JP2002345156A - Rechargeable battery or rechargeable battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rechargeable battery and a rechargeable battery pack, which include an interior circuit, capable of fully extracting the intrinsic performance of the battery. SOLUTION: In this rechargeable battery which is attached to an electronic system and supplies the power of a predetermined voltage to the electronic system, there are provided battery bodies, which generate voltage lower than the predetermined voltage by the voltage level of one internal battery body or more, a step-down voltage charging circuit which charges the battery body by receiving the power of the predetermined voltage or higher from the outside and step-down the voltage, a booster circuit which boosts the power from the battery body and supplies the power of the predetermined voltage to the outside, and a detecting means which detects whether it is in charged or discharged condition. In the charging battery, the step-down voltage charging circuit is made to operate in charging and the booster circuit is made to operate in discharging, according to the condition of the detecting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rechargeable battery or a rechargeable battery pack, and more particularly, to a rechargeable lithium-ion battery (hereinafter referred to as a "lithium battery") having a controller, a nickel cadmium battery, a hydrogen battery, or a rechargeable battery pack thereof. In addition, the present invention relates to a rechargeable battery and a rechargeable battery pack having an internal circuit that can sufficiently bring out the original performance of the battery.

[0002]

2. Description of the Related Art Conventionally, charging of a lithium battery or the like is performed under the control of a controller, and includes an overcharge protection circuit, an overdischarge protection circuit, and the like. In a rechargeable battery pack such as a lithium ion battery, circuits such as the controller, the overcharge protection circuit, and the overdischarge protection circuit are formed on a substrate, and the substrate and a plurality of battery bodies are integrated as a pack.

[0003] Rechargeable batteries and rechargeable battery packs of this type (hereinafter referred to as rechargeable batteries) are incorporated in electronic devices such as portable computers and hand-held electronic devices. When the voltage of the rechargeable battery drops below a predetermined value, the electronic devices are recharged. The charging is performed by the circuit on the side, the charging current is received, and the charging is terminated when the charging is completed. Also, when the battery is driven, discharging is performed to supply power to the electronic device. For this purpose, the controller for charge / discharge control switches the current direction by providing a relay or a relay device that allows current to flow bidirectionally between the positive electrode side of the rechargeable battery and the charging terminal. In addition, there is a diode switching circuit that inserts a diode in series in each of the charging and discharging directions to select a current in one direction and block a current in the opposite direction.

[0004] In an electronic device having such a rechargeable battery, when the electronic device is connected to an AC power source and the electronic device is not operating or is operating, the rechargeable battery is charged. When the electronic device is operated when the power is removed, the electronic device is operated by power from the rechargeable battery. On the other hand, recently, in order to realize long-time operation of an electronic device, the performance of a rechargeable battery has been improved, and a battery having a performance about 1.5 to 3 times that of a conventional battery has been developed and used. ing.

[0005]

A battery pack or a battery pack used in a battery-driven electronic device usually has a voltage of, for example, about 12 V corresponding to a DC voltage of a power supply circuit generated when an AC power supply is used. The power of the voltage of is output.
Therefore, about 4 to 8 battery bodies are connected in series inside the rechargeable battery. In addition, the overcharge protection circuit and overdischarge protection circuit detect and protect the voltage of each battery body, and operate the protection circuit with the average current flowing through many batteries connected in series. Let it. But,
The performance of each battery body varies, and the control is usually performed in accordance with the lower battery performance. For this reason, there is a problem that sufficient performance of each of the assembled or packed battery bodies cannot be obtained. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the related art, and to provide a rechargeable battery and a rechargeable battery pack having an internal circuit that can sufficiently bring out the original performance of the battery.

[0006]

A rechargeable battery or a rechargeable battery pack according to the present invention for achieving the above object is provided with a rechargeable battery mounted on an electronic device and supplying a predetermined voltage to the electronic device. A battery body that generates a voltage lower than a predetermined voltage by at least one built-in battery body, and receives a power of a predetermined voltage or more from the outside and reduces the voltage to reduce the battery body. A step-down charging circuit for charging, a boosting circuit for boosting power from the battery body and supplying power of a predetermined voltage to the outside, and a detecting means for detecting whether the battery is in a charged state or a discharged state. Accordingly, the step-down charging circuit is operated at the time of charging, and the step-up circuit is operated at the time of discharging.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, a step-down charging circuit and a step-up circuit are provided in a battery or a battery pack, and at the time of charging, the step-down charging circuit is operated to charge to a charge lower than a predetermined voltage supplied from an electronic device. The battery main body is charged by generating an appropriate voltage, and at the time of discharging, the booster circuit is operated to supply power of a predetermined voltage from the voltage lower than one built-in battery main body to the outside. Thus, when viewed from the outside, this battery or battery pack can be treated as being equivalent to a battery having a built-in battery body for generating power of a predetermined voltage. At this time, the number of built-in battery bodies is smaller by one or more battery bodies than the number of output equivalent voltages, and the performance variation of the battery body is reduced by that much. Since the number of battery bodies is small, it can be fully utilized.

[0008]

FIG. 1 is a circuit diagram mainly showing a lithium rechargeable battery built in an electronic apparatus according to an embodiment to which the rechargeable battery of the present invention is applied, FIG. 2 is a flowchart of the step-down charging process, and FIG. Is a flowchart of the boost discharge process. FIG. 4 is a circuit diagram of another embodiment. In FIG. 1, reference numeral 20 denotes an electronic device, which has a rechargeable battery 10 having a battery charge / discharge control circuit detachably mounted therein. The rechargeable battery 10 has an assembled battery of two lithium battery cells (hereinafter referred to as a battery main body) 1 a and 1 b connected in series.
4a, charge / discharge power supply line + Vcc (hereinafter power supply line + Vc
c) A charging current is received on the positive electrode side of the battery body 1a via the p-channel MOSFET transistor Q1 and the coil 13 (for example, a choke coil). On the other hand, the device main body 21 receives the discharge current from the battery main bodies 1a and 1b in the power supply circuit 22 through the coil 13, the transistor Q1, and the charging / discharging terminal 14a, switches the power supply, and receives the power from the rechargeable battery 10 therein. To supply. The battery body here may be one of the battery bodies 1a. Also, power supply line + Vcc
Are connected to the charging / discharging terminal 14a, and are connected to the apparatus main body 21 via this. Also, the ground line GND
L is connected to the ground terminal 14b connected to the negative electrode side of the battery main body 1b via the resistor Rs, and is connected to the ground GND of the device main body 21 via this.

A capacitor 12a is provided between a connection point N1 between the charging / discharging terminal 14a and the transistor Q1 and the ground line GNDL.
An n-channel MOSFET transistor Q2 is provided between a connection point N2 between the coil 13 and the ground line GNDL, and a connection point N3 between the coil 13 and the positive electrode of the battery body 1a.
And the ground line GNDL, a capacitor 12
b is provided. By the way, a built-in circuit built in the rechargeable battery 10 described here is usually a CMOS or the like, and a low power consumption type circuit with a low clock frequency is used. As for the operating power, the built-in circuit here operates with the power from the rechargeable battery except when it is in a charged state. The detection of full charge when the rechargeable battery 10 is fully charged is, for example, 4.3 V when the terminal voltage of one battery body has reached a predetermined value corresponding to full charge or more. Sometimes detected.

Here, the transistor Q1 is a step-down transistor that lowers the voltage of the electric power input to the charge / discharge terminal 14a under the switching control of the controller 2 to perform step-down charging.
The step-down charging circuit is constituted by the capacitor 12b. At this time, the coil 13 and the capacitor 12b form a smoothing circuit, and the transistor Q2
Synchronous commutation control for turning on the current during the FF and commutating the current flowing through the coil 13 is performed. Further, the transistor Q1 also functions as a protection switch at the time of overcharge or overdischarge. On the other hand, the transistor Q2 is connected to the controller 2
Is a transistor that performs step-up discharge by the switching control described above, and a transistor, the controller 2, the coil 13, and the capacitor 12a constitute a step-up circuit. At this time, the coil 13 becomes a flyback coil, and the capacitor 12a is charged with the boosted voltage, and the transistor Q1 is turned on when the transistor Q2 is turned off to rectify a high voltage flyback pulse. Control is performed.

The power supply circuit 22 includes a rechargeable battery 10 and a commercial AC
It has a switching circuit with the power supply,
The power from the power supply is supplied, and the apparatus main body 21 operates.
The ON / OFF of the transistors Q1 and Q2 is controlled by the controller 2 in accordance with charging and discharging, and the state of charging and discharging is detected by the current value detecting circuit 4. Inside the rechargeable battery 10, in addition to the controller 2, a voltage value detection circuit 3, a current value detection circuit 4, and a temperature detection circuit 5 are provided.

The voltage value detection circuit 3 is connected between the charge / discharge terminal 14a and the ground terminal 14b, and on each of the positive electrode side and the negative electrode side of the battery bodies 1a and 1b. 2 outputs the current voltage value to the controller 2 according to the control signal from the controller 2.
The controller 2 generates the above-mentioned control signal, obtains the terminal voltage of each battery body 1a, 1b from the voltage value detection circuit 3 corresponding to each battery body, and determines whether any one of the voltages is 4.2 V or more. , And 3.2 V or less. Then, one of the battery bodies 1a and 1b is overcharged according to the detected terminal voltage value of the battery body (4.
2 V) or overdischarge (when 3.2 V or less), the transistor Q1 is controlled to
FF, and the charge / discharge operation is stopped for each. In addition,
3.2 V is a discharge stop voltage, and 4.3 V is a charge stop voltage. The current value detection circuit 4 has a detection resistor Rs, which is inserted in series between the negative electrode of the battery body 1b and the ground line GNDL. Then, according to the control signal from the controller 2, the current value of the current charge / discharge and charging or discharging are given to the controller 2 by adding signs to the current value and output. Whether the charging current or the discharging current is determined by detecting the polarity of the terminal voltage of the detection resistor Rs.

The temperature detection circuit 5 has a temperature sensor (not shown), and receives a signal from the temperature sensor and outputs a current temperature value to the controller 2 according to a control signal from the controller 2. The controller 2 controls the transistor Q1 to be OFF when the current temperature is equal to or higher than the limit value, and stops the charge / discharge operation for each. The controller 2 is provided with an MPU 6, a memory 7, and an A / D conversion circuit (A / D) 8, and these circuits are mutually connected via a bus 11. Further, each control signal is sent to each circuit via the bus 11. Then, each detection signal value of the voltage value detection circuit 3, the current value detection circuit 4, and the temperature detection circuit 5 is passed to the MPU 6 via the A / D 8. The memory 7 includes a charge / discharge determination program 7a, a step-down charge control program 7b, and a step-up discharge control program 7.
c, and an overcharge / overdischarge protection control program 7d and the like are provided. The parameter storage area 7e stores a step-down control voltage value VL and a step-up voltage value VH, a flag indicating a charge state, a discharge state, a standby state, and the like. ing. Note that the step-down control voltage value VL and the step-up voltage value VH correspond to the respective battery bodies 1a, 1
It is written from outside according to the characteristic of b. Note that the step-down control voltage value VL corresponds to the voltage of the battery pack in the series circuit of the battery bodies 1a and 1b, and the boost voltage value VH is the voltage of the battery pack generated between the charge / discharge terminal 14a and the ground terminal 14b. Equivalent to terminal voltage.

Each step-down charging process will be described with reference to the flowchart of FIG. Here, the charge / discharge determination program 7a is periodically called at a predetermined cycle (every time Δt) and executed by the MPU 6. When this is executed by the MPU 6, the MPU 6 reads the current value detected by the current value detection circuit 4 and the sign thereof from the current value detection circuit 4 (step 101), and determines whether the battery is in a charged state, a discharged state, or a standby state. It is determined whether it is in the state (step 102).
When the current value is substantially “0”, it is determined to be in the standby state, and in this standby state, the parameter storage area 7 e
With reference to a state flag indicating whether the battery is in the charge state, the discharge state, or the standby state (step 103), the contents of the flag are determined (step 104), and the standby state (transistor Q)
1 and Q2 are not in the operating state) (when YES), the transistor Q1 is turned off.
(Step 105), and the process ends. If the state flag is not set to the standby state (NO in step 104),
The transistor Q1 is set to OFF, the state flag is set to the standby state (step 106), and the process ends.

If the detected current value in the step 102 indicates that the battery is in the charged state, the state flag is determined by referring to the state flag in the parameter storage area 7e (step 103a) and the state of the flag is determined (step 104a). When the state is not set (when NO), the state flag is set to the charging state (step 105a), the step-down charging control program 7b is called, and the MPU 6 executes the program.
The process enters the step-down charging process (step 106a). When the state flag is set to the charged state (step 104
In the case of the YES condition in a), this processing is terminated. If it is determined in step 102 that the current value is in the discharging state, the flag content is determined (step 103b) by referring to the parameter storage area 7e (step 103b).
b) When the state flag is not in the discharge state (the transistor Q2 is in the operation state) (when NO), the state flag in the parameter storage area 7e is set to the discharge state (step 105b), and the boost discharge control program 7c is set. Call is made to be executed by the MPU 6, and the boosting discharge process is started (step 106b). When the state flag is set to the discharging state (when the YES condition is satisfied in step 104b), the process ends.

When the MPU 6 executes the step-down charge control program 7b, the MPU 6 calculates the step-down voltage ΔV from ΔV = VH−VL with reference to the step-down control voltage value VL and the step-up voltage value VH (step 107). ), A pulse having a pulse width corresponding to the step-down voltage ΔV is generated to control the switching of the transistor Q1, and the transistor Q1 is turned off.
The synchronous commutation control for turning on the transistor Q2 when the F is performed is performed (step 108). Thus, the stepped-down voltage is charged to the capacitor 12b via the coil 13a to generate a charging voltage Vc at the capacitor 12b,
The charging of a and 1b is started. Further, the charging current value is periodically obtained from the current value detection circuit 4 and the charging current value is monitored (step 109). The switching pulse is set so that this current value becomes a predetermined constant current value for charging control. And the control is continued (step 110). After a certain period, the current value of the current value detection circuit 4 changes, and the constant current value is changed to constant voltage charging, and a pulse width corresponding to this is selected to switch the transistor Q1. Then, it is determined whether or not the charging is completed by determining whether the current value is equal to or less than a predetermined value (step 111). At the end (when the current value becomes equal to or less than a predetermined value), the transistor Q1 is turned off.
The charging is stopped by FF (step 105), the state flag of the parameter storage area 7e is set to the standby state, and the transistor Q1 is set to an inactive state (step 10).
6).

When the MPU 6 executes the boost discharge control program 7c, it enters the boost discharge processing of FIG. 3 as the processing after step 106b in the figure. Explaining the flow according to FIG. 3, the MPU 6 turns on the transistor Q1.
The state is set (step 201), and the voltage Vo (charged battery 1) between the current charge / discharge terminal 14a and the ground terminal 14b is set.
The output terminal voltage Vo as 0) is obtained from the voltage value detection circuit 4 according to the control signal (step 202), and the boosted voltage δV is calculated from the difference δV = VH−Vo from the boosted voltage value VH ( Step 203), a pulse having a pulse width corresponding to the boosted voltage δV is generated to perform switching control of the transistor Q2, and to perform synchronous rectification control of turning on the transistor Q1 when the transistor Q2 is off (Step 204). Thus, the charge of the voltage due to the flyback pulse boosted by the coil 13a is transferred to the capacitor 12a.
a, a discharge voltage Vo is generated in the capacitor 12a, and control is performed such that the discharge voltage between the charge / discharge terminal 14a and the ground terminal 14b becomes the boosted voltage value VH. Further, the current value from the current value detection circuit 4 is periodically obtained, and the discharge current value is monitored (step 205).
It is determined whether or not the charging is completed by determining whether or not the charge has become equal to or less than a predetermined value close to this (step 206).
At the end (when the current value becomes “0” or becomes a predetermined value or less), the transistors Q1 and Q2 are turned off to stop discharging (step 207). Then, the parameter storage area 7
e is set to the standby state and the transistor Q
1, Q2 is not in operation (step 20)
8).

Overcharge / overdischarge protection control program 7d
Is to obtain the current voltage value V of each battery body 1a, 1b according to a control signal from the voltage value detection circuit 4 by a periodic interrupt process separately from the above control, and to obtain the voltage of each battery body 1a, 1b. It is determined whether any one of the voltage values V is a predetermined monitoring voltage value, here 3.2 V or less or 4.3 V or more, and 3.2 V or less or 4.3 V or more. , The transistor Q1 is forcibly turned off to prevent overcharging and overdischarging.

FIG. 4 shows another embodiment, in which a p-channel MOSFET transistor Q3 for charge control and a p-channel MOSFET transistor Q4 for discharge control are connected in series in place of the transistor Q1. Is turned off to control the switching of the transistor Q3. At the time of discharging, the transistor Q3 is turned off to control the switching of the transistor Q4. Diodes D3 and D4 are provided in parallel with the respective transistors. When one of the transistors is in the OFF state, a charging current or a discharging current flows through the diode connected in parallel. In addition, as the diodes D3 and D4,
A parasitic diode (body diode) formed at the same time as the transistors Q3 and Q4 may be used. The operation other than the above is substantially the same as that of the embodiment of FIG. 1, and the description thereof is omitted.

As described above, in the embodiment, the switching of the step-down transistor Q1 is controlled.
Since this is smoothed by the coil 13, switching control can be performed, thereby improving the power conversion efficiency. However, for this step-down, the transistor Q
It is not necessary to perform switching control on 1. However, when switching control is not performed, there is a disadvantage that the amount of heat generated increases. Step-down transistor Q using a step-up coil
The switching control of 1 has the effect of reducing the amount of heat generated. In the embodiment, the example of the lithium battery is given, but the battery may be a nickel cadmium battery or a hydrogen battery as a matter of course. Since the current detection circuit and the voltage detection circuit are built in the battery or the battery pack, the charging operation of the battery other than the lithium battery by the step-down charging control program may be controlled by the constant voltage charging. Alternatively, constant current charging may be controlled.
Similarly, the control by the boost discharge control program is not limited to the constant voltage output, and the control of the constant current output is also possible. The number of battery bodies is not limited as long as the voltage of the battery body is at least one voltage lower than the terminal voltage on the discharge output side generated as a battery. Variations are reduced, and the performance of the battery body is more easily derived. Further, in the embodiment, a rechargeable battery in which a circuit including a battery main body and a controller is integrated as a rechargeable battery is described. Needless to say, the present invention can be applied to a rechargeable battery pack formed integrally.

[0021]

As described above, according to the present invention, the battery or the battery pack is provided with the step-down charging circuit and the step-up circuit, and at the time of charging, the step-down charging circuit is operated to be supplied from the electronic device. The battery body is charged by generating a voltage suitable for charging lower than the predetermined voltage, and at the time of discharging, the booster circuit is operated to supply power of a predetermined voltage from a voltage lower than one built-in battery body to the outside. . Thus, when viewed from the outside, this battery or battery pack can be treated as being equivalent to a battery having a built-in battery body for generating power of a predetermined voltage. At this time, the number of built-in battery bodies is one or more battery bodies smaller than the number of equivalent battery outputs, and the performance variation of the battery body is reduced by that much. Since the number of battery bodies is small, it can be fully utilized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram mainly showing a lithium rechargeable battery built in an electronic device of an embodiment to which a rechargeable battery of the present invention is applied.

FIG. 2 is a flowchart of the step-down charging process.

FIG. 3 is a flowchart of the boost discharge process.

FIG. 4 is a circuit diagram of another embodiment.

[Explanation of symbols]

1a, 1b: lithium battery body (battery body), 2: controller, 3: voltage value detection circuit, 4: current value detection circuit,
5: temperature detection circuit, 6: MPU, 7: memory, 7a: charge / discharge determination program, 7b: step-down charge control program,
7c: boost discharge control program, 7d: overcharge, overdischarge protection control program, 7e: parameter storage area, 8:
A / D conversion circuit (A / D), 10: rechargeable battery, 11: bus, 12a, 12b: capacitor, 13: coil, 20
... Electronic device, 21 ... Device main body, 22 ... Power supply circuit, 23 ...
MPU, Q1 to Q4 ... transistors.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshihiro Todaka 1-88, Ushitora, Ibaraki-shi, Osaka F-term in Hitachi Maxell, Ltd. 5G003 AA01 BA03 DA07 GA01 GB03 5H030 AS06 AS11 BB01 BB21 FF43 FF44 5H040 AA00 AA39 AA40 AS12 AS14 DD08

Claims (8)

[Claims] 1. A rechargeable battery mounted on an electronic device and supplying power of a predetermined voltage to the electronic device, comprising: a battery main body that generates a voltage lower than the predetermined voltage by at least one built-in battery main body; A step-down charging circuit for receiving the power of the predetermined voltage or higher from the outside and stepping down the voltage to charge the battery body; and boosting the power from the battery body to the outside of the predetermined voltage. A booster circuit for supplying the power of the power supply circuit, and a detecting means for detecting whether the battery is in a charged state or a discharged state. The step-down charging circuit is operated at the time of charging according to the detecting means, and the boosting circuit is operated at the time of discharging. And rechargeable battery. 2. The battery body according to claim 1, wherein the battery body is a battery pack having a plurality of battery bodies connected in series, and the detecting means determines a charge and a discharge respectively to detect a current value; 2. The rechargeable battery according to claim 1, further comprising: a determination unit configured to determine whether the battery is in a charged state or a discharged state according to a result of the determination detected by the current value detection unit and the current value. 3. The step-down charging circuit includes a step-down transistor for step-down inserted between a charge / discharge terminal for receiving charging power from the electronic device or outputting discharge power to the outside and a positive electrode of the battery body. A first control circuit for controlling the step-down transistor, wherein the booster circuit detects a voltage between the charge / discharge terminal and a reference line connected to a negative electrode of the battery body; A coil inserted in a wiring line between a charge / discharge terminal and a positive electrode of the battery body, a switching transistor and a capacitor respectively connected between a terminal of the coil and the reference line, and detected by the voltage detection circuit. Switching the switching transistor so that the voltage between the charge / discharge terminal and the reference line becomes a predetermined target voltage in accordance with the applied voltage. Rechargeable battery of claim 2, further comprising a second control circuit for. 4. The coil is provided on the positive electrode side of the battery main body with respect to the step-down transistor, and the first and second control circuits are one control circuit, and the step-down transistor controls this control. 4. The rechargeable battery according to claim 3, wherein switching is controlled by a circuit. 5. A rechargeable battery pack mounted on an electronic device and supplying power of a predetermined voltage to the electronic device, wherein a battery main body that generates a voltage lower than the predetermined voltage by at least one built-in battery main body. A step-down charging circuit that receives power of the predetermined voltage or higher from the outside and steps down the voltage to charge the battery body; and boosts power from the battery body to the outside by the predetermined voltage. A booster circuit that supplies power of a voltage of V. and a detecting unit that detects whether the battery is in a charged state or a discharged state. The step-down charging circuit is operated at the time of charging according to the detecting unit, and the booster circuit is operated at the time of discharging A rechargeable battery pack characterized by the following. 6. The battery main body is an assembled battery in which a plurality of battery main bodies are connected in series, and the detection means detects current value by judging charge and discharge respectively, and current value detection means; 6. The rechargeable battery pack according to claim 5, further comprising: a determination unit configured to determine whether the battery is in a charged state or a discharged state according to a result of the determination detected by the current value detection unit and the current value. 7. The step-down charging circuit includes a step-down transistor for step-down, which is inserted between a charge / discharge terminal for receiving charging power from the electronic device or outputting discharge power to the outside and a positive electrode of the battery body. A first control circuit for controlling the step-down transistor, wherein the booster circuit detects a voltage between the charge / discharge terminal and a reference line connected to a negative electrode of the battery body; A coil inserted in a wiring line between a charge / discharge terminal and a positive electrode of the battery body, a switching transistor and a capacitor respectively connected between a terminal of the coil and the reference line, and detected by the voltage detection circuit. Switching the switching transistor so that the voltage between the charge / discharge terminal and the reference line becomes a predetermined target voltage in accordance with the applied voltage. The second control circuit and charging the battery pack according to claim 6, further comprising a to. 8. The battery according to claim 1, wherein the coil is provided on a positive electrode side of the battery body with respect to the step-down transistor, and the first and second control circuits are one control circuit, and the step-down transistor controls this control. The rechargeable battery pack according to claim 7, wherein switching control is performed by a circuit.