AC motor stall protection circuit

Abstract

The present invention relates to the field of motor technology, and in particular to an AC motor stall protection circuit. The circuit comprises a current sampling resistor, a coupling capacitor, a motor drive circuit, a conversion circuit, and a control module. The current sampling resistor and the motor drive circuit are used to connect an AC voltage to the motor. The conversion circuit is used to generate a stall detection signal having a waveform identical to the AC voltage based on the voltage difference across the current sampling resistor. The control module is used to output a control signal when the peak difference of the stall detection signal exceeds a stall threshold, controlling the motor drive circuit to disconnect a first drive terminal from a second drive terminal. The AC motor stall protection circuit converts the AC voltage into a processable low-voltage stall detection signal via the coupling capacitor, replacing conventional operational amplifier circuits, simplifying the circuit structure, and reducing production costs.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to an AC motor stall protection circuit. Background Art

[0002] A food processor is a common food processor. Its primary load is the motor, which drives the blades through the motor shaft to grind and blend food. During operation, high food resistance can easily cause the motor to overload or stall. This can cause a sharp increase in motor current, potentially burning the motor and damaging the food processor. Therefore, it's essential to detect motor stalls and disable motor output control when an overload or stall occurs to prevent overcurrent damage.

[0003] Prior art AC motor stall protection circuits consist of at least a motor, a motor drive circuit, a current sampling circuit, a signal conversion circuit, and a main control circuit. The current sampling circuit, connected in series at both ends of the motor, converts the current signal flowing through the motor into a voltage signal. However, this AC motor stall protection circuit is not effective for AC motors because the AC current signal at both ends of the motor exceeds the power supply range of the main control circuit. Therefore, it must be converted into a voltage signal that the main control circuit can process. Prior art uses operational amplifiers to achieve this signal conversion, but operational amplifiers are expensive and complicate the circuit structure. Summary of the Invention

[0004] The purpose of the present invention is to provide an AC motor stall protection circuit to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0005] An AC motor stall protection circuit includes a current sampling resistor, a coupling capacitor, a motor drive circuit, a conversion circuit, and a control module;

[0006] One end of the current sampling resistor is connected to the first driving end of the motor driving circuit, the second driving end of the motor driving circuit is used to be connected to an input end of the AC motor, and the other end of the current sampling resistor and the other input end of the AC motor are used to receive the AC voltage;

[0007] The conversion input terminal of the conversion circuit is connected to one end of the current sampling resistor via a coupling capacitor, the reference voltage terminal of the conversion circuit is connected to the other end of the current sampling resistor, and the reference voltage terminal is connected to a reference voltage signal, so as to generate a stall detection signal having a waveform identical to the AC voltage based on the voltage difference across the current sampling resistor;

[0008] The detection end of the control module is connected to the conversion output end of the conversion circuit, and the control output end of the control module is connected to the control end of the motor drive circuit, and is used to output a control signal when the peak difference of the stall detection signal is higher than the stall threshold, controlling the motor drive circuit to disconnect the first drive end and the second drive end.

[0009] Further, the conversion circuit includes a first resistor and a second resistor;

[0010] One end of the coupling capacitor away from the current sampling resistor is connected to one end of the first resistor, one end of the second resistor and one end of the third resistor respectively. The other end of the first resistor is grounded, and the other end of the second resistor is connected to the reference voltage signal.

[0011] Furthermore, the conversion circuit further includes a third resistor;

[0012] One end of the third resistor is connected to an end of the coupling capacitor away from the current sampling resistor, and the other end of the third resistor is connected to the detection end of the control module.

[0013] Furthermore, the motor drive circuit includes a switch tube, a bidirectional thyristor, and a fourth resistor;

[0014] The input end of the switching tube is connected to the trigger end of the bidirectional thyristor, the output end of the switching tube is grounded, and the control end of the switching tube is connected to the control output end of the control module; one end of the bidirectional thyristor is connected to the current sampling resistor and is connected to the trigger end of the bidirectional thyristor through a fourth resistor, and the other end of the bidirectional thyristor is used to connect to the AC motor.

[0015] Further, the motor driving circuit includes a fifth resistor, a sixth resistor and a seventh resistor;

[0016] The input end of the switch tube is connected to the trigger end of the bidirectional thyristor through the fifth resistor, the control end of the switch tube is connected to the control output end of the control module through the sixth resistor, and the seventh resistor is connected between the control end and the output end of the switch tube.

[0017] Furthermore, the switch tube is an NPN transistor, the control end of the switch tube is the base of the NPN transistor, the input end of the switch tube is the collector of the NPN transistor, and the output end of the switch tube is the emitter of the NPN transistor.

[0018] Furthermore, the switch tube is an N-type field effect tube, the control end of the switch tube is the gate of the N-type field effect tube, the input end of the switch tube is the drain of the N-type field effect tube, and the output end of the switch tube is the source of the N-type field effect tube.

[0019] Furthermore, the control module is a single chip microcomputer.

[0020] The beneficial effects of the present invention are as follows: the AC voltage is converted into a processable low-voltage stall detection signal through a coupling capacitor, thereby replacing the previous operational amplifier circuit, simplifying the circuit structure, and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of an AC motor stall protection circuit provided by the first embodiment.

[0022] Figure 2 This is a schematic diagram of an AC motor stall protection circuit provided by a second embodiment.

[0023] Figure 3 This is a schematic diagram of an AC motor stall protection circuit provided by a third embodiment. DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with the embodiments and drawings.

[0025] Figure 1 This is a schematic diagram of an AC motor stall protection circuit provided by the first embodiment.

[0026] like Figure 1 As shown, the AC motor stall protection circuit includes a current sampling resistor Rs, a coupling capacitor C1, a motor drive circuit 100, a conversion circuit 200 and a control module 300, which is used to cut off the input voltage when the AC motor enters stall to achieve a protection effect.

[0027] The current sampling resistor Rs and the motor drive circuit 100 are connected to the voltage input circuit of the AC motor. Specifically, one end of the current sampling resistor Rs is connected to the first drive terminal of the motor drive circuit 100, and the second drive terminal of the motor drive circuit 100 is used to connect to an input terminal of the AC motor. The other end of the current sampling resistor Rs and the other input terminal of the AC motor are used to receive the AC voltage. The current sampling resistor Rs collects the current signal in the voltage input circuit. When the voltage input circuit is normally energized, a voltage difference is formed across the current sampling resistor Rs. The first and second drive terminals of the motor drive circuit 100 can both serve as voltage input terminals or output terminals and can be considered as a single wire.

[0028] The conversion circuit 200 is used to feed back the AC voltage of the voltage input circuit to the control module 300. Specifically, the conversion input terminal of the conversion circuit 200 is connected to one end of the current sampling resistor Rs via a coupling capacitor C1. The reference voltage Vcc terminal of the conversion circuit 200 is connected to the other end of the current sampling resistor Rs, and the reference voltage Vcc terminal is connected to the reference voltage Vcc signal. This generates a locked-rotor detection signal with a waveform identical to the AC voltage based on the voltage difference across the current sampling resistor Rs.

[0029] The principle of generating a stall detection signal is based on the "AC pass" characteristic of the coupling capacitor C1. The coupling capacitor C1 is connected to the voltage input circuit. When the voltage of the voltage input circuit increases, the coupling capacitor C1 accumulates charge. When the voltage of the voltage input circuit decreases, the coupling capacitor C1 releases the accumulated charge. The coupling capacitor C1 periodically accumulates and releases charge, and the released charge is combined with the reference voltage signal Vcc to form a stall detection signal.

[0030] Based on the stall detection signal, the control module 300 determines whether to shut down the motor drive circuit 100. Specifically, the detection terminal of the control module 300 is connected to the conversion output terminal of the conversion circuit 200, and the control output terminal of the control module 300 is connected to the control terminal of the motor drive circuit 100. The control module 300 is configured to output a control signal when the peak difference of the stall detection signal exceeds the stall threshold value, thereby controlling the motor drive circuit 100 to disconnect the first drive terminal and the second drive terminal.

[0031] The principle of the control module 300 determining whether to shut down the motor drive circuit 100 is that after the motor is stalled, a large back electromotive force will be generated at the moment of turning on, which exceeds the voltage peak of the normal AC voltage. The waveform of the stall detection signal formed by the AC voltage will also exceed the normal peak value. When receiving the stall detection signal, the control module 300 will collect the values ​​at each moment and filter out the peak voltage V max And the valley voltage V min , calculate the peak voltage V max And the valley voltage V min The difference between the two values ​​is used to determine whether it exceeds the peak value difference of the stall detection signal converted from the output normal AC voltage. If it is detected that the number of times exceeds the predetermined number, it is determined that the motor is stalled, and the AC voltage input is disconnected through the motor drive circuit 100.

[0032] Figure 2 This is a schematic diagram of an AC motor stall protection circuit provided by a second embodiment.

[0033] like Figure 2 As shown, based on the above embodiment, the conversion circuit 200 of this embodiment includes a first resistor R1, a second resistor R2 and a third resistor R3.

[0034] Specifically, one end of the coupling capacitor C1 away from the current sampling resistor Rs is connected to one end of the first resistor R1, one end of the second resistor R2, and one end of the third resistor R3. The other end of the first resistor R1 is grounded, and the other end of the second resistor R2 is connected to the reference voltage Vcc signal. One end of the third resistor R3 is connected to the end of the coupling capacitor C1 away from the current sampling resistor Rs, and the other end of the third resistor R3 is connected to the detection terminal of the control module 300.

[0035] The reference voltage Vcc flows to the signal ground after passing through the first resistor R1 and the second resistor R2, so that the stall detection signal is an AC signal with the signal ground as the midpoint. The coupling capacitor C1 releases charge from the common end of the first resistor R1 and the second resistor R2, changing the voltage value of the common end of the first resistor R1 and the second resistor R2 to form a stall detection signal. Finally, the control module 300 obtains the stall detection signal from the common end of the first resistor R1 and the second resistor R2 through the third resistor R3.

[0036] The motor driving circuit 100 described in this embodiment includes a switch tube Q1 , a bidirectional thyristor D1 , and a fourth resistor R4 .

[0037] Specifically, the input end of the switch tube Q1 is connected to the trigger end of the bidirectional thyristor D1, the output end of the switch tube Q1 is grounded, and the control end of the switch tube Q1 is connected to the control output end of the control module 300; one end of the bidirectional thyristor D1 is connected to the current sampling resistor Rs and is connected to the trigger end of the bidirectional thyristor D1 through the fourth resistor R4, and the other end of the bidirectional thyristor D1 is used to connect to the AC motor.

[0038] More specifically, the switch tube Q1 is an NPN transistor, the control end of the switch tube Q1 is the base of the NPN transistor, the input end of the switch tube Q1 is the collector of the NPN transistor, and the output end of the switch tube Q1 is the emitter of the NPN transistor.

[0039] More specifically, the motor drive circuit 100 includes a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7; the input end of the switch tube Q1 is connected to the trigger end of the bidirectional thyristor D1 through the fifth resistor R5, the control end of the switch tube Q1 is connected to the control output end of the control module 300 through the sixth resistor R6, and the seventh resistor R7 is connected between the control end and the output end of the switch tube Q1.

[0040] When the motor is stalled, the control output end of the control module 300 outputs a control signal to the control end of the switch tube Q1, turning on the switch tube Q1 and pulling down the level signal of the trigger end of the bidirectional thyristor D1. The two ends of the bidirectional thyristor D1 connected to the voltage input circuit are disconnected, thereby disconnecting the input voltage.

[0041] In this embodiment, the control module 300 is a single chip microcomputer.

[0042] Figure 3 This is a schematic diagram of an AC motor stall protection circuit provided by a third embodiment.

[0043] like Figure 3 As shown, based on the above embodiment, the switch tube Q1 described in this embodiment is an N-type field effect tube, the control end of the switch tube Q1 is the gate of the N-type field effect tube, the input end of the switch tube Q1 is the drain of the N-type field effect tube, and the output end of the switch tube Q1 is the source of the N-type field effect tube.

[0044] As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion of elements other than the listed elements and may also include additional elements not specifically listed.

[0045] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An AC motor stall protection circuit, characterized in that: Including current sampling resistor, coupling capacitor, motor drive circuit, conversion circuit and control module; One end of the current sampling resistor is connected to the first driving end of the motor driving circuit, the second driving end of the motor driving circuit is used to be connected to an input end of the AC motor, and the other end of the current sampling resistor and the other input end of the AC motor are used to access the AC voltage; The conversion circuit is used to feed back the AC voltage of the voltage input circuit to the control module; the conversion input terminal of the conversion circuit is connected to one end of the current sampling resistor via a coupling capacitor, the reference voltage terminal of the conversion circuit is connected to the other end of the current sampling resistor, and the reference voltage terminal is connected to a reference voltage signal, and is used to generate a stall detection signal with a waveform identical to the AC voltage based on the voltage difference across the current sampling resistor; Specifically, the coupling capacitor is connected to the voltage input circuit; when the voltage of the voltage input circuit increases, the coupling capacitor accumulates charges; when the voltage of the voltage input circuit decreases, the coupling capacitor releases the accumulated charges; Periodically collecting and releasing charges through the coupling capacitor, and combining the released charges with the reference voltage signal to form the stall detection signal; The detection end of the control module is connected to the conversion output end of the conversion circuit, and the control output end of the control module is connected to the control end of the motor drive circuit, and is used to output a control signal when the peak difference of the stall detection signal is higher than the stall threshold, so as to control the motor drive circuit to disconnect the first drive end and the second drive end; Specifically, when the control module receives the stall detection signal, it collects the values ​​at each moment and selects the peak voltage V max And the valley voltage V min , calculate the peak voltage V max And the valley voltage V min The difference between the two values ​​is used to determine whether it exceeds the peak difference of the stall detection signal converted from the output normal AC voltage. If the number of times it is detected that the number of times exceeds the predetermined number is more than the predetermined number, it is determined that the motor is stalled and the AC voltage input is disconnected through the motor drive circuit.

2. The AC motor stall protection circuit according to claim 1, characterized in that: The conversion circuit includes a first resistor and a second resistor; One end of the coupling capacitor away from the current sampling resistor is connected to one end of the first resistor, one end of the second resistor and one end of the third resistor respectively, the other end of the first resistor is grounded, and the other end of the second resistor is connected to the reference voltage signal.

3. The AC motor stall protection circuit according to claim 2, characterized in that: The conversion circuit further includes a third resistor; One end of the third resistor is connected to an end of the coupling capacitor away from the current sampling resistor, and the other end of the third resistor is connected to the detection end of the control module.

4. The AC motor stall protection circuit according to claim 1, characterized in that: The motor drive circuit includes a switch tube, a bidirectional thyristor, and a fourth resistor; The input end of the switching tube is connected to the trigger end of the bidirectional thyristor, the output end of the switching tube is grounded, and the control end of the switching tube is connected to the control output end of the control module; one end of the bidirectional thyristor is connected to the current sampling resistor and is connected to the trigger end of the bidirectional thyristor through a fourth resistor, and the other end of the bidirectional thyristor is used to connect to the AC motor.

5. The AC motor stall protection circuit according to claim 4, characterized in that: The motor drive circuit includes a fifth resistor, a sixth resistor and a seventh resistor; The input end of the switch tube is connected to the trigger end of the bidirectional thyristor through the fifth resistor, the control end of the switch tube is connected to the control output end of the control module through the sixth resistor, and the seventh resistor is connected between the control end and the output end of the switch tube.

6. The AC motor stall protection circuit according to claim 4 or 5, characterized in that: The switch tube is an NPN transistor, the control end of the switch tube is the base of the NPN transistor, the input end of the switch tube is the collector of the NPN transistor, and the output end of the switch tube is the emitter of the NPN transistor.

7. The AC motor stall protection circuit according to claim 4 or 5, characterized in that: The switch tube is an N-type field effect tube, the control end of the switch tube is the gate of the N-type field effect tube, the input end of the switch tube is the drain of the N-type field effect tube, and the output end of the switch tube is the source of the N-type field effect tube.

8. The AC motor stall protection circuit according to claim 1, characterized in that: The control module is a single chip microcomputer.

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