WO2012096198A2

WO2012096198A2 - Power supply device, inverter device, and power tool

Info

Publication number: WO2012096198A2
Application number: PCT/JP2012/000210
Authority: WO
Inventors: Yoshikazu Kawano; Kazuhiko Funabashi; Yasushi Nakano; Shinji Watanabe; Miyoji Onose; Haruhisa Fujisawa
Original assignee: Hitachi Koki Co., Ltd.
Priority date: 2011-01-14
Filing date: 2012-01-16
Publication date: 2012-07-19
Also published as: JP2012151920A; WO2012096198A3

Abstract

A power supply device includes: a battery pack; a transforming unit including a switching element and configured to transform a DC voltage supplied from the battery pack; a temperature detecting unit configured to detect a temperature of the switching element; and a control unit configured to control the switching element based on the detected temperature.

Description

POWER SUPPLY DEVICE, INVERTER DEVICE, AND POWER TOOL

The present invention relates to a power supply device, an inverter device and a power tool provided with the power supply device or the inverter device.

An electronic device provided with an inverter circuit is well-known. Such the electronic device boosts AC voltage supplied from a commercial power source, rectifies/smooths the boosted AC voltage into DC voltage, converts the DC voltage into predetermined AC voltage using the inverter circuit, and outputs the predetermined AC voltage to an AC motor provided in the electronic device.

Japanese Patent Application Publication No. 2009-278832 provides a technique that operates the AC motor provided in the electronic device with DC voltage supplied from a battery pack instead of the AC voltage supplied from the commercial power source.

In the above technique, an inverter device provided with a converting circuit, a booster circuit, a rectifying/smoothing circuit, and an inverter circuit are connected between the battery pack and the electronic device to supply AC power to the electronic device. The converting circuit and the inverter circuit have an FET, and convert the DC voltage into the AC voltage by turning ON/OFF the FET.

However, since an FET is easily damaged by an overcurrent, there is a possibility for the FETs to be damaged when an AC motor has a high load.

In view of the foregoing, it is an object of the present invention to provide a power supply device capable of suitably preventing a switching element, such as an FET, from malfunctioning when an AC motor has a high load.

In order to attain the above and other objects, the invention provides a power supply device including: a battery pack; a transforming unit including a switching element and configured to transform a DC voltage supplied from the battery pack; a temperature detecting unit configured to detect a temperature of the switching element; and a control unit configured to control the switching element based on the detected temperature.

It is preferable that the control unit controls an ON period of the switching element based on the detected temperature.

It is preferable that the power supply device further includes a current detecting unit configured to detect a current flowing in the transforming unit. The control unit controls switching element based on at least one of the detected current and the detected temperature.

It is preferable that the control unit controls an ON period of the switching element based on at least one of the detected current and the detected temperature.

It is preferable that the control unit controls the ON period of the switching element based on both the detected current and the detected temperature.

It is preferable that the control unit controls the ON period of the switching element regardless of the detected temperature when the detected current is greater than a predetermined value.

It is preferable that the switching element converts the DC voltage supplied from the battery pack into an AC voltage. The transforming unit includes: a rectifying/smoothing circuit configured to rectifies/smooths the AC voltage; and an inverter circuit configured to convert a voltage outputted from the rectifying/smoothing circuit into an AC voltage. The temperature detecting unit detects the temperature of the switching element, and the current detecting unit detects a current flowing in the inverter circuit.

Another aspect of the present invention provides an inverter device including: a converting circuit configured to convert a first DC power into a first AC power by a switching element; a rectifying/smoothing circuit configured to convert the first AC power into a second DC power; an inverter circuit configured to convert the second DC power into a second AC power; a current detecting unit configured to detect a current flowing in the inverter circuit; a temperature detecting unit configured to detect a temperature of the switching element; and a control unit configured to prevent the switching element from performing the ON/OFF operation based on at least one of the detected current and the detected temperature.

It is preferable that the control unit prevents the switching element from performing the ON/OFF operation based on both the detected current and the detected temperature.

It is preferable that the control unit allows the switching element to perform the OFF/OFF operation during an allowable period, and prevents the switching element from performing the ON/OFF operation when the allowable period has elapsed since the control unit allowed the switching element to perform the OFF/OFF operation. The control unit changes the allowable period based on at least one of the detected current and the detected temperature.

It is preferable that the control unit changes the allowable period based on both the detected current and the detected temperature.

It is preferable that the control unit sets the allowable period to a first allowable period when the detected current is a first current, and sets the allowable period to a second allowable period equal to or shorter than the first allowable period when the detected current is a second current greater than the first current.

It is preferable that the control unit prevents the switching element from performing the ON/OFF operation regardless of the temperature when the detected current is greater than a first current threshold.

It is preferable that the greater the detected current becomes, the shorter an ON duration of the switching element becomes.

It is preferable that the greater the detected temperature becomes, the shorter an ON duration of the switching element becomes.

It is preferable that the control unit changes the allowable period based on the detected temperature when the detected current is equal to or smaller than the first current threshold and greater than a second current threshold smaller than the first current threshold.

It is preferable that the control unit sets the allowable period to a first allowable period when the detected temperature is a first temperature, and sets the allowable period to a second allowable period equal to or shorter than the first allowable period when the detected temperature is a second temperature higher than the first temperature.

Another aspect of the present invention provides an inverter device including: an inverter circuit having a switching element configured to perform an ON/OFF operation to convert a DC power into an AC power; a current detecting unit configured to detect a current flowing in the inverter circuit; a temperature detecting unit configured to detect a temperature of the switching element; and a control unit configured to prevent the switching element from performing the ON/OFF operation based on at least one of the detected current and the detected temperature.

Another aspect of the present invention provides a power tool including: the power supply device; and an AC motor driven with the second AC power.

Another aspect of the present invention provides a power tool including: the inverter device; and an AC motor driven with the second AC power.

The power supply device of the present invention can suitably prevent an FET from malfunctioning when an AC motor has a high load.

Fig. 1 is a circuit diagram for an inverter device according to a preferred embodiment of the present invention. Fig. 2 is a table showing overload determination criteria used for preventing FETs from being turned on in the preferred embodiment. Fig. 3 is a flowchart illustrating steps in a process to halt output from the inverter device according to the preferred embodiment.

1 Inverter device
132 FET
14 Rectifying/smoothing circuit
16 Inverter circuit
161-164 FET
17 Current detection resistor
19 Control unit
2 Battery pack
3 Electronic device
30 Temperature detection unit

An inverter device 1 according to a preferred embodiment of the power supply device of the present invention will be described while referring to Figs. 1 through 3.

Fig. 1 is a circuit diagram for the inverter device 1. The inverter device 1 is connected between a battery pack 2 and an electronic device 3 to convert a DC power supplied from the battery pack 2 into an AC power and outputs the AC power to an AC motor 31 provided in the electronic device 3. When an operator operates a trigger switch 32 provided in the electronic device 3, the inverter device 1 converts DC power supplied from the battery pack 2 to AC power and supplies this AC power to the AC motor 31 of the electronic device 3. While the inverter device 1, electronic device 3, and battery pack 2 are detachably connected to one another, the following description assumes that these components are connected. The electronic device 3 includes a power tool driven with 100V of AC voltage, such as a lawn.

The inverter device 1 includes a battery voltage detection unit 11, a power supply unit 12, a booster circuit 13, a rectifying/smoothing circuit 14, a boost voltage detection unit 15, an inverter circuit 16, a current detection resistor 17, a PWM signal output unit 18, a control unit 19, and a temperature detection unit 30.

The battery voltage detection unit 11 includes battery voltage detection resistors 111 and 112. The battery voltage detection resistors 111 and 112 are connected in series between a plus terminal 21 and a minus terminal 22 of the battery pack 2 to output a divided voltage of the battery voltage of the battery pack 2 by the battery voltage detection resistors 111 and 112 to the control unit 19. The battery pack 2 shown in Fig. 1 has four 3.6-V lithium battery cells 2a connected in series for outputting a rated voltage of 14.4 V.

The power supply unit 12 includes a power switch 121 and a constant-voltage circuit 122 connected in series between the plus terminal 21 of the battery pack 2 and the control unit 19. The constant-voltage circuit 122 includes a three-terminal regulator 122a, and oscillation-prevention capacitors 122b and 122c. When an operator turns on the power switch 121, the constant-voltage circuit 122 converts the voltage supplied from the battery pack 2 into a prescribed DC voltage (5 V, for example) and supplies this voltage to the control unit 19 as drive voltage. When the operator switches off the power switch 121, the entire inverter device 1 is turned off because the drive voltage is no longer supplied to the control unit 19.

The booster circuit 13 is configured of a transformer 131, and a field effect transistor (FET) 132. The transformer 131 includes a primary winding 131a, and a secondary winding 131b. The primary winding 131a is connected between the plus terminal 21 and minus terminal 22 of the battery pack 2. The FET 132 is provided between the primary winding 131a of the transformer 131 and the minus terminal 22 of the battery pack 2. The control unit 19 inputs a first PWM signal into the gate of the FET 132 for switching the FET 132 on and off. Through on/off switching of the FET 132, the DC power supplied from the battery pack 2 to the primary winding 131a of the transformer 131 is converted into AC power. The AC voltage of this AC power is stepped up based on the ratio of the number of turns in the secondary winding 131b to the number of turns in the primary winding 131a, and is outputted from the secondary winding 131b.

The rectifying/smoothing circuit 14 is configured of rectifying diodes 141 and 142, and a smoothing capacitor 143. Through this configuration, the rectifying/smoothing circuit 14 converts the AC voltage stepped up by the transformer 131 to DC voltage (141 V, for example).

The boost voltage detection unit 15 includes

resistors

151 and 152 connected in series to output a divided voltage of the DC voltage outputted from the rectifying/smoothing circuit 14 (the voltage at the smoothing capacitor 143; 141 V, for example) by the

resistors

151 and 152 to the control unit 19.

The inverter circuit 16 is configured of four FETs 161-164. The

FETs

161 and 162 are connected in series, and the

FETs

163 and 164, with both pairs of FETs being connected to the smoothing capacitor 143 in parallel. More specifically, the drain of the FET 161 is connected to the cathodes of the rectifying diodes 141 and 142, while the source of the FET 161 is connected to the drain of the FET 162. Similarly, the drain of the FET 163 is connected to the cathodes of the rectifying diodes 141 and 142, while the source of the FET 163 is connected to the drain of the FET 164.

The inverter circuit 16 also includes

output terminals

165 and 166 that are connected to the AC motor 31 of the power tool 3. The source of the FET 161 and the drain of the FET 162 are connected to the output terminal 165, while the source of the FET 163 and the drain of the FET 164 are connected to the output terminal 166. The PWM signal output unit 18 outputs second PWM signals to the gates of the FETs 161-164 for switching the FETs 161-164 on and off. Through on/off switching of the FETs 161-164, the inverter circuit 16 converts the DC power outputted from the rectifying/smoothing circuit 14 into AC power and supplies this AC power to the power tool 3 (the AC motor 31).

The current detection resistor 17 is connected between the source of the FET 162 (FET 164) and the minus terminal 22 of the battery pack 2. The terminal of the current detection resistor 17 on the high-voltage side is also connected to the control unit 19. With this configuration, the control unit 19 can determine the current flowing to the AC motor 31 based on the voltage detected by the current detection resistor 17.

The temperature detection unit 30 includes a thermistor 30a disposed adjacent to the FET 132, and a resistor 30b connected in series with the thermistor 30a. The thermistor 30a and resistor 30b divide the prescribed voltage outputted from the three-terminal regulator 122a, and the temperature detection unit 30 outputs the divided voltage to the control unit 19 as a temperature signal.

The control unit 19 outputs the first PWM signal to the gate of the FET 132 based on the boosted voltage detected by the boost voltage detection unit 15 in order that the AC voltage outputted from the secondary side of the transformer 131 has the desired effective voltage (141 V, for example). The control unit 19 also outputs the second PWM signals to the gates of the FETs 161-164 via the PWM signal output unit 18 in order that the AC voltage outputted to the AC motor 31 has the desired effective voltage (100 V, for example). In the preferred embodiment, the

FETs

161 and 164 are treated as one set (hereinafter referred to as the "first set"), while the

FETs

162 and 163 are treated as another set (hereinafter referred to as the "second set"), and the control unit 19 outputs the second PWM signals for alternately turning on and off the first and second sets at a duty cycle of 100%.

The control unit 19 also determines whether over-discharge has occurred in the battery pack 2 based on the battery voltage detected by the battery voltage detection unit 11. More specifically, when the battery voltage detected by the battery voltage detection unit 11 is smaller than a prescribed over-discharge voltage, the control unit 19 determines that over-discharge has occurred in the battery pack 2 and outputs the first and second PWM signals in order to halt output to the AC motor 31. That is, the control unit 19 halts output of the first and second PWM signals.

The battery pack 2 is further provided with a built-in protection circuit or microcomputer and possesses a function for self-detecting over-discharge and for outputting an over-discharge signal to the control unit 19. When the control unit 19 receives an over-discharge signal from the battery pack 2 via a signal terminal LD, the control unit 19 outputs first and second PWM signals in order to halt output to the AC motor 31. That is, the control unit 19 halts output of the first and second PWM signals. This construction can prevent such over-discharge from shortening the lifespan of the battery pack 2.

Here, since an FET is easily damaged by an overcurrent, one measure for protecting FETs is to shut off the FET 132 when the current flowing in the current detection resistor 17 exceeds a prescribed overcurrent threshold. However, even if the detected current does not exceed the overcurrent threshold, there is still a possibility for the FETs to be damaged if the current remains above a prescribed level for an extended period of time. In addition, even if the current flowing to the FETs is too small to cause damage, the FETs can still be damaged by heat.

Therefore, the inverter device 1 according to the preferred embodiment prevents the FET 132 from performing an ON/OFF operation when the current detected with the current detection resistor 17 is too high and when the temperature detected by the temperature detection unit 30 is too high.

Fig. 2 is a table showing criteria according to the preferred embodiment for determining whether to prevent the FET 132 from performing the ON/OFF operation. As shown in Fig. 2, the overcurrent threshold is set to 10 A in the preferred embodiment. If a current of 10 A or greater flows in the inverter device 1 for 0.5 seconds or more, the inverter device 1 prevents the FET 132 from performing the ON/OFF operation (i.e., turns off the FET 132). The inverter device 1 also prevents the FET 132 from performing the ON/OFF operation even when the current flowing in the inverter device 1 is smaller than the overcurrent threshold of 10 A, such as when a current of at least 8 A and less than 10 A flows in the inverter device 1 for at least 1.0 seconds, when a current of at least 6 A and less than 8 A flows in the inverter device 1 for at least 3.0 seconds, and when a current of at least 5 A and less than 6 A flows in the inverter device 1 for at least 5.0 seconds. In other words, the inverter device 1 modifies the length of period that the FET 132 performs the ON/OFF operation based on the value of current flowing in the inverter device 1, shortening the period during which the FET 132 performs the ON/OFF operation as the current increases.

The inverter device 1 also prevents the FET 132 from performing the ON/OFF operation even when the current flowing through the inverter device 1 is less than 5 A but at least 4 A when the temperature of the FET 132 remains within the range 100-120 degree for at least 5.0 seconds, when the temperature of the FET 132 remains within the range 80-100 degree for at least 10.0 seconds, and when the temperature of the FET 132 remains within the range 60-80 degree for at least 20.0 seconds. This configuration can suitably prevent malfunctioning of the FET 132. In this way, the inverter device 1 varies the length of period that the FET 132 performs the ON/OFF operation based on the temperature of the FET 132 when the current flowing in the inverter device 1 is smaller and reduces the period during which the FET 132 performs the ON/OFF operation as the temperature increases.

Since it is highly unlikely that the temperature of the FET 132 will rise drastically when the current value is less than 4 A, the inverter device 1 periodically turns the FET 132 on and off according to normal operations in this case. The inverter device 1 also turns the FET 132 on and off periodically according to normal operations when the current value is greater than or equal to 4 A but less than 5 A, provided that the temperature of the FET 132 is lower than 60 degree, since it is also unlikely that the FET 132 will be damaged in this case.

Next, the control process performed by the control unit 19 according to the preferred embodiment for halting output to the AC motor 31 will be described with reference to the flowchart in Fig. 3.

The control unit 19 begins the process in Fig. 3 either when the power switch 121 is turned on while the battery pack 2 is mounted on the inverter device 1 or when the battery pack 2 is mounted on the inverter device 1 while the power switch 121 is in an ON state. When the power switch 121 is turned on, the constant-voltage circuit 122 generates a drive voltage for driving the control unit 19 from the battery voltage of the battery pack 2.

In S101 of the flowchart in Fig. 3, the control unit 19 outputs the first PWM signal to the gate of the FET 132 in order that the AC voltage outputted from the secondary side of the transformer 131 has the desired effective voltage (100 V, for example). In S102 the control unit 19 determines whether the effective voltage boosted by the transformer 131 is greater than the target voltage based on the voltage detected by the boost voltage detection unit 15.

If the boosted voltage is greater than the target voltage (S102: YES), in S103 the control unit 19 reduces the duty cycle of the FET 132. When the boosted voltage is less than or equal to the target voltage (S102: NO), in S104 the control unit 19 increases the duty cycle of the FET 132.

In S105 the control unit 19 determines whether the battery voltage of the battery pack 2 is less than a prescribed over-discharge voltage based on the voltage detected by the battery voltage detection unit 11. If the battery voltage is less than the prescribed over-discharge voltage (S105: YES), then the control unit 19 determines that the battery pack 2 is in an over-discharge state. Accordingly, in S108 the control unit 19 outputs first and second PWM signals for halting output to the AC motor 31. Specifically, the control unit 19 halts output of the first and second PWM signals. As a result, operations of the booster circuit 13 and inverter circuit 16 are shut down, thereby halting output from the inverter device 1 to the AC motor 31.

However, if the battery voltage of the battery pack 2 is greater than or equal to the prescribed over-discharge voltage (S105: NO), in S106 the control unit 19 determines whether an over-discharge signal was inputted from the battery pack 2 via the LD terminal. If an over-discharge signal was inputted (S106: YES), then the control unit 19 determines that the battery pack 2 is in an over-discharge state. Accordingly, in S108 the control unit 19 outputs the first and second PWM signals for halting output to the AC motor 31. Specifically, the control unit 19 halts output of the first and second PWM signals.

If an over-discharge signal was not inputted (S106: NO), in S107 the control unit 19 determines whether the current detected by the current detection resistor 17 and the temperature detected by the temperature detection unit 30 satisfy the determination criteria shown in Fig. 2. When the determination criteria is met (S107: YES), in S108 the control unit 19 turns off the FET 132. Specifically, the control unit 19 outputs a first PWM signal for preventing the FET 132 from turning on.

However, if the determination criteria is not met (S107: NO), the control unit 19 returns to S101.

As described above, the inverter device 1 according to the preferred embodiment shuts off the FET 132 (i.e., prevents the FET 132 from performing the ON/OFF operation) based on both the current detected by the current detection resistor 17 and the temperature detected by the temperature detection unit 30. Therefore, the inverter device 1 can suitably prevent the FET 132 from malfunctioning when the power tool 3 has a high load.

As shown in Fig. 2, the inverter device 1 varies an ON/OFF signal duration (allowable duration) before the FET 132 is prevented from performs the ON/OFF operation based on both the current detected by the current detection resistor 17 and the temperature detected by the temperature detection unit 30. Accordingly, the inverter device 1 can suitably prevent the FET 132 from malfunctioning when the power tool 3 has a high load.

As indicated in Fig. 2, when the current detected by the current detection resistor 17 exceeds 5 A, the inverter device 1 determines whether to turn off the FET 132 without regard for the temperature detected by the temperature detection unit 30. Accordingly, the inverter device 1 can suitably prevent the FET 132 from malfunctioning when the power tool 3 has a high load.

While the invention has been described in detail with reference to the preferred embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.

For example, while the inverter device 1 is configured to output the first and second PWM signals for halting output to the AC motor 31 in the preferred embodiment described above, the inverter device 1 may be configured to output only one of the PWM signals for halting output to the AC motor 31.

While the thermistor 30a is disposed adjacent to the FET 132 in the preferred embodiment described above, the thermistor 30a may be disposed adjacent to the FETs 161-164 instead. In this case, the inverter device 1 may shut off the FETs 161-164 using the second PWM signal based on both the current detected by the current detection resistor 17 and the temperature detected by the temperature detection unit 30.

Further, the battery pack 2 that is connected to the inverter device 1 in the preferred embodiment described above is a 14.4 V lithium battery pack, but the inverter device 1 may be configured to be connectable to different types of battery packs in addition to those housing lithium batteries, such as battery packs configured of nickel cadmium batteries or nickel metal hydride batteries, or may be configured to be connectable to a plurality of battery packs with various battery voltages.

Further, the processes for controlling the boosted voltage in S101-S104, for detecting over-discharge in S105-S106, and for controlling the halting of output in S107 described in the flowchart of Fig. 3 may be performed at any position in the flowchart or may be performed in parallel.

The inverter device 1 may also store a count value indicating the number of times that output to the AC motor 31 was halted, and may display this history of halted output. In addition, the inverter device 1 may be configured to notify the user that the battery pack 2 has reached the end of its service life when output to the AC motor 31 has been halted more than a prescribed number of times.

In the flowchart of Fig. 3, an overcurrent detection may be further performed. Specifically, the control unit 19 halts the operations of the booster circuit unit 13 and inverter circuit 16 when the current detected by the current detection resistor 17 has exceeded a predetermined current. With this construction, it can prevented that the battery pack 2, the AC motor 32, and FETs 132 and 161-164 are damaged due to the heat generated by the overcurrent.

Claims

A power supply device comprising:
a battery pack;
a transforming unit including a switching element and configured to transform a DC voltage supplied from the battery pack;
a temperature detecting unit configured to detect a temperature of the switching element; and
a control unit configured to control the switching element based on the detected temperature.
The power supply device according to claim 1, wherein the control unit controls an ON period of the switching element based on the detected temperature.
The power supply device according to claim 1, further comprising a current detecting unit configured to detect a current flowing in the transforming unit,
wherein the control unit controls switching element based on at least one of the detected current and the detected temperature.
The power supply device according to claim 3, wherein the control unit controls an ON period of the switching element based on at least one of the detected current and the detected temperature.
The power supply device according to claim 4, wherein the control unit controls the ON period of the switching element based on both the detected current and the detected temperature.
The power supply device according to claim 5, wherein the control unit controls the ON period of the switching element regardless of the detected temperature when the detected current is greater than a predetermined value.
The power supply device according to claim 3, wherein the switching element converts the DC voltage supplied from the battery pack into an AC voltage,
wherein the transforming unit comprises:
a rectifying/smoothing circuit configured to rectifies/smooths the AC voltage; and
an inverter circuit configured to convert a voltage outputted from the rectifying/smoothing circuit into an AC voltage, and
wherein the temperature detecting unit detects the temperature of the switching element, and the current detecting unit detects a current flowing in the inverter circuit.
An inverter device comprising:
a converting circuit configured to convert a first DC power into a first AC power by a switching element;
a rectifying/smoothing circuit configured to convert the first AC power into a second DC power;
an inverter circuit configured to convert the second DC power into a second AC power;
a current detecting unit configured to detect a current flowing in the inverter circuit;
a temperature detecting unit configured to detect a temperature of the switching element; and
a control unit configured to prevent the switching element from performing the ON/OFF operation based on at least one of the detected current and the detected temperature.
The inverter device according to claim 8, wherein the control unit prevents the switching element from performing the ON/OFF operation based on both the detected current and the detected temperature.
The inverter device according to claim 8, wherein the control unit allows the switching element to perform the OFF/OFF operation during an allowable period, and prevents the switching element from performing the ON/OFF operation when the allowable period has elapsed since the control unit allowed the switching element to perform the OFF/OFF operation, and
wherein the control unit changes the allowable period based on at least one of the detected current and the detected temperature.
The inverter device according to claim 10, wherein the control unit changes the allowable period based on both the detected current and the detected temperature.
The inverter device according to claim 10, wherein the control unit sets the allowable period to a first allowable period when the detected current is a first current, and sets the allowable period to a second allowable period equal to or shorter than the first allowable period when the detected current is a second current greater than the first current.
The inverter device according to claim 8, wherein the control unit prevents the switching element from performing the ON/OFF operation regardless of the temperature when the detected current is greater than a first current threshold.
The inverter device according to claim 10, wherein the greater the detected current becomes, the shorter an ON duration of the switching element becomes.
The inverter device according to claim 10, wherein the greater the detected temperature becomes, the shorter an ON duration of the switching element becomes.
The inverter device according to claim 13, wherein the control unit changes the allowable period based on the detected temperature when the detected current is equal to or smaller than the first current threshold and greater than a second current threshold smaller than the first current threshold.
The inverter device according to claim 16, wherein the control unit sets the allowable period to a first allowable period when the detected temperature is a first temperature, and sets the allowable period to a second allowable period equal to or shorter than the first allowable period when the detected temperature is a second temperature higher than the first temperature.
An inverter device comprising:
an inverter circuit having a switching element configured to perform an ON/OFF operation to convert a DC power into an AC power;
a current detecting unit configured to detect a current flowing in the inverter circuit;
a temperature detecting unit configured to detect a temperature of the switching element; and
a control unit configured to prevent the switching element from performing the ON/OFF operation based on at least one of the detected current and the detected temperature.
The inverter device according to claim 18, wherein the control unit prevents the switching element from performing the ON/OFF operation based on both the detected current and the detected temperature.
The inverter device according to claim 18, wherein the control unit allows the switching element to perform the OFF/OFF operation during an allowable period, and prevents the switching element from performing the ON/OFF operation when the allowable period has elapsed since the control unit allowed the switching element to perform the OFF/OFF operation, and
wherein the control unit changes the allowable period based on at least one of the detected current and the detected temperature.
The inverter device according to claim 18, wherein the control unit prevents the switching element from performing the ON/OFF operation regardless of the temperature when the detected current is greater than a first current threshold.
A power tool comprising:
the power supply device according to any one of claims 1-7; and
an AC motor driven with the second AC power.
A power tool comprising:
the inverter device according to any one of claims 8-21; and
an AC motor driven with the second AC power.