Battery protection circuit and protection method thereof

Abstract

The present invention relates to a battery protection circuit and a protection method thereof, which uses the following scheme: a charging / discharging FET is not connected on a current path between a battery and an external system, and when an abnormal situation occurs in the battery, a battery cell 0V voltage is transmitted to the external system by opening a voltage sensing line, thereby blocking an abnormal current of the battery in the external system.

Description

TECHNICAL FIELD

[0001] The present application relates to a battery protection circuit and a method for protecting a battery, and more particularly, to a battery protection circuit for protecting a battery from overcharge, overdischarge, and overcurrent and a method for protecting a battery. BACKGROUND

[0002] Batteries are widely used in various fields ranging from small electronic devices such as smartphones, notebook computers, and tablet computers to electric vehicles and energy storage systems (ESS).

[0003] However, while such a battery has efficiency and convenience that can be used in various fields, the battery has a risk of fire at the time of overheating due to the characteristics of high energy density. In addition, in the case of overdischarge, the performance of the battery can be degraded, and furthermore, a situation that damages safety can occur.

[0004] In order to secure the safety of such a battery, a battery protection circuit that protects a battery from overcharge, overdischarge, overcurrent, and short circuit is used.

[0005] On the other hand, generally, as shown in FIG. 1, a battery protection circuit 20 configures charge / discharge FETs 22a and 22b on a current path between a battery cell 10 and an output unit 30 to an external system, and uses a method of protecting a battery by blocking abnormal current by turning off the charge / discharge FETs 22a and 22b at the time of occurrence of an abnormality such as overcharge, overdischarge, or overcurrent. Figure 1

[0006] However, the charge / discharge FETs 22a and 22b configured on the current path must use a low-resistance FET having a small resistance value in order to prevent current loss and heat generated by current flowing through the current path. However, the low-resistance FET has the disadvantage of being larger and more expensive than a general FET, so that this causes problems such as an increase in the price and size of the battery protection circuit and an increase in the internal resistance of the battery.

[0007] Related prior art is disclosed in the following Patent Document 1.

[0008] (Patent Document 1) KR2045999 B1 SUMMARY

[0009] TECHNICAL PROBLEM

[0010] An object of the present application is to provide a battery protection circuit and a method for protecting a battery from abnormal situations such as overcharge, overdischarge, and overcurrent by using a general FET.

[0011] TECHNICAL SOLUTION

[0012] ​A battery protection circuit for protecting one or more battery cells from abnormal conditions including overcharge, overdischarge, and overcurrent according to the present application includes a current sensing unit connected in series on a current output path formed between one terminal of a battery cell and an output unit to an external system, and configured to sense a current of the battery cell flowing in the path; a voltage sensing unit connected to a voltage sensing line to sense a voltage of the battery cell, the voltage sensing line connected to both ends of the battery cell; a voltage information transmission unit configured to transmit a voltage value of the battery cell sensed by the voltage sensing unit to an external system; a control unit configured to determine whether an abnormal condition occurs in the battery cell using sensing values of the current sensing unit and the voltage sensing unit, and to disconnect the voltage sensing line according to a determination result; and a sensing line blocking FET provided on the voltage sensing line to be turned off to disconnect the voltage sensing line under control of the control unit.

[0013] In detail, the control unit includes a first determination unit configured to compare whether a voltage value of the battery cell sensed by the voltage sensing unit is equal to or greater than a predetermined first reference value, and to determine that the battery cell is in an overcharge state when the voltage value of the battery cell is greater than or equal to the predetermined first reference value and to output an overcharge signal; a second determination unit configured to compare whether the voltage value of the battery cell sensed by the voltage sensing unit is less than or equal to a predetermined second reference value, to determine that the battery cell is in an overdischarge state when the voltage value of the battery cell is less than or equal to the predetermined second reference value and to output an overdischarge signal; a third determination unit configured to compare whether a current value of the battery cell sensed by the current sensing unit is equal to or greater than a predetermined third reference value, and to determine that the battery cell is in an overcurrent state when the current value of the battery cell is equal to or greater than the predetermined third reference value and to output an overcurrent signal; and a blocking FET control unit configured to disconnect the voltage sensing line by turning off the sensing line blocking FET when any one of the overcharge signal, the overdischarge signal, and the overcurrent signal is output from the first determination unit, the second determination unit, and the third determination unit.

[0014] Further, when the voltage sensing line is disconnected by the blocking FET control unit, the voltage of the battery cell sensed by the voltage sensing unit is 0 V.

[0015] Accordingly, when the voltage information transmission unit transmits the 0 V voltage value of the battery cell to the external system, the external system senses that the current battery cell is in a low voltage state and turns off system power by itself.

[0016] A method of protecting one or more battery cells from abnormal conditions including overcharge, overdischarge, and overcurrent, includes: a cell state information measurement step of measuring a current value and a voltage value of a battery cell at predetermined periodic intervals by a sense resistor provided on a current output path between the battery cell and an output unit to an external system and a voltage sense line connected to both ends of the battery cell; an abnormal condition occurrence determination step of determining whether an abnormal condition occurs in the battery cell using the current value and the voltage value of the battery cell measured in the cell state information measurement step; a voltage sense line disconnection step of disconnecting the voltage sense line when it is determined that an abnormal condition occurs in the battery cell by the abnormal condition occurrence determination step; a cell voltage information transmission step of transmitting the voltage value of the battery cell measured by the voltage sense line disconnected by the voltage sense line disconnection step to the external system; and an external system shutdown step of automatically shutting down system power in the external system, which receives the voltage value of the battery cell measured by the disconnected voltage sense line by the cell voltage information transmission step.

[0017] In particular, the abnormal condition occurrence determination step includes: an overcharge determination step of comparing whether the voltage value of the battery cell measured in the cell state information measurement step is equal to or greater than a predetermined first reference value, and determining that the battery cell is in an overcharge state when the voltage value of the battery cell is equal to or greater than the predetermined first reference value; an overdischarge determination step of comparing whether the voltage value of the battery cell measured in the cell state information measurement step is less than or equal to a predetermined second reference value, and determining that the battery cell is in an overdischarge state when the voltage value of the battery cell is less than or equal to the predetermined second reference value; and an overcurrent determination step of comparing whether the current value of the battery cell measured in the cell state information measurement step is equal to or greater than a predetermined third reference value, and determining that the battery cell is in an overcurrent state when the current value of the battery cell is equal to or greater than the predetermined third reference value, wherein, when any one of overcharge, overdischarge, and overcurrent is determined, it is determined that an abnormal condition occurs in the battery cell.

[0018] Further, the voltage sense line disconnection step includes shutting down a sense line blocking FET configured on the voltage sense line.

[0019] Therefore, in the cell voltage information transmission step, the voltage value of the battery cell transmitted to the external system is 0 V.

[0020] Therefore, the external system shutdown step senses that the current battery cell is in a low voltage state, and shuts down system power in the external system when the 0 V voltage value of the battery cell is transmitted by the cell voltage information transmission step.

[0021] Further, the battery pack includes such a battery protection circuit.

[0022] Advantageous Effects

[0023] The battery protection circuit of the present application uses a general FET instead of a low-resistance FET to protect a battery from abnormal conditions such as overcharge, overdischarge, and overcurrent, thereby reducing the price of the battery protection circuit and reducing the size of the battery protection circuit. In addition, there is an effect of reducing the internal resistance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a circuit diagram schematically showing a conventional battery protection circuit.

[0025] Figure 2 is a circuit diagram schematically showing a battery protection circuit according to the present application.

[0026] Figure 3 is a block diagram showing a detailed configuration of a battery protection circuit according to the present application.

[0027] Figure 4 is a flowchart showing a battery protection method using a battery protection circuit according to the present application. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily practice the present application. However, the present application can be embodied in various forms and is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted for the sake of clarity in describing the present application, and the same reference numerals refer to the same elements throughout the specification.

[0029] Hereinafter, the present application will be described in detail with reference to the accompanying drawings.

[0030] 1. A battery protection circuit according to the present application

[0031] A battery protection circuit according to the present application will be described with reference to Figure 2 and Figure 3 The battery protection circuit 200 of the present application is a configuration for protecting a battery cell from abnormal conditions including overcharge, overdischarge, and overcurrent, and can include the following configurations.

[0032] 1.1 Current output path L1

[0033] First, a current output path is formed between one terminal of a battery cell 100 and an output unit 300 to an external system (not shown), and the current output path is a path through which current flows from the battery cell 100 to the output unit 300, and power can be supplied to the external system (not shown) through the path.

[0034] Here, the external system refers to an electronic device including, for example, a mobile phone, a notebook computer, a tablet computer, etc., which is connected to a connector (not shown) of the battery pack and uses current from the battery cell 100 as driving power.

[0035] Meanwhile, although Figure 2 only one battery cell 100 is shown in the middle, the present application is not limited thereto, and there can be more than one battery cell.

[0036] 1.2 Voltage sensing line L2

[0037] The voltage sensing line is a configuration for sensing the voltage of the battery cell 100 and is connected to both ends of the battery cell 100 as shown in Figure 2 , and the voltage sensing line L2 connected to the negative portion of the battery cell 100 can be connected in parallel with the current output path L1.

[0038] This voltage sensing line is a general configuration provided in a battery protection circuit to sense the voltage of the battery cell 100 and is different from a conventional voltage sensing line, and the voltage sensing line of the present application is different in that the FET 240 that disconnects the voltage sensing line is placed in the middle.

[0039] More specifically, in the case of the conventional battery protection circuit shown in Figure 1 , since this is a method of blocking abnormal current of the battery by connecting the charge / discharge FETs 22a and 22b on the current output path from the battery cell 10 to the external system (not shown), there is a problem in that the price and size of the protection circuit and the internal resistance of the battery pack increase due to the fact that the charge / discharge FETs 22a and 22b must be configured as low-resistance FETs. In contrast, the present application solves the above-mentioned problem by connecting the FET 240 to the voltage sensing line L2 instead of connecting the charge / discharge FET to the current output path L1. The principle will be described in detail when the control unit 250 is described below.

[0040] 1.3 Current sensing unit 210

[0041] The current sensing unit is a configuration connected in series on the current output path L1 to sense the current of the battery cell 100 flowing in the path, and can include, for example, a shunt resistor. The shunt resistor is a resistor for measuring current with an extremely low resistance value and high accuracy, and measures current by using the voltage applied to the resistor generated according to the size of the current.

[0042] 1.4 Voltage sensing unit 220

[0043] The voltage sensing unit is a configuration connected to both ends of the battery cell 100 through the voltage sensing line L2 to sense the voltage of the battery cell 100. The voltage sensing unit can sense the voltage of the battery cell 100 at a predetermined periodic interval.

[0044] Here, since the voltage sensing unit senses the voltage at the rear end of the sensing line blocking FET 240 provided on the voltage sensing line L2, when the sensing line blocking FET 240 provided on the voltage sensing line L2 is controlled to be turned off and the line L2 is disconnected, the voltage value of the battery cell 100 sensed by the voltage sensing unit becomes 0V.

[0045] 1.5 Voltage information transmission unit 230

[0046] The voltage information transmission unit is a configuration that transmits the voltage value of the battery cell 100 sensed by the voltage sensing unit 220 to an external system (not shown), and this can transmit the voltage value of the battery cell to the external system (not shown) through the connector (not shown) of the battery pack.

[0047] 1.6 Sensing line blocking FET 240

[0048] The sensing line blocking FET is a configuration provided on the voltage sensing line L2 to disconnect the voltage sensing line L2 under the control of the control unit 250 described later. When the sensing line blocking FET is turned on in the normal state in which the abnormal conditions including overcharge, overdischarge, and overcurrent do not occur in the battery cell 100, if the above abnormal conditions occur, the sensing line blocking FET switches to the off state to disconnect the voltage sensing line L2. In this case, the voltage sensing unit 220 that senses the voltage of the battery cell through the voltage sensing line L2 senses the voltage of the battery cell as 0V.

[0049] 1.7 Control unit 250

[0050] The control unit is a configuration that determines whether an abnormal condition including overcharge, overdischarge, and overcurrent occurs in the battery cell using the sensed values of the current sensing unit 210 and the voltage sensing unit 220 and disconnects the voltage sensing line L2 by turning off the sensing line blocking FET 240 according to the determination result. Such a control unit can be configured to include the following detailed configurations.

[0051] A. First determination unit 252

[0052] The first determination unit can compare whether the voltage value sensed by the voltage sensing unit 220 is equal to or greater than a predetermined first reference value, and when the voltage value is equal to or greater than the predetermined first reference value, the first determination unit can determine that the current battery cell 100 is in an overcharge state. In this case, an overcharge signal indicating the overcharge state of the battery cell 100 can be output.

[0053] Here, the predetermined first reference value means an overvoltage protection (OVP) value, which is a reference voltage value set to be cut off in advance for protecting the battery cell from overcharge.

[0054] B. Second determination unit 254

[0055] The second determination unit can compare whether the voltage value sensed by the voltage sensing unit 220 is equal to or less than a predetermined second reference value, and when the voltage value is equal to or less than the predetermined second reference value, the second determination unit can determine that the current battery cell 100 is in an overdischarge state. In this case, an overdischarge signal indicating the overdischarge state of the battery cell 100 can be output.

[0056] Here, the predetermined second reference value means an undervoltage protection (UVP) value, which is a reference voltage value set to be blocked in advance for protecting the battery cell from overdischarge.

[0057] C. Third determination unit 256

[0058] The third determination unit can compare whether the current value sensed by the current sensing unit 210 is equal to or greater than a predetermined third reference value, and when the current value is equal to or greater than the third reference value, the third determination unit determines that the current battery cell 100 is in an overcurrent state. In this case, an overcurrent signal indicating the overcurrent state of the battery cell 100 can be output.

[0059] Here, the predetermined third reference value means an overcurrent protection (OCP) value, which is a reference current value set to be cut off in advance for protecting the battery cell from overcurrent.

[0060] D. Sensing line blocking FET control unit 258

[0061] When any one of the overcharge signal, the overdischarge signal, and the overcurrent signal is output from the first determination unit 252, the second determination unit 254, and the third determination unit 256, the blocking FET control unit can recognize that an abnormal situation occurs in the current battery cell 100, and cut off the abnormal current of the battery cell by turning off the sensing line blocking FET 240 disposed in the voltage sensing line L2 to disconnect the voltage sensing line L2.

[0062] To explain the principle, when the voltage sensing line L2 is disconnected, the voltage of the battery cell sensed by the voltage sensing unit 220 becomes 0V. Then, the external system (not shown) recognizes that the voltage of the current battery cell is 0V through the voltage information transmission unit 230, so that the protection circuit of the external system itself senses the low voltage state of the battery and shuts down the system power by itself. Therefore, the current does not flow in the current output path L1 between the battery cell 100 and the output unit 300 of the external system, so that the abnormal current of the battery can be blocked.

[0063] In other words, in the case of the conventional battery protection circuit, compared with the method of directly blocking the abnormal current of the battery inside the protection circuit, the battery protection circuit according to the present application is a method for transmitting the 0V voltage of the battery cell to the external system by disconnecting the voltage sensing line to block the abnormal current of the battery in the external system.

[0064] At this time, with respect to the voltage sensing path L2, since the current does not flow, in order to prevent the current loss and heat generation like in the past, it is not necessary to use a low resistance FET, and even if a general FET is used, there is no problem of current loss and heat generation, and the battery can be protected from abnormal conditions including overcharge, overdischarge, and overcurrent while solving the above conventional problems.

[0065] Meanwhile, the above voltage sensing unit 220, voltage information transmission unit 230, and control unit 250 can be implemented in the protection IC.

[0066] 2. The battery protection method according to the present application (see Figure 4 )

[0067] The method of protecting the battery from abnormal conditions including overcharge, overdischarge, and overcurrent by using the battery protection circuit 200 according to the present application can include the following steps.

[0068] 2.1 Cell state information measurement step S100

[0069] The cell state information measurement step is a step of measuring the current value and the voltage value of the battery cell 100 through the sensing resistor 210 provided on the current output path L1 between the battery cell 100 and the output unit 300 to the external system and the voltage sensing line L2 connected to both ends of the battery cell 100, and can be performed at a predetermined periodic interval.

[0070] 2.2 Abnormal condition occurrence determination step S200

[0071] The abnormality occurrence determination step is a step of determining whether an abnormality including overcharge, overdischarge, and overcurrent occurs in the battery cell using the current value and the voltage value of the battery cell measured in the cell state information measurement step S100.

[0072] A. Overcharge determination step S210

[0073] The overcharge determination step can compare whether the voltage value of the battery cell measured in the cell state information measurement step S100 is equal to or greater than a predetermined first reference value, and when the voltage value is greater than or equal to the first reference value, the overcharge determination step determines that the battery cell is in an overcharge state (first determination unit 252).

[0074] B. Overdischarge determination step S220

[0075] The overdischarge determination step compares whether the voltage value of the battery cell measured in the cell state information measurement step (S100) is equal to or less than a predetermined second reference value, and when the voltage value is equal to or less than the predetermined second reference value, the overdischarge determination step can determine that the battery cell is in an overdischarge state (second determination unit 254).

[0076] C. Overcurrent determination step S230

[0077] The overcurrent determination step can compare whether the voltage value of the battery cell measured in the cell state information measurement step S100 is equal to or greater than a predetermined third reference value, and when the voltage value is greater than or equal to the third reference value, the overcurrent determination step determines that the battery cell is in an overcurrent state (third determination unit 256).

[0078] If any one of the overcharge, overdischarge, and overcurrent states of the battery cell is determined through the overcharge determination step S210, the overdischarge determination step S220, and the overcurrent determination step S230, the abnormality occurrence determination step can determine that an abnormality occurs in the battery cell.

[0079] 2.3 Voltage sensing line disconnection step S300

[0080] When it is determined in the abnormality occurrence determination step S200 that the battery cell corresponds to any one of the overcharge, overdischarge, and overcurrent states, the voltage sensing line disconnection step can disconnect the voltage sensing line. Disconnecting the voltage sensing line includes turning off the sensing line block FET 240 disposed on the voltage sensing line L2 connected to both ends of the battery cell. This step is performed by the sensing line block FET control unit 258 of the above-described control unit 250.

[0081] 2.4 Cell voltage information transmission step S400

[0082] The cell voltage information transmission step is a step of transmitting the voltage value of the battery cell measured through the disconnected voltage sensing line to the external system (voltage information transmission unit 230) by the voltage sensing line disconnection step S300. Through these steps, the external system can recognize the voltage state of the battery cell.

[0083] At this time, the voltage value of the battery cell transmitted to the external system in this step is 0V because it is a value measured through the disconnected voltage sensing line.

[0084] 2.5 External system shutdown step S500

[0085] The external system shutdown step is a step of automatically shutting down the system power by sensing that the current battery cell is in a low voltage state because the voltage value of the battery cell measured through the disconnected voltage sensing line, i.e., the 0V value, is received from the external system (not shown) by the cell voltage information transmission step S400. Accordingly, the charge / discharge current does not flow between the battery cell 100 and the external system (not shown), and thus the abnormal current of the battery corresponding to the abnormal situation is blocked.

[0086] Accordingly, by connecting the FET on the voltage sensing line in the case where the charge / discharge FET is not configured in the current output path between the battery cell and the external system, when the battery has an abnormal situation, since the external system recognizes that the battery is in a low voltage state and automatically shuts down the power by disconnecting the voltage sensing line, the abnormal current of the battery can be cut off.

[0087] On the other hand, although the technical idea of the present application has been specifically described according to the above embodiments, it should be noted that the above embodiments are for the purpose of explanation, not limitation. In addition, those skilled in the art of the technical field of the present application will be able to understand that various embodiments are possible within the spirit of the present application.

Claims

1. A battery protection circuit for protecting one or more battery cells from abnormal conditions including overcharge, overdischarge, and overcurrent, the battery protection circuit comprising: a current sensing unit connected in series on a current output path formed between one terminal of the battery cells and an output unit to an external system, and configured to sense a current of the battery cells flowing in the path; a voltage sensing unit connected to a voltage sensing line to sense a voltage of the battery cells, the voltage sensing line connected to both ends of the battery cells; a voltage information transmitting unit configured to transmit a voltage value of the battery cells sensed by the voltage sensing unit to the external system; a control unit configured to determine whether an abnormal condition occurs in the battery cells using sensing values of the current sensing unit and the voltage sensing unit, and to disconnect the voltage sensing line when it is determined that an abnormal condition occurs in the battery cells; and a sensing line blocking FET provided on the voltage sensing line to be turned off to disconnect the voltage sensing line under control of the control unit, wherein the external system receives a voltage value of the battery cells measured through the disconnected voltage sensing line from the voltage information transmitting unit, and automatically turns off system power in the external system.

2. The battery protection circuit of claim 1, wherein, The control unit includes: a first determination unit configured to compare whether the voltage value of the battery cells sensed by the voltage sensing unit is equal to or greater than a predetermined first reference value, and to determine that the battery cells are in an overcharge state and output an overcharge signal when the voltage value of the battery cells is greater than or equal to the predetermined first reference value; a second determination unit configured to compare whether the voltage value of the battery cells sensed by the voltage sensing unit is less than or equal to a predetermined second reference value, to determine that the battery cells are in an overdischarge state and output an overdischarge signal when the voltage value of the battery cells is less than or equal to the predetermined second reference value; a third determination unit configured to compare whether the current value of the battery cells sensed by the current sensing unit is equal to or greater than a predetermined third reference value, and to determine that the battery cells are in an overcurrent state and output an overcurrent signal when the current value of the battery cells is equal to or greater than the predetermined third reference value; and a blocking FET control unit configured to disconnect the voltage sensing line by turning off the sensing line blocking FET when any one of the overcharge signal, the overdischarge signal, and the overcurrent signal is output from the first determination unit, the second determination unit, and the third determination unit.

3. The battery protection circuit of claim 2, wherein, When the voltage sensing line is disconnected by the blocking FET control unit, the voltage of the battery cells sensed by the voltage sensing unit is 0 V.

4. The battery protection circuit of claim 3, wherein, When the voltage information transmitting unit transmits the 0 V voltage value of the battery cells to the external system, the external system senses that the current battery cells are in a low voltage state and turns off system power by itself.

5. A method of protecting one or more battery cells from abnormal conditions including overcharge, overdischarge, and overcurrent, the method comprising: a cell state information measuring step of measuring a current value and a voltage value of a battery cell at predetermined periodic intervals by a sense resistor provided on a current output path between the battery cell and an output unit to an external system and a voltage sense line connected to both ends of the battery cell; an abnormal condition occurrence determining step of determining whether an abnormal condition occurs in a battery cell using the current value and the voltage value of the battery cell measured in the cell state information measuring step; a voltage sense line disconnecting step of disconnecting the voltage sense line when it is determined by the abnormal condition occurrence determining step that an abnormal condition occurs in the battery cell; a cell voltage information transmitting step of transmitting a voltage value of a battery cell measured by the voltage sense line disconnected by the voltage sense line disconnecting step to an external system; and an external system shutdown step of automatically shutting down system power in the external system that receives the voltage value of the battery cell measured by the disconnected voltage sense line by the cell voltage information transmitting step. The abnormal condition occurrence determining step includes:

6. The method of claim 5, wherein, an overcharge determining step of comparing whether the voltage value of the battery cell measured in the cell state information measuring step is equal to or greater than a predetermined first reference value, and determining that the battery cell is in an overcharge state when the voltage value of the battery cell is equal to or greater than the predetermined first reference value; an overdischarge determining step of comparing whether the voltage value of the battery cell measured in the cell state information measuring step is less than or equal to a predetermined second reference value, and determining that the battery cell is in an overdischarge state when the voltage value of the battery cell is less than or equal to the predetermined second reference value; and an overcurrent determining step of comparing whether the current value of the battery cell measured in the cell state information measuring step is equal to or greater than a predetermined third reference value, and determining that the battery cell is in an overcurrent state when the current value of the battery cell is equal to or greater than the predetermined third reference value, wherein when any one of the overcharge, the overdischarge, and the overcurrent is determined, it is determined that an abnormal condition occurs in the battery cell. The voltage sense line disconnecting step includes shutting down a sense line blocking FET arranged on the voltage sense line.

7. The method of claim 5, wherein, In the cell voltage information transmitting step, the voltage value of the battery cell transmitted to the external system is 0 V.

8. The method of claim 5, wherein, The external system shutdown step senses that the current battery cell is in a low voltage state, and shuts down system power in the external system when the 0 V voltage value of the battery cell is transmitted by the cell voltage information transmitting step.

9. The method of claim 8, wherein, 10. A battery pack including the battery protection circuit according to any one of claims 1 to 4. ​

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