for detecting overvoltage or overdischarge of the battery voltage,
A timer circuit that includes a counter that performs a counting operation while one level is being output from the voltage detection circuit, and that generates an output signal when the output of the frequency division counter reaches a count value corresponding to a predetermined time setting. When,
A latch circuit that is stabilized at one level by an output signal of the timer circuit, and is inverted to the other level by outputting the other level from the voltage detection circuit;
The latch circuit is turned off by an output signal in a stable state at one level, is turned on by an output signal in a stable state at the other level, and is inserted in series into a current path of the secondary battery. And an overdischarge or overcharge protection switch. In the frequency division counter, the voltage detection circuit is reset by the other level, and a circuit for stopping the counting operation by controlling the overflow signal of the counting operation to close the gate provided at the input portion of the counting pulse. 2. The secondary battery protection circuit according to claim 1, wherein the secondary battery protection circuit is added. 3. The secondary battery protection circuit according to claim 1, wherein the protection circuit is integrated with a lithium ion battery as a battery pack. The protection circuit and the switch are for over-discharge protection, and the switch for over-charge protection is connected to the switch in series, and the switch for over-charge protection is switch-controlled by the corresponding protection circuit. 4. The secondary battery protection circuit according to claim 3, wherein:

Images