Microwave oven and filter circuit thereof

Abstract

The utility model relates to a microwave oven and a filter circuit thereof, the filter circuit is used for being matched with a drive circuit of the microwave oven, the drive circuit comprises a rectification circuit and an inversion circuit, and the filter circuit comprises a differential mode filter circuit used for being connected with an alternating current power supply to filter differential mode noise in the alternating current power supply; the common-mode filter circuit is connected with the differential-mode filter circuit and the rectifying circuit and is used for filtering common-mode noise in the alternating-current power supply; and the linear voltage stabilizing circuit is connected with the rectifying circuit and the inverter circuit, and is used for performing linear conversion on the direct-current power supply output by the rectifying circuit and outputting a linear power supply to the inverter circuit. According to the utility model, the alternating current power supply input to the microwave oven driving circuit can be filtered, the microwave oven is helped to meet the electromagnetic compatibility requirement, the stability of the direct current voltage is improved, and the working condition of the inverter circuit is more stable.

Description

Technical Field

[0001] The utility model relates to the technical field of microwave ovens, in particular to a microwave oven and a filter circuit thereof. Background Art

[0002] As microwave ovens become more and more popular among consumers, consumers have higher and higher requirements for their working stability. Due to the poor filtering performance of existing microwave ovens, they are easily affected by grid voltage fluctuations and noise from the grid. For example, the voltage during peak hours is significantly higher than the voltage during non-peak hours. Input voltage fluctuations will affect the stability of the microwave oven's inverter circuit, resulting in unstable microwave oven conditions. In the worst case, it will affect heating, and in the worst case, it will cause damage to electronic devices in the inverter circuit (such as magnetrons and power switch tubes). As for the noise from the grid, it may be amplified by the inverter circuit, causing the microwave oven to fail to meet electromagnetic compatibility. Utility Model Content

[0003] The technical problem to be solved by the utility model is to provide a microwave oven and a filter circuit thereof.

[0004] The technical solution adopted by the utility model to solve the technical problem is: construct a filter circuit for cooperating with a drive circuit of a microwave oven, the drive circuit includes a rectifier circuit and an inverter circuit, and the filter circuit includes:

[0005] A differential mode filter circuit for connecting to an AC power supply to filter out differential mode noise in the AC power supply;

[0006] a common mode filter circuit connected to the differential mode filter circuit and the rectifier circuit and used to filter out common mode noise in the AC power supply; and

[0007] A linear voltage stabilizing circuit connected to the rectifier circuit and the inverter circuit, used for linearly converting the DC power output by the rectifier circuit and outputting the linear power to the inverter circuit.

[0008] Preferably, the differential mode filter circuit includes a second inductor L2, an eighth capacitor C8, a third inductor L3 and a seventh capacitor C7;

[0009] The first end of the second inductor L2 is connected to one end of the AC power supply as the first input end of the differential mode filter circuit, and is connected to the first end of the third inductor L3 via the eighth capacitor C8. The second end of the second inductor L2 is connected to the common mode filter circuit as the first output end of the differential mode filter circuit, and is connected to the second end of the third inductor L3 via the seventh capacitor C7. The first end of the third inductor L3 is connected to the other end of the AC power supply as the second input end of the differential mode filter circuit, and the second end of the third inductor L3 is connected to the common mode filter circuit as the second output end of the differential mode filter circuit.

[0010] Preferably, the second inductor L2 and the third inductor L3 are differential mode inductors.

[0011] Preferably, the common mode filtering circuit comprises a common mode inductor L1, a third capacitor C3 and a fourth capacitor C4;

[0012] The first end of the first winding of the common-mode inductor L1 is connected to the first output end of the differential-mode filter circuit, the second end of the first winding of the common-mode inductor L1 is connected to the first AC input end of the rectifier circuit, and is simultaneously connected to the second end of the second winding of the common-mode inductor L1 and the second AC input end of the rectifier circuit via the third capacitor C3 and the fourth capacitor C4, the first end of the second winding of the common-mode inductor L1 is connected to the second output end of the differential-mode filter circuit, and the connection point of the third capacitor C3 and the fourth capacitor C4 is connected to the ground line.

[0013] Preferably, the linear voltage stabilization circuit comprises:

[0014] A filtering unit connected to the rectifier circuit and used for filtering the DC power output by the rectifier circuit;

[0015] a switch unit connected to the rectifier circuit and the inverter circuit and configured to output a linear power supply to the inverter circuit; and

[0016] A switch driving unit connected to the switch unit and the rectifier circuit and used to drive the switch unit.

[0017] Preferably, the switch driving unit comprises a twelfth resistor R12, a second capacitor C2 and a voltage regulator tube DZ1;

[0018] The first end of the twelfth resistor R12 is connected to the positive end of the DC power output of the rectifier circuit, the second end of the twelfth resistor R12 is simultaneously connected to the control end of the switch unit, the first end of the second capacitor C2 and the cathode of the Zener diode DZ1, and the second end of the second capacitor C2 and the anode of the Zener diode DZ1 are connected to the negative end of the DC power output of the rectifier circuit.

[0019] Preferably, the filtering unit comprises a sixth capacitor C6, and the DC power output positive terminal of the rectifier circuit is connected to the DC power output negative terminal of the rectifier circuit via the sixth capacitor C6;

[0020] The switch unit is an NPN transistor Q3, the collector of the NPN transistor Q3 is connected to the positive end of the DC power output of the rectifier circuit, the base of the NPN transistor Q3 is connected to the second end of the twelfth resistor R12, and the emitter of the NPN transistor Q3 is connected to the inverter circuit to input the linear power supply thereto.

[0021] Preferably, the filtering circuit further includes:

[0022] A lightning protection circuit is connected between the AC power supply and the differential mode filter circuit.

[0023] Preferably, the lightning protection circuit comprises a fuse FU1, a first varistor R1, a second varistor R2, a third varistor R11 and a gas discharge tube TV1;

[0024] The first end of the fuse FU1 is connected to one end of the AC power supply, the second end of the fuse FU1 is connected to the first input end of the differential mode filter circuit, and is simultaneously connected to the other end of the AC power supply and the second input end of the differential mode filter circuit via the first varistor R1 and the second varistor R2. The second end of the fuse FU1 is also connected to the second input end of the differential mode filter circuit via the third varistor R11, and the connection point of the first varistor R1 and the second varistor R2 is also connected to the ground wire via the gas discharge tube TV1.

[0025] The utility model also constructs a microwave oven, which comprises the above-mentioned filter circuit.

[0026] The implementation of the utility model has the following beneficial effects: providing a filtering circuit, filtering out differential mode noise in the AC power input to the microwave oven through a differential mode filtering circuit, filtering out common mode noise in the AC power input to the microwave oven through a common mode filtering circuit, so as to help the microwave oven meet the relevant requirements of electromagnetic compatibility, and also converting the DC power output by the rectifier circuit in the microwave oven into a linear power supply through a linear voltage stabilizing circuit, so as to power the inverter circuit of the microwave oven through the linear power supply, thereby improving the working stability of the inverter circuit, protecting the inverter circuit from the influence of AC power fluctuations, and always operating based on a stable DC voltage, thereby improving the heating stability of the microwave oven, and preventing the electronic devices in the inverter circuit from being damaged due to unstable input power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0028] Figure 1 It is a circuit principle diagram of the filter circuit in some embodiments of the utility model. DETAILED DESCRIPTION

[0029] In order to have a clearer understanding of the technical features, purposes and effects of the present utility model, the specific implementation methods of the present utility model are now described in detail with reference to the accompanying drawings.

[0030] like Figure 1 As shown, the utility model provides a filter circuit, which is used to cooperate with the drive circuit of the microwave oven, wherein the drive circuit includes a rectifier circuit 10 and an inverter circuit 20, the rectifier circuit 10 is used to rectify the AC power supply (such as 220V AC mains) to provide a DC power supply to the inverter circuit 20, and the inverter circuit 20 is used to drive the magnetron in the inverter circuit 20 to work to achieve a heating function. The filter circuit can filter the AC power input to the drive circuit to filter out power supply noise and improve the stability of the DC voltage, thereby improving the working stability of the inverter circuit 20. Figure 1 As shown, the filter circuit includes a differential mode filter circuit 1, a common mode filter circuit 2 and a linear voltage stabilization circuit 3.

[0031] like Figure 1 As shown, the differential mode filter circuit 1 is used to connect to an AC power supply to filter out differential mode noise in the AC power supply, thereby preventing the differential mode noise from being amplified by the inverter circuit 20, which helps the microwave oven meet the relevant requirements of electromagnetic compatibility.

[0032] In some embodiments, Figure 1 As shown, the differential mode filter circuit 1 includes a second inductor L2, an eighth capacitor C8, a third inductor L3 and a seventh capacitor C7. The first end of the second inductor L2 is connected to one end of the AC power supply as the first input end of the differential mode filter circuit 1, and is connected to the first end of the third inductor L3 via the eighth capacitor C8. The second end of the second inductor L2 is connected to the common mode filter circuit 2 as the first output end of the differential mode filter circuit 1, and is connected to the second end of the third inductor L3 via the seventh capacitor C7. The first end of the third inductor L3 is connected to the other end of the AC power supply as the second input end of the differential mode filter circuit 1, and the second end of the third inductor L3 is connected to the common mode filter circuit 2 as the second output end of the differential mode filter circuit 1.

[0033] In this embodiment, the second inductor L2, the eighth capacitor C8, the third inductor L3 and the seventh capacitor C7 form a differential mode noise filtering circuit, which can effectively filter out the differential mode noise in the AC power supply.

[0034] In order to improve the filtering effect of the differential mode filter circuit 1 , in some embodiments, the eighth capacitor C8 and the seventh capacitor C7 may be X capacitors, and the second inductor L2 and the third inductor L3 may be differential mode inductors.

[0035] like Figure 1 As shown, the common-mode filter circuit 2 is connected to the differential-mode filter circuit 1 and the rectifier circuit 10. The common-mode filter circuit 2 is used to filter out the common-mode noise in the AC power supply, thereby preventing the common-mode noise from being amplified by the inverter circuit 20, which helps to make the electromagnetic compatibility of the microwave oven meet relevant requirements.

[0036] In some embodiments, Figure 1 As shown, the common-mode filter circuit 2 includes a common-mode inductor L1, a third capacitor C3 and a fourth capacitor C4. The first end of the first winding of the common-mode inductor L1 is connected to the first output end of the differential-mode filter circuit 1, the second end of the first winding of the common-mode inductor L1 is connected to the first AC input end of the rectifier circuit 10, and is simultaneously connected to the second end of the second winding of the common-mode inductor L1 and the second AC input end of the rectifier circuit 10 via the third capacitor C3 and the fourth capacitor C4, the first end of the second winding of the common-mode inductor L1 is connected to the second output end of the differential-mode filter circuit 1, and the connection point of the third capacitor C3 and the fourth capacitor C4 is connected to the ground line.

[0037] In this embodiment, the common-mode inductor L1, the third capacitor C3 and the fourth capacitor C4 form a common-mode noise filtering circuit, which can effectively filter out the common-mode noise in the AC power supply.

[0038] In order to improve the filtering effect of the common mode filtering circuit 2 , in some embodiments, the third capacitor C3 and the fourth capacitor C4 may be Y capacitors.

[0039] like Figure 1 As shown, the linear voltage regulator circuit 3 is connected to the rectifier circuit 10 and the inverter circuit 20, and the linear voltage regulator circuit 3 is used to linearly convert the DC power output by the rectifier circuit 10 and output the linear power to the inverter circuit 20. The linear power supply is a DC power supply with a relatively stable voltage, which can protect the inverter circuit 20 from the influence of the fluctuation of the AC power supply and always work based on a stable DC voltage, thereby improving the working stability of the inverter circuit 20, improving the heating stability of the microwave oven, and preventing the electronic devices in the inverter circuit from being damaged due to the unstable input power supply. The linear power supply also has the advantage of low noise and can limit the noise from the power supply.

[0040] In some embodiments, Figure 1 As shown, the linear voltage stabilizing circuit 3 includes a filter unit 31 , a switch unit 32 and a switch driving unit 33 .

[0041] like Figure 1As shown, the filter unit 31 is connected to the rectifier circuit 10 , and the filter unit 31 is used to filter the DC power output by the rectifier circuit 10 to reduce the ripple of the DC power output by the rectifier circuit 10 .

[0042] In some embodiments, Figure 1 As shown, the filtering unit 31 includes a sixth capacitor C6, and the DC power output positive terminal of the rectifier circuit 10 is connected to the DC power output negative terminal of the rectifier circuit 10 via the sixth capacitor C6.

[0043] In this embodiment, the sixth capacitor C6 may be an electrolytic capacitor, which mainly functions to reduce the voltage fluctuation of the DC power supply output by the rectifier circuit 10 so that the voltage waveform of the DC power supply tends to be a smooth straight line.

[0044] In addition, it should be noted that Figure 1 As shown, the rectifier circuit 10 can be a rectifier bridge D1, and the two AC input terminals of the rectifier bridge D1 are respectively the first AC input terminal and the second AC input terminal of the rectifier circuit 10, the DC power supply output positive terminal of the rectifier bridge D1 corresponds to the DC power supply output positive terminal of the rectifier circuit 10, and the DC power supply output negative terminal of the rectifier bridge D1 corresponds to the DC power supply output negative terminal of the rectifier circuit 10.

[0045] like Figure 1 As shown, the switch unit 32 is connected to the rectifier circuit 10 and the inverter circuit 20 , and the switch unit 32 is used to output a linear power supply to the inverter circuit 20 .

[0046] In some embodiments, Figure 1 As shown, the switch unit 32 is an NPN transistor Q3, the collector of the NPN transistor Q3 is connected to the positive end of the DC power output of the rectifier circuit 10, the base of the NPN transistor Q3 is connected to the second end of the twelfth resistor R12, and the emitter of the NPN transistor Q3 is connected to the inverter circuit 20 to input a linear power supply with a stable voltage to the inverter circuit 20. The NPN transistor Q3 may be a transistor of model ZXTN2010ZTA.

[0047] like Figure 1 As shown, the switch driving unit 33 is connected to the switch unit 32 and the rectifier circuit 10, and the switch driving unit 33 is used to drive the switch unit 32. Specifically, the switch driving unit 33 is connected to the switch unit 32, and clamps the control terminal voltage of the switch unit 32, so that the output terminal of the switch unit 32 can output a linear power supply with a stable voltage.

[0048] In some embodiments, Figure 1As shown, the switch driving unit 33 includes a twelfth resistor R12, a second capacitor C2 and a voltage regulator DZ1. The first end of the twelfth resistor R12 is connected to the positive end of the DC power output of the rectifier circuit 10, the second end of the twelfth resistor R12 is simultaneously connected to the control end of the switch unit 32, the first end of the second capacitor C2 and the cathode of the voltage regulator DZ1, and the second end of the second capacitor C2 and the anode of the voltage regulator DZ1 are connected to the negative end of the DC power output of the rectifier circuit 10.

[0049] See also Figure 1 The working principle of the linear voltage regulator circuit 3 is as follows: under the pull-up action of the twelfth resistor R12, the base of the NPN transistor Q3 will be set to a high level, and the NPN transistor Q3 will be turned on. In addition, the base voltage of the NPN transistor Q3 will be stabilized to a fixed value (such as 270V) by the voltage regulator DZ1. Based on the conduction characteristics of the NPN transistor, it can be known that when the NPN transistor is turned on, the voltage Vbc between the base and the emitter is generally a fixed voltage. When the base voltage of the NPN transistor Q3 and the voltage Vbc between the base and the emitter are fixed, it can be deduced that the emitter voltage of the NPN transistor Q3 is also a fixed voltage value (the voltage value is jointly determined by the Vbc of the NPN transistor Q3 and the voltage regulation value of the voltage regulator DZ1). Therefore, the emitter of the NPN transistor Q3 can be used to output the linear power supply.

[0050] It should be noted that the main function of the linear voltage regulator circuit 3 is to make the voltage of the DC power supply input to the inverter circuit 20 fixed, and to take advantage of the low noise of the linear power supply, which can significantly improve the input power stability and quality of the inverter circuit 20. In addition, the specific circuit structure of the inverter circuit 20 can refer to Figure 1 Of course, the circuit structure of the inverter circuit 20 can also be other existing inverters or inverter modules, which is not limited here.

[0051] In order to improve the lightning protection performance of the microwave oven, in some embodiments, such as Figure 1 As shown, the filter circuit further includes a lightning protection circuit 4 connected between the AC power supply and the differential mode filter circuit 1 .

[0052] In some embodiments, Figure 1As shown, the lightning protection circuit 4 includes a fuse FU1, a first varistor R1, a second varistor R2, a third varistor R11 and a gas discharge tube TV1. The first end of the fuse FU1 is connected to one end of the AC power supply, the second end of the fuse FU1 is connected to the first input end of the differential mode filter circuit 1, and is connected to the other end of the AC power supply and the second input end of the differential mode filter circuit 1 through the first varistor R1 and the second varistor R2 at the same time, the second end of the fuse FU1 is also connected to the second input end of the differential mode filter circuit 1 through the third varistor R11, and the connection point of the first varistor R1 and the second varistor R2 is also connected to the ground wire through the gas discharge tube TV1.

[0053] In this embodiment, when lightning strikes the power grid and is introduced into the filter circuit, the first varistor R1, the second varistor R2, and the third varistor R11 will firstly drop to a low impedance due to overvoltage, which is equivalent to short-circuiting the AC power supply, so that the high voltage cannot be input to the subsequent circuit, thereby protecting the subsequent circuit. The lightning strike may also cause the input AC power to overcurrent. At this time, the fuse FU1 will quickly blow, disconnecting the entire filter circuit from the AC power supply, thereby protecting the electronic devices at the subsequent stage of the fuse FU1.

[0054] The utility model also provides a microwave oven, comprising the filter circuit provided by the embodiment of the utility model.

[0055] It can be understood that the above embodiments only express the preferred implementation methods of the utility model, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the utility model. It should be pointed out that, for ordinary technicians in this field, without departing from the concept of the utility model, the above-mentioned technical features can be freely combined, and several deformations and improvements can be made, which all belong to the protection scope of the utility model. Therefore, all equivalent changes and modifications made to the scope of the claims of the utility model should belong to the scope covered by the claims of the utility model.

Claims

1. A filter circuit for use with a drive circuit of a microwave oven, the drive circuit comprising a rectifier circuit (10) and an inverter circuit (20), characterized in that: The filtering circuit comprises: A differential mode filter circuit (1) for connecting to an AC power supply to filter out differential mode noise in the AC power supply; a common mode filter circuit (2) connected to the differential mode filter circuit (1) and the rectifier circuit (10) and used for filtering common mode noise in the AC power supply; and A linear voltage stabilizing circuit (3) connected to the rectifier circuit (10) and the inverter circuit (20) and used for linearly converting the DC power output by the rectifier circuit (10) and outputting the linear power to the inverter circuit (20).

2. The filter circuit according to claim 1, characterized in that: The differential mode filter circuit (1) comprises a second inductor L2, an eighth capacitor C8, a third inductor L3 and a seventh capacitor C7; The first end of the second inductor L2 is connected to one end of the AC power supply as the first input end of the differential mode filter circuit (1), and is connected to the first end of the third inductor L3 via the eighth capacitor C8; the second end of the second inductor L2 is connected to the common mode filter circuit (2) as the first output end of the differential mode filter circuit (1), and is connected to the second end of the third inductor L3 via the seventh capacitor C7; the first end of the third inductor L3 is connected to the other end of the AC power supply as the second input end of the differential mode filter circuit (1), and the second end of the third inductor L3 is connected to the common mode filter circuit (2) as the second output end of the differential mode filter circuit (1).

3. The filter circuit according to claim 2, characterized in that: The second inductor L2 and the third inductor L3 are differential mode inductors.

4. The filter circuit according to claim 1, characterized in that: The common-mode filter circuit (2) comprises a common-mode inductor L1, a third capacitor C3 and a fourth capacitor C4; The first end of the first winding of the common-mode inductor L1 is connected to the first output end of the differential-mode filter circuit (1); the second end of the first winding of the common-mode inductor L1 is connected to the first AC input end of the rectifier circuit (10), and is simultaneously connected to the second end of the second winding of the common-mode inductor L1 and the second AC input end of the rectifier circuit (10) via the third capacitor C3 and the fourth capacitor C4; the first end of the second winding of the common-mode inductor L1 is connected to the second output end of the differential-mode filter circuit (1); and the connection point between the third capacitor C3 and the fourth capacitor C4 is connected to the ground line.

5. The filter circuit according to claim 1, characterized in that: The linear voltage stabilizing circuit (3) comprises: A filtering unit (31) connected to the rectifier circuit (10) and used for filtering the DC power output by the rectifier circuit (10); a switch unit (32) connected to the rectifier circuit (10) and the inverter circuit (20) and used to output a linear power supply to the inverter circuit (20); and A switch driving unit (33) connected to the switch unit (32) and the rectifier circuit (10) and used for driving the switch unit (32).

6. The filter circuit according to claim 5, characterized in that: The switch driving unit (33) comprises a twelfth resistor R12, a second capacitor C2 and a voltage regulator tube DZ1; The first end of the twelfth resistor R12 is connected to the positive end of the DC power output of the rectifier circuit (10); the second end of the twelfth resistor R12 is simultaneously connected to the control end of the switch unit (32), the first end of the second capacitor C2 and the cathode of the voltage regulator tube DZ1; the second end of the second capacitor C2 and the anode of the voltage regulator tube DZ1 are connected to the negative end of the DC power output of the rectifier circuit (10).

7. The filter circuit according to claim 6, characterized in that: The filtering unit (31) comprises a sixth capacitor C6, and the DC power output positive terminal of the rectifier circuit (10) is connected to the DC power output negative terminal of the rectifier circuit (10) via the sixth capacitor C6; The switch unit (32) is an NPN transistor Q3, the collector of the NPN transistor Q3 is connected to the positive end of the DC power output of the rectifier circuit (10), the base of the NPN transistor Q3 is connected to the second end of the twelfth resistor R12, and the emitter of the NPN transistor Q3 is connected to the inverter circuit (20) to input the linear power supply thereto.

8. The filter circuit according to any one of claims 1 to 7, characterized in that: The filter circuit also includes: A lightning protection circuit (4) connected between the AC power supply and the differential mode filter circuit (1).

9. The filter circuit according to claim 8, characterized in that: The lightning protection circuit (4) comprises a fuse FU1, a first varistor R1, a second varistor R2, a third varistor R11 and a gas discharge tube TV1; The first end of the fuse FU1 is connected to one end of the AC power supply, the second end of the fuse FU1 is connected to the first input end of the differential mode filter circuit (1), and is simultaneously connected to the other end of the AC power supply and the second input end of the differential mode filter circuit (1) via the first varistor R1 and the second varistor R2. The second end of the fuse FU1 is also connected to the second input end of the differential mode filter circuit (1) via the third varistor R11, and the connection point between the first varistor R1 and the second varistor R2 is also connected to the ground wire via the gas discharge tube TV1.

10. A microwave oven, characterized in that: The filter circuit comprises the filter circuit described in any one of claims 1 to 9.

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