JPS61211985A - Electronic oven range - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a microwave oven in which the frequency of a commercial AC power source is converted by an inverter circuit, and the high frequency output is used to drive a magnetron in oscillation. [Prior Art] The circuit configuration of a conventional example of this type of microwave oven is shown in FIG. In the figure, a primary winding 3a of a magnetron drive transformer 3 and a semiconductor switching element 4 are connected in series to the output terminal of a DC power supply circuit 2 that rectifies and smoothes a commercial AC power supply 1 and converts it into a DC power supply. At the same time, the primary winding 3a
and a resonant capacitor 5 to form a resonant circuit.The resonant circuit is driven by the on/off operation of the semiconductor switching element 4, and is thereby connected to the secondary side of the drive transformer 3. magnetron 7
is configured to oscillate and drive. The control unit 8 that controls the on/off operation of the semiconductor switching element 4 includes a timing circuit 10 including a comparator 9, a triangular wave generation circuit 12 including a comparator 11, and a comparison circuit 1 including a comparator 13.
4, a processor 15 that generates a digital code signal as heating control information for the microwave oven, and a DA converter 16 that converts the digital code signal from the processor 15 into an analog signal. In the timing circuit 10, the output voltages across the primary winding 3a of the drive transformer 3, which are divided by the resistors 17 and 18 and the resistors 19 and 20, are compared by the comparator 9, and the voltages shown in FIG. 6(A) are compared. It is configured to obtain a waveform as shown by a broken line, and further to obtain a synchronization signal as shown by a solid line in FIG. Further, in the triangular wave generation circuit 12, the comparator 1
1 constitutes an unstable multi-by-break, and its oscillation period is set to be sufficiently longer than the oscillation period of the inverter circuit 6. With the above configuration, the comparator 13 uses the DA converter 1 corresponding to the heating control information from the processor 15.
Output from 6

[Indicated by the broken line in FIG. 6(B)] is the oscillating sawtooth wave output 4 generated at the integrating capacitor 21 at the input stage of the comparator 11.

[Indicated by solid line in Figure 6 (B)]
are compared, and an output with a waveform as shown in FIG. 6(C) is obtained. Further, the transistor 22, capacitor 23, and comparator 9 of the timing circuit 10 are connected to the drive transformer 3. The voltage across the primary winding 3a of

The output of the comparator 11 is set to L only during the period when [the waveform is shown in FIG. 6(D)] changes from positive to negative. Oscillation is repeated in synchronization with the output of the drive transformer 3. On the other hand, in the inverter circuit 6, the semiconductor switching element 4 is connected so that the waveform shown in FIG. As it oscillates at a period synchronized with the resonance operation, the comparator 13
The output is at a period synchronized with the resonance operation of the inverter circuit 6, and at an L level corresponding to the heating control information of the processor 15.
This becomes a pulse train with a level width, and this output is the drive circuit 2
The signal is input to the semiconductor switching element 4 via 4. The processor 15 monitors the power supply voltage and magnetron current, sequentially generates heating control information according to these values, and supplies it to the DA converter 16 for stable driving. By the way, the magnetron for high frequency generation has voltage and current characteristics as shown in FIG.
Under a power supply voltage such that the output of the secondary high voltage winding 3b does not reach the threshold voltage of the magnetron, no current flows through the magnetron, so the resonance period of the inverter circuit 6 becomes long. On the other hand, since the response of the DA converter 16, which converts the heating control information generated by the processor 15 from DA to analog depending on the values of the power supply voltage and magnetron current, is slow, the semiconductor switching element It is not possible to control the pulse width of the signal given to 4 to an optimum value. This is true for magnetrons where the load impedance suddenly changes from a predetermined threshold voltage as described above.
This means that stable output cannot be obtained with the configuration of the conventional example. Further, in the conventional example, the pulse width accuracy of the pulse signal applied to the semiconductor switching element 4 also depends on the temperature state of the capacitor and comparator, making the output even more unstable. [Object of the Invention] The present invention has been made in consideration of the above-mentioned problems in the conventional example, and it is possible to obtain stable output, greatly improve circuit integration, and reduce cost and size. The purpose is to provide a microwave oven that can achieve [Structure of the Invention] The microwave oven of the present invention has a primary winding of a magnetron drive transformer and a switching element connected in series to the output side of a rectifier that converts a commercial AC power source into a DC power source. In an inverter circuit in which a resonant circuit is formed by a wire and a resonant capacitor, the inverter circuit is resonantly driven by switching the switching element, and the control section of the switching element is controlled by the output of the drive transformer or similar to the drive transformer. a detection means for detecting the output of the sensor, an output information setting means for variably setting the output information according to various sensor information including the power supply voltage, and a control section based on the output of the detection means and the output information of the output information setting means. It is characterized by comprising a counter circuit and a pulse supply means comprising a flip-flop operated by the output of the counter circuit and supplying a pulse signal having a pulse width corresponding to the various sensor information to the switching element. [Example] An example of the present invention will be described in detail below with reference to FIGS. 1 to 4. FIG. 1 shows a schematic configuration of the circuit of the microwave oven of this embodiment, and the inverter circuit 27 converts the frequency of the commercial AC power supply 25 and drives the magnetron 26 in oscillation with the converted output. The primary winding 29a of the drive transformer 29 and the switching element 30 are connected in series to the output terminal of a DC power supply circuit 28 that rectifies and smoothes the commercial AC power supply 25 and converts it into a DC power supply. 'A29
A resonant capacitor 31, which forms a resonant circuit with a, is connected in parallel to the switching element 30. In addition, the resonant capacitor 31 may be connected in parallel to the primary winding 29a to form a resonant circuit. On the secondary side of the drive transformer 29, an auxiliary winding 32 separate from the step-up secondary winding 29b that supplies power to the magnetron 26 is provided.
The auxiliary winding 32 obtains an output voltage similar to the output J of the drive transformer 29, and the waveform shaping circuit 33 in the next stage shapes the output voltage. Alternatively, the output voltage similar to the output of the drive transformer 29 can be directly extracted from the primary winding 29a. A pulse signal for turning on/off the switching element 30 of the inverter circuit 27 is sent to the counter circuit 3.
The drive circuit 36 is configured to amplify one output of the flip-flop 35, which is set and reset by the output of the flip-flop 4. The counter circuit 34 performs an amplifying or down-operating operation by counting the clock signal of the clock generating circuit 37, and the timing for starting counting is controlled by a counter that outputs a timing signal according to the output of the waveform shaping circuit 33. The output timing from the counter circuit 34 to the flip-flop sub 35 is set based on digital data preset in the counter circuit 34 by the microcomputer 39. The digital data of the microcomputer 39 that provides output information to the counter circuit 34 is configured to be automatically and variably set according to changes in sensor input manually input to the microcomputer 39, such as magnetron current and power supply voltage. However, the microcomputer 39 may be replaced by a logic circuit including a register or the like that generates constant output data. FIG. 2 shows an example of a more specific configuration of the circuit configuration shown in FIG. has been
The waveform shaping circuit 33 receiving the output of the auxiliary winding 32 is biased below the human power threshold level of the inverter 40 that constitutes this circuit. The counter control circuit 38 includes a NOR gate 41, a NAND
The flip-flop 35 is set and reset via the inverter 50 according to the output of the counter circuit 34 and the output of the waveform shaping circuit 33, and one output Q2 of the flip-flop 35 and the output of the NAND gate 42 are connected to each other. According to the output, the microcomputer 39
The counter circuit 34 is configured to be preset with digital data from the counter circuit 34. The microcomputer 39 is composed of a logic operator that generates output information from sensor information such as power supply voltage, magnetron current, and heating temperature, manual output setting information, or device-specific control data, and a memory that stores calculation procedures.
In addition to the input terminal It is provided with output terminals 01 to 01 for outputting, output terminal OE for inputting the initial value of each control circuit such as the counter circuit 34, and the like. The DC power supply supplied to each control circuit is obtained by a DC constant voltage circuit 47 including a transformer 44, a Schenner diode 45, a transistor 46, and the like. In addition, this DC power source can also be obtained by dividing the voltage from the rectifier output of the DC power source circuit 28. This microwave oven has the above circuit configuration, and its operation will be explained below based on the waveform diagram shown in FIG. When the power supply path switch 48 is closed and power is supplied, the flip-flop 35 outputs its output Q1 due to the initial value cent signal output from the terminal OE of the microcomputer 39.
In other words, the switching element 30 of the inverter circuit 27 is set to OFF, and the counter circuit 3 is set to OFF.
4 is reset. Under the above initial state, when an external start signal is input to the microcomputer 39 by the start switch 49, output information is set in the output terminals O2 to 07 as a digital code, and is output from the clock generation circuit 37. A clock signal having a constant period is counted by a counter circuit 34. In the counter circuit 34, the output terminals 0. of the microcomputer 39 are output based on the preset signal input to the terminal PI. While presetting the digital data sent to ~07, the clock signal is received from the terminal CK and counted up, and when the count up to the above preset value is reached, a carry is generated, and this carry generation causes the terminal C to be counted up.
The output of Y is for one clock period, and is kept in the H output state during the normal count period. Here, counter circuit 3
Although the case where 4 is counted up and a carry is generated is shown, a configuration in which the number 4 is counted down and a borrow is generated may also be used. As shown by symbol a in FIG. 3(B), during the period when there is no input to the inverter 40 of the waveform shaping circuit 33, the waveform shaping circuit 3
The output of NOR gate 41 becomes H only when the counter circuit 34 generates a carry. On the other hand, the precent input of the counter circuit 34 is the N of the output Q2 of the flip-flop 35 and the output of the NOR gate 41.
Since it is an AND logic, during a period when there is no input to the inverter 40, a carry is obtained only when the output Qt of the flip-flop 35 is H and a carry occurs in the counter circuit 34. Furthermore, when the counter circuit 34 is not preset, a carry is obtained by reaching the maximum count value, and when it is preset, a carry is obtained by a count value according to the output information from the microcomputer 39. Therefore, the switching of the inverter circuit 27 The output Q of the flip-flop 35 applied to the element 30, the width of the high level is set to the above maximum count value, and the width of the H level is set to the time corresponding to the count value according to the above output information. The period a in FIG. 3(B) usually does not exist, and the switching of the switching element 30 of the inverter circuit 27 generates a voltage in the auxiliary winding 32 that is in the opposite phase to the primary side of the drive transformer 29, causing a flip-flop. When the output Q1 of the counter 35 is high, the counter circuit 34 counts the amplifier beyond the previously preset data, and generates a carry when it counts up to the maximum value. As a result, the output Ql of the flip-flop 35 is inverted and becomes L. In the switching element 30 of the inverter circuit 27, the flip-flop 3
Since a large current is flowing during the period when the output Q of No. 5 is H, the off state is reached with a slight delay due to the above-mentioned inversion operation. In the inverter circuit 27, the magnetic energy stored in the drive transformer 29 is regenerated through the resonance capacitor 31 due to resonance operation, so that the switching element 3
A voltage with a waveform as shown in FIG. A voltage output corresponding to the voltage is obtained, and this is input to the terminal AD1 of the microcomputer 39. The microcomputer 39 converts the output information into a value corresponding to the input from the terminal AD, and then sets/distributes this data to the output terminals 01-0°. On the other hand, in the NOR gate 41, the output of the auxiliary winding 32 becomes I, and the precent input of the counter circuit 34 is reversed to L, and the counting operation is stopped. The voltage between both terminals of the switching element 30 of the inverter circuit 27 decreases as shown in FIG. 3(A) due to the regenerated energy. Accordingly, when the input to the inverter 40 falls below the threshold level, the output of the NOR gate 41 changes to H. As a result, the output information from the microcomputer 39 is preset in the counter circuit 34, and the counting operation starts again, while the flip-flop 35
The output Q1 becomes H, and the switching element 30 is turned on. In this way, the on time and off time of the switching element 30 of the in-hark circuit 27 are determined. That is, the on time is determined by the output information (preset value) M processed by the microcomputer 39, the number of stages (maximum count value) N of the counter circuit 34, and the clock cycle time. (1), and the off time is determined by the resonance period time using regenerative energy. Since the heating output of the microwave oven is proportional to the on-time, it is possible to freely control the output of the microwave oven. Note that when the counter circuit 34 functions as a down counter, the above-mentioned on time is on time=MX t (2). In addition, in the above operation, assuming that the power supply voltage is non-smooth DC as shown in Figure 4 (C), the magnetron can be driven in oscillation as shown in Figure 4 (A) and (B). There is a period c-d of the power supply voltage in which the secondary high-voltage output of the drive transformer 29 exceeds the threshold voltage v0 of the magnetron. In this case, the terminal AD of the microcomputer 39,
Input the power supply voltage to terminal AD or input the magnetron current to terminal AD.
, the microcomputer 39 converts the output information, that is, the heating control information, according to the input data, so that the output can be provided only during the power supply voltage period c-d. Also, during the power supply voltage period c-d, the output information is varied so that the pulse width changes depending on the power supply voltage or magnetron current, that is, for example, as the power supply voltage increases, the pulse width becomes narrower. If it is possible to set the regenerative current, the regenerative current will be constant, and accordingly, the magnetron current will also be constant. Conversely, the same effect can be obtained even if the output information is variably set so that the magnetron current is constant. Furthermore, in the above case, as shown in FIG. 4(B), the period c-
The power factor of the power supply is inherently bad due to the presence of the rest period d other than d, but since the power supply current has a rectangular waveform as shown in Figure 4 (B) due to the control described above, the power factor This increases the power usage efficiency of the device. [Effects of the Invention] In the microwave oven of the present invention, in order to switch the switching element of the inverter circuit that drives the magnetron into oscillation, the output of the drive transformer of the inverter circuit or an output in phase with the output of the drive transformer of the inverter circuit is detected by the detection means. At the same time, the output information from the output information setting means is variably set according to various sensor information related to the microwave oven, such as power supply voltage and magnetron current, and the counter circuit constituting the pulse supply means is connected to the output of the detection means and the output. Since the count is controlled based on the output information from the information setting means and the output of the flip-flop operated by the output of this counter circuit is given as a pulse signal to the switching element, the pulse signal input to the switching element is The pulse width is automatically adjusted in response to changes in the power supply voltage, magnetron current, etc., and the output control is not affected by the analog amount on the circuit or other conditions, allowing the microwave to operate under stable output conditions. This has the effect that it can be done. Furthermore, it opens the door to integrating peripheral control circuit components into semiconductors, making it possible to significantly reduce costs and downsize devices.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a circuit configuration showing one embodiment of the present invention, Fig. 2 is a circuit diagram showing a concrete example of the configuration, Fig. 3 is a waveform diagram showing its operation, and Fig. 4 is a “non-smooth” circuit diagram. FIG. 5 is a circuit diagram showing the conventional example, FIG. 6 is a waveform chart showing the operation, and FIG. 7 is a graph showing the voltage-current characteristics of the magnetron. 26 is a magnetron, 27 is an inverter circuit, 28 is a DC power supply circuit, 29 is a drive transformer, 29a is a primary winding, 3
0 is a switching element, 31 is a resonant capacitor, 32 is an auxiliary winding (detection means), 33 is a waveform shaping circuit, 34 is a counter circuit, 35 is a flip-flop, 36 is a drive circuit, 37 is a clock generation circuit, and 38 is a counter. Control circuit, 39 is a microcomputer (output information setting means)
It is.

Claims (1)

[Claims] 1. The primary winding of the magnetron drive transformer and the switching element are connected in series to the output side of the rectifier that converts commercial AC power into DC power, and a resonant circuit is formed by the primary winding and the resonant capacitor. An inverter circuit consisting of
In the microwave oven, which is driven resonantly by switching the switching element, the control section of the switching element is configured to include a detection means for detecting the output of the drive transformer or an output similar thereto, and various sensor information including power supply voltage. the output information setting means for variably setting the output information according to the output information; a counter circuit controlled based on the output of the detection means and the output information of the output information setting means; and a flip-flop operated by the output of the counter circuit. 1. A microwave oven comprising pulse supply means for supplying a pulse signal having a pulse width corresponding to various sensor information to the switching element.