JP2005253220A - Power supply switching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent charging to a primary battery by the current from an AC adapter and to normally perform power supply switching even when an increase in contact failure or contact resistance are caused by generating oxide coating on a contact with a connecting terminal of the AC adapter. <P>SOLUTION: A positive electrode of the primary battery 17 is connected to a source of a FET1. A drain of the FET1 is connected to the drain of a FET2. The source of the FET2 is connected to the positive electrode of a load 19 side. The positive electrode of a connecting terminal 15 is so connected to the positive electrode of the load 19 side as the current flows from the positive electrode of the connecting terminal 15 to the positive electrode of the load 19 side through a reverse-current preventing circuit 18. By mutually connecting the positive electrode of the connecting terminal 15 to the gate of the FET1 and the FET2, for only the primary cell 17, the switching circuit is so switched that the electric power is supplied from the primary battery 17 to the load 19, and when the AC adapter is connected to the connecting terminal 15, the switching circuit is so switched that the electric power is supplied from the AC adapter to the load 19. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, when a DC power supply such as an AC adapter is connected to a connection terminal, power is switched so that power is not supplied to the load from the primary battery provided therein, but is supplied from the AC adapter to the load. Relates to the device.

  As such a conventional power supply switching circuit, there are a circuit that switches between an AC adapter and a primary battery and a circuit that needs to switch a power source used for memory backup or the like. For example, as a device that can be used by switching a dry battery and an AC adapter as a power source, there are a portable audio device, a small speaker with a built-in amplifier, and the like. In addition, UPS, notebook personal computers, and the like are devices that switch between two or more types of power sources such as memory backup.

[Prior art 1]
Here, a conventional power supply switching circuit (prior art 1) will be described with reference to FIG.

  The circuit shown in FIG. 5 performs the switching operation as described above using the connection terminal to which the AC adapter is connected. Specifically, the primary battery 17 is always mounted, and when the plug 13 of the AC adapter 11 is not connected to the connection terminal 15, the second terminal and the third terminal of the connection terminal 15 are in a connected state (short), Electric power from the primary battery 17 is supplied to the load 19.

  On the other hand, when the plug 13 of the AC adapter 11 is connected to the connection terminal 15, the second terminal and the third terminal of the connection terminal 15 are opened (open), and the power from the primary battery 17 to the load 19 is reduced. The power supply is stopped, and power from the AC adapter 11 is supplied to the load 19.

[Prior Art 2]
As a conventional power source switching circuit (prior art 2), a “power source switching circuit” described in Patent Document 1 has been reported.

  This circuit is provided with a socket having a movable piece that is in non-contact and contact state with the second connection terminal in contact with the negative electrode of the DC plug when the DC plug of the AC adapter is inserted or not inserted, and the positive electrode of the secondary battery On the side, an FET switch that is turned on and off according to the contact state and non-contact state of the movable section is provided. For this reason, in a power supply switching circuit that switches between driving by an external DC power supply and driving by a battery, there is an advantage that the limited battery capacity is efficiently used for a long time without increasing the size and cost. doing.

[Prior Art 3]
As a conventional power supply switching circuit (prior art 3), a “DC power supply switching circuit” described in Patent Document 2 has been reported.

In this circuit, the DC output plug of the AC adapter is connected to the first connection terminal to determine whether one terminal of the first connection terminal and one terminal of the second connection terminal are connected without a rectifying element. The first switch mechanically switches depending on whether or not the other terminal of the first connection terminal is connected to the other terminal of the second connection terminal. The second switch is electrically switched depending on whether or not voltage is supplied to the terminal. For this reason, in a DC power supply switching circuit that switches between an AC adapter input and a battery input, if a circuit component fails, even if a battery such as a lithium primary battery that does not increase the battery temperature even when charged is used, sufficient safety is ensured. It has the advantage that can be secured.
JP 2001-190034 A JP 2002-262477 A

  However, in the prior art 1 shown in FIG. 5, the second terminal and the third terminal of the connection terminal 15 are mechanically connected (short-circuited) depending on whether the plug 13 of the AC adapter 11 and the connection terminal 15 are connected. Since it is open (open), if an oxide film or the like is generated at the contact between the second terminal and the third terminal of the connection terminal 15, contact failure and increase in contact resistance are likely to occur, and mechanical connection ( (Short) and open (open) operations become unstable, so that they cannot operate normally. As a result, the primary battery 17 is charged, and a failure such as liquid leakage or power supply from the primary battery 17 becomes impossible. There was a problem such as the occurrence of a failure.

  In the prior art 2, the contact of the connection terminal is mechanically connected (shorted) and opened (opened) according to the insertion / removal of the DC plug of the AC adapter. When an increase in contact resistance occurs, there is a problem in that it does not operate normally. In addition, when a primary battery is used using the circuit shown in the prior art 2, since there is only one FET, if the source and drain of the FET are short-circuited, the primary battery will be charged and liquid leakage and other troubles will occur. There is a problem that a failure occurs such that power supply from the primary battery 17 becomes impossible.

  Furthermore, in the prior art 3, the contact of the connection terminal is mechanically connected (short) and opened (open) in accordance with the insertion / extraction of the DC plug of the AC adapter. When an increase in contact resistance occurs, there is a problem in that it does not operate normally.

  The present invention has been made in view of the above. The purpose of the present invention is to use an electric current from the AC adapter even when an oxide film is formed on the contact of the connection terminal of the AC adapter and a contact failure or an increase in contact resistance occurs. An object of the present invention is to provide a power supply switching circuit that can prevent charging of a primary battery and can perform a power supply switching operation normally.

  In order to solve the above-mentioned problem, the invention according to claim 1 includes a connection terminal connectable to the first DC power supply and a second DC power supply, and the second DC power supply includes the second DC power supply. In a power supply switching device that supplies power from a DC power supply to a load and switches the power supply from the first DC power supply to the load when the first DC power supply is connected to the connection terminal, the second DC Connect the positive pole of the power source and the source of the first field effect transistor, connect the drain of the first field effect transistor and the drain of the second field effect transistor, and connect the source of the second field effect transistor and the positive pole on the load side Then, the connection terminal is connected so that current flows from the positive electrode of the connection terminal to the positive electrode on the load side via a backflow prevention circuit, and the positive electrode of the connection terminal and the gates of the first and second field effect transistors are connected in common. Need to do To.

  According to the second aspect of the present invention, when the first DC power source is connected to the connection terminal, the drain and the source of the first and second field effect transistors are in a non-conductive state, respectively. The gist is to work.

  According to the third aspect of the present invention, when the first DC power source is not connected to the connection terminal, the drain and the source of the first and second field effect transistors are respectively brought into conduction. The gist is to work.

  According to a fourth aspect of the present invention, a third field effect transistor is provided between the source of the second field effect transistor and the positive electrode on the load side, and the source of the second field effect transistor and the third field effect transistor are provided. And the gates of the first to third field effect transistors are connected in common. The drains of the first to third field effect transistors are connected to each other.

  According to the fifth aspect of the present invention, when the first DC power supply is connected to the connection terminal, when the drain-source of either one of the second or third field effect transistor is short-circuited, the first The gist is to connect a direct current power source to a backflow prevention circuit via a connection terminal and prevent a current from flowing to the second direct current power source via the second or third field effect transistor.

  According to the sixth aspect of the present invention, the backflow prevention circuit includes a diode having an anode connected to the connection terminal and a cathode connected to the positive electrode on the load side, and a collector and a base connected to the connection terminal. Any one of a transistor in which an emitter is connected to the positive electrode on the load side, and a field effect transistor in which a drain and a gate are connected to the connection terminal and a source is connected to the positive electrode on the load side. It consists of the following.

  According to the first aspect of the present invention, the positive electrode of the second DC power supply and the source of the first field effect transistor are connected, the drain of the first field effect transistor and the drain of the second field effect transistor are connected, Connect the source of the second field-effect transistor and the positive electrode on the load side, connect the positive electrode of the connection terminal so that current flows from the positive electrode of the connection terminal to the positive electrode on the load side via the backflow prevention circuit, By connecting the gates of the first and second field effect transistors in common, when only the second DC power source is used, power is supplied from the second DC power source to the load, while the first DC power source is connected to the connection terminal. When connected, the first DC power supply can be switched to supply power to the load, and even when an oxide film is generated at the contact of the connection terminal and a contact failure or an increase in contact resistance occurs, the first DC power from It is possible to prevent the charging of the primary battery due to the flow, it is possible to perform the power switching operation normally.

  According to the second aspect of the present invention, when the first DC power supply is connected to the connection terminal, the drain and the source of the first and second field effect transistors are respectively in a non-conductive state. By doing so, charging to the primary battery by the current from the first DC power supply can be prevented, and the power supply switching operation can be performed normally.

  According to the third aspect of the present invention, when the first DC power supply is not connected to the connection terminal, the drain and the source of the first and second field effect transistors are operated to be in a conductive state. Thus, in the case of only the second DC power supply, power can be supplied from the second DC power supply to the load.

  According to the present invention, the third field effect transistor is provided between the source of the second field effect transistor and the positive electrode on the load side, and the source of the second field effect transistor and the third field effect transistor are By connecting the drain, connecting the source of the third field effect transistor and the positive electrode on the load side, and connecting the gates of the first to third field effect transistors in common, the second or third field effect transistor can be made simple. Even when a failure occurs, charging of the primary battery from the first DC power supply can be prevented.

  According to the fifth aspect of the present invention, when the first DC power source is connected to the connection terminal and the drain-source of one of the second or third field effect transistors is short-circuited, the first DC Even if a single failure occurs by connecting the power source to the backflow prevention circuit via the connection terminal and preventing the current from flowing to the second DC power source via the second or third field effect transistor, Charging of the primary battery from the first DC power supply can be prevented.

  According to the sixth aspect of the present invention, the backflow prevention circuit includes a diode having an anode connected to the connection terminal and a cathode connected to the positive electrode on the load side, and a collector and a base connected to the connection terminal. A second field-effect transistor having a positive electrode connected to an emitter, a drain and gate connected to a connection terminal, and a source connected to a positive electrode on the load side; It is possible to prevent DC power from being applied to the gates of the first to third field effect transistors. As a result, all the drain-sources of the first to third field effect transistors can be kept conductive.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

(Example 1)
FIG. 1 is a diagram showing a configuration of a power supply switching circuit 21 according to the first embodiment of the present invention. First, the configuration of the power supply switching circuit 21 shown in FIG. 1 will be described.

  The AC adapter 11 is connected to, for example, a 100V or 220V AC power source, and is configured to convert an AC voltage into a DC voltage and supply the voltage from the plug 13 to the outside.

  The connection terminal 15 is a terminal for connecting the plug 13 of the AC adapter 11. The first terminal of the connection terminal 15 has a positive polarity and is commonly connected to the anode of the diode D4, the resistor R1, the capacitor C1, and the gates of the FET1 and FET2. The second terminal of the connection terminal 15 is in an unconnected state, and this point is structurally different from the prior arts 1 to 3. The third terminal of the connection terminal 15 has a negative polarity, and is connected to the resistor R1, the capacitor C1, the negative pole of the primary battery 17, and the negative pole of the load 19.

  The resistor R1 is a resistor used to fix the gate potential of the FET1 and FET2 to the negative 0V potential (GND potential) of the primary battery 17 when the plug 13 of the AC adapter 11 is not connected to the connection terminal 15. . The capacitor C <b> 1 is a capacitor used to reduce noise generated when the plug 13 of the AC adapter 11 is inserted into the connection terminal 15.

  The primary battery 17 is a primary battery such as an alkaline battery or a manganese battery having a voltage Vcc2, the + pole of which is connected to the source of the FET 1, the-pole of which is the third terminal of the connection terminal 15, the resistor R1, the capacitor C1, Connected to the negative pole of the load 19.

  The diode D4 is a diode used for backflow prevention, and constitutes a backflow prevention circuit 18, and its anode is commonly connected to the first terminal of the connection terminal 15, the resistor R1, the capacitor C1, and the gates of the FET1 and FET2. . The cathode of the diode D4 is connected to the source of the FET 2 and the negative pole of the load 19. 1 is provided to prevent the voltage Vcc2 of the primary battery 17 from being applied to the gates of the FET1 and FET2.

  FET1 and FET2 are field effect transistors formed of P-MOSFETs (P channel), and diodes D1 and D2 for preventing backflow are provided therein. In FIG. 1, D is a drain, S is a source, and G is a gate.

  The connection state of FET1 and FET2 is that the positive electrode of the primary battery 17 and the source of FET1 are connected, the drain of FET1 and the drain of FET2 are connected, and the source of FET2 is connected to the positive electrode of the load 19. FET1 and FET2 are connected in series as a whole. The gates of FET1 and FET2 are commonly connected to the first terminal of the connection terminal 15, the anode of the diode D4, the resistor R1, and the capacitor C1.

  Next, the operation of the power supply switching circuit 21 will be described with reference to FIG. It is assumed that the voltage at the first terminal of the connection terminal 15 when the plug 13 of the AC adapter 11 is connected to the connection terminal 15 is Vcc1, and the voltage at the positive electrode of the primary battery 17 is Vcc2. Further, description will be made assuming that the voltage between the negative electrode of the primary battery 17 and the negative electrode of the connection terminal 15 is 0V.

[Operation with primary battery]
When power is supplied from the primary battery 17, Vcc2 is applied from the primary battery 17 to the source of the FET 1. Since the plug 13 of the AC adapter 11 is not connected to the connection terminal 15, the first terminal is in an open state, so that 0V is applied to the gate of the FET 1 via the resistor R 1.

  Here, the P-channel FET has a characteristic that the drain-source is conductive when the gate voltage is less than the source voltage. Therefore, when Vcc2 is applied to the source and 0 V is applied to the gate, the source and drain of FET1 are conductive. Vcc2 is applied to the drain of FET1 and the drain of FET2.

  Next, when Vcc2 is applied to the drain of the FET 2, a + voltage that is a voltage drop of VF of the diode D2 is generated at the source of the FET 2 via the diode D2 built in the FET 2, and the voltage is higher than the gate of the FET 2. Become. For this reason, the drain of the FET 2 and the source of the FET 2 become conductive, and Vcc 2 is applied from the source of the FET 2 to the positive pole of the load 19.

  On the other hand, the reverse flow from the cathode to the anode is prevented in the diode D4, so that Vcc2 generated at the source of the FET2 is not applied to the gates of the FET1 and FET2. For this reason, the gate voltages of FET1 and FET2 remain 0V, the gate voltage <the source voltage is maintained, both FET1 and FET2 become conductive, and the voltage Vcc2 of the primary battery 17 is supplied to the load 19 as a power source. The

[Operation with AC adapter]
When power is supplied from the AC adapter, since the plug 13 of the AC adapter 11 is connected to the connection terminal 15, Vcc1 is applied to the anode of the diode D4 and the gates of the FET1 and FET2 via the first terminal of the connection terminal 15. Is done.

  As described above, the P-channel FET has a characteristic that the drain-source is conductive when the gate voltage <the source voltage, and the drain-source is non-conductive when the gate voltage> the source voltage. Here, since the output voltage Vcc1 of the AC adapter is larger than the output voltage Vcc2 of the primary battery, FET1 and FET2 are in a non-conductive state.

  On the other hand, since the plug 13 of the AC adapter 11 is connected to the connection terminal 15, Vcc1 is applied to the anode of the diode D4 via the first terminal of the connection terminal 15, and the voltage drops by VF of the diode D4. (Vcc1 -VF) is supplied to the positive pole of the load 19 as a power source.

  Normally, the voltage supplied from the AC adapter 11 is substantially constant, so that no problem occurs even if a voltage drop corresponding to VF caused by the diode D4 occurs. However, in order to avoid a voltage drop corresponding to the voltage VF generated by the diode D4, it is only necessary to prevent the voltage drop by using an FET or a transistor.

(Example 2)
FIG. 2 is a diagram illustrating a configuration of the power supply switching circuit 31 according to the second embodiment of the present invention. First, the configuration of the power supply switching circuit 31 shown in FIG. 2 will be described.

  The feature of this embodiment is that FET 3 is provided between the source of FET 2 and the + pole on the load side, the source of FET 2 and the drain of FET 3 are connected, the source of FET 3 and the + pole on the load side are connected, The purpose is to connect the gates of the FETs 3 in common.

  Next, the operation of the power supply switching circuit 31 will be described with reference to FIG.

[Operation with primary battery]
When power is supplied from the primary battery 17, Vcc2 is applied from the primary battery 17 to the source of the FET 1. When Vcc2 is applied to the source and 0V is applied to the gate, the source and drain of FET1 become conductive, and Vcc2 is applied to the drain of FET1 and the drain of FET2.

  Next, when Vcc2 is applied to the drain of the FET 2, a + voltage that is a voltage drop of VF of the diode D2 is generated at the source of the FET 2 via the diode D2 built in the FET 2, and the voltage becomes higher than the gate of the FET 2. Therefore, the drain of FET2 and the source of FET2 become conductive, and Vcc2 is applied to the drain of FET3.

  Next, since the FET 3 operates in the same manner as the FET 2, it becomes conductive as with the FET 2.

  Since reverse flow from the cathode to the anode is prevented in the diode D4, Vcc2 generated at the source of the FET 3 is not applied to the gates of the FETs 1, 2 and 3. For this reason, the gate voltages of the FET1 to FET3 remain 0V, the gate voltage <the source voltage is maintained, the FET1 to FET3 are all turned on, and the voltage Vcc2 of the primary battery 17 is supplied to the load 19 as a power source. .

[Operation with AC adapter]
When power is supplied from the AC adapter, since the plug 13 of the AC adapter 11 is connected to the connection terminal 15, Vcc1 is applied to the anode of the diode D4 and the gates of FET1 to FET3 via the first terminal of the connection terminal 15. Is done. As a result, FET1 to FET3 are turned off.

  On the other hand, since the plug 13 of the AC adapter 11 is connected to the connection terminal 15, Vcc1 is applied to the anode of the diode D4 via the first terminal of the connection terminal 15, and the voltage drops by VF of the diode D4. (Vcc1 -VF) is supplied to the positive pole of the load 19 as a power source.

[Single failure]
Since the FET2 and FET3 operate in exactly the same manner, even if there is no FET3 as in the first embodiment shown in FIG.

  However, if the FET2 drain and source are short-circuited in a circuit without the FET3, Vcc1 supplied from the AC adapter 11 is applied to the FET1 drain. Further, since the FET 1 has a built-in diode D1, there is a risk that the Vcc1 supplied from the AC adapter 11 is applied to the primary battery 17 via the built-in diode D1 and charged.

  Therefore, as shown in FIG. 2, the presence of the FET 3 allows Vcc1 supplied from the AC adapter 11 to be supplied to the FET 1 by the diode built in the FET even when either the drain or the source of the FET 2 or FET 3 is short-circuited. Application to the drain can be prevented. As a result, the primary battery 17 can be prevented from being charged. The power supply switching circuit 21 shown in FIG. 1 supports such a single failure mode.

  As described above, according to the first and second embodiments, since the FET is used to switch the power source between the AC adapter serving as a DC power source and the primary battery, the oxidation generated at the contact of the connection terminal 15 as in the prior art. It is possible to prevent the primary battery from being charged due to poor contact due to a film or the like.

  Further, according to the second embodiment, since three FETs are connected in series, charging from the AC adapter to the primary battery can be prevented even if the FET causes a single failure.

  Furthermore, according to the second embodiment, since field effect transistors are used for FET1 to FET3, switching can be performed with a very small voltage drop.

(Modification 1)
FIG. 3 is a diagram illustrating a first modification of the backflow prevention circuit 18 provided in the power supply switching circuits 21 and 31 illustrated in FIGS. 1 and 2.

  The transistor Tr1 is a transistor used for backflow prevention, and constitutes a backflow prevention circuit 18. The collector and base of the transistor Tr1 are common to the first terminal of the connection terminal 15, the resistor R1, the capacitor C1, and the gates of the FET1, FET2, and FET3. It is connected. The emitter of the transistor Tr1 is connected to the source of the FET2 or FET3 and the positive pole of the load 19.

[Operation with primary battery]
When power is supplied from the primary battery 17 to the load 19, the voltage Vcc2 of the primary battery 17 is applied from the positive electrode of the load 19 to the gates of the FET 1, FET 2, and FET 3 by the backflow prevention circuit 18 configured by the transistor Tr 1. Can be prevented.

[Operation with AC adapter]
When the plug 13 of the AC adapter 11 is connected to the connection terminal 15, Vcc1 is applied to the base of the transistor Tr1 via the first terminal of the connection terminal 15, and the transistor Tr1 is turned on so that the collector-emitter is conductive. Then, Vcc1 is supplied to the positive pole of the load 19 as a power source.

(Modification 2)
FIG. 4 is a diagram illustrating a second modification of the backflow prevention circuit 18 provided in the power supply switching circuits 21 and 31 illustrated in FIGS. 1 and 2.

  The FET 5 is a field effect transistor composed of an N-MOSFET (N channel) used for backflow prevention, and constitutes a backflow prevention circuit 18, whose drain and gate are the first terminal of the connection terminal 15, the resistor R 1, and the capacitor C 1. , FET1, FET2, FET3 gate and resistor R3 are connected in common. The other end of the resistor R3 is connected to the third terminal of the connection terminal 15 and the negative pole of the load 19. The source of the FET 5 is connected to the source of the FET 2 or FET 3 and the + pole of the load 19.

[Operation with primary battery]
When power is supplied from the primary battery 17 to the load 19, the voltage Vcc2 of the primary battery 17 is applied from the positive electrode of the load 19 to the gates of the FET 1, FET 2, and FET 3 by the backflow prevention circuit 18 constituted by the FET 5. Can be prevented.

[Operation with AC adapter]
When the plug 13 of the AC adapter 11 is connected to the connection terminal 15, Vcc1 is applied to the gate of the FET 5 through the first terminal of the connection terminal 15, so that the FET 5 is turned on and conduction between the drain and source is established. Then, Vcc1 is supplied to the positive pole of the load 19 as a power source.

It is a figure which shows the structure of the power supply switching circuit 21 which concerns on Example 1 of this invention. It is a figure which shows the structure of the power supply switching circuit 31 which concerns on Example 2 of this invention. FIG. 6 is a diagram showing a first modification of the backflow prevention circuit 18. FIG. 10 is a diagram showing a second modification of the backflow prevention circuit 18. 1 is a diagram illustrating a configuration of a conventional power supply switching circuit 100. FIG.

Explanation of symbols

11 AC adapter 13 Plug 15 Connection terminal 17 Primary battery 18 Backflow prevention circuit 19 Load 21, 31 Power supply switching circuit C1 Capacitor D1, D2, D3, D4, D5 Diode FET1, FET2, FET3, FET5 Field effect transistor R1, R3 Resistance Tr1 Transistor

Claims (6)

A connection terminal connectable to the first DC power supply and a second DC power supply are provided. When only the second DC power supply is used, power is supplied from the second DC power supply to the load, while the connection terminal is supplied with the second DC power supply. In a power supply switching apparatus that switches so that power is supplied from a first DC power supply to a load when one DC power supply is connected,
The positive electrode of the second DC power supply and the source of the first field effect transistor are connected, the drain of the first field effect transistor and the drain of the second field effect transistor are connected, and the source of the second field effect transistor and the load side Connect the + pole,
Connect so that current flows from the positive pole of the connection terminal to the positive pole on the load side through a backflow prevention circuit,
A power supply switching circuit, wherein the positive electrode of the connection terminal and the gates of the first and second field effect transistors are connected in common.   2. The device according to claim 1, wherein when the first DC power source is connected to the connection terminal, the drain and source of the first and second field effect transistors are operated in a non-conductive state. Power supply switching circuit.   2. The device according to claim 1, wherein when the first DC power source is not connected to the connection terminal, the drain and the source of the first and second field effect transistors are operated in a conductive state. Power supply switching circuit. A third field effect transistor is provided between the source of the second field effect transistor and the positive electrode on the load side, the source of the second field effect transistor and the drain of the third field effect transistor are connected, and the third field effect transistor Connect the source of the load and the positive pole on the load side,
2. The power supply switching circuit according to claim 1, wherein gates of the first to third field effect transistors are connected in common.   When a first DC power supply is connected to the connection terminal, if either one of the drain and source of the second or third field effect transistor is short-circuited, a backflow prevention circuit is connected from the first DC power supply via the connection terminal. 5. The power supply switching circuit according to claim 4, wherein a current is prevented from flowing to the second DC power supply via the second or third field effect transistor. The backflow prevention circuit is
A diode having an anode connected to the connection terminal and a cathode connected to the positive electrode on the load side;
A transistor in which a collector and a base are connected to the connection terminal and an emitter is connected to the positive electrode on the load side;
A field effect transistor having a drain and a gate connected to the connection terminal and a source connected to the positive electrode on the load side;
The power supply switching circuit according to claim 1 or 5, comprising any one of the following.

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