KR920007544B1 - Inverter driving circuit for microwave oven - Google Patents

Abstract

The circuit protects the inverter circuit from the malfunction of the control circuit occurring when the magnetron is faulty. The microwave oven has a magnetron (4), an output feedback means (10) for detecting the secondary current of the transformer (T1) and modulating the pulse width to control the switching device (Q1), an inverter control means (9) for increasing/decreasing the pulse width according to the detected secondary current, and a driving circuit means (8) for driving the switching device (Q1). A magnetron trouble detection means (7) consists of two condensers (C6,C7), three diodes (D5-D7), a number of resistors (R15-R19), and two transistors (Q2,Q3). The magnetron trouble detection means controls the negative terminal of a comparator (CP1) in response to the current difference in normal or abnormal conditions of the magnetron.

Description

Inverter-driven microwave protection circuit

1 is a circuit block diagram of an inverter driving microwave oven according to the present invention.

2 is a detailed circuit diagram of FIG.

3 is a signal waveform diagram of each part for explaining the operation of the present invention and the conventional device.

4 is a circuit diagram of another embodiment of the present invention.

5 is a circuit block diagram of a conventional inverter driving microwave oven.

* Explanation of symbols for main parts of the drawings

4: magnetron 7,20: sensing circuit

8 drive circuit portion 9 inverter control circuit portion

10: output feedback circuit 21: microcomputer

C ₁ -C ₉ : condenser R ₁ -R ₂₁ : resistance

L ₁ , L ₂ : coil BD ₁ , BD ₂ : rectifier circuit

D ₁ -D ₂ : diode T ₁ : step-up transformer

Q ₁ -Q ₃ : Transistor OP ₁ -OP ₂ : OP Amplifier

CP _1, CP ₂ : comparator VR _x : clause variable element

NOR ₁ : NORGATE

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a protection circuit of an inverter drive microwave oven for protecting the inverter circuit from malfunction of a control circuit generated when a magnetron is defective or an endorsement of the magnetron is abnormal.

Conventionally, as shown in FIG. 5, filter means C ₁ and L ₁ for filtering the high frequency components of the commercial AC voltage, and rectification for rectifying the AC passing through the filter means into a pulsating DC voltage. means (BD ₁₎ and smoothing means (C _2, L ₂₎ and said smoothing means (C _2, L ₂₎ the output from which constant smoothing the pulsating direct-current voltage rectified by the rectifying means (BD ₁₎ A switching element Q ₁ for switching the applied voltage to the primary coil of the boost transformer T ₁ for the magnetron, and a voltage input from the switching element Q ₁ to receive a voltage required for the magnetron oscillation. Step-up transformer T ₁ and half-wave back pressure means C ₄ and D _{2 for} supplying the secondary high voltage boosted by the step-up transformer T ₁ for oscillation and non-oscillation operation of the magnetron 4; half-wave back pressure means (C _4, D ₂₎ oscillation of one cycle is output through, And a magnetron (4) for heating the high-frequency by the oscillating voltage, when the continuous oscillation of the magnetron (4) step-up transformer (T ₁₎ to sense the current flowing through the secondary side coil pulse to control the on-time of the switching device (Q ₁₎ Output feedback means (10) for width modulation, and inverter control means (9) for controlling to decrease or increase the pulse width modulation in accordance with the secondary current amount of the boost transformer T ₁ sensed by the output feedback means (10). And drive means 8 for driving the switching element Q ₁ by the output signal controlled by the inverter control means 9.

In such a conventional apparatus, when the magnetron 4 is broken or the connection is poor, that is, when the magnetron 4 that can handle a large load power of about 100W or more fails to perform its function, the capacitor C ₂ of the smoothing means The deviation V ₂ between the maximum value and the minimum value of the smoothed voltage waveform decreases, and the voltage applied to the capacitor C ₄ and the diode D ₂ of the secondary half-wave back pressure means of the boost transformer T ₁ increases. Therefore, the output feedback means 10 for sensing the secondary side current of the boost transformer T ₁ determines that a small current flows in the load, and further widens the pulse width modulation from the inverter control means 9 to the drive circuit portion 8. Many outputs go out, and the switching element Q ₁ through such an output accelerates the on-time of the switching at a higher speed, thereby raising the voltage across the secondary coil of the boost transformer T ₁ (see FIG. Of course, the voltages at both ends of the capacitor C ₄ and the diode D ₂ of the half-wave back pressure means are also increased as shown by the dotted line in FIG.

Therefore, when the battery is left in such a state, the back voltage capacitor C ₄ and the diode D ₂ are not only damaged by the withstand voltage rising as shown by the dotted line in FIG. 3D, but also the back voltage diode D ₂ . There are many problems, such as a short circuit phenomenon occurs during breakage, such that the instantaneous overcurrent that may cause human injury may also destroy the holder switching element Q _{1 in the} primary side of the boost transformer T ₁ .

The present invention has been proposed in order to solve the above-mentioned problems. When the magnetron is damaged or defective in wiring, the switching element for switching the boosting transformer primary side voltage by lowering the inverting stage of the comparator of the inverter control circuit to a low potential is turned on. Inverter capable of preventing the breakage of components from the secondary overcurrent of the boost transformer by adding a magnetron abnormal or non-sensing circuit that cuts off the time to the existing inverter drive microwave oven circuit, and improves the safety and reliability of the cooker. It is an object of the present invention to provide a protection circuit of a driving microwave, and the configuration of the present invention will be described in detail with reference to the accompanying drawings.

As shown in Figs. 1 and 2, the protection circuit of the inverter-driven microwave oven of the present invention passes through filter means C ₁ and L ₁ for filtering high frequency components of commercial AC voltage, and filter means thereof. Rectification means BD ₁ for rectifying the alternating current to a pulsating DC voltage, smoothing means C ₂ , L ₂ for smoothing the pulsating DC voltage rectified by the rectifying means BD ₁ , and the smoothing means. A switching element Q ₁ for resonating the voltage output through the switching element to be applied to the primary coil of the boost transformer T ₁ for the magnetron, and receiving the voltage switched from the switching element to generate the magnetron 4. A boost transformer T ₁ for boosting the voltage, half wave back pressure means C ₄ and D ₂ for implementing a secondary high voltage boosted by the boost transformer T ₁ by oscillation and non-oscillation of a magnetron, and the half wave back pressure 1 output through means A magnetron (4), a switching device by detecting the amount of current passing through the secondary side coil of the step-up transformer (T ₁₎ during continuous oscillation of the magnetron (4) for generating a microwave by the voltage oscillation and non-oscillation of the cycle the continuous The pulse width modulation is reduced or reduced according to the output feedback means 10 for pulse width modulation to adjust the on type of (Q ₁ ) and the secondary current amount of the boost transformer T ₁ sensed by the output feedback means 10. in the inverter control means (9) for controlling so as to increase, the inverter driving a microwave oven is provided with drive circuit means (8) for driving the switching element (Q ₁₎ by a control output signal from said inverter control means, Condensers C ₆ and C ₇ , diodes D ₅ -D ₇ , resistors R ₁₅ -R ₁₉ , and transistors Q ₂ and Q ₃ are used to smooth the smoothing means C ₂ and L ₂ . for the both-end voltage waveform of the capacitor (C ₂₎ So as to lower the low electric potential (-) enabled torch (4) inverted terminal of the comparator (CP ₁₎ of the inverter control means (9) in accordance with the current difference to charge the change current difference when the abnormality when the normal It is characterized in that it is made by interconnecting the sensing means (7) with or without an abnormal magnetron to control.

The operation and effects of the present invention configured as described above will be described with reference to FIGS. 2 and 3.

First, as in the conventional circuit operation, the high frequency component of the AC voltage AC input when the magnetron 4 is normal is filtered by the filter means C ₁ and L ₁ , and then pulsated by the rectifying means BD ₁ . Obtain a DC voltage.

The pulsating DC voltage is smoothed again by the smoothing means C ₂ and L ₂ , and the voltages between both ends of the smoothed smoothing capacitor C ₂ appear as shown in FIG. That is, when the magnetron 4 is normal, as shown in (e) of FIG. 3, the voltage across the smoothing capacitor C ₂ is pulse width during a half cycle in which 120 Hz flows for 8.3 m Sec when the input is 60 Hz. The difference between the maximum and the minimum of appears as a waveform with a higher amplitude of V ₁ . When the AC component pulse as shown in FIG. 3E passes through the resonant capacitor C ₃ , the boosting transformer T ₁ is switched by the switching element Q ₁ which switches to the pulse as shown in FIG. 3A. The AC waveform is applied to the secondary coil and generates a high voltage necessary for oscillation of the magnetron 4, and the high voltage is generated by the half-wave back pressure means C ₄ and D ₂ . It is represented by the same waveform as the solid line in FIG.

In this half-wave back pressure operation, oscillation voltages are formed at non-oscillation during half cycle and oscillation voltage during half cycle, as in the fresh waveform of (D) of Fig. 3 at both ends of anode and cathode of magnetron 4, and this oscillation voltage is magnetron 4 Is applied to the cathode side of the magnetron 4 to oscillate.

On the other hand, the output feedback means (10) for detecting a current flowing through the secondary side coil of the step-up transformer (T ₁₎ of said operation detecting the amount of current passing through the secondary side of the step-up transformer (T ₁₎ by the oscillation of the magnetron (4) And the second rectified voltage is resonated by the capacitor C ₈ when fed back to the switching element Q ₁ , and the inverting end (-) of the OP amplifier OP ₂ to which the resonance signal is applied, and the non-inverting The reference voltage level set from the output variable element VR ₁ connected to the terminal + is compared.

At this time, if the current flowing in the secondary coil of the boost transformer T ₁ is greater than the voltage level set by the output variable element VR ₁ of the output feedback circuit unit 10, the inverter control circuit unit 9 is the condenser C _{5 thereof} . And decreases the pulse width modulated oscillation voltage of the resistor R ₈ and, conversely, if it is less than the voltage level, causes the pulse to increase the modulation oscillation so that the comparator (CP ₁ ) and the resistors (R ₁ , R ₂ ) and a diode (D _3), the saw-inverting terminal of the comparator (CP ₂₎ formed by the (-) applied to, and that the comparator (CP ₂₎ is thereby amplified by which the secondary current of the step-up transformer (T ₁₎ reduced power The square wave signal thereof switches the switching element Q ₁ through the driving circuit unit 8.

As described above, when the magnetron operation is normal, the current I ₁ flowing through the coupling capacitor C ₆ of the magnetron abnormality detecting circuit 7 is

The current I ₁ obtained in the above ① expression is charged to the capacitor C ₇ through the diode D ₆ . The voltage V _C7 at both ends of the capacitor C ₇ to be charged is

Becomes

Accordingly, the transistor Q ₂ is turned on with the voltage between both ends charged in the capacitor C ₇ , and at the same time, the transistor Q ₃ is turned off and the boost transformer T ₁ of the output feedback circuit unit 10 applied to the diode D ₅ is applied. The feedback signal which senses the secondary current of the () is cut off, and the signal is applied to the inverting terminal (-) of the comparator CP ₂ of the inverter control circuit 9 so that normal operation continues.

On the other hand, when the magnetron 4 is not present or is damaged during use, the circuit operates normally as described above, and the current flowing to the secondary side of the boost transformer T ₁ causes the output control variable element VR of the output feedback circuit unit 10 to operate. _It becomes gradually lower than the voltage level set in ₁ ), and the inverter control circuit part 9 gradually widens a switching pulse width, and increases a pulse width modulation oscillation largely, and outputs it.

As a result, both ends of the back pressure condenser C ₄ of the half-wave back pressure means of the boost transformer T ₁ are represented by a rising voltage, such as a dotted line in FIG. 3C, and both ends of the anode and the cathode of the magnetron 4. The voltage is shown as a dotted line in Fig. 3D, and the voltages at both ends of the smoothing capacitor C ₂ are shown in Fig. 3B.

In this state, the current I ₂ flowing through the coupling capacitor C ₆ is

The current I ₂ obtained in the above Equation 3 is charged to the capacitor C ₇ through the diode D ₆ . At this time, the voltage (V _C7 ) of both ends of the capacitor (C ₇ ) to be charged,

Becomes

The voltage V _C7 at both ends of the capacitor C ₇ obtained here completely smoothes the pulsating DC voltage rectified by the rectifying circuit BD _{1 in} contrast to the above equation 2 when the magnetron 4 operation is normal. In order to achieve this, the capacity of the smoothing capacitor C ₂ must be large, so that the voltage across the smoothing capacitor C ₂ is remarkably different when the magnetron 4 operates normally or abnormally.

Therefore, the inversion terminal of the comparator CP ₂ in the inverter control circuit section 9 cannot conduct the transistor Q ₂ while conducting the transistor Q ₃ with the charging voltage of the capacitor C ₇ smaller than the formula ( ₂ ). Since the negative voltage is lowered to the low potential, the high signal appearing at the output terminal of the comparator CP ₂ is applied to the NOR gate NOR ₁ of the driving circuit unit 8, but the NOR gate NOR ₁ is one or two. Since there is no output even if an input is given, the on-time switching operation of the switching element Q ₁ is interrupted.

In addition, in another preferred embodiment of the present invention for the magnetron abnormality detection circuit (7), as shown in Figure 4 and the function belonging to the magnetron abnormality detection circuit portion 7 of FIG. On the collector side of the same switching transistor Q ₂ , a photo coupler PC ₁ which transmits an optical signal as an electrical signal according to the turn-off operation of the transistor Q ₂ , and an output signal of the photo coupler PC ₁ . Accordingly, the magnetron abnormality detection circuit 20, which is composed of the microcomputer 21 that controls the switching operation of the switching element Q ₁ to be turned on or off, may be used instead of the above, and the operation relationship thereof is the abnormality shown in FIG. Same as the presence detection circuit (7).

As described above, according to the protection circuit of the inverter-driven microwave oven of the present invention, when the magnetron is broken or the wiring is defective, the magnetron turns on or off the abnormality detection circuit according to the change of the voltage across the smoothing capacitor. By doing so, it is possible to improve the safety and reliability of the cooking appliance as well as to prevent the damage to the parts of the cooking appliance in advance.

Claims (2)

Filter means C _{1 and} L ₁ for filtering the high frequency components of the commercial AC voltage AC, rectifying means BD ₁ for rectifying the AC passing through the filter means into a pulsating DC voltage, and the rectifying means BD. ₁ ) smoothing means (C _2, L ₂ ) for smoothing the pulsating DC voltage rectified by the constant, and the voltage output through the smoothing means is resonated and applied to the primary coil of the boost transformer (T ₁ ) for the magnetron and a switching element (Q ₁₎ for switching so that receives applying a voltage switching from the switching element of the step-up in the step-up transformer (T ₁₎ and the step-up transformer (T ₁₎ to step-up the voltage required for the magnetron (4) oscillating Microwaves are generated by the half-wave back pressure means (C ₄ , D ₂ ) for implementing the secondary high voltage by oscillation and non-oscillation of the magnetron, and a voltage in which one cycle of oscillation and non-oscillation is outputted through the half-wave back pressure means. Do not let Yes torch (4), a continuous wave when the step-up transformer (T ₁₎ 2 output feedback means for sensing the amount of current passing through the primary coil of pulse width modulation to regulate the line of the switching device (Q ₁₎ of the magnetron (4) (10), and inverter control means (9) for controlling to decrease or increase the pulse width modulation according to the secondary current amount of the boost transformer T ₁ sensed from the output feedback means (10), and the inverter control means In an inverter drive microwave oven with drive circuit means 8 for driving said switching element Q ₁ by means of an output signal controlled by the capacitor C ₆ , C ₇ and a diode D ₅ -D ₇ . And resistors (R _15- R ₁₉ ) and transistors (Q ₂ , Q ₃ ), the magnetron (4) for the voltage waveforms of both ends of the smoothing capacitor (C ₂ ) of the smoothing means (C ₂ , L ₂ ) is normal. Charges the current difference between the time when it is abnormal and when it is abnormal An inverter driving a microwave oven, characterized by the interconnection yirueojim a and the magnetron abnormality detection means (7) for controlling so as to fall to a low voltage-comparator inverting terminal of the (CP ₁₎ of the inverter control means (9) () Protection circuit. The photo coupler of claim 1, wherein the magnetron abnormality detection unit 7 transmits an optical signal as an electrical signal according to a turn-off operation of the transistor Q ₂ to the collector side of the switching transistor Q ₂ . PC ₁ ) and a microcomputer (21) for controlling the switching operation of the switching element (Q ₁ ) in accordance with the output signal of the photo coupler (PC ₁ ) protection circuit of the inverter drive microwave oven.

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