CN113054887A - Overvoltage protection circuit and method of electric tool and electric tool - Google Patents
Overvoltage protection circuit and method of electric tool and electric tool Download PDFInfo
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- CN113054887A CN113054887A CN201911383371.1A CN201911383371A CN113054887A CN 113054887 A CN113054887 A CN 113054887A CN 201911383371 A CN201911383371 A CN 201911383371A CN 113054887 A CN113054887 A CN 113054887A
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- 238000000034 method Methods 0.000 title claims abstract description 21
- 239000003990 capacitor Substances 0.000 claims abstract description 157
- 238000001514 detection method Methods 0.000 claims description 17
- 238000006243 chemical reaction Methods 0.000 claims description 16
- 238000004804 winding Methods 0.000 claims description 13
- 239000010409 thin film Substances 0.000 claims description 4
- 230000002035 prolonged effect Effects 0.000 abstract description 7
- 238000007599 discharging Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 12
- 230000009286 beneficial effect Effects 0.000 description 4
- 238000001914 filtration Methods 0.000 description 4
- 230000020169 heat generation Effects 0.000 description 3
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000010408 film Substances 0.000 description 1
- 230000008707 rearrangement Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
- H02P29/02—Providing protection against overload without automatic interruption of supply
- H02P29/024—Detecting a fault condition, e.g. short circuit, locked rotor, open circuit or loss of load
- H02P29/0241—Detecting a fault condition, e.g. short circuit, locked rotor, open circuit or loss of load the fault being an overvoltage
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
- H02H7/09—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against over-voltage; against reduction of voltage; against phase interruption
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- Control Of Ac Motors In General (AREA)
Abstract
The embodiment of the invention discloses an overvoltage protection circuit and method of an electric tool and the electric tool, wherein the overvoltage protection circuit of the electric tool comprises: the circuit comprises a rectifying circuit, a first capacitor branch circuit, a second capacitor branch circuit, a driving circuit and a control circuit; the rectifying circuit is electrically connected with the driving circuit, the driving circuit is electrically connected with the brushless motor, and a first capacitor branch and a second capacitor branch are connected in parallel on a circuit connected with the rectifying circuit and the driving circuit; the first capacitor branch comprises a first capacitor, the second capacitor branch comprises a first switch and a second capacitor which are connected in series, and the capacitance value of the second capacitor is greater than that of the first capacitor; the control circuit is respectively electrically connected with the first switch and the driving circuit and is used for controlling the first switch to be conducted in the shutdown stage of the electric tool. According to the technical scheme provided by the embodiment of the invention, the charging and discharging time of the electrolytic capacitor is reduced by controlling the on-off of the first switch, so that the service life of the electrolytic capacitor is prolonged.
Description
Technical Field
The embodiment of the invention relates to the technical field of electronics, in particular to an overvoltage protection circuit and method for an electric tool and the electric tool.
Background
High voltage brushless motors are electronically commutated using semiconductor switching devices, i.e., electronic switching devices replace conventional contact commutators and brushes. The electric tool has the advantages of high reliability, no reversing spark, low mechanical noise and the like, and is widely applied to various electric tools.
When the armature of the brushless motor rotates, the electromotive force induced in the armature winding is called as counter electromotive force because the direction of the electromotive force is opposite to the current direction; due to the existence of the counter electromotive force, the brushless motor has follow current on a bus in the shutdown stage, so that voltage spike is generated. In the prior art, an electrolytic capacitor is usually adopted to stabilize input voltage, but when a brushless motor works, the electrolytic capacitor is continuously charged and discharged to cause large heat productivity, so that the service life of the electrolytic capacitor is short.
Disclosure of Invention
The embodiment of the invention provides an overvoltage protection circuit and method of an electric tool and the electric tool, so as to prolong the service life of an electrolytic capacitor.
In a first aspect, an embodiment of the present invention provides an overvoltage protection circuit for a power tool, including: the circuit comprises a rectifying circuit, a first capacitor branch circuit, a second capacitor branch circuit, a driving circuit and a control circuit;
the rectifying circuit is used for converting the accessed alternating current into direct current and outputting the direct current; the rectifying circuit is electrically connected with the driving circuit, the driving circuit is electrically connected with the motor, and a first capacitor branch and a second capacitor branch are connected in parallel on a circuit connected with the rectifying circuit and the driving circuit;
the first capacitor branch circuit comprises a first capacitor, and the first capacitor branch circuit is electrically connected with the rectifying circuit to filter the direct current output by the rectifying circuit; the second capacitor branch comprises a first switch and a second capacitor which are connected in series, and the capacitance value of the second capacitor is greater than that of the first capacitor; the control circuit is respectively electrically connected with the first switch and the driving circuit, and the control circuit is used for outputting a conducting signal to the first switch in the power-off stage of the electric tool so as to control the first switch to be conducted.
In a second aspect, the embodiment of the invention further provides an overvoltage protection method for an electric tool, where the overvoltage protection method for the electric tool is executed by the overvoltage protection circuit for the electric tool provided by the embodiment of the invention;
the overvoltage protection method of the electric tool comprises the following steps:
when the control circuit detects a shutdown signal of the electric tool, the control circuit outputs a conducting signal to the first switch to control the first switch to be conducted, and the second capacitor is connected to the bus.
In a third aspect, an embodiment of the present invention further provides an electric tool, including the overvoltage protection circuit and the motor of the electric tool provided in the embodiment of the present invention; the power tool also includes a housing.
According to the embodiment of the invention, the first capacitor branch and the second capacitor branch are connected in parallel on a line connected with the rectifying circuit and the driving circuit. The first capacitor branch circuit comprises a first capacitor and is used for filtering the voltage output by the rectifying circuit; the second capacitor branch comprises a first switch and a second capacitor, and when the electric tool is in a shutdown stage, the control circuit controls the first switch to be conducted, and the second capacitor is connected to the bus to absorb a voltage spike on the bus. According to the technical scheme provided by the embodiment of the invention, the second capacitor is connected to the power-off stage of the electric tool to absorb the voltage spike generated on the bus by the follow current of the brushless motor, and the second capacitor is connected to the bus only when the electric tool is powered off, so that the service life of the second capacitor is prolonged.
Drawings
Fig. 1 is a block diagram of an overvoltage protection circuit of an electric tool according to an embodiment of the present invention;
fig. 2 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the invention;
fig. 3 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the invention;
fig. 4 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the invention;
fig. 5 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the invention;
fig. 6 is a schematic structural diagram of an electric tool according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Fig. 1 is a block diagram of an overvoltage protection circuit of an electric tool according to an embodiment of the present invention. Referring to fig. 1, the overvoltage protection circuit of the power tool includes: the circuit comprises a rectifying circuit 10, a first capacitor branch 20, a second capacitor branch 30, a driving circuit 40 and a control circuit 50;
the rectifying circuit 10 is used for converting the accessed alternating current into direct current and outputting the direct current; the rectifying circuit 10 is electrically connected with the driving circuit 40, the driving circuit 40 is electrically connected with the brushless motor 70, and a first capacitor branch 20 and a second capacitor branch 30 are connected in parallel on a line connected with the rectifying circuit 10 and the driving circuit 40;
the first capacitor branch circuit 20 comprises a first capacitor C1, and the first capacitor branch circuit 20 is electrically connected with the rectifier circuit 10 to filter the direct current output by the rectifier circuit 10; the second capacitor branch 30 comprises a first switch K1 and a second capacitor C2 which are connected in series, and the capacitance value of the second capacitor C2 is larger than that of the first capacitor C1; the control circuit 50 is electrically connected to the first switch K1 and the driving circuit 40, and the control circuit 50 is configured to output a conducting signal to the first switch K1 to control the first switch K1 to be conducted during a power-off stage of the power tool.
Specifically, the power supply 60 is an ac power supply, the rectifying circuit 10 converts the ac power output by the power supply 60 into dc power to provide the operating voltage for the driving circuit 40, the first capacitor branch 20 includes a first capacitor C1, and the first capacitor C1 can be used to filter the dc power output by the rectifying circuit 10. Because the first capacitor C1 is a filter capacitor, if the first capacitor C1 is an electrolytic capacitor, the first capacitor C1 generates a large amount of heat due to continuous charging and discharging when the electric tool is in operation, thereby shortening the service life of the first capacitor C1. Therefore, in some embodiments, the first capacitor C1 is a thin film capacitor, which is not easily damaged by heat.
The control circuit 50 outputs a PWM signal to the drive circuit 40, and the drive circuit 40 controls the motor 70 to rotate according to the received PWM signal. The motor 70 may be a brushless motor, and when an armature of the brushless motor rotates, a counter electromotive force in a direction opposite to a current direction is generated in an armature winding. When the power tool is turned off (i.e., the motor 70 is turned off), a voltage spike is formed on the bus bar due to a free-wheeling between the armature windings caused by the back emf of the motor 70.
In the embodiment of the present invention, the second capacitor branch 30 is connected in parallel to the line connecting the rectifying circuit 10 and the driving circuit 40 to absorb the voltage spike generated by the power tool in the shutdown stage. The second capacitor branch 30 includes a first switch K1 and a second capacitor C2, when the power tool is in a shutdown phase, the control circuit 50 generates a conducting signal of the first switch K1 according to the shutdown signal, the first switch K1 is closed, the second capacitor C2 is connected to the bus, and the second capacitor C2 absorbs a voltage spike on the bus. When the electric tool works normally, the first switch K1 is in an off state, the second capacitor C2 does not participate in the work, and the service life of the second capacitor C2 can be prolonged. Illustratively, the capacitance value of the second capacitor C2 is greater than that of the first capacitor C1, and the capacitance value of the second capacitor C2 is greater, so that when the bus voltage suddenly changes, the second capacitor C2 can absorb the energy of the sudden change wave through greater charges, so that the sudden change wave is gentle, and the voltage spike on the bus can be absorbed more favorably.
According to the embodiment of the invention, the first capacitor branch and the second capacitor branch are connected in parallel on a line connected with the rectifying circuit and the driving circuit. The first capacitor branch comprises a first capacitor and is used for filtering direct current output by the rectifying circuit; the second capacitor branch comprises a first switch and a second capacitor, and when the electric tool is in a shutdown stage, the control circuit controls the first switch to be conducted, and the second capacitor is connected to the bus to absorb a voltage spike on the bus. According to the technical scheme provided by the embodiment of the invention, the second capacitor is connected to the power-off stage of the electric tool to absorb the voltage spike generated on the bus by the follow current of the brushless motor, and the second capacitor is connected to the bus only when the electric tool is powered off, so that the service life of the second capacitor is prolonged.
Optionally, based on the above embodiment, the first capacitor C1 is a film capacitor, and the second capacitor C2 is an electrolytic capacitor.
Specifically, the first capacitor C1 may be a thin film capacitor for filtering the dc power output by the rectifier circuit 10, and the capacitance value of the thin film capacitor is small relative to the capacitance value of the electrolytic capacitor, so that the voltage spike cannot be absorbed. The second capacitor C2 may be an electrolytic capacitor, and is configured to absorb an overvoltage on the bus during a shutdown phase of the power tool, where a capacitance value of the electrolytic capacitor is large, and when the overvoltage occurs on the bus, the electrolytic capacitor absorbs surge energy generated by a voltage spike of the overvoltage through a large electric charge, so as to stabilize a voltage on the bus. And the second capacitor C2 is connected to the bus only in the shutdown stage of the electric tool, so that the heat productivity of the electrolytic capacitor can be reduced, and the service life of the second capacitor C2 can be prolonged.
Optionally, fig. 2 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the present invention. On the basis of the above embodiment, referring to fig. 2, the first switch K1 includes the transistor T, and the rectifier circuit 10 includes the first output terminal a1 and the second output terminal a 2; a first end of the transistor T is electrically connected to the first output end a1 of the rectifier circuit 10, a second end of the transistor T is electrically connected to the first end of the second capacitor C2, a second end of the second capacitor C2 is electrically connected to the second output end a2 of the rectifier circuit 10, a third end of the transistor T is electrically connected to the second output end D2 of the control circuit 50, and the first output end D1 of the control circuit 50 is electrically connected to the control end B3 of the drive circuit 10.
In particular, the transistor T may be an IGBT with a relatively high switching frequency, and can be turned on quickly during the power tool shutdown phase, so as to quickly connect the second capacitor C2 into the bus line. The shutdown phase of the power tool may be understood as a time period from turning off the power switch to stopping the rotation of the motor 70, or a time period from detecting the shutdown signal to stopping the rotation of the motor 70. For example, when the power tool detects a shutdown signal through a software program, the control circuit 50 sends a conducting signal of the transistor T, and the transistor T is turned on according to the conducting signal, so that the second capacitor C2 is connected to the bus line to absorb a voltage spike in the bus.
Optionally, the transistor T is turned on during the power tool shutdown phase, and the second capacitor C2 is connected to the bus. The advantage of this arrangement is that since the second capacitor C2 is an electrolytic capacitor, during operation, the electrolytic capacitor is prone to heat and the service life of the electrolytic capacitor is reduced, so that the transistor T is turned on only during the shutdown phase of the power tool, and the second capacitor C2 is connected to the bus to absorb the voltage spike; when the electric tool is in normal operation, the transistor T is turned off, the second capacitor C2 is out of operation, the operation time of the second capacitor C2 is reduced, and the service life of the second capacitor C2 can be prolonged.
Optionally, fig. 3 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the present invention. On the basis of the above embodiment, referring to fig. 3, the control circuit 50 includes a controller 51 and a driving chip 52, and the driving chip 52 includes a control terminal F1 and an output terminal F2;
the controller 51 includes a first output terminal E1 and a second output terminal E2, the first output terminal E1 of the controller 51 is electrically connected to the control terminal F1 of the driving chip 52, the second output terminal E2 of the controller 51 is electrically connected to the third terminal of the transistor T, and the output terminal F2 of the driving chip 52 outputs a driving signal to the driving circuit 40.
Specifically, the driving circuit 40 may be a bridge structure, and is composed of three sets of electronic switches, and the driving chip 52 is configured to control the electronic switches in the driving circuit 40 to be turned on or off. The driving chip 52 is connected in series between the controller 51 and the driving circuit 40, receives the control signal output by the controller 51, and controls the electronic switch in the driving circuit 40 to be turned on or off according to the control signal. For example, the control signal output by the controller 51 may be a PWM control signal. In the present embodiment, the driving chip 52 is shown as being separate from the controller 51, and in other embodiments, the driving chip 52 and the controller 51 may be integrated into a single body.
Optionally, on the basis of the above embodiment, with continued reference to fig. 3, the overvoltage protection circuit of the power tool further includes a power conversion circuit 80 and a second switch K2, and the driving chip 52 further includes a power supply terminal F3;
the second switch K2 is used to turn on or off the motor 70; the power conversion circuit 80 comprises a first input end G1, a second input end G2 and an output end G3, the first input end G1 of the power conversion circuit 80 is electrically connected with the first output end a1 of the rectifying circuit 10, the second input end G2 of the power conversion circuit 80 is electrically connected with the second output end a2 of the rectifying circuit 10, and the output end G3 of the power conversion circuit 80 is electrically connected with the power supply end F3 of the driving chip 52 or the controller 51 through a second switch K2; the controller 51 is configured to output a turn-on signal to the first switch K1 to control the first switch K1 to turn on when the second switch K2 is turned off; the second switch K2 is an electronic switch or a mechanical switch.
Specifically, the power conversion circuit 80 may be a DC/DC circuit for converting the rectified DC voltage into the operating voltage required by the driving chip 52. The second switch K2 may be a start switch of the power tool for starting or stopping the motor 70, or the shutdown phase of the power tool may be a period of time after the second switch is turned off. The second switch K2 may be an electronic switch or a mechanical switch, when the second switch K2 is closed, the driving chip 52 and/or the controller 51 receives an electrical signal from the power conversion circuit 80, and the motor 70 is powered on; when the second switch K2 is turned off, the electrical connection between the driving chip 52 and/or the controller 51 and the power conversion circuit 80 is cut off, and the motor 70 is powered off. Illustratively, the second switch K2 is closed, the power conversion circuit 80 converts the dc voltage output by the rectifying circuit 10 into the working voltage required by the driver chip 52 or the controller 51, and the driver chip 52 and the controller 51 are started; the controller 51 outputs a PWM control signal to the driving chip 52, and the driving chip 52 controls the conduction of the electronic switch in the driving circuit 40 according to the PWM control signal output by the controller 51, so as to drive the motor 70 to rotate. When the second switch K2 is turned off, the controller 51 outputs a conducting signal of the transistor T, and the second capacitor C2 is connected to the bus after the transistor T is turned on, so as to absorb a voltage spike generated on the bus by the follow current when the motor 70 is turned off. When the electric tool is turned on again, the controller 51 controls the transistor T to be turned off, and the second capacitor C2 is out of operation, so as to reduce the heat generation of the second capacitor C2, which is beneficial to delaying the service life of the second capacitor C2.
Optionally, fig. 4 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the present invention. On the basis of the above embodiment, referring to fig. 4, the overvoltage protection circuit of the power tool according to the embodiment of the present invention further includes a voltage detection circuit 90, and the controller 51 further includes an input terminal E3;
the voltage detection circuit 90 includes an input terminal H1 and an output terminal H2, the input terminals H1 of the voltage detection circuit 90 are electrically connected to the three-phase windings of the motor 70, respectively, and the output terminal H2 of the voltage detection circuit 90 is electrically connected to the input terminal E3 of the controller 51.
Specifically, the voltage detection circuit 90 is used to detect the phase voltage of the motor 70. The power tool further includes a current detection circuit (not shown) for detecting the current applied to the stator winding. A rotor position calculation unit (not shown in the figure) is configured to estimate the rotor position of the brushless motor from at least the phase voltages of the brushless motor and the currents of the stator windings. For example, the inductance value of the stator winding is estimated from the phase voltage of the motor 70 and the current of the stator winding, and a one-to-one matching relationship between the inductance value and the rotor position is established (the matching relationship is established by a table lookup method, a formula modeling method, or the like), so as to obtain the position of the rotor. The controller 51 outputs a PWM control signal to the driving circuit 40 according to the rotor position obtained by the rotor position calculating unit so that the motor 70 generates a continuous torque, and the motor 70 rotates under the torque.
Of course, during normal operation of the power tool, when the voltage detection circuit 90 detects an overvoltage of the motor 70, the controller 51 outputs a turn-on signal of the transistor T to absorb a voltage spike of the overvoltage through the second capacitor C2.
Optionally, fig. 5 is a block diagram of an overvoltage protection circuit of another power tool according to an embodiment of the present invention. On the basis of the above embodiments, referring to fig. 5, the specific working principle of the overvoltage protection circuit of the power tool provided by the embodiment of the invention is as follows:
the power supply 60 supplies an alternating voltage, the rectifying circuit 10 converts the alternating voltage output by the power supply 60 into a direct voltage, and the first capacitor C1 filters the direct voltage output by the rectifying circuit 10. The switch K2 is closed, the power conversion circuit 80 converts the dc voltage output by the rectification circuit 60 into the voltage required by the driver chip 52, so as to provide the working voltage for the driver chip 52, and the driver chip is started; the controller 51 outputs a PWM control signal to the driver chip 52, and the driver chip 52 controls the electronic switches Q1-Q6 in the driver circuit 40 to be turned on according to the PWM control signal output by the controller 51. The voltage detection circuit 90 detects the phase voltage of the motor 70, and the electric power tool further includes a current detection circuit (not shown) for detecting the current applied to the stator winding. A rotor position calculation unit (not shown in the figure) is configured to estimate the rotor position of the motor from at least the phase voltages of the brushless motor and the currents of the stator windings. For example, the inductance value of the stator winding is estimated from the phase voltage of the motor 70 and the current of the stator winding, and a one-to-one matching relationship between the inductance value and the rotor position is established (the matching relationship is established by a table lookup method, a formula modeling method, or the like), so as to obtain the position of the rotor. The controller 51 adjusts the output PWM control signal to the driving circuit 40 according to the rotor position obtained by the rotor position calculating unit so that the motor 70 generates a continuous torque, and the motor 70 rotates under the action of the torque.
When the second switch K2 is turned off, the electrical connection between the driving chip 52 and/or the controller 51 and the power conversion circuit 80 is cut off, the motor 70 is powered off, the controller 51 outputs a conducting signal of the transistor T, and the second capacitor C2 is connected to the bus after the transistor T is conducted, so as to absorb a voltage spike generated on the bus by follow current when the motor 70 is turned off. When the electric tool is turned on again, the controller 51 controls the transistor T to be turned off, and the second capacitor C2 is out of operation, so as to reduce the heat generation of the second capacitor C2, which is beneficial to delaying the service life of the second capacitor C2. During the normal operation of the power tool, when the voltage detection circuit 90 detects that the motor 70 has an overvoltage, the controller 51 outputs a turn-on signal of the transistor T, and the voltage spike of the overvoltage is absorbed through the second capacitor C2, so as to further protect the safety and reliability of the power tool.
Optionally, an embodiment of the present invention further provides an overvoltage protection method for a power tool, and referring to fig. 5, the method is performed by an overvoltage protection circuit for a power tool provided in an embodiment of the present invention, where the overvoltage protection method for a power tool includes:
when the control circuit 50 detects a shutdown signal of the electric tool, it outputs a conduction signal to the first switch K1 to control the first switch K1 to be conducted, and the second capacitor C2 is connected to the bus.
Specifically, the shutdown signal may be a signal that the second switch K2 is triggered to shut down the brushless motor, or may be an abnormal protection shutdown signal, such as an overcurrent shutdown, where the brushless motor shutdown includes braking the brushless motor and stopping the brushless motor from driving for a free shutdown. When the second switch K2 is turned off, the controller 51 outputs a conducting signal of the transistor T, and the second capacitor C2 is connected to the bus after the transistor T is turned on, so as to absorb a voltage spike generated on the bus by the follow current when the motor 70 is turned off. When the electric tool is turned on again, the controller 51 controls the transistor T to be turned off, and the second capacitor C2 is out of operation, so as to reduce the heat generation of the second capacitor C2, which is beneficial to delaying the service life of the second capacitor C2.
Optionally, with continued reference to fig. 5, the method of overvoltage protection for a power tool further comprises: during normal operation, if the voltage detection circuit 90 detects an overvoltage, an overvoltage signal is output, the control circuit 50 outputs a turn-on signal according to the overvoltage signal, the first switch K1 is turned on, and the second capacitor C2 is connected to the bus.
Specifically, during the normal operation of the power tool, when the voltage detection circuit 90 detects that the motor 70 has an overvoltage, the controller 51 outputs a turn-on signal of the first switch K1, and the second capacitor C2 absorbs the voltage spike of the overvoltage, thereby further protecting the safety and reliability of the power tool.
According to the embodiment of the invention, the first capacitor branch and the second capacitor branch are connected in parallel on a line connected with the rectifying circuit and the driving circuit. The first capacitor branch circuit comprises a first capacitor and is used for filtering the voltage output by the rectifying circuit; the second capacitor branch comprises a first switch and a second capacitor, and when the electric tool is in a shutdown stage, the control circuit controls the first switch to be conducted, and the second capacitor is connected to the bus to absorb a voltage spike on the bus. According to the technical scheme provided by the embodiment of the invention, the second capacitor is connected to the power-off stage of the electric tool to absorb the voltage spike generated on the bus by the follow current of the brushless motor, and the second capacitor is connected to the bus only when the electric tool is powered off, so that the service life of the second capacitor is prolonged.
Optionally, fig. 6 is a schematic structural diagram of an electric power tool according to an embodiment of the present invention, the electric power tool includes the overvoltage protection circuit and the brushless motor of the electric power tool according to the embodiment, and the electric power tool further includes a housing. . While the present embodiment relates to a sander, it should be understood that the present invention is not limited to the disclosed embodiments, but is applicable to other types of power tools, including but not limited to angle grinders, power drills, power wrenches, power saws.
The electric tool provided by the embodiment of the present invention includes the overvoltage protection circuit of the electric tool in the above embodiment, and therefore, the electric tool provided by the embodiment of the present invention also has the beneficial effects described in the above embodiment, and details are not described herein again.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. An overvoltage protection circuit for a power tool, comprising: the circuit comprises a rectifying circuit, a first capacitor branch circuit, a second capacitor branch circuit, a driving circuit and a control circuit;
the rectifying circuit is used for converting the accessed alternating current into direct current and outputting the direct current;
the rectifying circuit is electrically connected with the driving circuit, the driving circuit is electrically connected with the motor, and a first capacitor branch and a second capacitor branch are connected in parallel on a circuit connected with the rectifying circuit and the driving circuit;
the first capacitor branch circuit comprises a first capacitor, and the first capacitor branch circuit is electrically connected with the rectifying circuit to filter the direct current output by the rectifying circuit;
the second capacitor branch comprises a first switch and a second capacitor which are connected in series, and the capacitance value of the second capacitor is greater than that of the first capacitor; the control circuit is respectively electrically connected with the first switch and the driving circuit, and the control circuit is used for outputting a conducting signal to the first switch in the power-off stage of the electric tool so as to control the first switch to be conducted.
2. The over-voltage protection circuit for a power tool of claim 1, wherein the first capacitor is a thin film capacitor and the second capacitor is an electrolytic capacitor.
3. The over-voltage protection circuit for a power tool of claim 1, wherein the first switch comprises a transistor, and the rectifying circuit comprises a first output terminal and a second output terminal; the first end of the transistor is electrically connected with the first output end of the rectifying circuit, the second end of the transistor is electrically connected with the first end of the second capacitor, the second end of the second capacitor is electrically connected with the second output end of the rectifying circuit, the third end of the transistor is electrically connected with the second output end of the control circuit, and the first output end of the control circuit is electrically connected with the control end of the driving circuit.
4. The over-voltage protection circuit for a power tool of claim 3, wherein the transistor is turned on during a shutdown phase of the power tool to connect the second capacitor to the bus.
5. The over-voltage protection circuit for a power tool according to claim 3, wherein the control circuit comprises a controller and a driver chip, the driver chip comprising a control terminal and an output terminal;
the controller comprises a first output end and a second output end, the first output end of the controller is electrically connected with the control end of the driving chip, the second output end of the controller is electrically connected with the third end of the transistor, and the output end of the driving chip outputs a driving signal to the driving circuit.
6. The overvoltage protection circuit for a power tool according to claim 5, further comprising a power conversion circuit and a second switch, wherein the driver chip further comprises a power supply terminal;
the second switch is used for starting or closing the motor;
the power supply conversion circuit comprises a first input end, a second input end and an output end, the first input end of the power supply conversion circuit is electrically connected with the first output end of the rectifying circuit, the second input end of the power supply conversion circuit is electrically connected with the second output end of the rectifying circuit, and the output end of the power supply conversion circuit is electrically connected with a power supply end of the driving chip or the controller through the second switch;
the controller is used for outputting a conducting signal to the first switch to control the first switch to be conducted when the second switch is disconnected; the second switch is an electronic switch or a mechanical switch.
7. The over-voltage protection circuit for a power tool of claim 5, further comprising a voltage detection circuit, the controller further comprising an input;
the voltage detection circuit comprises an input end and an output end, the input end of the voltage detection circuit is respectively electrically connected with the three-phase winding of the motor, and the output end of the voltage detection circuit is electrically connected with the input end of the controller.
8. A method of overvoltage protection for a power tool, wherein the method of overvoltage protection for a power tool is performed by an overvoltage protection circuit for a power tool according to any one of claims 1 to 7;
the overvoltage protection method of the electric tool comprises the following steps:
when the control circuit detects a shutdown signal of the electric tool, the control circuit outputs a conducting signal to the first switch to control the first switch to be conducted, and the second capacitor is connected to the bus.
9. The method of claim 8, further comprising: in the normal operation process, if the voltage detection circuit detects overvoltage, an overvoltage signal is output, the control circuit outputs a conduction signal according to the overvoltage signal, the first switch is conducted, and the second capacitor is connected to the bus.
10. A power tool comprising the overvoltage protection circuit of the power tool of any one of claims 1 to 7 and a motor;
the power tool also includes a housing.
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| CN113054887B (en) | 2024-01-05 |
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