JP2001352670A - Apparatus and method for connection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection apparatus which can be manufactured at low cost and by which a loss is not generated in a power supply, so that the apparatus itself or a connected apparatus will not break down, even if power supply is supplied at an erroneous voltage. SOLUTION: A USB-type B-port 33 inputs the power supply from a second apparatus. A jack 34 inputs an external power supply. An allowable-input- voltage detection circuit 51 judges whether the voltage of the external power supply is normal. A relay 52 selects the external power supply, to be supplied to a first apparatus when the voltage of the external power supply is judged as being normal. When the voltage of the external power supply is judged to be not normal, the power supply which is input from the second apparatus is selected so as to be supplied to the first apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection apparatus and method, and more particularly to a connection apparatus and method for inputting and outputting data and supplying power to connected equipment.

[0002]

2. Description of the Related Art USB devices, such as a USB (Universal Serial Bus) hub, are connected to a connected device by DC.
(Direct Current) 5V power can be supplied.

A USB hub having a self-power mode stabilizes the voltage of the power inside. More specifically, U
The SB hub receives power from an AC adapter that supplies power of a voltage higher than DC 5 V (for example, 6 V), and drops the voltage of the power by a regulator provided therein to obtain a more accurate power of 5 V.

[0004]

However, since the voltage is stabilized by the regulator provided inside, there is a problem that a loss occurs in the power supply and the USB hub becomes expensive.

When an AC adapter that supplies a voltage higher than the rated voltage is connected and a high-voltage power is input,
The USB hub is destroyed or destroys connected devices.

The present invention has been made in view of such a situation, and can be manufactured at a low cost. Further, it is possible to prevent a loss in the power supply and to prevent a power supply of an incorrect voltage from being supplied. The purpose is to prevent yourself or the connected equipment from being destroyed.

[0007]

According to a first aspect of the present invention, there is provided a connection device comprising: first power input means for inputting power from a second device; second power input means for inputting external power; Determining means for determining whether or not the voltage of the power supply is normal;
When it is determined that the voltage of the external power supply is normal, the external power supply is selected and supplied to the first device. When it is determined that the voltage of the external power supply is not normal, the external power supply is input from the second device. Selecting means for selecting a power supply and supplying the selected power to the first device.

[0008] The determining means can determine whether or not the voltage of the external power supply is normal based on the upper and lower limits of the voltage.

According to a third aspect of the present invention, in the connection method, a first power input step for inputting power from the second device, a second power input step for inputting external power, and the voltage of the external power is normal. A determining step of determining whether or not the external power supply voltage is normal; and if it is determined that the external power supply voltage is normal, the external power supply is selected and supplied to the first device, and it is determined that the external power supply voltage is not normal. In this case, a power supply input from the second device is selected and supplied to the first device.

[0010] The connecting device according to the first aspect and the third aspect.
In the connection method described in 1, the power is input from the second device, the external power is input, it is determined whether the voltage of the external power is normal, and it is determined that the voltage of the external power is normal. In this case, the external power source is selected and supplied to the first device. If it is determined that the voltage of the external power source is not normal, the power source input from the second device is selected and the first power source is selected.
Equipment.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
FIG. 2 is a diagram illustrating an embodiment of an iversal serial bus) hub. The USB hub 2 is a device for making a tree connection (also referred to as a star connection) of devices to be connected to a bus. For example, a personal computer 1, a USB floppy (registered trademark) disk drive 3, and a US
It is connected to the B mouse 4.

In this connection example, the personal computer 1 has a role of a host or a root hub.

The USB hub 2 outputs the data supplied from the personal computer 1 to the USB floppy disk drive 3, and outputs the data supplied from the USB floppy disk drive 3 or the USB mouse 4 corresponding to the operation of the USB mouse 4. Is output to the personal computer 1.

The USB hub 2 is an AC (Alternating curr)
ent) When the power adapter 5 is not connected, the DC power supplied from the personal computer 1
It is supplied to the B floppy disk drive 3 and the USB mouse 4.

When the AC power adapter 5 is connected, the USB hub 2 supplies the DC power supplied from the AC power adapter 5 to the USB floppy disk drive 3 and the USB mouse 4.

FIG. 2 is a view for explaining the external appearance of the USB hub 2. Each of the USB ports 31-1 to 31-4 has a connector of a device or cable connected to the USB hub 2 inserted therein.

A port LED (Light-Emitting Diode) lamp 32-1 blinks green when a device connected via the USB port 31-1 is initialized, and is connected via the USB port 31-1. Lights green when a connected device is recognized. The port LED lamp 32-1 is
Lights red when the current supplied to the device connected via the USB port 31-1 exceeds the allowable current value.

When the device connected via the USB port 31-2 is initialized, the port LED lamp 32-2 blinks green, and the device connected via the USB port 31-2 is recognized. Lights green when The port LED lamp 32-2 lights red when the current supplied to the device connected via the USB port 31-2 exceeds the allowable current value.

When the device connected via the USB port 31-3 is initialized, the port LED lamp 32-3 blinks green, and the device connected via the USB port 31-3 is recognized. Lights green when The port LED lamp 32-3 lights red when the current supplied to the device connected via the USB port 31-3 exceeds the allowable current value.

The port LED lamp 32-4 blinks green when the device connected via the USB port 31-4 is initialized, and the device connected via the USB port 31-4 is recognized. Lights green when The port LED lamp 32-4 lights red when the current supplied to the device connected via the USB port 31-4 exceeds the allowable current value.

The USB type B port 33 is a host for controlling the USB bus. For example, a connector of a cable for connecting the personal computer 1 is inserted into the USB type B port 33, and the personal computer 1 supplies a bus 5V power.

The jack 34 is connected to the connector of the AC power adapter 5 and inputs a DC power supplied from the AC power adapter 5.

A USB type B port 33 is inserted with a connector for a cable for connecting a personal computer 1 which is a host for controlling a USB bus, for example.
When the personal computer 1 is supplied with power from the bus 5V, the power LED lamp 35 lights up in green.

Hereinafter, the USB ports 31-1 to 31-4
Are simply referred to as a USB port 31 when it is not necessary to individually distinguish between them. Hereinafter, when it is not necessary to individually distinguish the port LED lamps 32-1 to 32-4, they are simply referred to as port LED lamps 32.

As shown in FIG.
When the connector of the power adapter 5 is connected,
The SB hub 2 is connected to a device connected to the USB port 31,
An external 5V power supplied from the AC power adapter 5 is supplied.

FIG. 4 is a diagram for explaining a connection state when two USB hubs 2 are cascaded. USB
When the personal computer 1 is connected to the USB type B port 33-1 and the personal computer 1 is the first layer of the tree connection hierarchy, the hub 2-1 forms the second layer of the tree connection hierarchy.

The USB hub 2-1 is connected to an external 5 input from the AC power adapter 5-1 via the jack 34-1.
The V power is supplied to a device connected to the USB port 31 of the USB hub 2-1.

One end of the cable is the USB hub 2-1
B port 31-1-1 and the other end of the cable is connected to the USB type B port 33-2 of the USB hub 2-2. Configure the third layer. USB of USB hub 2-2
The device connected to the port 31-1-2 forms the third layer of the tree connection hierarchy.

The USB hub 2-2 is connected to an external 5 input from the AC power adapter 5-2 via the jack 34-2.
V power supply to the USB port 31-1-
2 to the equipment connected to it.

FIG. 5 is a diagram for explaining a configuration example of the USB hub 2. AC power adapter 5 via jack 34
Is supplied to the allowable input voltage detection circuit 51 and the relay 52 as an external 5V power supply.

The allowable input voltage detection circuit 51 is based on the voltage of the external 5 V power supply input from the AC power adapter 5 and
Generates a relay control signal and relays the relay control signal to relay 5.
2 to control the relay 52.

The relay 52 receives an external 5V power input from the AC power adapter 5 and an input from a host such as the personal computer 1 or another higher-level device via the USB type B port 33 and the upstream port 53. The supplied bus 5V power and the relay control signal supplied from the allowable input voltage detection circuit 51 are input.

The relay 52 selects one of an external 5 V power supply and a bus 5 V power supply based on the relay control signal and supplies the selected power supply to the overcurrent protection circuit 56 as a 5 V power supply.

The upstream port 53 separates power and data supplied from a device connected via the USB type B port 33, and supplies the separated data to the hub control unit 54. The relay 52 and DC (Dire
ct Current) -to the DC converter 55. The upstream port 53 outputs the data supplied from the hub control unit 54 to a device connected via the USB type B port 33.

The DC-DC converter 55 is based on a bus 5V power supply and has a 3.3V system voltage of 3.3V.
, And supplies the generated 3.3 V power for the system to the hub control unit 54.

The hub control unit 54 includes a control unit 61,
System-on-power reset circuit 62, EEPROM (Electr
ically Erasable Programmable Read-only Memory) 6
3 and an LED control unit 64.

The control unit 61 executes a program stored in the EEPROM 63 and
Based on the destination of that data,
Supply to the downstream port 57 and the corresponding USB
While outputting to the port 31, the data supplied from the downstream port 57 is supplied to the upstream port 53 corresponding to another USB port 31 based on the destination of the data, or to the downstream port 57. It is supplied and output to the corresponding USB type B port 33 or USB port 31.

The control section 61 sends a control signal for controlling the output of the power supply of the overcurrent protection circuit 56 to the overcurrent protection circuit 5.
6 and the LED control unit 64.

The system-on-power reset circuit 62
When the USB hub 2 is powered on and activated, a reset signal is supplied to the control unit 61 and the LED control unit 64. The control unit 61 and the LED control unit 64 are reset when a reset signal is input.

The LED control section 64 is a port LED lamp based on a control signal supplied from the control section 61 and a status signal (indicating whether or not the power is cut off) supplied from the overcurrent protection circuit 56. 32 is controlled.

The overcurrent protection circuit 56 is controlled by a control signal supplied from the control unit 61, and supplies the 5V power supplied from the relay 52 to the device connected to the USB port 31 via the downstream port 57. Supply or cut off the power supply.

The overcurrent protection circuit 56 includes a 500 mA protection circuit 71 and a 1 A protection circuit 72.

The 500 mA protection circuit 71 cuts off the 5 V power supplied to the downstream port 57 when the current of the 5 V power exceeds a predetermined value based on 500 mA. The 1A protection circuit 72 is connected to the downstream port 5 when the current of the 5V power supply exceeds a predetermined value based on 1A.
The 5V power supplied to 7 is cut off.

FIG. 6 shows the relay 52 and the overcurrent protection circuit 5
6 is a diagram for explaining a power supply path constituted by a power supply 6 and a downstream port 57. FIG. The relay 52
Based on the relay control signal supplied from the allowable input voltage detection circuit 51, one of the external 5V power supply and the bus 5V power supply is selected, and the selected power supply is supplied to the overcurrent protection circuit 56 as a 5V power supply.

The 5 V power input to the overcurrent protection circuit 56 is input to the 500 mA protection circuit 71 and the 1 A protection circuit 72.

When the current of the 5V power supply supplied to the USB port 31-3 exceeds a predetermined value based on 500 mA, the 500 mA protection circuit 71
Then, the 5V power supplied to the USB port 31-3 via the USB port 7 is shut off. When the current of the 5V power supply supplied to the USB port 31-4 exceeds a predetermined value based on 500 mA, the 500 mA protection circuit 71
7, the 5V power supply to the USB port 31-4 is cut off.

The 1A protection circuit 72 is based on 1A,
When the current of the 5 V power supply supplied to the B port 31-1 exceeds a predetermined value (a value larger than the 500 mA protection circuit 71), the USB via the downstream port 57
The 5V power supplied to the port 31-1 is cut off. The 1A protection circuit 72 is connected via the downstream port 57 when the current of the 5V power supply supplied to the USB port 31-2 exceeds a predetermined value (a value larger than that of the 500mA protection circuit 71) based on 1A. Then, the 5V power supply to the USB port 31-2 is cut off.

FIG. 7 shows a 500 mA protected IC (Integrated Circuit) with two circuits and a 500 m protected IC with four circuits.
FIG. 3 is a diagram illustrating a more detailed configuration example of a 500 mA protection circuit 71 and a 1 A protection circuit 72 when configured with an A protect IC.

The 500 mA protection circuit 71 includes 500 mA protectors 91-1 and 91-2. The 500 mA protector 91-1 corresponding to one circuit of the two-circuit 500 mA protect IC, when the current of the 5V power supply supplied to the USB port 31-3 exceeds a predetermined value based on 500 mA, sets the downstream port 57 The 5V power supply supplied to the USB port 31-3 via the is shut off.

The 500 mA protector 91-2 corresponding to the other circuits of the 500 mA protect IC with two circuits is composed of 5
5 to supply to USB port 31-4 based on 00mA
When the current of the V power supply exceeds a predetermined value, the 5 V power supply to the USB port 31-4 via the downstream port 57 is cut off.

The 1A protection circuit 72 includes 500 mA protectors 92-1 to 92-4.

One of the 500 mA protected ICs containing four circuits
500 mA protector 92-1 corresponding to one circuit
When the current of the 5V power supply supplied to the USB port 31-1 exceeds a predetermined value based on 500 mA, the 5V power supply supplied to the USB port 31-1 via the downstream port 57 is cut off. 500 mA protector 92 corresponding to other circuits of 500 mA protect IC with 4 circuits
-2, when the current of the 5V power supply supplied to the USB port 31-1 exceeds a predetermined value based on 500 mA, the USB port 31-1 is connected via the downstream port 57.
5V power supply to the power supply is cut off.

That is, the current of the 5V power supply supplied to the USB port 31-1 is diverted to the 500 mA protectors 92-1 and 92-2.
The 5V power supplied to the USB port 31-1 is cut off when the current exceeds a predetermined value based on 1A.

A 500 mA protector 92-3 corresponding to still another circuit of a 500 mA protect IC containing four circuits.
Shuts off the 5V power supplied to the USB port 31-2 via the downstream port 57 when the current of the 5V power supplied to the USB port 31-2 exceeds a predetermined value based on 500mA. A 500 mA protector 92-4 corresponding to still another circuit of the 500 mA protect IC including four circuits is provided with a USB port 3 based on 500 mA.
When the current of the 5V power supply supplied to 1-2 exceeds a predetermined value, the 5V power supply supplied to the USB port 31-2 via the downstream port 57 is cut off.

That is, the current of the 5 V power supply supplied to the USB port 31-2 is divided into the 500 mA protector 92-3 and the 500 mA protector 92-4.
The 5V power supplied to the USB port 31-2 is cut off when the current exceeds a predetermined value based on 1A.

FIG. 8 shows a 500 mA protection circuit 71 and a 1 A protection circuit 72 in the case of a two-circuit 500 mA protection IC and a two circuit 1 A protection IC.
FIG. 8 is a diagram illustrating another more detailed configuration example of FIG. 500m
Since the A protection circuit 71 is the same as that shown in FIG. 7, the description is omitted.

The 1A protection circuit 72 includes the 1A protector 10
1-1 and 101-2. 1 with 2 circuits
The 1A protector 101-1 corresponding to one circuit of the A protect IC has a USB port 31-1 based on 1A.
When the current of the 5 V power supply supplied to the USB port 31 exceeds a predetermined value, the USB port 31-
The 5V power supply to 1 is shut off.

The 1A protector 101-2 corresponding to the other circuit of the 1A protect IC with two circuits, when the current of the 5V power supply supplied to the USB port 31-2 exceeds a predetermined value on the basis of 1A, becomes down. The 5V power supplied to the USB port 31-2 via the stream port 57 is cut off.

FIG. 9 shows, for example, a 500 mA protector 9.
500mA with 2 circuits corresponding to 2-1 and 92-2
FIG. 3 is a diagram illustrating a protection IC 111. 500mA
The protect IC 111 is a 500 mA protector 92-.
1 and a circuit corresponding to the 500 mA protector 92-2.
When the current of the 5V power supply supplied to the SB port 31-1 exceeds a predetermined value, the 5V power supply supplied to the USB port 31-1 via the downstream port 57 is cut off.

As described above, the USB hub 2 has 50 devices connected to the USB port 31-1 or 31-2.
Even if an inrush current exceeding 0 mA is requested, a current exceeding 500 mA is supplied without shutting off the power supply, and the power is shut off when a current exceeding 1 A is requested.

As described above, the USB hub 2 can operate these devices stably even if devices requiring a current exceeding 500 mA due to an inrush current or the like are connected. Is not stopped (so-called freeze).

In addition, 500 mA protect I with 4 circuits
By using C, the 1A protection circuit 72 shown in FIG.
Can be constituted by one IC.

FIG. 10 is a block diagram illustrating the configuration of the allowable input voltage detection circuit 51. Reference voltage generation circuit 15
1 generates a reference voltage that is a constant voltage, and supplies the generated reference voltage to the maximum threshold input determination circuit 152 and the minimum threshold input determination circuit 153.

The maximum threshold value input determination circuit 152 determines whether or not the voltage of the external 5 V power supply is lower than a predetermined voltage (for example, 5.3 V) based on the reference voltage supplied from the reference voltage generation circuit 151. The determination is made, and a determination signal H corresponding to the result of the determination is supplied to the AND circuit 154.

The minimum threshold value input determination circuit 153 converts the voltage of the external 5V power supply to another predetermined voltage (for example, 4.6) based on the reference voltage supplied from the reference voltage generation circuit 151.
V) is determined, and a determination signal L corresponding to the determination result is supplied to the AND circuit 154.

Based on the determination signal H and the determination signal L, the AND circuit 154 determines that the voltage of the external 5 V power supply is lower than a predetermined voltage (for example, 5.3 V) and that another predetermined voltage (for example, 4. 6V), the relay 52 is connected to the external 5
A control signal for outputting the V power is supplied.

Based on the judgment signal H and the judgment signal L, the AND circuit 154 determines whether the voltage of the external 5 V power supply is equal to or higher than a predetermined voltage (for example, 5.3 V) or another predetermined voltage (for example, 4. 6V) or less, the relay 52 is supplied with a control signal for outputting the bus 5V power supplied from the upstream port 53.

FIG. 11 is a circuit diagram illustrating a configuration example of the allowable input voltage detection circuit 51. Reference voltage generation circuit 151
Generates a reference voltage based on the bus 5V power supply, and supplies the generated reference voltage to the maximum threshold input determination circuit 152 and the minimum threshold input determination circuit 153.

The maximum threshold input determination circuit 152 includes a voltage dividing circuit composed of a resistor and the like and an operational amplifier 171
Etc. The operational amplifier 171 compares the divided voltage of the external 5 V power supply with the reference voltage,
A result corresponding to whether the voltage of the power supply is lower than a predetermined voltage is output.

The minimum threshold value input determining circuit 153 includes a voltage dividing circuit composed of a resistor and the like and an operational amplifier
Etc. The operational amplifier 172 compares the voltage of the divided external 5V power supply (having a different division ratio with the maximum threshold input determination circuit 152) with the reference voltage, and
A result corresponding to whether or not the voltage of the V power supply is higher than another predetermined voltage is output.

The output of the operational amplifier 171 indicates that the voltage of the external 5 V power supply is lower than the predetermined voltage,
When the output of 72 indicates that the voltage of the external 5V power supply is higher than another predetermined voltage, the transistor driving the relay 52 is turned on, so that the relay 52 outputs the external 5V power supply as the 5V power supply.

FIG. 12 is a diagram for explaining the operation of the allowable input voltage detection circuit 51. FIG. 12 (A) and FIG.
As shown in (B), when the voltage of the external 5V power supply is less than 5.3V, the determination signal H is set to 1, and when the voltage of the external 5V power supply is 5.3V or more, the determination signal H becomes It is set to 0.

As shown in FIGS. 12A and 12C, when the voltage of the external 5V power supply exceeds 4.6V, the determination signal L is set to 1 and the voltage of the external 5V power supply is set to 4.6V.
In the following cases, the determination signal L is set to 0.

The control signal is calculated by an AND operation of the determination signal H and the determination signal L, that is, the voltage of the external 5V power supply is less than 5.3V, and the voltage of the external 5V power supply exceeds 4.6V. When the voltage of the external 5V power supply is equal to or higher than 5.3V or when the voltage of the external 5V power supply is equal to or lower than 4.6V, it is set to 0.

When the control signal is 1, that is, when the voltage of the external 5V power supply is less than 5.3V and the voltage of the external 5V power supply exceeds 4.6V, the relay 52 switches the external 5V power supply to the 5V power supply. Output as When the control signal is 0, that is, when the voltage of the external 5 V power supply is 5.3 V or higher, or when the voltage of the external 5 V power supply is 4.6 V or lower, the relay 52 uses the bus 5 V power supply as a 5 V power supply. Output.

That is, the USB hub 2 is connected to the jack 34
When the external power is supplied via the external power supply, the voltage of the external power is less than 5.3 V, and the voltage of the external power is 4.6.
When the voltage exceeds V, an external 5V power supply is output as a 5V power supply, so that an expensive regulator or the like is not required. Therefore, the USB hub 2 can be manufactured at low cost. Further, the USB hub 2 does not cause power loss due to the regulator.

The USB hub 2 is connected to an AC power adapter that supplies power of 5.3 V or more.
Since no external power is supplied to the USB port 31, the USB port 31
The device connected to the port 31 does not break down.

Although the description has been made on the assumption that the USB hub 2 supplies a predetermined current based on 1 A, a device having a USB port such as the personal computer 1 supplies a predetermined current based on 1 A. Is also good. The number of the USB ports 31 for supplying a predetermined current based on 1A is not limited to two, and a desired number of USB ports 31 for supplying a predetermined current based on 1A may be provided.

Although the USB hub 2 generates the reference voltage based on the bus 5V power supply, the USB hub 2 may generate the reference voltage using a regulator.

Note that the present invention is not limited to USB,
(Institute of Electrical and Electronic Engineers
) Any bus that supplies power to connected devices, such as a bus specified by 1394, can be applied.

In this specification, the system is
It represents the entire device composed of a plurality of devices.

[0082]

According to the connection device of the first aspect and the connection method of the third aspect, power is input from the second device, external power is input, and the voltage of the external power is normal. It is determined whether or not the voltage of the external power supply is normal, if the external power supply is selected and supplied to the first device, and if it is determined that the voltage of the external power supply is not normal, The power input from the second device is selected and the first
Power supply, so that it can be manufactured inexpensively, prevent loss of power, and even if power of the wrong voltage is supplied, it is connected to itself or Equipment can be prevented from being destroyed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating one embodiment of a USB hub according to the present invention.

FIG. 2 is a diagram illustrating the appearance of the USB hub 2.

FIG. 3 is a diagram illustrating a connection mode of a USB hub 2.

FIG. 4 is a diagram illustrating a connection mode of a USB hub 2.

FIG. 5 is a diagram illustrating a configuration example of a USB hub 2.

FIG. 6 is a diagram illustrating a power supply path configured by a relay 52, an overcurrent protection circuit 56, and a downstream port 57.

FIG. 7 shows a 500 mA protection circuit 71 and a 1 A protection circuit 7
FIG. 2 is a diagram illustrating a more detailed configuration example of FIG.

FIG. 8 shows a 500 mA protection circuit 71 and a 1 A protection circuit 7
FIG. 3 is a diagram for explaining another more detailed configuration example of FIG.

FIG. 9 shows, for example, a 500 mA protect I with two circuits corresponding to the 500 mA protectors 92-1 and 92-2.
It is a figure explaining C111.

FIG. 10 is a block diagram illustrating a configuration of an allowable input voltage detection circuit 51.

11 is a circuit diagram illustrating a configuration example of an allowable input voltage detection circuit 51. FIG.

FIG. 12 is a diagram illustrating the operation of an allowable input voltage detection circuit 51.

[Explanation of symbols]

1 personal computer, 2 USB hub, 3
USB floppy disk drive, 4 USB mouse, 5 AC power adapter, 31-1 to 31
-4 USB port, 32-1 to 32-4 port LED lamp, 33 USB type B port, 34
Jack, 35 power LED lamp, 51 allowable input voltage detection circuit, 52 relay, 53 upstream port, 54 hub control section, 55
DC-DC converter, 56 overcurrent protection circuit,
57 downstream port, 61 control unit, 7
1 500mA protection circuit, 72 1A protection circuit, 9
1-1 and 91-2500 mA protector, 92-
1 to 92-4 500 mA protector, 101-1
And 101-2 1A protector, 152 maximum threshold input determination circuit, 153 minimum threshold input determination circuit, 154 AND circuit

Claims (3)

[Claims] 1. A connection device for inputting and outputting data to and from a connected first device and a second device, and for supplying power to the first device, wherein power is input from the second device. First power input means, second power input means for inputting external power, determination means for determining whether the voltage of the external power is normal, and that the voltage of the external power is normal If determined, the external power source is selected and supplied to the first device, and if it is determined that the voltage of the external power source is not normal, the power source input from the second device is selected. And a selection supply unit for supplying the first device with the selection device. 2. The connection device according to claim 1, wherein the determination unit determines whether the voltage of the external power supply is normal based on an upper limit value and a lower limit value of the voltage. 3. A connection method of a connection device for inputting / outputting data to / from a first device and a second device connected thereto and supplying power to the first device, wherein a power source is supplied from the second device. A first power input step of inputting an external power, a second power input step of inputting an external power, a determining step of determining whether or not the voltage of the external power is normal, and a voltage of the external power being normal. Is determined, the external power supply is selected and supplied to the first device, and when it is determined that the voltage of the external power supply is not normal, the power input from the second device is determined. Selecting and supplying the selected device to the first device.