JP2005312218A - Power supply switching circuit and portable electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply switching circuit for surely switching a power supply to a battery when a voltage supplied from an external power supply is interrupted and optimally reducing a loss on a power supply line. <P>SOLUTION: The power supply switching circuit is provided with an external power input 1 connected to the external power supply, a battery power input 2 connected to the battery, an output terminal 6, a P-channel MOSFET 11 having a drain connected to the output terminal 6, a load switch connected between the output terminal 6 and the battery power input terminal 2, a Schottky barrier diode 12 having a cathode connected to a source of the first P-channel MOSFET 11 and an anode connected to the external power input 1, and control circuits 5, 13, 23. The load switch comprises P-channel MOSFETs 21, 22. The control circuits 5, 13, 23 turn on one of the first P-channel MOSFET 1 and the load switch connected between the output terminal 6 and the battery power input terminal 2 in response to a voltage at the external power input 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power supply switching circuit, and more particularly to a power supply switching circuit suitable for switching a plurality of power supplies in a portable electronic device.

  Many portable electronic devices are configured to be able to use two power sources: a battery and an external power source (typically an AC adapter connected to a commercial power source). Such a portable electronic device is driven by an external power supply when connected to an external power supply, and is driven by a battery when disconnected from the external power supply. Such an operation is important to prevent the internal power source from being consumed and to increase the maximum drive time.

  Such a portable electronic device is equipped with a power supply switching circuit for switching between an external power supply and a battery. A typical power supply switching circuit preferentially outputs the power supplied from the external power source when power is supplied from the external power source, and is supplied from the battery when only the battery is connected. Output power. The power output from the power supply switching circuit is supplied to each component of the portable electronic device.

  The simplest method for switching between the external power source and the battery is a method using a diode switch (see the conventional technology section of Patent Document 1). FIG. 1 shows a power supply switching circuit for switching between an external power supply and a battery by a diode switch. The known power supply switching circuit includes an input terminal 101, a charger 102, a protection diode 103, a rechargeable battery 104, an output terminal 108, a switch 109, and switching diodes 111 and 112. . A DC voltage Vm is supplied to the input terminal 101 from an external power source. When the voltage power source Vm is higher than the voltage of the battery 104, the switching diode 111 is turned on, the switching diode 112 is turned off, and the DC voltage Vm is output from the output terminal 108. On the other hand, in the opposite case, the voltage of the battery 104 is output from the output terminal 108.

  Patent Document 1 points out the following two drawbacks with respect to the power supply switching circuit of FIG. The first drawback is that the power supply switching circuit must have the DC voltage Vm higher than the voltage of the battery 104 in order to output the DC voltage Vm supplied from the external power supply from the output terminal 108. When the voltage of the battery 104 is high, the power of the battery 104 is consumed even if the external power supply is connected to the power supply switching circuit. It is not preferable from the viewpoint of extending the power supply time of the battery 104 that the power of the battery 104 is consumed even when the external power supply is connected to the power supply switching circuit.

  A second disadvantage is that a loss generated in the switching diode is large. Patent Document 1 discloses that when switching with a Schottky barrier diode, a loss of 0.5 W occurs to output a load current of 1 A (paragraph 0023). It should be noted that Patent Document 1 denies the use of a Schottky barrier diode as a means for reducing loss.

  In order to eliminate such drawbacks, Patent Document 1 discloses a technique for switching between an external power source and a battery by a P-channel MOSFET (metal oxide semiconductor field effect transistor). FIG. 2 is a circuit diagram of a power supply switching circuit disclosed in Patent Document 1. The power supply switching circuit includes an input terminal 201, a charger 202, protective diodes 203a and 203b, a rechargeable battery 204, an output terminal 208, P-channel MOSFETs 209a and 209b, an N-channel MOSFET 209c, a comparator 215, and a control logic 221. ing.

  The voltage switching circuit of FIG. 2 switches between the external power source and the battery by exclusively turning on the P-channel MOSFETs 209a and 209b. When the DC voltage Vm is higher than the predetermined reference voltage Eo, the P-channel MOSFET 209a is turned on. When the P-channel MOSFET 209a is turned on, the DC voltage Vm is output from the output terminal 208 via the P-channel MOSFET 209a. When the DC voltage Vm is lower than the predetermined reference voltage Eo, the P-channel MOSFET 209b is turned on, and the voltage of the battery 204 is output from the output terminal 208.

  The power supply switching circuit of FIG. 2 can reliably select the external power supply when the external power supply is connected by appropriately setting the reference voltage Eo. In addition, since the power supply switching circuit of FIG. 2 uses a P-channel MOSFET having a low on-resistance, loss can be reduced.

  On the other hand, Patent Document 2 discloses a power supply switching circuit that switches between an external power supply and a battery by an N-channel MOSFET. The operation of the power supply switching circuit disclosed in Patent Document 2 is similar to that of the power supply switching circuit of FIG. 2 except that an N-channel MOSFET is used instead of a P-channel MOSFET. The advantage of using the N-channel MOSFET is that the reflected wave supplied from the load to the output terminal of the voltage switching circuit can be blocked by the action of the parasitic diode existing in the N-channel MOSFET. This is preferable in order to reduce noise caused by the reflected wave.

  One requirement for the power supply switching circuit is to reliably switch the voltage output to the output terminal to the battery voltage when the supply of voltage from the external power supply is stopped. It is not preferable that the voltage from the battery flows backward to the external power supply because it may be one factor that hinders switching of the voltage output to the output terminal. For example, in the power supply switching circuit of FIG. 2, if the voltage of the battery 204 flows backward to the input terminal 201 when the supply of voltage from the external power supply is stopped, switching of the voltage output to the output terminal 208 is hindered. . In order to prevent such backflow, the power supply switching circuit of FIG. 2 includes a protective diode 203a.

  Another requirement for the power supply switching circuit is to reduce the loss in the power supply line, that is, the path from the external power supply to the output terminal. Loss in the power supply line leads to an increase in the amount of heat generated in the power supply switching circuit. An increase in the amount of heat generation is not preferable from the viewpoint of protecting the elements constituting the power supply switching circuit.

It is desired that the power supply switching circuit can reliably perform switching to the battery when the supply of voltage from the external power supply is stopped, and reduce the loss in the power supply line.
JP-A-8-130839 JP-A-8-280142

  An object of the present invention is to provide a power supply switching circuit that can reliably perform switching to a battery when the supply of voltage from an external power supply is stopped and is suitable for reducing loss in a power supply line.

  In order to achieve the above object, the present invention employs the following means. In the description of technical matters included in the means, in order to clarify the correspondence between the description of [Claims] and the description of [Best Mode for Carrying Out the Invention] Number / symbol used in the best mode for doing this is added. However, the added numbers and symbols shall not be used for the interpretation of the technical scope of the invention described in [Claims].

  The power supply switching circuit according to the present invention includes a first input terminal (1) connected to an external power supply, a second input terminal (2) connected to a battery, an output terminal (6), and an output terminal (6). A first P-channel MOSFET (11) having a drain connected thereto, a load switch (21, 22) connected between the output terminal (6) and the second input terminal (2), and a first P-channel MOSFET (11) A Schottky barrier diode (12) having a cathode connected to the source and an anode connected to the first input terminal (1), and a first P-channel MOSFET (11) in response to the voltage of the first input terminal (1) And a control circuit (5, 13, 23) for turning on one of the load switch (21, 22).

  In the power supply switching circuit, since the first input terminal (1) and the output terminal (6) are connected by a P-channel MOSFET suitable for reducing the on-resistance, the first input terminal (1) is connected to the output terminal. There is little loss of the power line connected to (6). In addition, since a Schottky barrier diode (12) is interposed between the first input terminal (1) and the first P-channel MOSFET (11), the voltage from the battery to the first input terminal (1) is reduced. No backflow occurs. This makes it possible to reliably switch between the external power source and the battery. In addition, since the Schottky barrier diode (12) has a low forward voltage drop, it is preferable to use the Schottky barrier diode (12) in order to prevent backflow for reducing power supply line loss.

  In order to reduce the loss of the power supply line connecting the second input terminal (2) to the output terminal (6), it is preferable that the load switch (21, 22) is composed of a P-channel MOSFET. More specifically, the load switch (21, 22) includes a second P-channel MOSFET (21) having a source connected to the second input terminal (2) and a third P having a source connected to the output terminal (6). And the drain of the second P-channel MOSFET (21) is connected to the drain of the third P-channel MOSFET (23), and the gates of the second P-channel MOSFET (21) and the third P-channel MOSFET (22). Is preferably connected to the control node (25). In this case, the control circuit (5, 13, 23) controls the potential of the gate of the first P-channel MOSFET (11) and the control node (25) in response to the voltage of the first input terminal (1).

  The power supply switching circuit of the present invention is suitably used for a portable electronic device equipped with a battery.

  According to the present invention, there is provided a power supply switching circuit capable of reliably switching to a battery when voltage supply from an external power supply is stopped and reducing loss in a power supply line.

  Hereinafter, the best embodiment of a power supply switching circuit according to the present invention will be described with reference to the drawings.

Configuration of First Power Supply Switching Circuit FIG. 3 is a block diagram showing the configuration of the power supply switching circuit according to the present invention. The power supply switching circuit 10 includes an external power supply input 1, a battery power supply input 2, an external power supply system 3, a battery power supply system 4, a selection circuit 5, an output terminal 6, and an electrolytic capacitor 7. External power input 1 is a terminal which is powered voltages V ₁ from the external power supply, battery power input 2 is a terminal which is supplying the power supply voltage V ₂ from the battery. The external power supply system 3 is a circuit for outputting the power supply voltage V ₁ supplied from the external power supply from the output terminal 6, and the battery power supply system 4 outputs the power supply voltage V ₂ supplied from the battery from the output terminal 6. It is a circuit for doing. Selection circuit 5 is a circuit for selecting the power supply voltages V ₁ supplied from the external power supply, the output voltage Vo output from the output terminal 6 from among the power supply voltage V ₂ supplied from the battery. The electrolytic capacitor 7 is interposed between the output terminal 6 and the ground terminal 8 and is used to stabilize the output voltage Vo generated at the output terminal 6.

1. Configuration of External Power Supply System The external power supply system 3 includes a P-channel MOSFET 11, a Schottky barrier diode 12, and a gate control circuit 13.

The P-channel MOSFET 11 and the Schottky barrier diode 12 are inserted in a power supply line that sends the power supply voltage V ₁ supplied from the external power supply to the external power supply input ₁ to the output terminal 6. The P-channel MOSFET 11 is used as a load switch that connects an external power supply to the output terminal 6, and the Schottky barrier diode 12 is used to prevent a backflow of current from the output terminal 6 to the external power supply input 1. Specifically, the drain of the P-channel MOSFET 11 is connected to the output terminal 6, and the source is connected to the cathode of the Schottky barrier diode 12. The anode of the Schottky barrier diode 12 is connected to the external power input 1. The substrate terminal of the P-channel MOSFET 11 is connected to the source. Therefore, the parasitic diode of the P-channel MOSFET 11 has its anode connected to the output terminal 6 and its cathode connected to the cathode of the Schottky barrier diode 12.

The gate control circuit 13 is a circuit for turning on and off the P-channel MOSFET 11. Off of the P-channel MOSFET11 is in response to the selection signal _{S C} supplied from the selection circuit 5. Specifically, the gate control circuit 13 includes an N-channel MOSFET 13a and resistors 13b to 13d. The source of N-channel MOSFET13a is connected to the ground terminal 13e, a gate is connected through a resistor 13b to the control input 14 of selection signal _{S C} is input. The drain of the N-channel MOSFET 13a is connected to the gate of the P-channel MOSFET 11 through the resistor 13c, and is connected to the cathode of the Schottky barrier diode 12 through the resistor 13d.

2. Configuration of Battery Power Supply System The battery power supply system 4 includes P-channel MOSFETs 21 and 22 and a gate control circuit 23.

The P-channel MOSFETs 21 and 22 constitute a load switch that is inserted into a power supply line that sends a voltage V ₁ supplied from the battery power supply to the battery power supply input 2 to the output terminal 6. The source of the P channel MOSFET 21 is connected to the battery power input 2, and the drain of the P channel MOSFET 21 is connected to the drain of the P channel MOSFET 22. The source of the P-channel MOSFET 22 is connected to the output terminal 6. The gates of the P-channel MOSFETs 21 and 22 are connected to the control node 25. Note that the parasitic diode orientation of the P-channel MOSFETs 21 and 22 is reversed.

The gate control circuit 23 is a circuit for turning on and off the P-channel MOSFETs 21 and 22. Off of the P-channel MOSFET21,22 is in response to the selection signal _{S C} supplied from the selection circuit 5. Specifically, the gate control circuit 23 includes N-channel MOSFETs 23a and 23b and resistors 23c to 23e. The source of N-channel MOSFET23a is connected to the ground terminal 23f, the gate of N-channel MOSFET23a is connected to the control input 24 to select signal _{S C} is input. The drain of the N-channel MOSFET 23a is connected to the battery power supply input 2 through the resistor 23c, and is connected to the gate of the N-channel MOSFET 23b. The source of the N-channel MOSFET 23b is connected to the ground terminal 23g. The drain of the N-channel MOSFET 23b is connected to the control node 26 via a resistor 23d. As described above, the control node 25 is connected to the gates of the P-channel MOSFETs 21 and 22.

3. Configuration of Selection Circuit The selection circuit 5 includes a capacitor 31, a voltage detection circuit 32, and a resistor 33. The capacitor 31 is for removing noise of a signal input to the voltage detection circuit 32. The voltage detection circuit 32 is a circuit that detects whether or not the power supply voltage V ₁ is supplied to the external power supply input 1. Voltage detection circuit 32, when the power supply voltages V ₁ from the external power supply to the external power input 1 is supplied, to pull up the selection signal S _C to the High level, otherwise, selection signal S _C Low level Pull down to. As the voltage detection circuit 32, a comparator can be typically used. Voltage detection circuit 32, when the voltage of the external power supply input of the external power input 1 is higher than a predetermined threshold voltage, and pull up the selection signal S _C to the High level, otherwise, Low level selection signal S _C Pull down to. The threshold voltage is set to a voltage lower than the power supply voltage V ₁ considered to be normally supplied to the external power input 1. Selection signal _{S C} is supplied to the control input 14, 24 of the gate control circuit 13, 23, P-channel MOSFET11 of external power supply system 3, and are used to control the P-channel MOSFET21,22 battery power supply system 4. Resistor 33 is interposed between the output and the ground terminal 34 of the voltage detection circuit 32, when necessary, the output of the voltage detection circuit 32, i.e., is used to pull down the selection signal S _C.

Second Operation of Power Supply Switching Circuit According to the Present Embodiment The operation of the power supply switching circuit according to the present embodiment is performed in the following four cases:
- When the power supply voltage V ₁ of the external power supply is supplied,
- when the supply voltage V ₂ from the battery power is supplied,
· If an external power supply, the power supply voltage from both of the battery power is supplied, and - an external power supply, when the supply voltage from both of the battery power is supplied, the supply of the power supply voltages V ₁ from the external power supply is stopped Each case will be described in detail.

1. Only the power supply voltages V ₁ from the external power supply is powered voltages V ₁ from the external power supply when it is supplied, when the power supply voltage V ₂ from the battery power source is not supplied, the power supply switching circuit of the present embodiment, the following outputs the power supply voltages V ₁ from the external power source from the output terminal 6 by operating as described.

Voltage detecting circuit 32 is pulled up to the High level detected and selected signal S _C that is the power supply voltages V ₁ is supplied.

In response to the pull-up of the selection signal _{S C,} P-channel MOSFET11 of external power supply system 3 are turned on. This is because, by the pull-up of the selection signal _{S C,} because N-channel MOSFET13a receiving at the gate a selection signal _{S C} is turned on, the gate of the P-channel MOSFET11 is pulled down to the Low level. When the P-channel MOSFET 11 is turned on, the external power supply input 1 is connected to the output terminal 6, and the power supply voltage V ₁ from the external power supply is output from the output terminal 6.

Since P-channel MOSFET21,22 battery power supply system 4 in response to the pull-up of the selection signal _{S C} is turned off, the power supply voltages _{V 1} from the external power source is not transmitted to the battery power input 2. When the selection signal _{S C} is pulled up, N-channel MOSFET23a receiving a selection signal _{S C} at the gate is turned on. When the N-channel MOSFET 23a is turned on, the gate of the N-channel MOSFET 23b is pulled down to the low level, so that the N-channel MOSFET 23b is turned off. When N-channel MOSFET23b is turned off, the gate of P-channel MOSFETs 21, the power supply voltages _{V 1} from the external power source resistors 23e, is supplied via 23d. Accordingly, the P-channel MOSFETs 21 and 22 are turned off, and the battery power input 2 is disconnected from the external power input 1.

  The connection of the external power supply input 1 to the output terminal 6 by the P-channel MOSFET 11 (not the N-channel MOS transistor) is important for reducing the on-resistance of the power supply line and thus reducing the loss of the power supply line. It is. In order to turn on the N-channel MOS transistor with a low on-resistance, it is necessary to make the gate potential higher than the source potential. Therefore, when an N-channel MOS transistor is used as a load switch inserted in the power supply line, it is necessary to incorporate a boost circuit for increasing the gate potential in the power supply switching circuit in order to reduce the on-resistance. is there. This is undesirable because it increases the circuit scale. Therefore, it is preferable to use a P-channel MOSFET in order to reduce the power line loss.

2. Only the power supply voltage V ₂ from the battery power supply is the power supply voltage V ₂ supplied from the battery power source when supplied, when the power supply voltage V ₁ of the external power source is not supplied, the power supply switching circuit of the present embodiment, the following outputs the power supply voltage V ₂ from the battery power supply from the output terminal 6 by operating as described.

Voltage detecting circuit 32 detects and pulls down the selection signal S _C to the Low level to the power supply voltage V ₁ is not supplied to the power switching circuit.

P-channel MOSFET21,22 battery power supply system 4 is turned on in response to the pull-down of the selection signal _{S C.} In response to the pull-down of the selection signal _{S C,} N-channel MOSFET23a receiving a selection signal _{S C} at the gate is turned off. When N-channel MOSFET23a is turned off, the gate of the N channel MOSFET 23B, the power supply voltage _{V 2} from the battery power input 2 is supplied through a resistor 23c, therefore, the N-channel MOSFET 23B is turned on. When the N-channel MOSFET 23b is turned on, a low level is supplied to the gate of the P-channel MOSFET 21 via the control node 25, so that the P-channel MOSFET 21 is turned on. When the P-channel MOSFET 21 is turned on, the P-channel MOSFET 22 connected to the P-channel MOSFET 21 is turned on by an avalanche effect due to a parasitic diode. When both P-channel MOSFETs 21 and 22 are turned on, the battery power input 2 is connected to the output terminal 6, and the power supply voltage V ₂ from the battery power is output from the output terminal 6.

  As with the connection of the external power input 1 to the output terminal 6, the connection of the battery power input 2 to the output terminal 6 by the P-channel MOSFETs 21 and 22 is effective for reducing the on-resistance of the power line. It is.

Since P-channel MOSFET11 of the external power supply system 3 in response to the pull-down of the selection signal S _C is turned off, the power supply voltage V ₂ from the battery power source, not transmitted to the external power input 1.

3. When the external power supply, if the power supply voltage from both of the battery power is supplied external power supply voltage from both of the battery power is supplied, the power supply switching circuit of the present embodiment, only the power supply voltage V ₁ of the external power supply As in the case where the power is supplied, the power supply voltage V ₁ from the external power supply is selectively output from the output terminal 6. This is because the voltage detection circuit 32, since detected and pulls up the selection signal S _C to the High level that the power supply voltages V ₁ is supplied. The potential of the selection signal S _C It should be noted that it is independent of the presence or absence of the supply of the power supply voltage V ₂ from the battery power source. In response to the pull-up of the selection signal _{S C,} P-channel MOSFET11 of external power supply system 3 is turned on, P-channel MOSFET21,22 battery power supply system 4 is turned off. As a result, the power supply voltage V ₁ from the external power supply is output from the output terminal 6.

4). External power supply, when the supply voltage from both of the battery power is supplied, when the when the external power supply of the power supply voltages V ₁ from the external power supply is stopped, the power supply voltage from both of the battery power is supplied , the supply of the power supply voltages V ₁ from the external power supply is stopped, the power switching circuit, the output voltage Vo output from the output terminal 6 is switched to the supply voltage V ₂ from the battery power source. Specifically, the voltage detection circuit 32, pulls down the selection signal S _C to the Low level by detecting that the supply of the power supply voltage V ₁ is stopped. In response to the pull-down of the selection signal _{S C,} P-channel MOSFET11 of external power supply system 3 is turned off, P-channel MOSFET21,22 battery power supply system 4 is turned on. When the P-channel MOSFETs 21 and 22 are turned on, the battery power source input 2 is connected to the output terminal 6, and the power source voltage V ₂ from the battery power source is output from the output terminal 6.

A problem that may arise when switching the output voltage Vo output from the output terminal 6 to the power supply voltage V ₂ from the battery power supply is that the power supply voltage V ₂ can flow backward from the drain to the source of the P-channel MOSFET 11. After the supply of the power supply voltages V ₁ from the external power source is stopped, because it takes some time until selection signal S _C is pulled down, immediately after the supply of the power supply voltages V ₁ from the external power supply is stopped , P-channel MOSFET 11 remains turned on. If the P-channel MOSFET 11 remains turned on, the power supply voltage V ₂ from the battery power source can flow backward from the drain to the source of the P-channel MOSFET 11. When the power supply voltage V ₂ from the battery power source from flowing back to the external power input 1, the voltage detecting circuit 32 is likely to erroneously recognize the power supply voltages V ₁ from the external power source is supplied.

Schottky barrier diode 12, when the switching of the output voltage Vo, the power supply voltage V ₂ from the battery power supply is prevented from flowing back to the external power input 1, plays a role of reliably for switching the output voltage Vo . Since the cathode of the Schottky barrier diode 12 is connected to the P-channel MOSFET 11 and the anode is connected to the external power supply input 1, when the supply of the power supply voltage V ₁ from the external power supply is stopped, the Schottky barrier diode 12 is connected to the Schottky barrier diode 12. Is applied with a reverse bias. Therefore, the power supply voltage V ₂ from the battery power source does not flow back to the external power input 1. For this reason, the voltage detection circuit 32 correctly detects a decrease in the voltage of the external power input 1.

  Other diodes may be used in place of the Schottky barrier diode 12 if only for the purpose of preventing backflow; however, the use of the Schottky barrier diode 12 is a power supply that connects the external power input 1 to the output terminal 6. It is effective in reducing the loss generated in the line. The Schottky barrier diode 12 has a low forward voltage drop. This effectively reduces the loss generated in the power line. The reduction in loss reduces the amount of heat generated in the Schottky barrier diode 12.

Third Summary As described above, the power supply switching circuit of the present embodiment is configured to switch the power supply in response to the voltage of the external power supply input 1, and therefore the power supply voltage V from the external power supply. When there is a supply of ₁ , the external power supply can be selected reliably. This is effective for reducing the amount of power consumed in the battery.

  In addition, since the external power input 1 and the battery power input 2 are connected to the output terminal 6 via the P-channel MOSFET, the power supply switching circuit of this embodiment has a low resistance of the power supply line. Therefore, the power line loss is small.

Further, in the power supply switching circuit of the present embodiment, the P-channel MOSFET 11 and the external power supply input 1 are connected via the Schottky barrier diode 12, so that the battery voltage V ₂ from the battery power supply is applied to the external power supply input 1. Backflow is prevented and switching from an external power source to a battery power source can be performed reliably. Using the Schottky barrier diode 12 to prevent backflow is also effective in reducing power supply line loss.

FIG. 1 is a circuit diagram of a known power supply switching circuit. FIG. 2 is a circuit diagram of another known power supply switching circuit. FIG. 3 is a circuit diagram of the power supply switching circuit according to the embodiment of the present invention.

Explanation of symbols

1: External power input 2: Battery power input 3: External power system 4: Battery power system 5: Selection circuit 6: Output terminal 7: Electrolytic capacitor 8: Ground terminal 11: P channel MOSFET
12: Schottky barrier diode 13: Gate control circuit 13a: N-channel MOSFET
13b, 13c, 13d: Resistance 13e: Ground terminal 21, 22: P-channel MOSFET
23: Gate control circuit 23a, 23b: N-channel MOSFET
23c, 23d, 23e: resistors 23f, 23g: ground terminal 31: capacitor 32: voltage detection circuit 33: resistor 34: ground terminal

Claims (4)

A first input terminal connected to an external power source;
A second input terminal connected to the battery;
An output terminal;
A first P-channel MOSFET having a drain connected to the output terminal;
A load switch connected between the output terminal and the second input terminal;
A Schottky barrier diode having a cathode connected to a source of the first P-channel MOSFET and an anode connected to the first input terminal;
A power supply switching circuit comprising: a control circuit that turns on one of the first P-channel MOSFET and the load switch in response to a potential of the first input terminal. The power supply switching circuit according to claim 1,
The load switch is a power switching circuit composed of a P-channel MOSFET. The power supply switching circuit according to claim 1,
The load switch is
A second P-channel MOSFET having a source connected to the second input terminal;
A third P-channel MOSFET having a source connected to the output terminal,
The drain of the second P-channel MOSFET is connected to the drain of the third P-channel MOSFET,
The gates of the second P-channel MOSFET and the third P-channel MOSFET are connected to a control node,
The control circuit controls a potential of the gate of the first P-channel MOSFET and the control node in response to the voltage of the first input terminal. Batteries,
Power supply switching circuit,
The power switching circuit is
A first input terminal connected to an external power source;
A second input terminal connected to the battery;
An output terminal;
A first P-channel MOSFET having a drain connected to the output terminal;
A load switch connected between the output terminal and the second input terminal;
A Schottky barrier diode having a cathode connected to a source of the first P-channel MOSFET and an anode connected to the first input terminal;
A portable electronic device comprising: a control circuit that turns on one of the first P-channel MOSFET and the load switch in response to a potential of the first input terminal.

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