Field of the Invention
The present invention relates to a DC connection
device suitable for DC power distribution systems such as a
solar photovoltaic power generator or a household fuel cell.
Background of the Invention
Recently, DC power distribution systems such as a
solar photovoltaic power generator and a household fuel cell
have been used in common households. The power voltage of
these DC power distribution systems is 400 V or so, which is
higher than 100 V or 200 V that is the power voltage of
conventional DC power distribution systems. As known in the
art, if the voltage of a power source increases, an electric
arc is generated when a connection device such as a
connector or an outlet is connected or disconnected.
Particularly, if, in case of DC power, an electric arc is
generated when a connection device is disconnected, current
is not easily cut off, and continuously flows through a
load. Hence, there is a problem of safety. Here, there has
been proposed a DC connection device having a capacitor
connected between terminals of a plug for DC connection to
prevent an electric arc from being generated when the plug
is pulled out of an outlet, as described in Japanese Patent

Application Publication No. 2009-146783. According to this
DC connection device, when the plug is pulled out of the
outlet, an electric charge charged in the capacitor is
discharged, and the voltage across the terminals of the plug
is almost equalized to the voltage across the terminals of
the outlet by the discharged current, thereby preventing the
generation of an electric arc.
Since the DC connection device has a simple structure,
it is possible to provide a small and low-priced DC
connection device. However, since the capacitor is provided
only at the plug in a load side, it is not possible to
prevent an electric arc from being generated when the plug
is inserted into the outlet.
Summary of the Invention
In view of the above, the present invention provides a
DC connection device capable of preventing an electric arc
from being generated when a plug is inserted into and
removed from an outlet.
In accordance with an aspect of the invention, there
is provided a DC connection device including a first
connector connected to a DC power source or a load; and a
second connector connected to the first connector, wherein
the first connector or the second connector has a
semiconductor switch that is turned on when a portion of at

least one of terminals of one of the first and second
connectors is brought into contact with a terminal of the
other of the first and second connectors, and is turned off
before the terminal of the one of the first and second
connectors is completely separated from the terminal of the
other of the first and second connectors.
In accordance with another aspect of the invention,
there is provided a DC connection device including a first
connector connected to a DC power source or a load, the
first connector having a pair of first connection terminals;
and a second connector connected to the first connector, the
second connector having a pair of second connection
terminals to be electrically connected to the first
connection terminals, wherein the first connector includes a
semiconductor switch connected in series between the DC
power source or the load and any one of the first connection
terminals; a connection-state detecting unit for detecting a
relative positional relationship between the second
connection terminal and the first connection terminal; and a
control circuit for turning on or off the semiconductor
switch according to a result detected by the connection-
state detecting unit, wherein the connection-state detecting
unit detects a change in the relative position of the second
connection terminal to the first connection terminal, and
wherein the control circuit turns on and off the
semiconductor switch when the relative position of the

second connection terminal to the first connection terminal
ensures that the first connection terminal and the second
connection terminal are electrically connected.
In the above configuration, to ensure that the first
connection terminal and the second connection terminal are
electrically connected preferably means a position where the
second connection terminal cannot relatively move any more
with respect to the first connection terminal in the
connection direction of the second connection terminal to
the first connection terminal, or in the vicinity just
before the position.
Preferably, the control circuit turns off the
semiconductor switch while the relative position of the
second connection terminal to the first connection terminal
is moved from a state where an electrical connection between
the first connection terminal and the second connection
terminal is completed to a state where an electrical
disconnection between the first connection terminal and the
second connection terminal is completed.
Preferably, the connection-state detecting unit is
provided at the position in which the second connection
terminal cannot relatively move any more with respect to the
first connection terminal in the connection direction of the
second connection terminal to the first connection terminal
or in the vicinity just before the position, and includes a
mechanical switch to be brought into contact with the second

contacting terminal.
Preferably, the connection-state detecting unit is provided
at the position in which the second connection terminal
cannot relatively move any more with respect to the first
connection terminal in the connection direction of the
second connection terminal to the first connection terminal
or in the vicinity just before the position, and includes an
optical sensor having a light emitting and light receiving
elements for detecting the existence of the second
connection terminal.
Preferably, the connection-state detecting unit
includes a sensor or a switch provided in a main body of the
first connector to detect that a main body of the second
connector comes into contact with the main body of the first
connector.
Preferably, the first connector has a current
detection circuit for detecting a current flowing through
the load, and the control circuit turns off the
semiconductor switch when a current value detected by the
current detection circuit exceeds a predetermined current
threshold value and turns on the semiconductor switch when
the current value becomes less than or equal to the current
threshold value.
Preferably, the first connector has a voltage
detection circuit for detecting a voltage applied to the
load, and the control circuit turns off the semiconductor

switch when a voltage value detected by the voltage
detection circuit exceeds a predetermined voltage threshold
value and turns on the semiconductor switch when the voltage
value becomes less than or equal to the voltage threshold
value.
Preferably, the first connector has a current
detection circuit for detecting a current flowing through
the load and a voltage detection circuit for detecting a
voltage applied to the load. The semiconductor switch has
two FETs connected in series so that sources and drains of
the two FETs are opposed to each other. The control circuit
turns off one of the two FETs when a current value detected
by the current detection circuit exceeds a predetermined
current threshold value, and turns on the one of the two
FETs when the current value becomes less than or equal to
the current threshold value. The control circuit turns off
the other of the two FETs when a voltage value detected by
the voltage detection circuit exceeds a predetermined
voltage threshold value, and turns on the other of the two
FETs when the voltage value becomes less than or equal to
the voltage threshold value.
Preferably, the first connector has a current
detection circuit for detecting a current flowing through
the load and a voltage detection circuit for detecting a
voltage applied to the load. The semiconductor switch is a
bidirectional switching element having a lateral transistor

structure using a GaN/AlGaN structure. The control circuit
turns off the bidirectional switching element when a current
value detected by the current detection device exceeds a
predetermined current threshold value or when a voltage
value detected by the voltage detection circuit exceeds a
predetermined voltage threshold value and turns on the
bidirectional switching element when the current value
becomes less than or equal to the current threshold value or
when the voltage value becomes less than or equal to the
voltage threshold value.
Preferably, the control circuit has a timer, and the
control circuit detects, by using the timer, a time duration
during which the current value detected by the current
detection circuit exceeds the current threshold value and
turns off the semiconductor switch when the time duration
exceeds a predetermined time threshold value.
Preferably, the first connector further includes a
contact switching device connected in series between the
first connection terminals and the semiconductor switch.
Preferably, the control circuit turns on the
semiconductor switch after the electrical connection between
the first connection terminal and the second connection
terminal is completed and the contact switching device is
turned on.
Preferably, the control circuit turns off the contact
switching device after the semiconductor switch is turned

off while the relative position of the second connection
terminal to the first connection terminal is moved from the
state where the electrical connection between the first
connection terminal and the second connection terminal is
completed to the state where the electrical disconnection
between the first connection terminal and the second
connection terminal is completed.
Preferably, the movement of the second connection
terminal to the first connection terminal includes any one
of a liner motion and a rotary motion or both the linear and
rotary motions, and the control circuit turns on the contact
switching device after the second connection terminal cannot
relatively move any more with respect to the first
connection terminal in the connection direction of the
second connection terminal to the first connection terminal.
Preferably, the first connector further includes a
fixing mechanism for fixing the state where the second
connection terminal cannot relatively move any more with
respect to the first connection terminal in the connection
direction of the second connection terminal to the first
connection terminal, and the control circuit turns on and
off the contact switching device while the second connection
terminal is fixed to the first connection terminal by the
fixing mechanism.
Preferably, the first connector further includes a
pair of third connection terminals to be connected to an AC

power source or the load.
Preferably, the first connector further includes an AC
circuit breaker connected in series between the AC power
source side and any one of the pair of third connection
terminals, an AC grounding current detection circuit for
detecting a grounding current flowing in an AC circuit
between the AC power source and the load or another load,
and a DC grounding current detection circuit for detecting a
grounding current flowing in a DC circuit between the DC
power source and the load, and the control circuit turns off
both the semiconductor switch connected to the DC power
source and the AC circuit breaker connected to the AC power
source when the grounding current is detected by any one of
the DC grounding current detection circuit and the AC
grounding current detection circuit.
Preferably, the DC grounding current detection circuit
and the AC grounding current detection circuit are at least
partially common.
In accordance with the present invention, a
semiconductor switch is turned on/off only in a state where
a portion of a terminal (first connection terminal) of the
first connector is connected with a terminal (second
connection terminal) of the second connector. For example,
when the second connector (e.g., a plug) is connected to the
first connector (e.g., an outlet), the semiconductor switch
is not turned on until the terminal of the first connector

and the terminal of the second connector are electrically
connected to each other, so that no electric arc is
generated between the terminal of the first connector and
the terminal of the second connector. In addition, when the
second connector is removed from the first connector, the
semiconductor switch is first turned off, and the terminal
of the first connector is then disconnected from the
terminal of the second connector, so that no electric arc is
generated between the terminal of the first connector and
the terminal of the second connector. The contact state
between the terminal of the first connector and the terminal
of the second connector can be detected, for example, by a
sensor provided in the first connector, or the like.
Brief Description of the Drawings
Fig 1 is a block diagram showing a general
configuration of a DC connection device in accordance with
an embodiment of the present invention;
Fig. 2 is a view showing a specific configuration of a
connection-state detecting unit in the DC connection device;
Fig. 3 is a view showing another specific
configuration of the connection-state detecting unit in the
DC connection device;
Fig. 4 is a view showing still another specific
configuration of the connection-state detecting unit in the

DC connection device;
Fig. 5 is a block diagram showing a configuration of a
modification of the DC connection device;
Fig 6 is a view showing an exemplary circuit
configuration of a semiconductor switch using FETs;
Fig 7 is a view showing an exemplary circuit
configuration of a semiconductor switch using a
bidirectional switching element having a lateral transistor
structure using a GaN/AlGaN structure, instead of two FETs;
Fig 8 is a plan view showing a configuration of a
bidirectional switching element (single gate);
Fig. 9 is an enlarged view of area A in FIG. 8;
Fig. 10 is a sectional view taken along line X-X in
FIG. 8;
Fig. 11 is a plan view showing a configuration of a
bidirectional switching element (dual gate);
Fig. 12 is a sectional view taken along line XII-XII
in FIG. 11;
Fig. 13 is a block diagram showing a configuration of
another modification of the DC connection device;
Fig. 14 is a view showing an example of a method of
connecting and disconnecting a first connector (plug) to and
from a second connector (outlet);
Fig. 15 is a view showing an example of a mechanism
for fixing the first connector (plug) to the second
connector (outlet);

Fig. 16 is a block diagram showing still another
modification of the DC connection device;
Fig. 17 is a block diagram showing still another
modification of the DC connection device; and
Fig. 18 is a block diagram showing still another
modification of the DC connection device.
Detailed Description of the Embodiments
Hereinafter, embodiments of the present invention will
be described in detail with reference to the accompanying
drawings which form a part hereof. Throughout the drawings,
like reference numerals are used to designate like or
similar parts and redundant descriptions thereof will be
omitted.
A DC connection device in accordance with an
embodiment of the present invention will be described. The
DC connection device includes a first connector connected to
a DC power source side or a load side and a second connector
connected to the first connector. The first connector has a
pair of first connection terminals, and the second connector
has a pair of second connection terminals electrically
connected to the respective first connection terminals. The
shape and the use of the first connector and the second
connector are not particularly limited, and the shape and
the engagement of the first connection terminal and the

second connection terminal are also not limited. For
convenience, as described below, a connector which includes
a semiconductor switch, a connection-state detecting unit
and a control circuit is referred to as the first connector,
and a connector includes none of them therewith is referred
to as the second connector.
FIG 1 is a block diagram showing a general
configuration of a DC connection device 1 in accordance with
an embodiment of the present invention. In FIG. 1, for
example, an outlet 10 provided in a wall 4 of a building is
illustrated as the first connector, and a plug 20 is
illustrated as the second connector. The outlet 10 is
connected to a DC power source 2, and the plug 20 is
connected to a load 3 driven by DC power, for example, via a
cable. The plug 20 has a pair of second connection
terminals 21 and 22 protruding from a main body 20a of the
plug 2 0. The outlet 10 has a pair of first connection
terminals 11 and 12 electrically connected to the respective
second connection terminals 21 and 22 of the plug 20, and a
semiconductor switch (SW) 13 connected in series between the
DC power source 2 and any one (e.g., the first connection
terminal 11) of the pair of first connection terminals 11
and 12. Also, the outlet 10 has a connection-state
detecting unit 14 for detecting a relative positional
relationship between the second connection terminals 21 and
22 and the first connection terminals 11 and 12, and a

control circuit 15 for turning on or off the semiconductor
switch according to a result detected by the connection-
state detecting unit 14.
The semiconductor switch 13 is, for example, a
semiconductor switch element such as a field effect
transistor (FET), and the control circuit 15 controls the
gate voltage of the FET according to a result detected by
the connection-state detecting unit 14. The configuration
of the connection-state detecting unit 14 is not
particularly limited, but may detect a change in the
relative position of the second connection terminals 21 and
22 of the plug 20 with respect to the first connection
terminals 11 and 12 of the outlet 10 when the plug 20 is
connected to and removed from the outlet 10.
As shown in FIG. 2, the connection-state detecting
unit 14 is provided at a position in which the second
connection terminals 21 and 22 cannot relatively move any
more with respect to the first connection terminal 11 and 12
in the connection direction of the second connection
terminal 21 and 22 to the first connection terminal 11 and
12 or in the vicinity just before the position. The
connection-state detecting unit 14 may be configured to
include a mechanical switch 31 which comes in contact with
the second connection terminal 21 or 22.
When the plug 20 is connected to the outlet 10, the
second connection terminal 21 or 22 is brought into contact

with the mechanical switch 31 at a position where the second
connection terminal 21 or 22 cannot relatively move any more
with respect to the first connection terminal 11 or 12 in
the connection direction of the second connection terminal
21 and 22 to the first connection terminal 11 and 12 or in
the vicinity just before the position, so that the
mechanical switch 31 is turned on or off. Thus, the control
circuit 15 can ensure that the first connection terminal 11
or 12 has been electrically connected to the second
connection terminal 21 or 22, whereby the semiconductor
switch 13 is turned on.
That is, when the plug 20 is connected to (put into)
the outlet 10, a potential difference between the second
connection terminal 21 or 22 of the plug 20 and the first
connection terminal 11 or 12 of the outlet 10 is small, and
therefore, no electric discharge between the first
connection terminal 11 or 12 and the second connection
terminal 21 or 22 occurs.
Meanwhile, when the plug 2 0 is removed from (pulled
out of) the outlet 10, slight displacement of the second
connection terminal 21 or 22 in a reverse direction with
respect to the first connection terminal 11 or 12 separates
the second connection terminal 21 or 22 from the mechanical
switch 31, so that the mechanical switch 31 is turned off or
on. In this step, the first connection terminal 11 or 12
remains electrically connected to the second connection

terminal 21 or 22. For this reason, the control circuit 15
rapidly turns off the semiconductor switch 13 before the
first connection terminal 11 or 12 is completely
disconnected from the second connection terminal 21 or 22.
That is, when the plug 20 is removed from (pulled out of)
the outlet 10, the semiconductor switch 13 is first turned
off, and then, the potential of the first connection
terminal 11 or 12 becomes equal to that of the second
connection terminal 21 or 22. Thus, no electrical discharge
occurs between the first connection terminal 11 or 12 and
the second connection terminal 21 or 22.
Alternatively, as shown in FIG. 3, the connection-
state detecting unit 14 may be configured to include an
optical sensor 32 having a light emitting element 32a and a
light receiving element 32b, which are provided at
substantially the same position as that of the mechanical
switch 31. In this case, the second connection terminal 21
or 22 blocks the light emitted from the light emitting
element 32a at a position where the second connection
terminal 21 or 22 cannot relatively move any more with
respect to the first connection terminal 11 or 12 in the
connection direction of the second connection terminal 21
and 22 to the first connection terminal 11 and 12 or in the
vicinity just before the position. Thus, an output signal
of the light receiving element 32b changes from a high level
to a low level. Accordingly, the control circuit 15 can

ensure that the first connection terminal 11 or 12 has been
electrically connected to the second connection terminal 21
or 22, whereby the semiconductor switch 13 is turned on.
Meanwhile, in the case where the plug 20 is removed from
(pulled out of) the outlet 10, when the second connection
terminal 21 or 22 is slightly displaced in a reverse
direction with respect to the first connection terminal 11
or 12, the light emitted from the light emitting element 32a
enters the light receiving element 32b. Then, the output
signal of the light receiving element 32b changes from a low
level to a high level, and thus, the control circuit 15
turns off the semiconductor switch 13.
Alternatively, as shown in FIG. 4, the connection-
state detecting unit 14 may be configured to include a
projection 23 provided on the main body 20a of the plug 20,
a push-on switch 33 provided in the outlet 10, and the like.
In this case, when the plug 20 is connected to the outlet 10
and the main body 20a of the plug 20 comes into contact with
a main body 10a of the outlet 10, the projection 23 turns on
the push-on switch 33. Accordingly, the control circuit 15
can ensure that the first connection terminal 11 or 12 has
been electrically connected to the second connection
terminal 21 or 22, whereby the semiconductor switch 13 is
turned on. Note that, without the projection on the main
body 2 0a of the plug 20, the connection-state detecting unit
14 may be configured so that a front end portion of the

push-on switch 33 protrudes out of the main body 10a of the
outlet 10. However, the connection-state detecting unit 14
is preferably configured as shown in Fig. 4, in
consideration of children's mischief. A sensor for
detecting whether or not the main body 20a of the plug 20 is
in contact with the main body 10a of the outlet 10 may be
used instead of the push-on switch 33.
FIG. 5 shows a modification of the DC connection
device 1 according to this embodiment. In this
modification, the outlet 10 further includes a current
detection circuit (A) 41 for detecting current flowing
through the load 3 and a voltage detection circuit (V) 42
for detecting voltage applied to the load 3. Further, at
least one current threshold value and at least one voltage
threshold value are determined in the control circuit 15.
When the current value detected by the current detection
circuit (A) 41 exceeds the current threshold value, the
control circuit 15 controls the semiconductor switch 13 to
be turned off. When the current value becomes less than or
equal to the current threshold value, the control circuit 15
controls the semiconductor switch 13 to be turned on.
Depending on the kind of loads driven by DC power, a
transient current (rush current) may flow when the power is
supplied. For example, in a case where an FET (field effect
transistor) is used as the semiconductor switch 13, this
semiconductor switch 13, the current detection circuit (A)

41, and the control circuit 15 may configure a rush current
prevention circuit. The control circuit 15 controls a duty
ratio of the FET, thereby suppressing the rush current. In
addition, when the voltage value detected by the voltage
detection circuit (V) 42 exceeds the voltage threshold
value, the control circuit 15 controls the semiconductor
switch 13 to be turned off. When the voltage value becomes
less than or equal to the voltage threshold value, the
control circuit 15 controls the semiconductor switch 13 to
be turned on. For example, when another load is connected
to the DC power source 2 via another outlet or the like to
lower the voltage of the power source, or when the DC power
source is stopped, the voltage on the load 3 side
instantaneously increases, and a reverse current flows from
the load 3 side to the DC power source 2 side. In a case
where the FET is used as the semiconductor switch 13, this
semiconductor switch 13, the voltage detection circuit 42,
and the control circuit 15 may configure a reverse current
prevention circuit. When a reverse transient voltage is
generated, the semiconductor switch 13 is turned off,
thereby preventing the reverse current from flowing from the
load 3 side to the DC power source 2 side. Both the current
detection circuit (A) 41 and the voltage detection circuit
(V) 42 need not be provided, but either one of both the
circuits may be provided.
FIG. 6 shows an exemplary circuit configuration using

FETs as the semiconductor switch 13. The semiconductor
switch 13 is configured to connect, in series, two FETs 131
and 132 whose sources and drains are opposed to each other.
The control circuit 15 includes an IC 141 integrally formed
with the current detection circuit (A) 41 and a gate control
circuit of the FET 131; and an IC 142 integrally formed with
the voltage detection circuit (V) 42 and a gate control
circuit of the FET 132. As such, the two FETs as the
semiconductor switch are reversely connected to each other,
and are independently controlled, thereby simultaneously
preventing both the transient current (rush current) and the
reverse current. In addition, a function of a timer may be
further provided in the IC 141, and a time threshold value
may be further set therein. The IC 141 (control circuit)
detects a time duration during which the current value
detected by the current detection circuit (A) 41 exceeds the
current threshold value, and turns off the FET 131 when the
detected time duration exceeds the time threshold value.
Accordingly, the DC power distribution system can be
protected from transient current caused by a short circuit
of the load, or the like. Similarly, the FET 132 is
controlled to be turned off when the voltage value detected
by the voltage detection circuit (V) 142 exceeds the voltage
threshold value, and the FET 132 is controlled to be turned
on when the voltage value becomes less than or equal to the
voltage threshold value. By doing so, it is possible to

prevent reverse current from flowing from the load 3 side to
the DC power source 2 side.
FIG. 7 shows an exemplary circuit configuration using
a bidirectional switching element 100 having a lateral
transistor structure using a GaN/AlGaN structure instead of
the aforementioned two FETs, as the semiconductor switch 13.
Since the FET has a diode structure, a current flows when a
forward voltage is applied to the diode regardless of a gate
voltage. For this reason, as described above, the two FETs
should be connected in series so as to apply a reverse
voltage to the diode. On the other hand, since the
bidirectional switching element has no diode structure, the
same function can be performed using only one element.
Advantageously, the bidirectional switching element having
the lateral transistor structure using the GaN/AlGaN
structure has no loss due to the diode structure, whereby
its loss is lowered as compared with the FET, and also can
integrate the control circuits. That is, the control can be
performed using an IC 143 in which the current detection
circuit (A) 41, the voltage detection circuit (V) 42, the
control circuit 15 and the timer are integrated.
The bidirectional switching element 100 having the
lateral transistor structure using the GaN/AlGaN structure
will be described in detail with reference to FIGS, 8 to 10.
FIG. 8 is a plan view showing the configuration of the
bidirectional switching element 100, FIG. 9 is an enlarged

view of area A, and FIG. 10 is a sectional view taken along
line X-X in FIG. 8. The bidirectional switching element 100
is provided with only one gate G between two electrodes Dl
and D2 and is therefore referred to as a single gate type.
As shown in FIG. 10, a substrate 101 of the
bidirectional switching element 100 includes a conductor
layer 101a, and a GaN layer 101b and an AlGaN layer 101c
which are laminated on the conductor layer 101a. In this
embodiment, a two-dimensional electron gas layer generated
on an AlGaN/GaN heterogeneous interface is used as a channel
layer. As shown in FIG. 8, on a surface 10 Id of the
substrate 101, there are formed a first electrode Dl and a
second electrode D2 respectively connected in series to the
DC power source 2 and the load 3; and an intermediate
potential portion S that has an intermediate potential
between a potential of the first electrode Dl and a
potential of the second electrode D2. In addition, a
control electrode {gate} G is formed on the intermediate
potential portion S. For example, a schottky electrode is
used as the control electrode G, The first electrode Dl and
the second electrode D2 are formed in comb shapes having
electrode portions 111, 112, 113, ... and electrode portions
121, 122, 123, ... arranged in parallel with one another,
respectively. The comb-shaped electrode portions of the
first electrode Dl are arranged opposite to those of the
second electrode. The intermediate potential portion S and

the control electrode G are arranged between the comb-shaped
electrode portions 111, 112, 113, ... and 121, 122, 123, ..., to
have a shape (a shape of a backbone of a fish) similar to
the planer shape of a space defined between the electrode
portions.
Next, the lateral transistor structure of the
bidirectional switching element 100 will be described. As
shown in FIG. 9, the electrode portion 111 of the first
electrode Dl and the electrode portion 121 of the second
electrode D2 are arranged so that the center lines of the
electrode portions in the widthwise direction are aligned.
The intermediate potential portion S and the control
electrode G are provided in parallel with the electrode
portion 111 of the first electrode Dl and the electrode
portion 121 of the second electrode D2. The distances from
the electrode portion 111 of the first electrode Dl and the
electrode portion 121 of the second electrode D2 to the
intermediate potential portion S and the control electrode G
are set so that a predetermined withstand voltage can be
maintained. The distances in the longitudinal direction of
the electrode portion 111 of the first electrode Dl and the
electrode portion 121 of the second electrode D2, i.e.,
perpendicular to the widthwise direction are also set in the
same manner.
In addition, such a relationship is similarly applied
to the other electrode portions 112, 113, ... and 122, 123, ....

That is, the intermediate potential portion S and the
control electrode G are arranged at a position where the
predetermined withstand voltage can be maintained with
respect to the first electrode Dl and the second electrode
D2.
For this reason, assuming that the first electrode Dl
is in a high potential side and the second electrode D2 is
in a low potential side, when the bidirectional switching
element 100 is turned off, a current is completely
interrupted between at least the first electrode Dl, the
control electrode G and the intermediate potential portion
S (the current is blocked immediately below the control
electrode (gate) G).
Meanwhile, when the bidirectional switching element
100 is turned on, i.e., when a signal having a voltage of a
predetermined threshold value or more is applied to the
control electrode G, a current flows along the path of the
first electrode Dl (electrode portions 111, ...) , the
intermediate potential portion S and the second electrode D2
(electrode portions 121, ...) as shown by arrows in FIG. 9,
and vice versa. As a result, even if the threshold voltage
of the signal applied to the control electrode G is lowered
to a desired minimum level, the bidirectional switching
element 100 can be surely turned on/off, thereby enabling a
low on-resistance. Further, since the electrode portions
111, 112, 113, ... of the first electrode Dl and the electrode

portions 121, 122, 123, ... of the second electrode D2 can be
arranged in a comb shape, high current can be obtained
without enlarging a chip size of the bidirectional switching
element 100.
FIGS. 11 and 12 show a configuration of another
bidirectional switching element 300 having a lateral
transistor structure using the GaN/AlGaN structure. FIG. 11
is a plan view showing the configuration of the
bidirectional switching element 300, and FIG. 12 is a
sectional view taken along line XII-XII in FIG. 11. The
bidirectional switching element 300 is provided with two
gates Gl and G2 between two electrodes Dl and D2, and
therefore, is referred to as a dual gate transistor.
As shown in FIGS. 11 and 12, the bidirectional
switching element 300 having the dual gate transistor
structure is configured to have a single portion for
maintaining a withstand voltage, so that it is possible to
implement a bidirectional element with a small loss. That
is, each of the drain electrodes Dl and D2 is formed to
reach the GaN layer, and each of the gate electrodes Gl and
G2 is formed on the AlGaN layer. In a state where no
voltage is applied to the gate electrodes Gl and G2, an
electron depletion region occurs in the two-dimensional
electron gas layer generated on the AlGaN/GaN heterogeneous
interface immediately below the gate electrodes Gl and G2,
and current does not flows. Meanwhile, when a voltage is

applied to the gate electrodes Gl and G2, a current flows
toward the drain electrode D2 from the drain electrode Dl
(or reversely) in the AlGaN/GaN heterogeneous interface. To
obtain a withstand voltage between the gate electrodes Gl
and G2, a predetermined distance is required between the
gate electrodes Gl and G2. However, no withstand voltage is
required between the drain electrode Dl and the gate
electrode Gl, and between the drain electrode D2 and the
gate electrode G2. For this reason, the drain electrode Dl
and gate electrode Gl, or the drain electrode D2 and gate
electrode G2 may be overlapped with each other through an
insulation layer In interposed therebetween. The element
with such a configuration needs to be controlled based on
the voltages of the drain electrodes Dl and D2, and driving
signals are necessarily input to the respective gate
electrodes Gl and G2 (hence, the element is referred to as a
dual gate transistor structure).
FIG. 13 shows another modification of the DC
connection device 1 according to this embodiment. In this
modification, the outlet 10 further includes a contact
switching device 16 connected in series between the first
connection terminals 11 and 12 and the semiconductor switch
13. The control circuit 15 turns on the semiconductor
switch 13 after the electrical connection between the first
connection terminals 11 and 12 and the second connection
terminals 21 and 22 is completed and the contact switching

device 16 is turned on. Also, the control circuit 15 turns
off the contact switching device 16 after the semiconductor
switch 13 is turned off while the relative position of the
second connection terminal 21 or 22 to the first connection
terminal 11 or 12 is moved from a state where an electrical
connection between the first connection terminal 11 or 12
and the second connection terminal 21 or 22 is completed to
a state where an electrical disconnection between the first
connection terminal 11 or 12 and the second connection
terminal 21 or 22 is completed. For example, a relay,
breaker, or the like may be used as the contact switching
device 16. As such, in a state where the plug 20 is not
connected to the outlet 10, contact points of the contact
switching device 13 are opened, and the first connection
terminals 11 and 12 of the outlet 10 are physically
disconnected from the DC power source 2. For this reason,
even though the semiconductor switch 13 is broken, it is
possible to ensure safety. Further, although chattering
occurs when the plug 2 0 is connected to or separated from
the outlet 10, it is possible to prevent electric discharge
from being generated between the first connection terminals
11 and 12 and the second connection terminals 21 and 22.
A method of connecting and disconnecting the plug 2 0
to and from the outlet 10, i.e., the movement of the second
connection terminal 21 or 22 with respect to the first
connection terminal 11 or 12 may be implemented not only

through a linear motion such as a typical insertion and
separation, but also through a rotary motion or a
combination of the rotary motion and the linear motion, for
example, as shown in FIG. 14. After the connection of the
plug 20 to the outlet 10 is completed, i.e., after the
second connection terminal 21 or 22 cannot relatively move
any more with respect to the first connection terminal 11 or
12 in the connection direction of the second connection
terminal 21 and 22 to the first connection terminal 11 and
12, the control circuit 15 turns on the contact switching
device 16, and then, turns on the semiconductor switch 13.
In a case where the outlet 10 does not have the contact
switching device 16, the control circuit 15 turns on the
semiconductor switch 13 after the second connection terminal
21 or 22 cannot relatively move any more with respect to the
first connection terminal 11 or 12 in the connection
direction of the second connection terminal to the first
connection terminal in the connection direction of the
second connection terminal 21 and 22 to the first connection
terminal 11 and 12.
In addition, as shown in FIG. 15, there may be
provided a mechanism for fixing the plug 20 to the outlet 10
after the plug 20 is connected to the outlet 10. For
example, locking hooks 24 are respectively provided at both
side portions of the main body 20a of the plug 20, and
locking holes 17 are provided in the main body 10a of the

outlet 10. A switch 34 is also provided near the locking
hole 17 in the main body 10a of the outlet 10. If the plug
2 0 is connected to (inserted into) the outlet 10, the
locking hooks 24 are deformed due to the elasticity of
resin, thereby being fitted into the locking holes 17.
Then, the locking hooks 24 are locked to the locking holes
17 by the elastically restoring force. Accordingly, the
plug 20 is fixed to the outlet 10. Simultaneously, a front
end portion of the locking hook 24 is brought into contact
with the switch 34, and the switch 34 is turned on. After
the switch 34 is turned on, the control circuit 15 turns on
the contact switching device 16, and then, turns on the
semiconductor switch 13. In order to remove the plug 20
from the outlet 10, a user presses both the locking hooks 24
toward the main body 20 to deform them. By doing so, the
front end portion of the locking hook 2 4 is separated from
the switch 34, and the switch 34 is turned off. If the
switch 34 is turned off, the control circuit 15 immediately
turns off the semiconductor switch 13, and then, also turns
off the contact switching device 16. In this state, the
user pulls out the plug 20 from the outlet 10. The fixing
mechanism is not limited to that shown in this figure, but
other structures may be applied. That is to say, the
control circuit 15 may be configured to turn on/off the
contact switching device 16 while the second connection
terminals 21 and 22 are fixed to the first connection

terminals 11 and 12 by the fixing mechanism.
FIG. 16 shows still another modification of the DC
connection device 1 according to this embodiment. In this
modification, the outlet 10 is configured to have a hybrid
type in which a single outlet 10 is equipped with DC power
distribution and AC power distribution. With the wide use
of a solar photovoltaic power generator or a household fuel
cell, it is expected that an electric device such as an air
conditioner or refrigerator driven directly using DC power
will be developed. However, the solar photovoltaic power
generation is likely to be influenced by weather or season,
and the amount of power generated is unstable. In addition,
the solar photovoltaic power generation cannot be performed
after sunset.
For this reason, a secondary battery is generally used
together with the solar photovoltaic power generator, and
power charged in the secondary battery is used. However,
the power charged in the secondary battery is not enough to
cover the power demanded in all electronic appliances. The
electric appliances with a large power consumption such as
an air conditioner or refrigerator may be designed to have a
hybrid type so as to use the conventional AC power source as
a backup power. Thus, the outlet 10 shown in FIG. 16 is
provided with a pair of third connection terminals 18 and 19
connected to the AC power source 5. Terminals 51 and 52 of
an AC plug 50 are connected to the third connection

terminals 18 and 19.Herein, a voltage as high as 100 V or
200 V is employed in the AC power source 5. However, unlike
the DC power distribution system, even if an arc discharge
occurs when the plug 50 is pulled out of the outlet 10, the
AC power distribution system is easy to extinguish the arc.
Hence, a semiconductor switch is not particularly provided.
The contact switching device 16, for example,
comprising a relay or a breaker is connected in series
between the AC power source 5 and the pair of third
connection terminals 18 and 19 (any one of them is possible)
and functions as an AC circuit breaker. Alternatively,
separately from the contact switching device 16, an AC
circuit breaker may be connected between the AC power source
5 and the pair of third connection terminals 18 and 19. In
addition, the outlet 10 is provided with a DC grounding
current detection circuit (A' ) 4 3 for detecting grounding
current flowing in the DC circuit between the DC power
source 2 and the load 3; and an AC grounding current
detection circuit {A") 44 for detecting grounding current
flowing in the AC circuit between the AC power source 5 and
the load 3. For example, a Hall element or the like may be
used as the DC grounding current detection circuit 43. In
addition, a zero current transformer (ZCT) or the like may
be used as the AC grounding current detection circuit 44.
Alternatively, as shown in FIG. 17, the DC circuit and the
AC circuit may pass through a common core of a single zero

current transformer, whereby the DC grounding current
detection circuit 44 and the AC grounding current detection
circuit 4 4 are partially made common. Accordingly, it is
possible to realize the miniaturization and low cost of the
outlet 10.
When any one of the DC grounding current detection
circuit 43 and the AC grounding current detection circuit 44
detects the grounding current, the control circuit 15 turns
off both the semiconductor switch 13 connected to the DC
power source 2 and the contact switching device 16 (or AC
circuit breaker) connected to the AC power source 5. In
this case, it will be apparent that the off-timing of the
semiconductor switch 13 is sifted to be earlier than the
off-timing of the contact switching device 16 connected to
the DC circuit.
The present invention is not limited to 'the
descriptions of the aforementioned embodiments, and various
modifications and applications are possible. FIG. 18 shows
an exemplary configuration in which an outlet 10' is also
provided at the side of the load 3 and is connected to the
outlet 10 of the side of the DC power source 2 through a
cable 36. The outlet 10' at the side of the load 3 is
connected to an internal power source (DC/DC converter or
inverter) 35 of the load 3. The plugs 20 and 20' are
respectively connected at both ends of the cable 36. In
this case, the projection-depression of the second

connection terminals 21 and 22 of the plug 20 is reverse to
that of second connection terminals 21' and 22' of the plug
20' . Similarly, the projection-depression of the first
connection terminals 11 and 12 of the outlet 10 is reverse
to that of first connection terminals 11' and 12' of the
outlet 10'. As such, the outlet 10 or 10' that is the first
connector is not necessarily connected to the DC power
source 2, and may be connected to the load 3 or the internal
power source 35 of the load 3. Alternatively, the outlet 10
or 10' may be connected to a circuit breaker or the like of
a power distributing board connected to the DC power source.
The plug 2 0 or 20' that is the second connector is not
necessarily connected directly to the load, and may be
connected to the cable 36 through which the DC power source
2 and the load 3 are connected.
The aforementioned various embodiments can be
implemented by appropriate combination thereof. For
example, the optical sensor shown in FIG. 3 can be applied
to the DC connection device shown in FIG. 16.
While the invention has been shown and described with
respect to the embodiments, the present invention is not
limited thereto. It will be understood by those skilled in
the art that various changes and modifications may be made
without departing from the scope of the invention as defined
in the following claims.

WE CLAIM:
- 1. A DC connection device, comprising:
a first connector connected to a DC power source or a
load; and
a second connector connected to the first connector,
wherein the first connector or the second connector
has a semiconductor switch that is turned on when a portion
of at least one of terminals of one of the first and second
connectors is brought into contact with a terminal of the
other of the first and second connectors, and is turned off
before the terminal of the one of the first and second
connectors is completely separated from the terminal of the
other of the first and second connectors.
2. A DC connection device, comprising:
a first connector connected to a DC power source or a
load, the first connector having a pair of first connection
terminals; and
a second connector connected to the first connector,
the second connector having a pair of second connection
terminals to be electrically connected to the first
connection terminals,
wherein the first connector comprises:
a semiconductor switch connected in series between the
DC power source or the load and any one of the first

connection terminals;
a connection-state detecting unit for detecting a
relative positional relationship between the second
connection terminal and the first connection terminal; and
a control circuit for turning on or off the
semiconductor switch according to a result detected by the
connection-state detecting unit,
wherein the connection-state detecting unit detects a
change in the relative position of the second connection
terminal to the first connection terminal, and
wherein the control circuit turns on and off the
semiconductor switch when the relative position of the
second connection terminal to the first connection terminal
ensures that the first connection terminal and the second
connection terminal are electrically connected.
3. The DC connection device of claim 2, wherein the first
connection terminal and the second connection terminal are
certainly electrically connected at a position where the
second connection terminal cannot relatively move any more
with respect to the first connection terminal in the
connection direction of the second connection terminal to
the first connection terminal, or in the vicinity just
before the position.
4. The DC connection device of claim 3, wherein the

control circuit turns off the semiconductor switch while the
relative position of the second connection terminal to the
first connection terminal is moved from a state where an
electrical connection between the first connection terminal
and the second connection terminal is completed to a state
where an electrical disconnection between the first
connection terminal and the second connection terminal is
completed.
5. The DC connection device of claim 3 or 4, wherein the
connection-state detecting unit is provided at the position
in which the second connection terminal cannot relatively
move any more with respect to the first connection terminal
in the connection direction of the second connection
terminal to the first connection terminal or in the vicinity
just before the position, and the connection-state detecting
unit includes a mechanical switch to be brought into contact
with the second contacting terminal.
6. The DC connection device of claim 3 or 4, wherein the
connection-state detecting unit is provided at the position
in which the second connection terminal cannot relatively
move any more with respect to the first connection terminal
in the connection direction of the second connection
terminal to the first connection terminal or in the vicinity
just before the position, and the connection-state detecting

unit includes an optical sensor having a light emitting
element and a light receiving element for detecting the
existence of the second connection terminal.
7. The DC connection device of any one of claims 2 to 4,
wherein the connection-state detecting unit includes a
sensor or a switch provided in a main body of the first
connector to detect that a main body of the second connector
comes into contact with the main body of the first
connector.
8. The DC connection device of any one of claims 2 to 7,
wherein the first connector has a current detection circuit
for detecting a current flowing through the load, and
wherein the control circuit turns off the
semiconductor switch when a current value detected by the
current detection circuit exceeds a predetermined current
threshold value and turns on the semiconductor switch when
the current value becomes less than or equal to the current
threshold value.
9. The DC connection device of any one of claims 2 to 8,
wherein the first connector has a voltage detection circuit
for detecting a voltage applied to the load, and
wherein the control circuit turns off the
semiconductor switch when a voltage value detected by the

voltage detection circuit exceeds a predetermined voltage
threshold value and turns on the semiconductor switch when
the voltage value becomes less than or equal to the voltage
threshold value.
10. The DC connection device of any one of claims 2 to 7,
wherein the first connector comprises a current detection
circuit for detecting a current flowing through the load and
a voltage detection circuit for detecting a voltage applied
to the load,
wherein the semiconductor switch comprises two FETs
connected in series so that sources and drains of the two
FETs are opposed to each other, and
wherein the control circuit turns off one of the two
FETs when a current value detected by the current detection
circuit exceeds a predetermined current threshold value, and
turns on the one of the two FETs when the current value
becomes less than or equal to the current threshold value;
and the control circuit turns off the other of the two FETs
when a voltage value detected by the voltage detection
circuit exceeds a predetermined voltage threshold value, and
turns on the other of the two FETs when the voltage value
becomes less than or equal to the voltage threshold value.
11. The DC connection device of any one of claims 2 to 7,
wherein the first connector comprises a current detection

circuit for detecting a current flowing through the load and
a voltage detection circuit for detecting a voltage applied
to the load,
wherein the semiconductor switch comprises a
bidirectional switching element having a lateral transistor
structure using a GaN/AlGaN structure, and
wherein the control circuit turns off the
bidirectional switching element when a current value
detected by the current detection device exceeds a
predetermined current threshold value or when a voltage
value detected by the voltage detection circuit exceeds a
predetermined voltage threshold value; and the control
circuit turns on the bidirectional switching element when
the current value becomes less than or equal to the current
threshold value or when the voltage value becomes less than
or equal to the voltage threshold value.
12. The DC connection device of any one of claims 8, 10 and
11, wherein the control circuit comprises a timer, and
wherein the control circuit detects, by using the
timer, a time duration during which the current value
detected by the current detection circuit exceeds the
current threshold value and turns off the semiconductor
switch when the time duration exceeds a predetermined time
threshold value.

13. The DC connection device of any one of claims 2 to 12,
wherein the first connector further comprises a contact
switching device connected in series between the first
connection terminals and the semiconductor switch.
14. The DC connection device of claim 13, wherein the
control circuit turns on the semiconductor switch after the
electrical connection between the first connection terminal
and the second connection terminal is completed and the
contact switching device is turned on.
15. The DC connection device of claim 14, wherein the
control circuit turns off the contact switching device after
the semiconductor switch is turned off while the relative
position of the second connection terminal to the first
connection terminal is moved from the state where the
electrical connection between the first connection terminal
and the second connection terminal is completed to the state
where the electrical disconnection between the first
connection terminal and the second connection terminal is
completed.
16. The DC connection device of any one of claims 13 to 15,
wherein the movement of the second connection terminal with
respect to the first connection terminal includes any one of
a linear motion and a rotary motion or both the linear

motion and the rotary motions, and
wherein the control circuit turns on the contact
switching device after the second connection terminal cannot
relatively move any more with respect to the first
connection terminal in the connection direction of the
second connection terminal to the first connection terminal.
17. The DC connection device of any one of claims 13 to 16,
wherein the first connector further comprises a fixing
mechanism for fixing the state where the second connection
terminal cannot relatively move any more with respect to the
first connection terminal in the connection direction of the
second connection terminal to the first connection terminal,
and
wherein the control circuit turns on and off the
contact switching device while the second connection
terminal is fixed to the first connection terminal by the
fixing mechanism.
18. The DC connection device of any one of claims 2 to 17,
wherein the first connector further comprises a pair of
third connection terminals connected to an AC power source
or the load.
19. The DC connection device of claim 18, wherein the first
connector further comprises an AC circuit breaker connected

in series between the AC power source and any one of the
third connection terminals, an AC grounding current
detection circuit for detecting a grounding current flowing
in an AC circuit between the AC power source and the load or
another load, and a DC grounding current detection circuit
for detecting a grounding current flowing in a DC circuit
between the DC power source and the load, and
wherein the control circuit turns off both the
semiconductor switch connected to the DC power source and
the AC circuit breaker connected to the AC power source when
the grounding current is detected by any one of the DC
grounding current detection circuit and the AC grounding
current detection circuit.
20. The DC connection device of claim 19, wherein the DC
grounding current detection circuit and the AC grounding
current detection circuit are at least partially common.