JPH08294238A - Charging/discharging control circuit - Google Patents

Abstract

PURPOSE: To obtain a charging/discharging control circuit in which unbalanced consumption of the secondary batteries is prevented by connecting a buffer having very high impedance with a terminal for detecting the terminal potential of a plurality of secondary batteries connected in series thereby equalizing the currents being fed to respective secondary batteries. CONSTITUTION: The charging/discharging control circuit is connected, at the outer terminal -VO or +VO thereof, with a plurality of secondary batteries 101, 102 through a switch circuit 103. The terminal for detecting the potential between the plurality of secondary batteries is connected with a buffer 110 which is fed with power through the terminals -VO and VO. The buffer 110 outputs the potential between secondary batteries to the joint of a plurality of voltage divider circuits 104, 105. When the buffer 110 is constituted of an MOSFET, a substantially infinite input impedance can be obtained because the gate-drain impedance and the gate-source impedance are infinite, and thereby no current flow into the input terminal.

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 capable of controlling charge / discharge of a plurality of secondary batteries connected in series.

[0002]

2. Description of the Related Art As a conventional rechargeable power supply device composed of a plurality of secondary batteries, a circuit as shown in FIG. 2 is known. That is, the switch circuit 1 is connected to the external terminal -V0 or + V0.
A plurality of secondary batteries 101 and 102 are connected in series via 03. Further, a charging / discharging control circuit is connected in parallel to each secondary battery. The charge / discharge control circuit has a function of detecting the voltage of the secondary battery. This charge / discharge control circuit is configured as follows, for example.

Voltage dividing circuits 104 and 105 are connected in parallel to the respective secondary batteries, and comparators using the outputs of the voltage dividing circuits 104 and 105 and the output signals of the reference voltage sources 106 and 107 as input signals. Circuit 108,1
09 are connected to each. Comparator circuit 1
08 and 109 compare the voltage of the secondary batteries 101 and 102 with the reference voltage sources 106 and 107 so that the voltage of the secondary battery is overcharged (the voltage is higher than a predetermined high voltage value) or overdischarged. A state (state in which the voltage is lower than a predetermined voltage value) is detected. Comparator circuits 108 and 109
Is an input signal of the control circuit 111, and when either of the secondary batteries is in the overcharged state or the overdischarged state, a signal is output from the control circuit 111 to turn off the switch circuit 103. . Therefore, in the over-discharged state, the switch circuit 103 is turned off and the external terminal -V
0 or stop charging from the primary power source connected to + V0 to the secondary power source. In the overcharged state, the switch circuit 103 is turned off to stop the supply of energy to the load connected to the external terminal -V0 or + V0. That is, the charge / discharge control circuit controls the switch circuit 103 between the secondary batteries 101 and 102 and the external terminals to excessively charge the secondary batteries 101 and 102 and prevent the secondary battery 1 from being charged.
It is possible to prevent an excessive decrease in the storage capacity of the secondary battery due to the energy supply to the loads 01 and 102.

[0004]

However, in the conventional charge / discharge control circuit, when a plurality of secondary batteries connected in series are controlled to form a power supply device, the voltage dividing circuit is also connected in series. However, in that case, due to the difference in the internal impedance of each voltage dividing circuit, even if the load is not connected to the external terminal, current will flow to the battery connection terminal that detects the voltage between the secondary batteries, and each secondary battery The current flowing through the battery varies depending on the direction of the current flowing through the battery connection terminal. Therefore, one of the secondary batteries consumes electric charge earlier than the other secondary batteries, and a voltage difference occurs between the two batteries. This phenomenon is called "single slip" of the secondary battery.

When the secondary battery having one-sided slip is recharged, the potential difference between the two batteries causes one secondary battery to be fully charged before the other secondary battery is overcharged. I will end up. At this point, the charge / discharge control circuit detects overcharge and stops charging, so that one of the secondary batteries is not fully charged and the capacity of the secondary battery cannot be effectively used. Further, when the power supply device thus charged with one-sided slippage is used, one secondary battery having a low battery voltage is over-discharged earlier than the other secondary battery. At that point, the discharge is stopped by the charge / discharge control circuit even though one of the secondary batteries can supply energy.

As described above, in the rechargeable power supply device using a plurality of secondary batteries, if the secondary battery causes one-sided slip, the charge of the secondary battery cannot be effectively used and the life of the power supply device is shortened. I will end up. In an extreme case, one battery will be overcharged and the other battery will be overdischarged, and charging / discharging will not be possible, making it completely unusable.

Therefore, an object of the present invention is to provide a circuit for controlling charging / discharging without promoting one-sided slip in order to solve such a problem.

[0008]

In order to solve the above problems, the present invention provides a charge / discharge control circuit by providing a buffer having a very large input impedance at the battery connection terminals of a plurality of secondary batteries connected in series, The potential of this battery connection terminal is input to one terminal of the voltage dividing circuit as the output of the buffer so that no current flows between this terminal and the battery connection terminal.

[0009]

[Function] Since the potentials of the battery connection terminals of a plurality of secondary batteries are output through the buffer having a very large input impedance and the current does not flow to the battery connection terminals, the same amount of current flows to each of the plurality of secondary batteries. Prevent the secondary battery from slipping, and extend the life of the rechargeable power supply using the secondary battery.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of a charge / discharge control circuit of the present invention. A plurality of secondary batteries 101, 102 are connected to the external terminal -V0 or + V0 via a switch circuit 103. The resistance value of the switch circuit 103 is ideally 0
, The external terminal -V0 outputs the lowest potential of the secondary battery, and + V0 outputs the highest potential. A buffer 110, which is supplied with power from the terminals -V0 and V0, is connected to the terminals for detecting the potential between the plurality of secondary batteries. The buffer 110 includes a plurality of voltage division circuits 104 and 105.
The potential between the secondary batteries is output to the connection point of. At this time, if the buffer 110 is composed of MOSFETs, the impedance between the gate and the drain and between the gate and the source are infinite, so that the input impedance can be configured to be almost infinite, and no current flows through the input terminal. However, the buffer 110 does not have to be composed of a MOSFET, and may be composed of any element as long as the impedance of the input terminal is very large.

Further, voltage dividing circuits 104 and 105 are connected in parallel to the respective secondary batteries 101 and 102. The voltage dividing circuits 104 and 105 are buffer 110
The output of is used as one of the inputs. This voltage dividing circuit 1
The output signals of the comparators 108 and 109 for comparing the outputs of the reference voltage sources 04 and 105 with the voltages of the reference voltage sources 106 and 107 serve as inputs to the control circuit 111, and the control circuit 111 uses the secondary battery 1
A signal for controlling the switch circuit 103 connected in series with 01 and 102 is output. Therefore, even if there is a difference in internal impedance between the plurality of voltage dividing circuits 104 and 105, the current flowing through each secondary battery is determined only by the current flowing through the voltage dividing circuits 104 and 105 in series. Therefore, it is possible to prevent the slippage due to the difference in the currents flowing through the plurality of secondary batteries 101 and 102.

According to the present invention, as shown in FIG. 3, even when three or more secondary batteries are used, the buffer 110 supplied with power from the lowest potential terminal -V0 and the highest potential terminal + V0 is connected to each battery connection terminal. It can also be realized by FIG. 4 shows another example of the embodiment of the present invention. Multiple secondary batteries 1
A switch circuit 103 is connected in series to 01 and 102, and a charge / discharge control I for controlling the switch circuit 103 is connected.
C201 is connected in parallel to the secondary batteries 101 and 102. If the charge / discharge control IC 201 can control a plurality of secondary batteries and has an intermediate potential detection terminal for detecting the intermediate potential of the secondary batteries, the intermediate potential detection terminal can detect the maximum potential of the secondary batteries 101 and 102. It can also be realized by connecting the buffer 110 that supplies power from the lowest potential to the outside. By detecting this intermediate potential through the buffer 110, the difference in current generated due to the difference in impedance between the respective detection terminals is suppressed, and the secondary batteries 101 and 1 are suppressed.
02 can be prevented from slipping.

Further, the present invention provides a circuit for controlling charging / discharging of a plurality of secondary batteries 101, 102 by connecting several charging / discharging control ICs 201, 202 in parallel for controlling charging / discharging of secondary batteries as shown in FIG. When configured, a plurality of secondary batteries 10
A plurality of secondary batteries 101, 1 are connected to the battery connecting terminals of 1, 102.
This can also be realized by connecting the buffer 110 that supplies power from the highest potential and the lowest potential of 02. In this case, even if the internal impedances of the plurality of charge / discharge control ICs 201 and 202 are different, no current flows in the intermediate potential, so that the currents flowing in the plurality of secondary batteries are equal and the non-uniformity of the secondary batteries can be prevented. it can.

The present invention can also be realized in the case of controlling a plurality of secondary batteries 101 and 102 using a charge / discharge control IC 202 having a switch circuit built therein as shown in FIG.

[0015]

According to the charge / discharge control circuit of the present invention, a battery connection terminal of the charge / discharge control circuit is provided by providing a buffer having a very large input impedance at the terminal for detecting the potential of the terminal to which a plurality of secondary batteries connected in series are connected. Since a current can be prevented from flowing to each of the secondary batteries, it is possible to supply a power supply device having a long life by making the currents flowing through the respective secondary batteries equal to each other and preventing the secondary batteries from slipping.

[Brief description of drawings]

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

FIG. 2 is a circuit block diagram of a conventional rechargeable power supply device.

FIG. 3 is a circuit block diagram of a charge / discharge control circuit according to another embodiment of the present invention.

FIG. 4 is a circuit block diagram of a charge / discharge control circuit according to another embodiment of the present invention.

FIG. 5 is a circuit block diagram of a charge / discharge control circuit according to another embodiment of the present invention.

FIG. 6 is a circuit block diagram of a charge / discharge control circuit according to another embodiment of the present invention.

[Explanation of symbols]

 101, 102 Secondary battery 103 Switch circuit 104, 105 Voltage division circuit 106, 107 Reference voltage source 108, 109 Comparator 110 Buffer 111 Control circuit 201 Charge / discharge control IC 202 Switch circuit built-in charge / discharge control IC

Claims (2)

[Claims] 1. A power source in which a plurality of secondary batteries are connected in series,
A buffer circuit that outputs a connection terminal voltage of each of the plurality of secondary batteries, a voltage detection circuit that detects an output voltage of the buffer circuit, and an input process of a signal from the voltage detection circuit to control charge and discharge. And a control circuit that outputs the signal of 1. 2. A power source in which a plurality of secondary batteries are connected in series,
In a charge / discharge control circuit comprising a voltage detection circuit for detecting respective voltages of the plurality of secondary batteries and a control circuit for input-processing a signal from the voltage detection circuit and outputting a signal for controlling charge / discharge, A charging / discharging control circuit, wherein a buffer circuit for outputting each connection terminal voltage of the secondary battery is provided at an input of the voltage detection circuit.