FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
OVERVOLTAGE DETECTION CIRCUIT
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
Field
[0001] The present disclosure relates to an overvoltage
detection circuit for protecting a power supply circuit from
5 a surge voltage.
Background
[0002] Conventionally, an overvoltage detection circuit
for protecting a circuit from a steep fluctuation of a power
10 supply voltage has been known. Patent Literature 1 discloses
a configuration that includes a first comparison circuit for
high-speed response and a second comparison circuit for lowspeed response, and lowers a setting voltage for a frequency
lower than a response limit frequency and increases the
15 setting voltage for a frequency higher than the response
limit frequency. Furthermore, Patent Literature 1 discloses
a configuration in which an overvoltage detection circuit
has time response characteristics, the setting voltage is
lowered for a long operation time, and the setting voltage
20 is increased for a short operation time.
Citation List
Patent Literature
[0003] Patent Literature 1: Japanese Patent Application
25 Laid-open No. 2003-52120
Summary
Technical Problem
[0004] In the related art, only a DC voltage on a bus
30 voltage side is compared. Therefore, the related art has
problems in that, since a rectifier detects an overvoltage
of a rectified DC voltage, detection sensitivity of
overvoltage protection is poor for a surge voltage that is
3
a steep overvoltage to be superimposed on a power supply
voltage or the like, and protection is delayed.
[0005] The present disclosure has been made in view of
the above, and an object of the present disclosure is to
5 obtain an overvoltage detection circuit for protecting a
power supply circuit from a surge voltage that is a steep
overvoltage to be superimposed on a power supply voltage and
an increase in the power supply voltage for a long time, in
an area where the power supply voltage is unstable.
10
Solution to Problem
[0006] In order to solve the above-described problems and
achieve the object, an overvoltage detection circuit
according to the present disclosure includes a bus voltage
15 detection circuit that detects a bus voltage, a first delay
circuit that delays the bus voltage detected by the bus
voltage detection circuit by a first delay time, a first
comparison unit that outputs a first comparison result
obtained by comparing the bus voltage delayed by the first
20 delay circuit with a first interruption threshold, a power
supply voltage detection circuit that detects a power supply
voltage, a second delay circuit that delays the power supply
voltage detected by the power supply voltage detection
circuit by a second delay time, a second comparison unit
25 that outputs a second comparison result obtained by comparing
the power supply voltage delayed by the second delay circuit
with a second interruption threshold, and a relay that
switches on/off of power reception of an outdoor unit from
an AC power supply on the basis of the first comparison
30 result output from the first comparison unit and the second
comparison result output from the second comparison unit.
The first delay time is longer than the second delay time.
The first interruption threshold is lower than the second
4
interruption threshold.
Advantageous Effects of Invention
[0007] An overvoltage detection circuit according to the
5 present disclosure achieves an effect that the overvoltage
detection circuit can protect a power supply circuit from a
surge voltage that is a steep overvoltage to be superimposed
on a power supply voltage and an increase in the power supply
voltage for a long time, in an area where the power supply
10 voltage is unstable.
Brief Description of Drawings
[0008] FIG. 1 is a diagram illustrating a configuration
of an air conditioner according to a first embodiment.
15 FIG. 2 is a circuit diagram illustrating details of a
power supply overvoltage detection circuit, a bus
overvoltage detection circuit, a relay control unit, and a
relay control circuit included in the air conditioner
according to the first embodiment.
20 FIG. 3 is a time chart of a waveform of a power supply
voltage that increases in the long time and a relay control
signal.
FIG. 4 is a time chart of a waveform of a steep surge
voltage of a power supply system and the relay control signal.
25 FIG. 5 is a flowchart illustrating a procedure of an
operation performed by the air conditioner according to the
first embodiment.
FIG. 6 is a diagram illustrating a configuration of an
overvoltage detection circuit according to a second
30 embodiment.
FIG. 7 is a diagram illustrating a processor in a case
where a part or all of a control unit included in an outdoor
unit of the air conditioner according to the first embodiment
5
is implemented by the processor.
FIG. 8 is a diagram illustrating processing circuitry
in a case where a part or all of the control unit included
in the outdoor unit of the air conditioner according to the
5 first embodiment is implemented by the processing circuitry.
Description of Embodiments
[0009] Hereinafter, an overvoltage detection circuit
according to embodiments will be described in detail with
10 reference to the drawings.
[0010] First Embodiment.
FIG. 1 is a diagram illustrating a configuration of an
air conditioner 1 according to a first embodiment. Although
details will be described later, the air conditioner 1
15 includes an overvoltage detection circuit. The air
conditioner 1 includes an indoor unit 2 and an outdoor unit
3. The indoor unit 2 includes a terminal block 21, a
converter circuit 22, a smoothing capacitor 23, a bus voltage
detection circuit 24, an indoor unit control circuit 25, a
20 relay 26, and a serial communication circuit 27. The indoor
unit control circuit 25 controls a fan of the indoor unit 2,
processes a signal from a remote controller or the like, and
communicates with the outdoor unit 3. The fan and the remote
controller are not illustrated in FIG. 1.
25 [0011] One end of the relay 26 is connected to an AC power
supply 50. Another end of the relay 26 is connected to the
serial communication circuit 27. The relay 26 switches power
supply to the outdoor unit 3 and serial communication in
accordance with a coil energization state, on the basis of
30 a control signal from the indoor unit control circuit 25.
In FIG. 1, the AC power supply 50 that supplies power to the
air conditioner 1 is also illustrated. The AC power supply
50 applies a power supply voltage to the air conditioner 1.
6
[0012] The outdoor unit 3 includes a terminal block 20,
a relay 4, a converter circuit 5, a smoothing capacitor 6,
a bus voltage detection circuit 7, an inverter circuit 8, a
compressor 9, a relay 10, a serial communication circuit 11,
5 a bus overvoltage detection circuit 14, a power supply
overvoltage detection circuit 12, a control unit 15, a relay
control circuit 13, and a current detection circuit 19.
[0013] The terminal block 20 is connected to the converter
circuit 5 of the outdoor unit 3 via the relay 4. The terminal
10 block 20 is also connected to the AC power supply 50 in
parallel with the indoor unit 2.
[0014] The relay 4 includes a so-called A-contact relay.
One end of the relay 4 is connected to the AC power supply
50 via the terminal block 20. Another end of the relay 4 is
15 connected to the converter circuit 5.
[0015] The converter circuit 5 includes a rectifier
circuit 51 and a power factor corrector 52 and converts AC
into DC. The rectifier circuit 51 includes, for example, a
diode bridge circuit. The power factor corrector 52 includes,
20 for example, a boost chopper circuit. The converter circuit
5 is connected to the smoothing capacitor 6.
[0016] The control unit 15 includes a converter control
unit 16 that controls the power factor corrector 52, a relay
control unit 17 that controls on/off of the relay 4 on the
25 basis of a value from the bus voltage detection circuit 7
that detects the bus voltage, and an inverter control unit
18 that controls the inverter circuit 8 on the basis of a
command from the serial communication circuit 11 of the
outdoor unit 3 and a value from the current detection circuit
30 19. The control unit 15 has a function for outputting a
switching determination signal regarding switching
determination between on and off of the relay control circuit
13 on the basis of the bus voltage detected by the bus
7
voltage detection circuit 7. The control unit 15 further
has a function for detecting an on/off state of the relay
control circuit 13.
[0017] The relay 10 includes a so-called C-contact relay.
5 The relay 10 is connected to the AC power supply 50 via the
indoor unit 2 in a state where a coil is not energized. The
relay 10 is connected to the serial communication circuit 11
when the coil energized in response to a control signal from
the control unit 15, and as a result, the serial
10 communication circuit 11 can communicate with the serial
communication circuit 27 of the indoor unit 2.
[0018] FIG. 2 is a circuit diagram illustrating details
of the power supply overvoltage detection circuit 12, the
bus overvoltage detection circuit 14, the relay control unit
15 17, and the relay control circuit 13 included in the air
conditioner 1 according to the first embodiment. More
specifically, FIG. 2 illustrates a configuration of the
overvoltage detection circuit according to the first
embodiment. In FIG. 2, components other than the power
20 supply overvoltage detection circuit 12, the bus overvoltage
detection circuit 14, the relay control unit 17, and the
relay control circuit 13 among all components included in
the outdoor unit 3 of the air conditioner 1 are illustrated.
In FIG. 2, the AC power supply 50 is also illustrated.
25 [0019] The power supply overvoltage detection circuit 12
includes an overvoltage detection unit 30 that is a second
comparison unit, a second delay circuit 31, and a power
supply voltage detection circuit 32 that detects the power
supply voltage. The overvoltage detection unit 30 includes
30 a comparator 30a, resistors R8, R9, and R10, and a capacitor
C4. The resistors R8 and R9 are connected in series between
a comparator power supply voltage 30b and a ground potential,
and divides a voltage of the comparator power supply voltage
8
30b and applies the voltage to the comparator 30a. The
capacitor C4 is connected between the comparator power supply
voltage 30b and the ground potential, as a bypass capacitor.
An output of the comparator 30a is connected to a pull-up
5 voltage 30c via the resistor R10 and is connected to the
relay control circuit 13.
[0020] The second delay circuit 31 configures an
integration circuit including a resistor R7 and a capacitor
C3. An output node of the second delay circuit 31 is
10 connected to the comparator 30a of the overvoltage detection
unit 30, and an input node of the second delay circuit 31 is
connected to the power supply voltage detection circuit 32.
The second delay circuit 31 delays the power supply voltage
detected by the power supply voltage detection circuit 32 by
15 a second delay time. The overvoltage detection unit 30
outputs a second comparison result obtained by comparing the
power supply voltage delayed by the second delay circuit 31
and a second interruption threshold.
[0021] The power supply voltage detection circuit 32
20 includes resistors R5, R6, and R15 and diodes D1 and D2.
One end of the resistor R5 is connected to the relay 4 and
the converter circuit 5, and another end of the resistor R5
is connected to an anode of the diode D1. One end of the
resistor R6 is connected to the AC power supply 50, and
25 another end of the resistor R6 is connected to an anode of
the diode D2. A cathode of the diode D1 is connected to a
cathode of the diode D2. The cathode of the diode D1 and
the cathode of the diode D2 are connected to one end of the
resistor R15 and are connected to the second delay circuit
30 31. Another end of the resistor R15 is connected to the
ground potential.
[0022] The bus overvoltage detection circuit 14 includes
an overvoltage detection unit 28 that is a first comparison
9
unit and a first delay circuit 29. The overvoltage detection
unit 28 includes a comparator 28a, resistors R2, R3, and R4,
and a capacitor C2. The resistors R2 and R3 are connected
in series between a comparator power supply voltage 28b and
5 the ground potential and divides a voltage of the comparator
power supply voltage 28b and applies the voltage to the
comparator 28a. The capacitor C2 is connected between the
comparator power supply voltage 28b and the ground potential,
as a bypass capacitor. An output of the comparator 28a is
10 connected to a pull-up voltage 28c via the resistor R4.
[0023] The first delay circuit 29 configures an
integration circuit including a resistor R1 and a capacitor
C1. A capacitance value of the capacitor C1 is larger than
a capacitance value of the capacitor C3 included in the
15 second delay circuit 31. An output node of the first delay
circuit 29 is connected to the comparator 28a, and an input
node of the first delay circuit 29 is connected to the bus
voltage detection circuit 7. The first delay circuit 29
delays the bus voltage detected by the bus voltage detection
20 circuit 7 by a first delay time. The overvoltage detection
unit 28 outputs a first comparison result obtained by
comparing the bus voltage delayed by the first delay circuit
29 and a first interruption threshold. The relay 4 switches
on/off of power reception of the outdoor unit 3 from the AC
25 power supply 50, on the basis of the first comparison result
output from the overvoltage detection unit 28 and the second
comparison result output from the overvoltage detection unit
30.
[0024] The outdoor unit 3 further includes resistors R11
30 and R12. The relay control unit 17 is connected to the bus
voltage detection circuit 7 so as to read a value of the bus
voltage, and is connected to the relay control circuit 13
via the resistor R11 so as to read a relay control state.
10
Furthermore, the relay control unit 17 is connected to the
relay control circuit 13 via the resistor R12, so as to
open/close the relay 4 by software control.
[0025] The relay control circuit 13 is a circuit that
5 switches on/off of power reception from the AC power supply
50 and includes a transistor Q1 and resistors R13 and R14.
The transistor Q1 is a driving transistor that drives the
relay 4 on the basis of the first comparison result output
from the overvoltage detection unit 28, the second comparison
10 result output from the overvoltage detection unit 30, and
the switching determination signal output from the control
unit 15. An output of the overvoltage detection unit 28, an
output of the overvoltage detection unit 30, and an output
of the relay control unit 17 are connected to a base terminal
15 of the transistor Q1.
[0026] The resistor R13 is connected to a base of the
transistor Q1, and the resistor R14 is connected between the
base and an emitter of the transistor Q1. The outdoor unit
3 further includes a diode D3. One end of the diode D3 is
20 connected to the relay control circuit 13, and another end
of the diode D3 is connected to the control unit 15. A coil
portion 4a of the relay 4 is connected to the diode D3 in
parallel. That is, one end of the coil portion 4a is
connected to the control unit 15, and another end of the
25 coil portion 4a is connected to a collector of the transistor
Q1.
[0027] The overvoltage detection circuit according to the
first embodiment includes the bus voltage detection circuit
7, the first delay circuit 29, the comparator 28a, the power
30 supply voltage detection circuit 32, the second delay circuit
31, the comparator 30a, and the relay 4.
[0028] Next, an operation of the air conditioner 1
according to the first embodiment will be described. In a
11
case where the air conditioner 1 performs a normal operation,
the relay 26 is turned off under control of the indoor unit
control circuit 25 of the indoor unit 2. The relay 10 of
the outdoor unit 3 is connected to the serial communication
5 circuit 11 by the control signal from the control unit 15.
The relay 4 is turned on under control of the relay control
circuit 13, and therefore, the AC power supply 50 directly
supplies power to the converter circuit 5.
[0029] FIG. 3 is a time chart of a waveform of a power
10 supply voltage that increases in the long time and a relay
control signal. FIG. 3 illustrates a state where the relay
control state, the relay control signals of the power supply
overvoltage detection circuit 12, the bus overvoltage
detection circuit 14, and the relay control unit 17, and the
15 power supply voltage change with time. As illustrated in
FIG. 3, for example, in a case where an amplitude of the
power supply voltage increases by ΔVa in the long time with
respect to a rated value Vtyp, an output voltage of the bus
voltage detection circuit 7 increases. Although the increase
20 in the output voltage is delayed by the first delay circuit
29 of the bus overvoltage detection circuit 14, when the
output voltage exceeds a potential at a midpoint between the
resistors R2 and R3 connected in series, an output of the
comparator 28a becomes Low, and the potential becomes the
25 ground potential. Therefore, the transistor Q1 of the relay
control circuit 13 is turned off, the relay 4 is interrupted,
and a subsequent circuit of the relay 4 is protected from an
overvoltage.
[0030] FIG. 4 is a time chart of a waveform of a steep
30 surge voltage of a power supply system and the relay control
signal. FIG. 4 illustrates a state where the relay control
state, the relay control signals of the power supply
overvoltage detection circuit 12, the bus overvoltage
12
detection circuit 14, and the relay control unit 17, and the
power supply voltage change with time. As illustrated in
FIG. 4, for example, in a case where a steep surge voltage
ΔVb is superimposed on the rated Vtyp of the amplitude value
5 of the power supply voltage, a voltage detected by the power
supply voltage detection circuit 32 of the power supply
overvoltage detection circuit 12 sharply increases.
Although the steep increase in the voltage is delayed by the
second delay circuit 31, when the voltage exceeds a potential
10 of a midpoint between the resistors R8 and R9 connected in
series, the output of the comparator 30a becomes Low, and
the potential becomes the ground potential. Therefore, the
transistor Q1 of the relay control circuit 13 is turned off,
the relay 4 is interrupted, and as a result, the subsequent
15 circuits of the relay 4 are protected from an overvoltage.
[0031] After the relay 4 is interrupted, power supply to
the converter circuit 5 of the outdoor unit 3 is stopped,
and the bus voltage gradually decreases. The smoothing
capacitor 6 is discharged, the bus voltage becomes equal to
20 or less than a predetermined voltage, and the function of
the outdoor unit 3 is stopped. The smoothing capacitor 6 is
a bus capacitor.
[0032] At this time, by setting a delay time used by the
second delay circuit 31 of the power supply overvoltage
25 detection circuit 12 to be shorter than a delay time used by
the first delay circuit 29 of the bus overvoltage detection
circuit 14 and setting an interruption threshold used by the
overvoltage detection unit 30 of the power supply overvoltage
detection circuit 12 to be higher than the interruption
30 threshold used by the overvoltage detection unit 28 of the
bus overvoltage detection circuit 14, the converter circuit
5 that is a power supply circuit can be protected from an
overvoltage surge to be superimposed on the power supply
13
voltage. Moreover, it is possible to protect an electronic
circuit from an increase in the power supply voltage for a
long time to be close to a withstand voltage of a circuit
component and an increase in the bus voltage. As a result,
5 since it is not necessary to use a component having a voltage
rating higher than necessary for the electronic circuit of
the outdoor unit 3, it is possible to reduce component cost.
Therefore, in the first embodiment, the delay time used by
the second delay circuit 31 is set to be shorter than the
10 delay time used by the first delay circuit 29, and the
interruption threshold used by the overvoltage detection
unit 30 is set to be higher than the interruption threshold
used by the overvoltage detection unit 28.
[0033] FIG. 5 is a flowchart illustrating a procedure of
15 the operation performed by the air conditioner 1 according
to the first embodiment. In FIG. 5, a procedure of an
operation from detection of an overvoltage to recovery in
the first embodiment is illustrated. The bus voltage
detection circuit 7 detects the bus voltage (S1), and the
20 bus overvoltage detection circuit 14 determines whether or
not the bus voltage detected by the bus voltage detection
circuit 7 is equal to or more than a threshold of the bus
overvoltage detection circuit 14 (S2). In a case where the
bus overvoltage detection circuit 14 determines that the bus
25 voltage is lower than the threshold (No in S2), after the
operation in step S2 is performed, the operation in step S1
is performed.
[0034] The relay control unit 17 determines whether or
not the bus voltage detected by the bus voltage detection
30 circuit 7 is equal to or more than an overvoltage protection
threshold of the relay control unit 17 (S3). In a case where
the relay control unit 17 determines that the bus voltage is
lower than the overvoltage protection threshold (No in S3),
14
after the operation in step S3 is performed, the operation
in step S1 is performed.
[0035] The power supply voltage detection circuit 32
detects the power supply voltage (S4), and the power supply
5 overvoltage detection circuit 12 determines whether or not
the power supply voltage detected by the power supply voltage
detection circuit 32 is equal to or more than a threshold of
the power supply overvoltage detection circuit 12 (S5). In
a case where the power supply overvoltage detection circuit
10 12 determines that the power supply voltage is lower than
the threshold (No in S5), after the operation in step S5 is
performed, the operation in step S4 is performed.
[0036] In a case where the bus overvoltage detection
circuit 14 determines that the bus voltage detected by the
15 bus voltage detection circuit 7 is equal to or more than the
threshold of the bus overvoltage detection circuit 14 (Yes
in S2), the comparator 28a outputs a signal indicating Low
(S6). In a case where the relay control unit 17 determines
that the bus voltage detected by the bus voltage detection
20 circuit 7 is equal to or more than the overvoltage protection
threshold of the relay control unit 17 (Yes in S3), the relay
control unit 17 outputs the signal indicating Low (S7). In
a case where the power supply overvoltage detection circuit
12 determines that the power supply voltage detected by the
25 power supply voltage detection circuit 32 is equal to or
more than the threshold of the power supply overvoltage
detection circuit 12 (Yes in S5), the comparator 30a outputs
the signal indicating Low (S8). After the operation in steps
S6, S7, or S8 is performed, the operation in step S9 is
30 performed.
[0037] In step S9, the relay 4 is turned off. That is,
in a case where any one of the bus overvoltage detection
circuit 14, the relay control unit 17, and the power supply
15
overvoltage detection circuit 12 detects an overvoltage (Yes
in S2, S3, and S5), the relay 4 is turned off (S9). The
relay control unit 17 confirms a control state of the relay
4 via the resistor R11 and detects that Low is output from
5 the overvoltage protection circuit of any one of the bus
overvoltage detection circuit 14, the relay control unit 17,
and the power supply overvoltage detection circuit 12 (S6,
S7, S8), and outputs a Low signal and continues a state where
the relay 4 is turned off (S9). The power supply to the
10 outdoor unit 3 is stopped, and the outdoor unit 3 is stopped
(S10).
[0038] Since power supply to the converter circuit 22 of
the indoor unit 2 continues, after a predetermined time has
elapsed after the outdoor unit 3 is stopped, the bus voltage
15 detection circuit 24 determines whether or not the bus
voltage is a normal value (S11). In a case where the bus
voltage detection circuit 24 determines that the bus voltage
is not the normal value (No in S11), the operation in step
S11 is performed. In a case where the bus voltage detection
20 circuit 24 determines that the bus voltage is the normal
value (Yes in S11), the relay 26 is turned on (S12). As a
result, the power supply to the converter circuit 5 of the
outdoor unit 3 is started. That is, the bus voltage is
supplied to the outdoor unit 3 (S13).
25 [0039] After charging of the smoothing capacitor 6 that
is the bus capacitor is completed and the control unit 15
can confirm that the bus voltage is the normal value, the
relay 26 is turned off again (S14). The relay 10 is turned
on (S15) and then serial communication can be performed.
30 Thereafter, the relay control unit 17 outputs an on signal
to the relay control circuit 13, and this turns on the relay
4 (S16), and the state of the air conditioner 1 transitions
to a state where a normal operation is performed.
16
[0040] As described above, since the delay time used by
the second delay circuit 31 of the power supply overvoltage
detection circuit 12 is set to be shorter than the delay
time used by the first delay circuit 29 of the bus
5 overvoltage detection circuit 14 and the interruption
threshold used by the overvoltage detection unit 30 of the
power supply overvoltage detection circuit 12 is set to be
higher than the interruption threshold used by the
overvoltage detection unit 28 of the bus overvoltage
10 detection circuit 14, the converter circuit 5 can be
protected from an overvoltage surge superimposed on the power
supply voltage. In addition, it is possible to protect the
electronic circuit from the increase in the power supply
voltage for a long time to be close to the withstand voltage
15 of the circuit component and the increase in the bus voltage.
As a result, since it is not necessary to use the component
having the voltage rating higher than necessary for the
electronic circuit of the outdoor unit 3, it is possible to
reduce the component cost. That is, the overvoltage
20 detection circuit according to the first embodiment can
protect the power supply circuit from the surge voltage that
is a steep overvoltage superimposed on the power supply
voltage and the increase in the power supply voltage for a
long time, in the area where the power supply voltage is
25 unstable.
[0041] Second Embodiment.
In the overvoltage detection circuit according to the
first embodiment, the single power supply overvoltage
detection circuit 12 and the single bus overvoltage detection
30 circuit 14 are provided, and the overvoltage detection
circuit according to the first embodiment protects the
electronic circuit from the surge voltage on the power supply
system side, using the power supply overvoltage detection
17
circuit 12 and the bus overvoltage detection circuit 14.
FIG. 6 is a diagram illustrating a configuration of the
overvoltage detection circuit according to the second
embodiment. As illustrated in FIG. 6, the overvoltage
5 detection circuit according to the second embodiment
includes the bus voltage detection circuit 7, the power
supply overvoltage detection circuit 12, the n bus
overvoltage detection circuits 14, and the relay 4. The
reference character n is an integer equal to or more than
10 two.
[0042] In the second embodiment, the delay time used by
the second delay circuit 31 of the power supply overvoltage
detection circuit 12 is t [ac], and the interruption
threshold used by the overvoltage detection unit 30 of the
15 power supply overvoltage detection circuit 12 is Vth [ac].
A delay time used by the first delay circuit 29 of the n-th
bus overvoltage detection circuit 14 among the n bus
overvoltage detection circuits 14 is t [n], and an
interruption threshold used by the overvoltage detection
20 unit 28 of the n-th bus overvoltage detection circuit 14 is
Vth [n]. A delay time used by each of the first delay
circuits 29 of the n bus overvoltage detection circuits 14
is different from the delay times used by the first delay
circuits 29 of the other bus overvoltage detection circuits
25 14. The interruption threshold used by each of the
overvoltage detection units 28 of the n bus overvoltage
detection circuits 14 is different from the interruption
thresholds used by the overvoltage detection units 28 of the
other bus overvoltage detection circuits 14.
30 [0043] The delay time and the interruption threshold
satisfy the following relationship.
delay time: t[ac]Vth[n]>Vth[n-1],...
18
Vth[2]>Vth[1]
[0044] As described above, since the overvoltage
detection circuit according to the second embodiment
includes the plurality of bus overvoltage detection circuits
5 14 having different delay times and interruption thresholds
to be used, it is possible to protect the circuit from
generation of a plurality of overvoltages.
[0045] FIG. 7 is a diagram illustrating a processor 91 in
a case where a part or all of the control unit 15 included
10 in the outdoor unit 3 of the air conditioner 1 according to
the first embodiment is implemented by the processor 91.
That is, some or all of functions of the control unit 15 may
be implemented by the processor 91 that executes a program
stored in a memory 92. The processor 91 is a central
15 processing unit (CPU), a processing system, an arithmetic
system, a microprocessor, or a digital signal processor (DSP).
In FIG. 7, the memory 92 is also illustrated.
[0046] In a case where some or all of the functions of
the control unit 15 are implemented by the processor 91, the
20 some or all of the functions are implemented by the processor
91 and software, firmware, or a combination of software and
firmware. The software or the firmware is written as a
program and stored in the memory 92. The processor 91
implements the some or all of the functions of the control
25 unit 15 by reading and executing the program stored in the
memory 92.
[0047] In a case where the some or all of the functions
of the control unit 15 are implemented by the processor 91,
the outdoor unit 3 includes the memory 92 that stores a
30 program to execute some or all of steps executed by the
control unit 15 as a result. It can be said that the program
stored in the memory 92 causes a computer to execute at least
a part of a procedure or a method executed by the control
19
unit 15.
[0048] The memory 92 is, for example, a nonvolatile or a
volatile semiconductor memory such as a random access memory
(RAM), a read only memory (ROM), a flash memory, an erasable
5 programmable read only memory (EPROM), or an electrically
erasable programmable read-only memory (EEPROM, registered
trademark), a magnetic disk, a flexible disk, an optical
disk, a compact disk, a mini disk, a digital versatile disc
(DVD), or the like.
10 [0049] FIG. 8 is a diagram illustrating processing
circuitry 93 in a case where a part or all of the control
unit 15 included in the outdoor unit 3 of the air conditioner
1 according to the first embodiment is implemented by the
processing circuitry 93. That is, a part or all of the
15 control unit 15 may be implemented by the processing
circuitry 93.
[0050] The processing circuitry 93 is dedicated hardware.
The processing circuitry 93 corresponds to, for example, a
single circuit, a composite circuit, a programmed processor,
20 a parallel-programmed processor, an application specific
integrated circuit (ASIC), a field-programmable gate array
(FPGA), or a combination thereof.
[0051] A part of the control unit 15 may be implemented
by dedicated hardware different from a rest of the control
25 unit 15.
[0052] A part of the plurality of functions of the control
unit 15 may be implemented by software or firmware, and the
rest of the plurality of functions may be implemented by
dedicated hardware. In this way, the plurality of functions
30 of the control unit 15 can be implemented by hardware,
software, firmware, or a combination thereof.
[0053] The configurations indicated in the above
embodiments indicate examples and can be combined with other
20
known techniques. Furthermore, the embodiments can be
combined with each other, and some configurations can be
partially omitted or changed without departing from the gist.
5 Reference Signs List
[0054] 1 air conditioner; 2 indoor unit; 3 outdoor
unit; 4, 10, 26 relay; 4a coil portion; 5 converter
circuit; 6 smoothing capacitor; 7 bus voltage detection
circuit; 8 inverter circuit; 9 compressor; 11 serial
10 communication circuit; 12 power supply overvoltage
detection circuit; 13 relay control circuit; 14 bus
overvoltage detection circuit; 15 control unit; 16
converter control unit; 17 relay control unit; 18 inverter
control unit; 19 current detection circuit; 20, 21 terminal
15 block; 22 converter circuit; 23 smoothing capacitor; 24
bus voltage detection circuit; 25 indoor unit control
circuit; 27 serial communication circuit; 28 overvoltage
detection unit; 28a, 30a comparator; 28b comparator power
supply voltage; 28c pull-up voltage; 29 first delay
20 circuit; 30 overvoltage detection unit; 30b comparator
power supply voltage; 30c pull-up voltage; 31 second delay
circuit; 32 power supply voltage detection circuit; 50 AC
power supply; 51 rectifier circuit; 52 power factor
corrector; 91 processor; 92 memory; 93 processing
25 circuitry; C1, C2, C3, C4 capacitor; D1, D2, D3 diode; Q1
transistor; R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R11,
R12, R13, R14, R15 resistor.

WE CLAIM:
1. An overvoltage detection circuit comprising:
a bus voltage detection circuit to detect a bus voltage;
a first delay circuit to delay the bus voltage detected
5 by the bus voltage detection circuit by a first delay time;
a first comparison unit to output a first comparison
result obtained by comparing the bus voltage delayed by the
first delay circuit with a first interruption threshold;
a power supply voltage detection circuit to detect a
10 power supply voltage;
a second delay circuit to delay the power supply voltage
detected by the power supply voltage detection circuit by a
second delay time;
a second comparison unit to output a second comparison
15 result obtained by comparing the power supply voltage delayed
by the second delay circuit with a second interruption
threshold; and
a relay to switch on/off of power reception of an
outdoor unit from an AC power supply on a basis of the first
20 comparison result output from the first comparison unit and
the second comparison result output from the second
comparison unit, wherein
the first delay time is longer than the second delay
time, and
25 the first interruption threshold is lower than the
second interruption threshold.
2. The overvoltage detection circuit according to claim 1,
wherein
30 the first delay circuit includes a first resistor and
a first capacitor,
the second delay circuit includes a second resistor and
a second capacitor, and
22
a capacitance value of the first capacitor is larger
than a capacitance value of the second capacitor.
3. The overvoltage detection circuit according to claim 1
5 or 2, further comprising:
a relay control circuit to switch on/off of the power
reception from the AC power supply; and
a control unit to output a switching determination
signal regarding on/off switching determination of the relay
10 control circuit on a basis of the bus voltage detected by
the bus voltage detection circuit, wherein
the relay control circuit includes a driving transistor
that drives the relay on a basis of the first comparison
result, the second comparison result, and the switching
15 determination signal.
4. The overvoltage detection circuit according to claim 3,
wherein
the control unit has a function for detecting an on/off
20 state of the relay control circuit, and
an output of the first comparison unit, an output of
the second comparison unit, and an output of the control
unit are connected to a base terminal of the driving
transistor.
25
5. An overvoltage detection circuit comprising:
n bus overvoltage detection circuits;
a power supply voltage detection circuit to detect a
power supply voltage;
30 a second delay circuit to delay the power supply voltage
detected by the power supply voltage detection circuit by a
predetermined delay time;
a second comparison unit to output a second comparison
23
result obtained by comparing the power supply voltage delayed
by the second delay circuit and a predetermined interruption
threshold; and
a relay, wherein
5 n is an integer equal to or more than two,
each of the n bus overvoltage detection circuits
includes
a bus voltage detection circuit that detects a bus
voltage,
10 a first delay circuit that delays the bus voltage
detected by the bus voltage detection circuit by a
predetermined delay time, and
a first comparison unit that outputs a first
comparison result obtained by comparing the bus voltage
15 delayed by the first delay circuit and a predetermined
interruption threshold,
the relay switches on/off of power reception of an
outdoor unit from an AC power supply on a basis of the first
comparison result output from the first comparison unit
20 included in each of the n bus overvoltage detection circuits
and the second comparison result output from the second
comparison unit,
the delay time used by the second delay circuit is
defined as t [ac], the interruption threshold used by the
25 second comparison unit is defined as Vth [ac], the delay
time used by the first delay circuit included in an n-th bus
overvoltage detection circuit among the n bus overvoltage
detection circuits is defined as t [n], and the interruption
threshold used by the first comparison unit included in the
30 n-th bus overvoltage detection circuit among the n bus
overvoltage detection circuits is defined as Vth [n],
24
the delay time satisfies a relationship of
t[ac]Vth[n]>Vth[n-1],... Vth[2]>Vth[1].