A control circuit for a single-phase AC motor

Abstract

The present invention discloses a control circuit for a single-phase AC motor that can adjust the speed of the single-phase AC motor and provide all-round protection for the single-phase AC motor, including: a working power supply, a bidirectional thyristor, a trigger circuit for controlling the bidirectional thyristor, a timing synchronization circuit, and an over-voltage and under-voltage sampling circuit, an overheat sampling circuit, and an overcurrent sampling circuit. The trigger circuit includes: a pulse width modulation circuit and a triggering photoelectric isolation circuit. The two output pins of the triggering photoelectric isolation circuit are respectively connected to the two main electrodes of the bidirectional thyristor through an output-side current limiting resistor, and the gate of the bidirectional thyristor is connected to the corresponding output pin of the triggering photoelectric isolation circuit; the output pin of the pulse width modulation circuit is connected to the control end of the triggering photoelectric isolation circuit, and an anti-interference circuit is provided between the power pin of the triggering photoelectric isolation circuit and the working power supply. The control circuit described in the present invention can be widely used in various single-phase AC motors.

Description

Technical Field

[0001] The invention relates to a control circuit of an AC motor, and in particular to a control circuit of a single-phase AC motor. Background Art

[0002] At present, the AC motors in traditional handheld threading machines all use a fixed speed, that is, their speed cannot be adjusted. Therefore, their control circuits are relatively simple, and usually only a fuse (fuse) is connected in series in the power supply circuit of the AC motor. In actual use, on the one hand, the starting current is large, which makes the temperature rise of the AC motor large, shortening the service life of the AC motor; on the other hand, since the AC motor reaches the rated speed quickly in an instant, there are serious safety hazards for the operator and related personnel around; in addition, the control circuit can only protect the AC motor from overcurrent, and cannot sense the overvoltage, undervoltage and overheating of the AC motor, so it cannot provide all-round protection for the AC motor, shortening the service life of the AC motor. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a control circuit for a single-phase AC motor which can adjust the speed of the single-phase AC motor and provide all-round protection for the single-phase AC motor.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a control circuit of a single-phase AC motor, whose structure includes: a working power supply, a bidirectional thyristor, a trigger circuit for controlling the bidirectional thyristor, a timing synchronization circuit for synchronizing the trigger circuit, and an over-voltage and under-voltage sampling circuit, an overheat sampling circuit and an overcurrent sampling circuit. The specific structure of the trigger circuit includes: a pulse width modulation circuit and a triggering photoelectric isolation circuit, the two output pins of the triggering photoelectric isolation circuit are respectively connected to the two main electrodes of the bidirectional thyristor through the output side current limiting resistor, and the gate of the bidirectional thyristor is connected to the corresponding output pin of the triggering photoelectric isolation circuit; the output pin of the pulse width modulation circuit is connected to the triggering photoelectric isolation circuit. The trigger photoelectric isolation circuit is connected to the control end of the trigger photoelectric isolation circuit, and an anti-interference circuit is arranged between the power supply pin of the trigger photoelectric isolation circuit and the working power supply. The anti-interference circuit includes: a PNP type secondary transistor, an NPN type primary transistor, a diode, an input side current limiting resistor and a pair of voltage-dividing resistors. The pair of voltage-dividing resistors includes: a power supply side voltage-dividing resistor and a grounding side voltage-dividing resistor. The resistance of the power supply side voltage-dividing resistor is greater than twice the grounding side voltage-dividing resistor. One end of the power supply side voltage-dividing resistor is connected to one end of the grounding side voltage-dividing resistor and then to the positive electrode of the diode. The other end of the power supply side voltage-dividing resistor is connected to the positive electrode of the working power supply. The other end of the grounding side voltage-dividing resistor is connected to the negative electrode of the working power supply. The negative electrode of the tube is connected to the base of the primary triode, the collector of the primary triode is connected to the base of the secondary triode through the input side current limiting resistor, the emitter of the primary triode is connected to the negative electrode of the working power supply, the emitter of the secondary triode is connected to the positive electrode of the working power supply, and the collector of the secondary triode is connected to the power pin of the trigger photoelectric isolation circuit; the specific structure of the over-undervoltage sampling circuit includes: a transformer, a half-wave rectifier diode, a charging capacitor, an over-undervoltage output resistor, a pull-down resistor, an over-undervoltage output filter capacitor, a power side diode, a ground side diode and upper and lower limit voltage dividing resistors, the primary coil of the transformer is connected to the alternating current, and the phase lines of the secondary coil of the transformer are of the same name The end is connected to the positive electrode of the half-wave rectifier diode, the negative electrode of the half-wave rectifier diode is connected to one end of the upper limit voltage-dividing resistor, the other end of the upper limit voltage-dividing resistor is connected to one end of the lower limit voltage-dividing resistor and the corresponding end of the charging capacitor, the other end of the charging capacitor and the other end of the lower limit voltage-dividing resistor are grounded, and the connected ends of the upper and lower limit voltage-dividing resistors serve as the over-voltage and under-voltage output ends, one end of the pull-down resistor, the corresponding end of the over-voltage and under-voltage output filter capacitor, the positive electrode of the power supply side diode, and the negative electrode of the grounding side diode are connected to the over-voltage and under-voltage output ends, and the other end of the pull-down resistor, the other end of the over-voltage and under-voltage output filter capacitor, the negative electrode of the power supply side diode, and the positive electrode of the grounding side diode are grounded.

[0005] As a preferred solution, in the control circuit of the single-phase AC motor, the timing synchronization circuit includes: a photoelectric isolation circuit for synchronization, the two input ends of the photoelectric isolation circuit for synchronization are connected in series to the AC power supply circuit through an AC current limiting resistor, the power pin on the receiving side of the photoelectric isolation circuit is connected to the working power supply through a pull-up resistor, and the output pin on the receiving side of the photoelectric isolation circuit is connected in series with a resistor to form an output end to output a synchronous timing signal.

[0006] As a preferred solution, in the control circuit of the single-phase AC motor, the timing synchronization circuit also includes: a power supply side diode and a grounding side diode, the positive electrode of the power supply side diode and the negative electrode of the grounding side diode are connected to the output end of the receiving side of the photoelectric isolation circuit, the negative electrode of the power supply side diode is connected to the positive electrode of the working power supply, and the positive electrode of the grounding side diode is connected to the negative electrode of the working power supply.

[0007] As a preferred solution, in the control circuit of the single-phase AC motor, a RC absorption circuit is arranged between the two main electrodes of the bidirectional thyristor, and the RC absorption circuit includes an absorption resistor and an absorption capacitor connected in series.

[0008] As a preferred solution, in the control circuit of the single-phase AC motor, an anti-interference filter capacitor is arranged between one end of the pair of voltage-dividing resistors connected to the positive electrode of the diode and the negative electrode of the working power supply.

[0009] As a preferred solution, in the control circuit of the single-phase AC motor, the specific structure of the overcurrent sampling circuit includes: a current transformer, a ninth filter capacitor and a nineteenth resistor are connected in parallel between the two output ends of the current transformer, and a capacitor to ground is provided on the corresponding end of the current transformer, and an overcurrent output resistor is connected in series as the overcurrent output end, and the other end of the current transformer is grounded.

[0010] As a preferred solution, in the control circuit of the single-phase AC motor, the control circuit also includes a ninth transient diode, the cathode of the ninth transient diode is connected to the corresponding end of the current transformer, and the anode of the ninth transient diode is grounded.

[0011] As a preferred solution, in the control circuit of the single-phase AC motor, the specific structure of the overheat sampling circuit includes: a temperature sensor, the corresponding end of the temperature sensor serves as the overheat output end, and the other end is grounded, and the overheat output end is provided with a twenty-first resistor and an eleventh filter capacitor to the ground.

[0012] As a preferred solution, in the control circuit of the single-phase AC motor, the control circuit further includes a tenth transient diode, the cathode of the tenth transient diode is connected to the overheat output terminal, and the anode of the tenth transient diode is grounded.

[0013] As a preferred solution, in the control circuit of the single-phase AC motor, a charging filter capacitor is connected in parallel at both ends of the charging capacitor.

[0014] The beneficial effects of the present invention are as follows: the control circuit described in the present invention is simple and practical, with low cost, and can realize stepless speed regulation for the AC motor, thus avoiding the situation that the AC motor generates heat due to excessive current when starting, and prolonging the service life of the AC motor. Moreover, since the AC motor can be started at a relatively low speed and then the speed can be increased according to the actual situation, the personal safety of the operator and the surrounding personnel is more reliably guaranteed; in addition, the present invention provides all-round protection for the AC motor by setting an over-voltage sampling circuit, an under-voltage sampling circuit, an overheating sampling circuit and an over-current sampling circuit, so that the AC motor will not be damaged due to sudden abnormalities, greatly prolonging the service life of the AC motor. In addition, the over-voltage sampling circuit, the under-voltage sampling circuit, the overheating sampling circuit and the over-current sampling circuit adopted by the present invention are simple and practical in structure, greatly reducing the cost and increasing the market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the electrical principle structure of the control circuit of the single-phase AC motor described in the present invention. DETAILED DESCRIPTION

[0016] The specific implementation scheme of the control circuit of a single-phase AC motor according to the present invention is described in detail below with reference to the accompanying drawings.

[0017] like Figure 1As shown, a control circuit of a single-phase AC motor described in the present invention includes: a working power supply VCC5, a bidirectional thyristor Q3 of model BAT41, a trigger circuit for controlling the bidirectional thyristor Q3, a timing synchronization circuit for synchronizing the trigger circuit, and an over-voltage and under-voltage sampling circuit, an overheat sampling circuit, and an overcurrent sampling circuit. The timing synchronization circuit includes: an optocoupler U2 as a synchronization optoelectronic isolation circuit, a power supply side diode D7, and a grounding side diode D8. The two input pins of the optocoupler U2 are connected in series to the AC power supply circuit through an AC current limiting resistor, resistors R11, R12, and R13 are connected in parallel to form a first parallel resistor group, resistors R14, R15, and R16 are connected in parallel to form a second parallel group, and the first parallel group and the second parallel group are connected in series to form an AC current limiting resistor. The power pin on the receiving side of the optocoupler U2 is connected to the working power supply VCC5 through a pull-up resistor R17, and the output pin on the receiving side of the optocoupler U2 is connected in series to the working power supply VCC5. After connecting the resistor R18, the output end outputs the synchronous timing signal, the output end of the receiving side of the optical coupler U2 is connected to the positive electrode of the diode D7 on the power supply side and the negative electrode of the diode D8 on the grounding side, the negative electrode of the diode D7 on the power supply side is connected to the positive electrode of the working power supply VCC5, and the positive electrode of the diode D8 on the grounding side is connected to the negative electrode of the working power supply VCC5; the specific structure of the trigger circuit includes: a pulse width modulation circuit (which belongs to the conventional technology in this field, not shown in the figure, and can of course be generated by microprocessor simulation), and an optical coupler U1 of model MOC3163 as a triggering photoelectric isolation circuit, one output pin of the optical coupler U1 is connected to a main electrode of the bidirectional thyristor Q3 through the output side current limiting resistor R4, the other output pin of the optical coupler U1 is connected to the other main electrode of the bidirectional thyristor Q3 through the output side current limiting resistor R5, and the other output pin of the optical coupler U1 is connected to the gate of the bidirectional thyristor Q3;The output pin of the pulse width modulation circuit is connected to the control pin of the optical coupler U1, and an anti-interference circuit is arranged between the power pin of the optical coupler U1 and the working power supply VCC5, and the anti-interference circuit includes: a PNP type secondary transistor Q2, an NPN type primary transistor Q1, a diode D1, an input side current limiting resistor R3 and a pair of voltage-dividing resistors, and the pair of voltage-dividing resistors includes: a power side voltage-dividing resistor R1 and a ground side voltage-dividing resistor R2, the resistance value of the power side voltage-dividing resistor R1 is greater than twice the resistance value of the ground side voltage-dividing resistor R2, and preferably the resistance value of the power side voltage-dividing resistor R1 is greater than three times the resistance value of the ground side voltage-dividing resistor R2 (here, a 36KΩ resistor is selected as the power side voltage-dividing resistor R1, and an 8KΩ resistor is selected as the ground side voltage-dividing resistor R2). One end of the source side voltage-dividing resistor R1 is connected to one end of the ground side voltage-dividing resistor R2 and then to the positive electrode of the diode D1. The other end of the power side voltage-dividing resistor R1 is connected to the positive electrode of the working power supply VCC5. The other end of the ground side voltage-dividing resistor R2 is connected to the negative electrode of the working power supply VCC. The negative electrode of the diode D1 is connected to the base of the first-level transistor Q1. The collector of the first-level transistor Q1 is connected to the base of the second-level transistor Q2 through the input side current-limiting resistor R3. The emitter of the first-level transistor Q1 is connected to the negative electrode of the working power supply VCC5 (commonly known as grounding). The emitter of the second-level transistor Q2 is connected to the positive electrode of the working power supply VCC5. The collector of the second-level transistor Q2 is connected to the power pin of the optocoupler U1. In this embodiment, a resistance-capacitance absorption circuit is arranged between the two main electrodes of the bidirectional thyristor Q3, and the resistance-capacitance absorption circuit includes: an absorption resistor R6 and an absorption capacitor C2 connected in series, and an anti-interference filter capacitor C1 is arranged between one end of the power supply side voltage divider resistor R1 and the ground side voltage divider resistor R2 connected to the positive electrode of the diode D1 and the negative electrode of the working power supply VCC5;The over-voltage and under-voltage sampling circuit includes: a transformer T1 (reused with a power supply circuit), a half-wave rectifier diode D3, a charging capacitor C6, an over-voltage and under-voltage output resistor R9, a pull-down resistor R10, an over-voltage and under-voltage output filter capacitor C8, a power supply side diode D5, a grounding side diode D6, and an upper limit voltage divider resistor R7 and a lower limit voltage divider resistor R8. The two ends of the primary coil of the transformer T1 are respectively connected to the LIN and NIN of the alternating current, the same-name end of the phase line (LIN) of the secondary coil of the transformer T1 is connected to the positive electrode of the half-wave rectifier diode D3, and the negative electrode of the half-wave rectifier diode D3 is connected to one end of the upper limit voltage divider resistor R7. The upper limit voltage-dividing resistor R7 is connected, the other end of the upper limit voltage-dividing resistor R7 is connected to one end of the lower limit voltage-dividing resistor R8 and the corresponding end of the charging capacitor C6, the two ends of the charging capacitor C6 are also connected in parallel with the charging filter capacitor C7, the other end of the charging capacitor C6 and the other end of the lower limit voltage-dividing resistor R8 are grounded, the connected ends of the upper and lower limit voltage-dividing resistors R7 and R8 are used as over-undervoltage output ends, and are connected to one end of the pull-down resistor R10, the corresponding end of the over-undervoltage output end filter capacitor C8, and the positive electrode of the power supply side diode D5 and the negative electrode of the grounding side diode D6, the other end of the pull-down resistor R10, the other end of the over-undervoltage output end filter capacitor C8, the power supply side diode D5 The cathode of the tube D5 and the anode of the grounding side diode D6 are grounded; the specific structure of the overcurrent sampling circuit includes: a current transformer (which belongs to the conventional technology in this field, not shown in the figure) and a ninth transient diode D9, a ninth filter capacitor C9 and a nineteenth resistor R19 are connected in parallel between the two output ends of the current transformer through a plug CT and a corresponding socket (which belongs to the conventional technology in this field, not shown in the figure), a capacitor C10 to ground is provided at the corresponding end of the current transformer, and an overcurrent output resistor R20 is connected in series as the overcurrent output end, the other end of the current transformer is grounded through a plug TEMP, and the cathode of the ninth transient diode D9 is connected to the The corresponding ends of the current transformer are connected, and the positive pole of the ninth transient diode D9 is grounded; the specific structure of the overheat sampling circuit includes: a temperature sensor (which belongs to the conventional technology in this field, not shown in the figure), and a tenth transient diode D10. The temperature sensor uses the corresponding end as the overheat output end through the plug TEMP and the corresponding socket (which belongs to the conventional technology in this field, not shown in the figure), and the other end is grounded. The overheat output end D10 is provided with a twenty-first resistor R21 and an eleventh filter capacitor C11 to the ground, and the negative pole of the tenth transient diode D10 is connected to the overheat output end, and the positive pole of the tenth transient diode D10 is grounded. ;

[0018] In summary, the above is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes and modifications made to the shape, structure, characteristics and spirit described in the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A control circuit for a single-phase AC motor, comprising: A working power supply, a bidirectional thyristor, a trigger circuit for controlling the bidirectional thyristor, a timing synchronization circuit for synchronizing the trigger circuit, and an over-voltage and under-voltage sampling circuit, an overheat sampling circuit and an overcurrent sampling circuit, characterized in that the specific structure of the trigger circuit includes: a pulse width modulation circuit and a triggering photoelectric isolation circuit, the two output pins of the triggering photoelectric isolation circuit are respectively connected to the two main electrodes of the bidirectional thyristor through an output-side current limiting resistor, and the gate of the bidirectional thyristor is connected to the corresponding output pin of the triggering photoelectric isolation circuit; the output pin of the pulse width modulation circuit is connected to the control end of the triggering photoelectric isolation circuit, and the power supply of the triggering photoelectric isolation circuit An anti-interference circuit is arranged between the pin and the working power supply, and the anti-interference circuit includes: a PNP type secondary transistor, an NPN type primary transistor, a diode, an input side current limiting resistor and a pair of voltage-dividing resistors, and the pair of voltage-dividing resistors include: a power supply side voltage-dividing resistor and a grounding side voltage-dividing resistor, the resistance of the power supply side voltage-dividing resistor is greater than twice the grounding side voltage-dividing resistor, one end of the power supply side voltage-dividing resistor is connected to one end of the grounding side voltage-dividing resistor and then to the positive electrode of the diode, the other end of the power supply side voltage-dividing resistor is connected to the positive electrode of the working power supply, the other end of the grounding side voltage-dividing resistor is connected to the negative electrode of the working power supply, the negative electrode of the diode is connected to the base of the primary transistor, and the primary The collector of the transistor is connected to the base of the secondary transistor through the input-side current-limiting resistor, the emitter of the primary transistor is connected to the negative electrode of the working power supply, the emitter of the secondary transistor is connected to the positive electrode of the working power supply, and the collector of the secondary transistor is connected to the power pin of the trigger photoelectric isolation circuit; the specific structure of the over-undervoltage sampling circuit includes: a transformer, a half-wave rectifier diode, a charging capacitor, an over-undervoltage output resistor, a pull-down resistor, an over-undervoltage output filter capacitor, a power-side diode, a grounding diode and upper and lower limit voltage-dividing resistors, the primary coil of the transformer is connected to the alternating current, and the same-name end of the phase line of the secondary coil of the transformer is connected to the half-wave rectifier. The positive pole of the diode is connected, the negative pole of the half-wave rectifier diode is connected to one end of the upper limit voltage-dividing resistor, the other end of the upper limit voltage-dividing resistor is connected to one end of the lower limit voltage-dividing resistor and the corresponding end of the charging capacitor, the other end of the charging capacitor and the other end of the lower limit voltage-dividing resistor are grounded, the connected ends of the upper and lower limit voltage-dividing resistors serve as the over- and under-voltage output ends, one end of the pull-down resistor, the corresponding end of the over- and under-voltage output filter capacitor, the positive pole of the power supply side diode, and the negative pole of the grounding side diode are connected to the over- and under-voltage output ends, the other end of the pull-down resistor, the other end of the over- and under-voltage output filter capacitor, the negative pole of the power supply side diode, and the positive pole of the grounding side diode are grounded.

2. The control circuit of the single-phase AC motor according to claim 1, characterized in that: The timing synchronization circuit includes: a photoelectric isolation circuit for synchronization, the two input ends of the photoelectric isolation circuit for synchronization are connected in series to an AC power supply circuit through an AC current limiting resistor, the power pin on the receiving side of the photoelectric isolation circuit is connected to the working power supply through a pull-up resistor, and the output pin on the receiving side of the photoelectric isolation circuit is connected in series with a resistor to form an output end to output a synchronous timing signal.

3. The control circuit of the single-phase AC motor according to claim 1, characterized in that: The timing synchronization circuit also includes: a power supply side diode and a grounding side diode, the positive electrode of the power supply side diode and the negative electrode of the grounding side diode are connected to the output end of the receiving side of the photoelectric isolation circuit, the negative electrode of the power supply side diode is connected to the positive electrode of the working power supply, and the positive electrode of the grounding side diode is connected to the negative electrode of the working power supply.

4. The control circuit of the single-phase AC motor according to claim 1, characterized in that: A resistance-capacitance absorption circuit is arranged between the two main electrodes of the bidirectional thyristor, and the resistance-capacitance absorption circuit comprises an absorption resistor and an absorption capacitor connected in series.

5. The control circuit of the single-phase AC motor according to claim 1, characterized in that: An anti-interference filtering capacitor is arranged between one end of the pair of voltage-dividing resistors connected to the positive electrode of the diode and the negative electrode of the working power supply.

6. The control circuit of the single-phase AC motor according to any one of claims 1 to 5, characterized in that: The specific structure of the overcurrent sampling circuit includes: a current transformer, a ninth filter capacitor and a nineteenth resistor are connected in parallel between the two output ends of the current transformer, and a capacitor to ground is arranged on the corresponding end of the current transformer, and an overcurrent output resistor is connected in series as the overcurrent output end, and the other end of the current transformer is grounded.

7. The control circuit of the single-phase AC motor according to claim 6, characterized in that: The control circuit further includes a ninth transient diode, the cathode of the ninth transient diode is connected to the corresponding end of the current transformer, and the anode of the ninth transient diode is grounded.

8. The control circuit of the single-phase AC motor according to any one of claims 1 to 5, characterized in that: The specific structure of the overheat sampling circuit includes: a temperature sensor, a corresponding end of the temperature sensor is used as an overheat output end, and the other end is grounded, and the overheat output end is provided with a twenty-first resistor and an eleventh filter capacitor to the ground.

9. The control circuit of the single-phase AC motor according to claim 8, characterized in that: The control circuit further includes a tenth transient diode, the cathode of the tenth transient diode is connected to the overheat output terminal, and the anode of the tenth transient diode is grounded.

10. The control circuit of the single-phase AC motor according to any one of claims 1 to 5, characterized in that: The two ends of the charging capacitor are also connected in parallel with a charging filter capacitor.

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