JPH10229636A - Charge and discharge control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a small FET element of ON-resistance as the FET of a switching circuit for charge and discharge control. SOLUTION: This charge and discharge control of a secondary battery 10 are performed by turning on FETs 12 and 3 connected in series, and in a charge and discharge control circuit 102, in which the overcharge detection and the overcurrent detection are both performed through a resistor 10 for prevention of breakage in reverse contact, a threshold level Vs for detection if an overcurrent detection circuit 130 is raised, in the case that the overcharge condition has already been detected by an overcharge detection circuit 119. As a result, even of a through-current flows to the resistor 106 and the input level of the overcorrect detection circuit 130 is apparently raised when the FET 113 is turned off by overcharge detection, overcurrent detection is not performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge / discharge control circuit for controlling charging / discharging of a secondary battery by turning on / off a switch circuit.

[0002]

2. Description of the Related Art As a charge / discharge control circuit for controlling the charge / discharge of a secondary battery by turning on / off a switch circuit, a circuit as shown in FIG. 5 is known. This charge / discharge control circuit 1 connects a secondary battery 5 to an external power supply terminal + VO or -VO via a switch circuit 4 including field effect transistors (hereinafter abbreviated as FETs) 2 and 3,
In this circuit, the FETs 2 and 3 of the switch circuit 4 are turned on and off in accordance with the state of charge and discharge of the secondary battery 5 to control the charge and discharge of the secondary battery 5. The terminal Vss is connected to the negative electrode of the secondary battery 5, and the terminal Vcc is connected to the positive electrode of the secondary battery 5 via the resistor 6. The control unit main body 10 generally configured as an IC circuit includes a circuit for detecting overcharge and overdischarge from the state of the terminal voltage of the secondary battery 5 and a load connected between the external power supply terminals + VO and -VO. (Not shown)
A circuit for detecting an overcurrent state from the magnitude of the current flowing through the circuit is incorporated. FIG. 2 shows an overcharge detection circuit 11 and an overcurrent detection circuit 12 among them.

When the overcharge detecting circuit 11 detects that the terminal voltage of the secondary battery 5 has become higher than a predetermined level, the FET 2 of the switch circuit 4 is turned off to inhibit the charging of the secondary battery 5, and In order to control the switch circuit 4 so as to allow only the discharge of the switch 5, the gate circuit of the FET 2 is provided with a switch circuit 13 for controlling the gate voltage. The switch circuit 13 is controlled to be turned on and off by the overcharge detection circuit 11, whereby the FET 2 is turned on and off. This switch circuit 13
Controls the gate-source voltage of FET2,
As shown in FIG. 2, a resistor 8 provided between the source of the FET 2 and the terminal VM for preventing breakdown at the time of reverse connection of the charger is connected, and controls the gate-source voltage of the FET 2.

On the other hand, an overcurrent detection circuit 12 is used to effectively detect the level of the current flowing from the secondary battery 5 to a load (not shown) connected between the external power supply terminals + VO and -VO. In general, a voltage drop generated at both ends of the switch circuit 4 is detected, and a voltage drop component generated at both ends of the switch circuit 4 is input to the overcurrent detection circuit 12 via the resistor 8. .

As described above, in the conventional charge / discharge control circuit, the resistor 8 for preventing destruction at the time of reverse connection, together with the switching circuit 13, responds to the output of the overcharge detection circuit 11 by the FE.
In addition to configuring a circuit that controls the turning on and off of T2,
The resistor 8 is also connected in series to the input of the overcurrent detection circuit 12 for detecting overcurrent.

According to this conventional configuration, when overcharge is detected, FET2 is turned off. Thereafter, when a load (not shown) is connected, a discharge current flows therethrough due to a parasitic diode 2D generated between its drain and source.
The voltage drop there is then typically about 0.6-0.7
About V. However, in the overcurrent detection circuit 12, the reference voltage for the detection is determined by the above-described voltage drop value generated by the parasitic diode 2D so that the voltage change of the terminal VM generated when the overcurrent flows can be reliably detected. It is determined in consideration of.

[0007]

By the way, in recent years, with the development of semiconductor technology, those having the above-mentioned voltage drop value of about 0.2 to 0.3 V caused by the parasitic diode 2D are becoming widespread. Therefore, this type of F having a small on-resistance is
If ET is used as a switch element of the switch circuit 4, the loss there is small, which is advantageous for power supply to a load.

However, the use of this kind of FET having a low on-resistance as the FET 2 causes the following problem. That is, when an element having a small on-resistance is used as the FET 2, it is necessary to reduce the reference voltage value to be set in the overcurrent detection circuit 12 for overcurrent detection. However, when the reference voltage value for overcurrent detection is reduced, a through current generated when the switch circuit 13 is turned off when overcharge is detected in the overcharge detection circuit 11 flows through the resistor 8. Due to the generated voltage drop, the overcurrent detection circuit 12 may be operated, and an erroneous operation may occur in which the FET 3 of the switch circuit 4 is turned off. When this malfunction occurs, both the FETs 2 and 3 are turned off, and the secondary battery 5
Charging and discharging cannot be performed at the same time, which causes a problem that power supply to the load is stopped.

Therefore, an object of the present invention is to reliably detect an overcharge or overcurrent state and use a secondary battery even if an FET element having a small on-resistance is used as an FET of a switch circuit for charge / discharge control. An object of the present invention is to provide a charge / discharge control circuit capable of reliably protecting against overcharge, overcurrent, and destruction at the time of reverse connection.

[0010]

A feature of the present invention to solve the above-mentioned problem is that the charge / discharge control of a secondary battery connected in series to a power supply terminal via a switch circuit is performed by configuring the switch circuit. A charge / discharge control circuit which controls the first FET for charge control and the second FET for discharge control to perform on / off control detects whether or not the battery is overcharged in response to a terminal voltage of the secondary battery. Overcharge detection circuit,
A resistor connected at one end between the first FET and the low-voltage side terminal of the external power supply terminal for preventing destruction at the time of reverse connection of a charger; and connected between the other end of the resistor and the gate of the first FET. And responding to the output of the overcharge detection circuit.
A semiconductor switch circuit for performing on / off control of the FET, an overcurrent detection circuit for detecting an overcurrent state of the secondary battery in accordance with a potential at the other end of the resistor, and an overcurrent detection circuit A circuit for turning off the second FET when a current state is detected, and a threshold for detection of the overcurrent detection circuit when the overcharge state is detected by the overcharge detection circuit. The point is that the value level is increased.

When the overcharge detection circuit does not detect overcharge, the first FET is on, and the secondary battery is charged by the charger connected to the external power supply terminal. When charging proceeds and the secondary battery becomes overcharged, the semiconductor switch circuit is activated by the overcharge detection circuit and the first FET is turned off. At this time, a through current generated by turning off the semi-moving body switch element in the semiconductor switch circuit flows through the resistor, and at the same time, the threshold level for detection by the overcurrent detection circuit increases. Therefore, even if the input voltage to the overcurrent detection circuit becomes high due to the flow of the through current through the resistor, the overcurrent detection is prevented from being performed in response to this. Therefore, there is no problem that both the first and second FETs are turned off when overcharge is detected, and both charging and discharging of the secondary battery are prohibited.

When the reference voltage applied to the overcurrent detection circuit is changed in order to increase the threshold level for detection by the overcurrent detection circuit, the reference voltage for overcurrent detection is set to the second FET. It is preferable to increase the forward voltage drop of the parasitic diode between the drain and the source so as not to exceed the forward voltage drop.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit block diagram of a charge / discharge control circuit of the present invention. The secondary battery 101 is connected to the external power supply terminal -VO via the switch circuit 103.
Are connected. The switch circuit 103 is composed of two N-ch FETs. In the illustrated embodiment, an FET 112 for overdischarge and overcurrent control is provided on the secondary battery 101 side, and the external power supply terminal -VO side Is provided with an FET 113 for overcharge control. The voltage of the secondary battery 101 is controlled by a charge / discharge control circuit 102 as described later.
, And according to the detection result, the FET 112,
113 is turned on and off. Charge / discharge control circuit 102
A reference voltage circuit 116 for applying a predetermined reference voltage Vr to each of the-input terminals of the overcharge detection comparator 119, the overdischarge detection comparator 118, the overcharge detection comparator 119, and the overdischarge detection comparator 118; A voltage dividing circuit 120 including resistors R1 to R4 for dividing the terminal voltage, another voltage dividing circuit 121 including resistors R5 to R7 for dividing the terminal voltage of the secondary battery 101, and an output control logic circuit 124 are provided. ing.

The two outputs from the output control logic circuit 124 are connected to terminals 125A and 125B, respectively, and further connected to the gates of the FETs 112 and 113 of the switch circuit 103 via signal lines 107A and 107B. The output control logic circuit 124 sends on / off control signals to the FETs 112 and 113 of the switch circuit 103. Charger 108 for charging secondary battery 101 and load 10 that can be driven by secondary battery 101
9 is connected between the external power supply terminals + VO and -VO.

The overcharge detection comparator 119 compares the reference voltage Vr of the reference voltage circuit 116 with the divided voltage representing the terminal voltage of the secondary battery 101 generated across the resistor R1 of the voltage dividing circuit 120 to overcharge. It has a function to detect the status.

The output of the overcharge detection comparator 119 becomes high when the level of the divided output voltage inputted to its + input terminal becomes higher than the reference voltage Vr. , The FET 113 is turned off. In addition, since the output of the overcharge detection comparator 119 becomes high level, F
The specific circuit configuration for turning off the ET 113 is the same as the circuit configuration shown in FIG. Therefore, here
External power supply terminal -VO and terminal 11 of charge / discharge control circuit 102
5 shows only a resistor 106 for preventing the battery from being destroyed at the time of reverse connection of the charger, and a FET in cooperation with the resistor 106.
A circuit corresponding to the switch circuit 13 in FIG. 2 configured in the output control logic circuit 124 for controlling the turning on and off of the switch 113 is omitted from illustration. Reference numeral 122 denotes an overcharge detection comparator 119
Is turned on when the output of R
2 is a FET for short-circuiting 2 and increasing the level of the + input terminal of the overcharge detection comparator 119 to give hysteresis to the operation of the overcharge detection comparator 119.

The over-discharge detection comparator 118 compares the reference voltage Vr of the reference voltage circuit 116 with the divided output voltage representing the terminal voltage of the secondary battery 101 generated at both ends of the resistor R5 of the voltage dividing circuit 121. It has a function to detect the discharge state.

The output of the over-discharge detection comparator 118 becomes high when the level of the divided output voltage inputted to its + input terminal becomes higher than the reference voltage Vr, and the output control logic circuit 124 , The FET 112 is turned off. In addition, since the output of the over-discharge detection comparator 118 becomes high level, F
Since a specific circuit configuration for turning off the ET 112 is a known circuit configuration, it is omitted in FIG. It is to be noted that what is indicated by reference numeral 123 is that when the output of the over-discharge detection comparator 118 is turned to a high level state, the resistor R6 is short-circuited and the level of the + input terminal of the over-discharge detection comparator 118 is raised. This is an FET for giving hysteresis to the operation of the overdischarge detection comparator 118.

Reference numeral 130 denotes an overcurrent detection circuit for detecting whether an overcurrent is flowing to the load 109 in response to the potential of the external power supply terminal -VO obtained via the resistor 106. The overcurrent detection circuit 130 includes an overcurrent detection comparator 131 whose + input terminal is connected to the terminal 115 of the charge / discharge control circuit 102, and an overcurrent detection comparator 131.
And a reference voltage supply circuit 132 provided at the-input terminal.

The reference voltage supply circuit 132 includes a reference voltage circuit 133 for supplying a predetermined constant reference voltage Vs, and resistors 134 and 135 for dividing the constant reference voltage Vs.
Switch 136 for short-circuiting the resistor 134
Are connected as shown in the figure. Normally open switch 1
36 is closed in response to the output of the overcharge detection comparator 119 going high. Therefore, when overcharge detection is not performed by the overcharge detection comparator 119, the normally open switch 136 is open, the constant reference voltage Vs of the reference voltage circuit 133 is divided, and the voltage is lower than the constant reference voltage Vs. Is overcurrent detection comparator 1
31 is applied to the-input terminal. On the other hand, when overcharge is detected by the overcharge detection comparator 119, the normally open switch 136 is closed and the reference voltage circuit 13
The constant reference voltage Vs of 3 is directly applied to the minus input terminal of the overcurrent detection comparator 131.

As described above, the threshold value for overcurrent detection in the overcurrent detection circuit 130 is changed as described above depending on whether or not the overcharge detection state is present. Therefore, when overcharge detection is not detected by the overcharge detection comparator 119, the overcurrent detection circuit 130 can perform overcurrent detection only by slightly increasing the level of the terminal 115.
When overcharge is detected by the overcharge detection comparator 119, overcurrent detection is performed when the level of the terminal 115 rises more than that. Reference numeral 127 denotes an FET that is turned on when the overcurrent detection comparator 131 enters a high-level output state, short-circuits the resistor R4, and provides hysteresis to the operation of the overcharge detection comparator 119. .

Since the charge / discharge control circuit 102 is configured as described above, it operates as follows. That is, if neither overcharge, overdischarge, or overcurrent is detected,
The FETs 112 and 113 are both turned on to charge the secondary battery 101 and load the secondary battery 101 from the load 109.
Discharge to any of them. If overdischarge is detected by the overdischarge detection comparator 118, the FET 11
2 is turned off, and discharge from the secondary battery 101 to the load 109 is not performed. However, when the charger 108 is connected, the voltage of the external power supply terminal −VO becomes lower than the negative electrode 111 of the secondary battery, so that the charging current flows to the secondary battery 101 via the diode of the FET 112. Become. In other words, after overdischarge is detected, charging is possible while discharging is disabled. When the current flowing from the secondary battery 101 to the load 109 increases and an overcurrent state occurs, the voltage drop generated in the switch circuit 103 increases, and both ends of the resistor 135 applied to the minus input terminal of the overcurrent detection comparator 131 When the voltage is exceeded, the output of the overcurrent detection comparator 131 becomes high level, and the FET1
12 is turned off, and the flow of current from the secondary battery 101 to the load 109 is stopped.

Next, the operation in the case of overcharge detection will be described. Overcharge detection comparator 11 when overcharged
The output of No. 9 is at a high level, and the FET 113 is turned off. At this time, as described with reference to FIG. 2, the through current flows through the resistor 106, so that the potential of the + input terminal of the overcurrent detection comparator 131 greatly increases even though the overcurrent state is not established. However, since the normally open switch 136 is closed in response to the output of the overcharge detection comparator 119 being in the high level state, the level of the reference voltage applied to the − input terminal of the overcurrent detection comparator 131 increases, Overcurrent detection comparator 131
Can be prevented from becoming high level. The magnitude of the reference voltage applied to the negative input terminal of the overcurrent detection comparator 131 needs to be determined so as not to be higher than the forward voltage of the parasitic diode 113D of the FET 113. After the overcharge state is detected in this manner, when a current flows to the load 109 and the terminal voltage of the secondary battery 101 decreases, the output of the overcharge detection comparator 119 becomes low level, and the normally open switch 136 is turned off. open.
Therefore, the normal overcurrent detection operation can be performed in the overcurrent detection circuit 130 thereafter.

As described above, even if a through current flows through the resistor 106, it is possible to effectively prevent the overcurrent detection circuit 130 from malfunctioning, so that an element with a small on-resistance can be used as the FET 113. Thus, the loss in the switch circuit 103 can be reduced and the efficiency can be improved.

In the embodiment shown in FIG. 1, the resistors 134 and 135 and the normally open switch 136 are used to connect the overcurrent comparator 131 to increase the threshold level for detection by the overcurrent detection circuit. The configuration in which the level of the reference voltage is changed according to the detection result of the overcharge detection comparator 119 has been described. However, the present invention is not limited to the configuration shown in this embodiment. In other words, in order to increase the threshold level for detection by the overcurrent detection circuit, two reference voltages are prepared in advance and these are switched, and the threshold value is set by giving the overcurrent comparator 131 an offset. A configuration in which the level is switched to be higher, or a configuration in which two overcurrent comparators 131 having different threshold levels for detection are prepared and switched, may be used.

Further, in the embodiment shown in FIG. 1, the voltage dividing circuits 120, 121 and the FETs 122, 123, 1
The operation of the overcharge detection comparator 119, the overdischarge detection comparator 118, and the overcurrent detection comparator 131 is provided with hysteresis by using a combination circuit with 27, but this is an example, and the configuration of the present invention is It is needless to say that the hysteresis operation may be realized by another known circuit configuration without limiting the present invention.

The embodiment shown in FIG. 1 has described an example of a configuration in which only one secondary battery 101 is subjected to charge / discharge control. However, the present invention is not limited to the case where only one secondary battery is subjected to charge / discharge control, and can be similarly applied to the case where charge / discharge control is performed on a plurality of secondary batteries. is there.

FIG. 2 shows an embodiment in which the present invention is applied to a charge / discharge control circuit for two cells. FIG.
The charge / discharge control circuit shown in FIG.
The charge / discharge control of another secondary battery 101 'is performed in the same manner as in the case shown in FIG. In this charge / discharge control circuit, the terminal 201 of the charge / discharge control circuit 200
To 205, secondary battery 101, 101 ', resistor 2
06, 208, 210, capacitors 207, 209, 2
11 are connected as shown. In addition, among the units in FIG. 2, portions corresponding to the units in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 3 shows a schematic configuration of the charge / discharge control circuit 200. The charge / discharge control circuit 200 includes the secondary battery 1
01 and the secondary battery 1
And a voltage dividing circuit 221 for dividing the voltage of 01 ′. The output of the voltage dividing circuit 220 allows the secondary battery 101
Circuit 23 for charge / discharge and overcurrent control of
0 activates. The comparator circuit 240 for charging / discharging the secondary battery 101 'and controlling overcurrent is operated by the output of the voltage dividing circuit 221. The output of the overcharge detection comparator 231 of the comparator circuit 230 and the output of the overcharge detection comparator 241 of the comparator circuit 240 are supplied to the overcurrent detection circuit 250, and one of the overcharge detection comparator 231 and the overcharge detection comparator 241 is provided. When overcharging is detected also in the output, the threshold level for overcurrent detection in the overcurrent detection circuit 250 is increased, and as a result, as in the case shown in FIG. Even if a through current flows, malfunction of the overcurrent detection circuit 250 due to this can be effectively prevented.

In the above description, the switching circuit 10
3 shows an example in which each of the FETs 112 and 113 uses Nch. However, the switching circuit 103
Of course, it is also possible to configure using an FET.

FIG. 4 shows an example of an embodiment in such a case. This embodiment is for three cells, but the switch circuits 301 are all Pch FETs 30.
Therefore, the switch circuit 301 is provided on the terminal + VO side. Terminal 325
A and 325B correspond to the terminals 125A and 125B in FIG. 1, respectively, and the resistor 306 corresponds to the resistor 106 in FIG. In this circuit configuration, when the terminal 325B is opened, the FET 303 is turned off by the pull-up resistor 304.

[0032]

According to the present invention, as described above, even when a through current flows through the resistor for preventing reverse-connection destruction of the charger when the overcharge control FET element is turned off due to the detection of overcharge, the overcurrent does not occur. Since the circuit for current protection can be prevented from operating, the F used for the switch circuit for charge / discharge control
An element having a small on-resistance can be used as the ET element. As a result, power loss in the switch circuit can be reduced by using an element having a small on-resistance as the FET element for overcharge control, and charging and discharging can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of an embodiment of a charge / discharge control circuit according to the present invention.

FIG. 2 is a circuit diagram showing an example of an embodiment in which the charge / discharge control circuit according to the present invention is applied to a circuit for two cells.

FIG. 3 is a main part circuit diagram showing the configuration of the charge / discharge control circuit shown in FIG. 2;

FIG. 4 shows a charge / discharge control circuit according to the present invention as a Pch FET.
FIG. 1 is a circuit diagram showing an example of an embodiment in the case of using a switch circuit according to the present invention.

FIG. 5 is a main part circuit diagram for explaining a problem of the conventional charge / discharge control circuit.

[Explanation of symbols]

101, 101 'Secondary battery 102, 200 Charge / discharge control circuit 103, 301 Switch circuit 106, 306 Resistor 109 Load 112, 113, 302, 303 FET (field effect transistor) 116, 133 Reference voltage circuit 119, 231, 241 Overcharge detection comparators 120, 121, 220, 221 Voltage division circuit 130, 250 Overcurrent detection circuit 131 Overcurrent detection comparator 132 Reference voltage supply circuit 134, 135 Resistor 136 Normally open switch + VO, -VO External power supply terminal

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[Procedure amendment]

[Submission date] May 18, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H02J 7/00 H02J 7/00 T 7/10 7/10 P

Claims (2)

[Claims] A charge / discharge control of a secondary battery connected in series via a switch circuit to an external power supply terminal is performed by controlling a first field effect transistor for charge control and a second field effect transistor for discharge control constituting the switch circuit. A charge / discharge control circuit configured to perform on / off control of a field-effect transistor, wherein an overcharge detection circuit that detects whether or not the battery is in an overcharge state in response to a terminal voltage of the secondary battery; A resistor for preventing destruction at the time of reverse connection, one end of which is connected between an effect transistor and a low-voltage side terminal of the external power supply terminal; and a resistor connected between the other end of the resistor and the gate of the first field effect transistor. A semiconductor switch circuit for performing on / off control of the first field effect transistor in response to an output of the overcharge detection circuit; and an overcurrent of the secondary battery according to a potential at the other end of the resistor. An overcurrent detection circuit that detects an overcurrent state, and a circuit for turning off the second field effect transistor when the overcurrent detection circuit detects an overcurrent state. Wherein a threshold level for detection by the overcurrent detection circuit is increased when the overcurrent is detected. 2. The method according to claim 1, wherein when the overcharge detection circuit detects an overcharge state, a threshold level for detection of the overcurrent detection circuit is a parasitic level between a drain and a source of the first field effect transistor. 2. The charge / discharge control circuit according to claim 1, wherein the charge / discharge control circuit is set to be smaller than a forward voltage drop of the diode.