JPS60250588A - Cooking device - 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 [Technical Field of the Invention] The invention relates to a cooking appliance such as a microwave oven having a magnetron.

[Technical background of the invention]

Conventionally, this type of microwave oven connects a magnetron to the secondary winding of a leakage transformer via a voltage doubler rectifier circuit consisting of a capacitor and a diode, and supplies AC power voltage to the primary winding of the leakage transformer. This causes the magnetron to operate in oscillation. In addition, a switch is provided in the AC power supply voltage supply path to the primary winding of the leakage transformer, and the desired output is obtained by turning this switch on and off and changing the on and off duty of the switch. It is designed to deal with defrosting food, stewing, low output cooking, etc.

However, such output control by turning on and off electricity (in units of tens of seconds) alternates between maximum output (full power) and zero output, so it may affect the quality of the cooking. However, it is desirable to be able to perform continuous output control if possible.

However, the magnetron is a diode vacuum tube, and the second
As shown in the figure, when a voltage of approximately 4000 V is applied, a current begins to flow, and the current has a characteristic that it increases with a nearly constant applied voltage with a slight slope. It was very difficult to control.

In addition, since the magnetron heater is also connected to the secondary side of the leakage transformer, the energization can be turned on or off as shown above.
In output control by turning off the magnetron, there is a delay by the preheating time of the heater before the magnetron actually starts oscillating when the magnetron is turned on, making it difficult to control the output appropriately.

Furthermore, since the leakage transformer is heavy and large, there is a problem in design that there is not enough space for its arrangement, and that the entire cooking device becomes heavier and larger.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose is to be able to perform continuous and appropriate output control, thereby achieving good performance! To provide an excellent cooking device which enables the cooking device to be weighed and downsized as a whole.

[Summary of the invention]

In this invention, an inverter circuit is configured with a rectifier circuit, a switching element, a transformer, etc., and the anode and cathode of the magnetron are connected to the secondary side of the transformer of the inverter circuit via a voltage doubler rectifier circuit consisting of a capacitor and a diode. At the same time, a means is provided that is connected to the secondary side of the transformer of the inverter circuit to supply constant power to the heater of the magnetron, and further controls the output by turning on and off the switching elements of the inverter circuit. Place at the time of injection.

It is equipped with an output control circuit that maintains the output below a certain value for a certain period of time. In other words, an inverter circuit is composed of a rectifier circuit, a switching element, a transformer, etc., and this inverter circuit supplies power to the magnetron.By employing this inverter circuit, continuous and appropriate output control and transformer control are possible. This makes it possible to reduce the size and size of the device, and also eliminates the need for a heater transformer by obtaining constant power from the secondary side of the inverter circuit transformer and applying it to the magnetron heater. .

(Embodiment of the Invention) An embodiment of this starter will be described below with reference to the drawings.

In FIG. 1, 1 is a commercial current power source, and this power source 1 has a diode bridge 2.・Chimmy Kucoil for noise removal 3. The primary winding of the transformer 6 and the wire 6a are connected through a rectifier circuit 5 comprising a smoothing capacitor 4 and a smoothing capacitor 4. A switching element such as an NPN type transistor reflector and emitter is connected to the -next side winding and li 6 a circuit, and a regeneration diode (damper diode) 8 is connected between the collector and emitter. Ru. On the other hand, the anode and cathode of the magnetron 11 are connected to the secondary winding 6b of the transformer 6 via a voltage doubler rectifier circuit including a capacitor 9 and a diode 10. Further, a resonance capacitor 12 is connected in parallel to the secondary winding 6b of the transformer 6. Further, a constant power means, for example, a constant voltage circuit 20 is connected to the secondary winding 6C of the transformer 6.
The input terminal of the constant voltage circuit 200' is connected to the constant voltage circuit 200', and the heater (cathode) of the magnetron 11 is connected to the output terminal of the constant voltage circuit 200'. Note that the anode of the magnetron 11 is grounded.

As shown in FIG. 3, the constant voltage circuit 200 has an input terminal 2.
00a, 200b, a rectifying diode 201, a smoothing capacitor 202, and a PNPN upper type resistor 203 for making the voltage of the smoothing capacitor 202 constant. resistance 20
4. Zener diode 205 and output terminal 200
c, 200d, and provides a constant voltage to the heater of the magnetron 11.

, that is, the rectifier circuit 5. A resonant circuit consisting of the reactance of a transformer 6 and a resonant capacitor 12.

A high frequency inverter circuit is constituted by a transistor 7 that excites this resonant circuit, a regeneration diode 8, and the like, and power is supplied to the magnetron 11 by this high frequency inverter circuit.

In this case, the resonance capacitor 12 is not connected to the primary side of the transformer 6, but is connected to the secondary side, but even if it is connected to the secondary side, it is equivalent to connecting it to the primary side. Moreover, if it is connected to the secondary side, the turn ratio between the primary side winding and the secondary winding of the transformer is 〇, so the withstand voltage is n.
Even if it is doubled, the current flowing through the resonant capacitor 12 is only 1/n of that in the case of the primary side, and in that case, the capacitance of the resonant capacitor 12 should be 1/n2 of that when connected to the primary side. This is because the resonance capacitor 12 can be made smaller (the resonance capacitor 12 and the capacitor of the voltage doubler rectifier circuit can be made into one block capacitor, which greatly contributes to the miniaturization of the entire cooker). do)
.゛Also, when the resonance capacitor 12 is connected to the secondary side of the transformer 6, if the leakage inductance of the transformer 6 is large, there is a risk that a spike voltage will be generated in the transistor 7 when the transistor 7 switches. In order to eliminate this problem, the transformer 6 is constructed as shown in FIG.

That is, the primary winding 6a with a small number of turns (solid line shown)
is first wound around the core 6C (single-layer winding without overlapping), and then the secondary winding 6b (broken line in the figure) with a large number of turns is wound thereon (single-layer winding without overlapping) with an insulating paper interposed therebetween. Further, the negative side winding 6a is divided into a plurality of windings that are parallel to each other.

Thus, an output control circuit 20 is connected to the power source 1.

This output control circuit 20 includes a DC power supply circuit 30. which is a constant voltage power supply. and an output setting circuit 40 connected to the DC power lines P and N of the DC power supply circuit 30. Oscillation circuit 50. It consists of a drive circuit 1oo.

Here, as shown in FIG. 5, the DC power supply circuit 30 includes a transformer 31 connected to the power supply 1 and having a primary winding 31a and two secondary windings 31b and 3.1c. secondary winding 31b.

rectifier circuits 32 and 33 connected to the respective terminals 31C and whose negative output terminals and positive output terminals are commonly connected; and an NPN transistor 34 that makes the output voltage of the rectifier circuits 32 and 33 constant. Resistance 35. Zener diode 36. Smoothing capacitor 37, DC power supply line P to which both AT voltages of this smoothing capacitor 37 are supplied, N1 rectifier circuit 32.33
The terminal 3C) a is connected to the emitter of the transistor 7. In this case, by applying the voltage at the common connection point of the rectifier circuits 32 and 33 to the emitter of the transistor 7 via the terminal 3oa, the base charge of the transistor 7 is quickly removed when the transistor 7 is turned off.

The output setting circuit 40 has a variable resistor 40r, as shown in FIG.

As shown in FIG. 6, the oscillation circuit 50 includes the rectifier circuit 5
An input terminal 50a is supplied with the positive output voltage of the transistor 7, and an input terminal 50b is supplied with the collector voltage of the transistor 7.
, a comparison circuit 60. which compares the input voltages of the input terminals 50a and 50b. A trigger circuit 70 that responds to the comparison output of the comparison circuit 60; a main oscillation circuit 80 that is triggered by the circuit 70; It consists of a pulse width determining circuit 90 for changing the pulse width, an output terminal 50c to which the output of the pulse width determining circuit 90 is supplied, and the like. It emits a pulse signal with a corresponding pulse width.

The comparator circuit 60 has a resistor 62 to which an input voltage at an input terminal 50a is applied via a resistor 61, an input voltage to an input terminal 50b is applied via a resistor 63, and a diode 6.
4, and a comparator (operational amplifier) 66 that compares the voltage across the resistor 65 and the voltage across the resistor 62.

The trigger circuit 70 includes a resistor 71 to which a DC power supply voltage is applied.
．． 72 in series, a series circuit of resistors 74 and 75 to which the DC power supply voltage is applied between the PNP transistor transmitter and collector, and a resistor 76 connected to the positive DC power line P and the base of the transistor 73. , a series circuit of a capacitor 77 and a resistor 78 connected between the heath of the transistor 73 and the output terminal of the comparator 66;
6. A comparator (calculator) that compares the voltage generated at the interconnection point of resistor 79 and resistor 71.72 connected in parallel to the series circuit of capacitor 77 and resistor 78 with the voltage generated at the interconnection point of resistor 74.75. amplifier) 701.

The main oscillation circuit 80 includes a resistor 81 to which a direct power supply voltage is applied.
, 82 and a capacitor 83, a series circuit of resistors 84 and 85 to which DC power supply voltage is applied, and a capacitor 8.
The voltage at resistor 84.3 is compared with the voltage appearing at one interconnection point of resistor 84.
A comparator 87 connected to the interconnection point of 85, a resistor 81 .
82 and the output terminal of a comparator 87, the output terminal of the comparator 87 being connected to the output terminal of the trigger circuit 70. Note that the voltage of the capacitor 83 is used as the output.

The pulse width determining circuit 90 includes a parallel circuit of a resistor 91 and a capacitor 92 to which a DC power supply voltage is applied via the variable resistor 40r of the output setting circuit 40, and a voltage of this parallel circuit and an output voltage of the main oscillation circuit 80. a comparator (operational amplifier) 93 for comparing the values, a resistor 94 connected between the positive power supply line P and the output terminal of the comparator 93, and a comparator 93 and an output terminal 500.
It consists of a resistor 95 connected between.

On the other hand, the drive circuit 100 includes, as shown in FIG. is applied to the resistor 10
1,102. The collector of the NPN transistor 103
A series circuit between the emitters and the resistors 104 and 105, a series circuit between the resistor 106 to which the DC power supply voltage is applied, and the collector-emitter of the NPN transistor 107.
PNP transistor 108 to which DC power supply voltage is applied
Between the emitter and collector of the resistor 109. diode 11
0. The base of the transistor 10.3 is connected to the input terminal 100a, and the base of the transistor 10.3 is connected to the input terminal 100a.
the base of is connected to the interconnection point of resistors 104 and 105,
The base of transistor 108 is connected to the interconnection point of resistors 101, 102, and the base of transistor 111 is connected to the collector of transistor 107 through a parallel circuit of speed-up capacitor 112 and resistor 113. The interconnection point between the resistor 109 and the diode 110 is connected to the output terminal 100b. That is, the transistor 7 is turned on according to the output of the oscillation circuit 50,
It is turned off, and when the voltage at the input terminal 1'OOa becomes high level, a high level voltage is generated at the output terminal 100b and the transistor 7 is turned on.

Next, the operation in the above configuration will be explained.

First, the operation of the high frequency inverter and its peripheral parts will be explained with reference to FIG.

Now, when the transistor 7 is turned on at timing to, the collector current IC of the transistor 7 increases in a sawtooth waveform. In this case, the collector current 1c once becomes negative, but this is a regenerative current due to the energy stored in the reactance of the transformer 6 (a in the figure). When the collector current IC increases, a voltage proportional to the number of collector currents is generated in the secondary winding 6b of the transformer 6.・
This generated voltage is designed in advance so that the sum of the voltage charged in the capacitor 9 becomes the operating voltage of the magnetron 11 (approximately 4000 cm). Further, a voltage is also generated in the secondary winding 6C of the transformer 6, and this voltage is rectified and made constant by the constant voltage circuit 200, and the magnetron 1
1 heater. Therefore, current flows through the magnetron 11, and the magnetron 11 operates in oscillation. Note that the current of 1 m gradually decreases, but this is due to the capacitor 9.
This is because the charged charge is discharged.

When transistor 7 is turned off at timing t1,
Resonance occurs between the reactance of the transformer 6 and the resonance capacitor 12, and a voltage Vce is generated between the collector and emitter of the transistor 7. This voltage Vce has a substantially sinusoidal waveform with a peak voltage of several hundred volts. However,
When the voltage Vce is generated, the secondary winding 6b of the transformer 6
A voltage is generated at the capacitor 9 via the diode 10.
is charged. Further, a voltage is generated in the secondary winding 6C of the transformer 6, and this voltage is rectified and made constant by the constant voltage circuit 200, and is applied to the heater of the magnetron 11.

In addition, in Fig. 8, VCt is the resonance capacitor 1.
2 voltage, vc2c; t' is the voltage of capacitor 9,
The voltage VC2 of the capacitor 9 changes only slightly due to discharge and remains approximately constant.

Then, the above operation is repeated by turning on the transistor 7 again at the point where the voltage Vce becomes zero (timing t2).

Therefore, the on period (to) of the transistor 7.

If the current flowing through the magnetron 11 (m
The effective value of is increased, and the oscillation output of the magnetron 110 can be increased. Conversely, if the on period of the transistor 7 is short, the effective value of the current Im flowing through the magnetron 11 becomes small, and the oscillation output of the magnetron 11 can be lowered.

Next, the operation of the oscillation circuit 50 will be explained with reference to FIG. 9.

During operation, a rectified voltage v1 is generated at the positive output terminal of the rectifier circuit 5, and a voltage Vc due to resonance is generated at the collector of the transistor.
A voltage V2 is generated corresponding to e. Therefore, the voltage VCa
is occurring, the voltage V2 is at a higher level than the voltage ■1, and therefore the output v3 of the comparator 66 is at logic "1'".
''. Then, when the voltage Vce becomes zero, the voltage V2 becomes a lower level than the voltage V1, and the output of the comparator 66 becomes
is inverted to logic "OII".

On the other hand, when the output v3 of the comparator circuit 60 is logic 111 II, the trigger circuit 70 outputs the capacitor 7 through the resistor 79.
At the same time, the transistor 73 is maintained in an off state, and the output 4 of the comparator 701 is maintained at logic II II II by turning off the transistor 73. When the output V3 of the comparator circuit 60 is inverted to logic "O", the capacitor 77 is charged, and the transistor 2 and 73 are turned on for the charging period (very short time).When the transistor 73 is turned on, the comparator is turned on for that ON period. The output v4 of 7Q1 is inverted to the logic 110 II.Then, when the transistor 73 is turned off, the output V4 is again the logic di1
．． It becomes 11.

Moreover, when the DC power supply voltage is generated, the main oscillation circuit 80 has a resistor 84.85 if the output V5 of the comparator 87 is logic tr 1 pr and the output 4 of the trigger circuit 70 is logic "1". The voltage V6 at the interconnection point of resistor 84.85
At the same time, the capacitor 83 becomes high level due to the divided voltage of
is charged, and its voltage V7 gradually rises. Therefore, the output Vs of comparator 87 is initially logical 111 I
If you leave it as it is, the capacitor 83 will eventually become I.
Voltage v7 exceeds the level of voltage v6, and output V5 of comparator 87 is inverted to logic "0°". However, before that, the output ■4 of the trigger circuit 70 becomes logic 110 II, and as a result, the resistor 86 is connected in parallel to the resistor 85, and the voltage v
6 becomes a low level, the charge in the capacitor 83 is discharged, and the voltage 7 of the capacitor 83 decreases. Therefore, the output ■5 of the comparator 87 is logic "'1"
' to logic 'OTl. Then, capacitor 8
When the voltage 7 of voltage 3 drops to the level of voltage 6, the output V5 of the comparator 87 becomes logic 11111 again, and at this time, the output 4 of the trigger circuit 70 is already at logic ``1°'', so the capacitor 83 In other words, the voltage V7 of the capacitor 83 becomes the oscillation output.

The pulse width determining circuit 90 uses a comparator 93 to compare the voltage Va generated in the parallel circuit of the resistor 91 and the capacitor 92 based on the output setting value of the output setting circuit 40 with the output voltage 7 of the main oscillation circuit 80 . Therefore, the output of the comparator 93 becomes a logic 110 IT if the voltage V7 is higher than the voltage ■8, and a logic 11 IT if the voltage ■7 becomes lower than the voltage Va'.
1 Becomes IT. Then, the output of the comparator 93 is generated as V9 at the output terminal 50C, and when the output V9 is a logic voltage of 1, the transistor 7 is turned on by the drive circuit 100.

That is, when the voltage yce generated by resonance becomes zero, the transistor 7 is turned on, thereby allowing the resonant circuit to oscillate normally. Furthermore, by adjusting the variable resistor 40r in the output setting circuit 40 and changing the level of the voltage V8, the on/off duty of the transistor 7 can be changed, and thereby the effective value of the current flowing through the magnetron 11 can be adjusted. The output can be continuously varied.

In addition, since the variable resistor 40r of the output setting circuit 40 and the capacitor 92 constitute a time constant circuit, the level of voltage 8 gradually increases at the start of cooking (when the power is turned on). As a result, the on-period of the transistor 7 is initially short and gradually becomes longer, and the output gradually increases from the zero state at a predetermined slope and eventually corresponds to the set value. In this case, the voltages generated in the secondary windings 6b and 5c of the transformer 6 will also gradually rise from when the power is turned on, and first the output voltage of the constant voltage circuit 200 will reach the constant voltage level. The heater of the magnetron 11 is heated, and then a voltage of a level necessary for oscillation operation is applied between the anode and cathode of the magnetron 11.

In this way, power is supplied to the magnetron 11 by a high-frequency inverter circuit, so the output can be controlled continuously, and an output of several hundred watts can be instantaneously generated during low-power cooking such as defrosting or stewing. Nothing is added to the food, and you can always get good quality cooking. Moreover, by adopting a high-frequency inverter circuit, it is no longer necessary to use a conventional leakage transformer (transformer 6 is lightweight and small), making it possible to make the entire cooker lighter and smaller. 50H2/6081). In addition, since the heater power of the magnetron 11 is obtained from the secondary side of the transformer 6, there is no need to use a dedicated transformer for the heater, and in addition to eliminating the leakage transformer mentioned above, it is possible to significantly reduce the size and size. . Furthermore, since the resonance capacitor 12 is connected to the secondary side of the transformer 6 and the resonance capacitor 12 is made smaller, it can greatly contribute to weight reduction. In this case, since the winding configuration of the transformer 6 is designed to minimize leakage inductance as shown in Figure 4, even if the resonance capacitor 12 is connected to the secondary side, an abnormal spike voltage will appear on the transistor 7. This will not occur and is safe.

In addition, since the output is gradually increased at the start of cooking, no abnormal voltage is generated on the secondary side of the transformer 6, and no abnormal current flows through the transistor 7, ensuring the safety of various devices. Protection can be measured. In particular, since the operating voltage is applied to the magnetron 11 after the heater has finished preheating, the magnetron 11 is not adversely affected and a so-called cooling start is possible.

Furthermore, during cooking, the operating voltage is applied to the magnetron 11 while the heater is always heated, so there is no time delay in the oscillation operation of the magnetron 11, and an appropriate output can be obtained. I can do it.

In the above embodiment, a time constant circuit is configured in the output setting circuit 40 and the pulse width determining circuit 90 to gradually increase the output at a predetermined gradient at the start of cooking. However, for example, a timer circuit may be provided. , the output is maintained at a constant level (corresponding to the drive power of the heater of the magnetron 11) for a predetermined time from the start of cooking to sufficiently preheat the heater, and after that predetermined time, the output immediately corresponds to the set value. You may also do so. In other words, the key is when the power is turned on.

Any device that maintains the output below a certain value for a predetermined period of time may be used.

Further, in the above embodiment, a case has been described in which power is supplied to the magnetron 11 by a high frequency inverter circuit having a resonant circuit consisting of the reactance of the transformer 6 and the resonant capacitor 12, but as shown in FIG. 12 is removed and power is supplied to the magnetron 11 by a high frequency inverter circuit without a resonant circuit.

In this case, a feedback circuit from the high frequency inverter circuit to the oscillation circuit 50 is not required, the comparison circuit 60 and the trigger circuit 70 in the oscillation path 50 are not required, and the damper diode 8 is also not required, thus simplifying the configuration. It has the advantage of being able to measure

Further, in the above embodiment, the constant voltage circuit 200 is used as a constant power means for supplying electric power from the secondary side of the transformer 6 to the heater of the magnetron 11.
As shown in FIG. 1, the capacitor 9 of the voltage doubler rectifier circuit may be divided into a pair of series capacitors 9a and 9b, and both ends of one of the capacitors 9b may be connected to the heater of the magnetron 11. That is, as explained in FIG. 8, a substantially constant voltage VC2 that only slightly changes due to discharge is generated in the capacitor 9 of the voltage doubler rectifier circuit. Focusing on this, the voltage VC2 is changed to the capacitor 9a, 9b is used to divide the pressure and apply it to the heater. In this case, capacitor 9a.

9b, the capacitance of capacitor 9b is made larger to obtain sufficient voltage to drive the heater.

Further, this embodiment can be implemented in the same manner even when using a high frequency inverter circuit without a resonant circuit as shown in FIG. 10.

In addition, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without changing the gist.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to perform continuous and appropriate output control, which allows for good quality cooking, and furthermore, it is possible to reduce the size and size of the entire cooking device. We can provide excellent cooking equipment.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of a control circuit showing an embodiment of the present invention, Fig. 2 is a diagram showing the characteristics of a magnetron, and Fig. 3 is a diagram showing the characteristics of a magnetron.
The figure shows a specific configuration diagram of a constant voltage circuit according to an embodiment of the present invention, FIG. 4 is a schematic configuration diagram of a transformer according to an embodiment of this invention, and FIG. FIG. 6 is a specific configuration diagram of the oscillation circuit in the same embodiment, FIG. 7 is a specific configuration diagram of the drive circuit in the same embodiment, and FIG. 8 is a high-frequency inverter circuit and 9 is a time chart for explaining the operation of the oscillation circuit in the same embodiment, and FIG. 10 is the entire control circuit showing another embodiment of the present invention. Fig. 11 is an overall block diagram of a control circuit showing still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Commercial AC power supply, 5... Rectifier circuit, 6... Transformer, 7... NPN transistor (switching element), 9... Capacitor, 10... Diode, 11... ... Magnetron, 12... Resonance capacitor, 20... Output control circuit, 200... Constant voltage circuit (constant power means). Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 7 Figure 8

Claims (3)

[Claims] (1) An inverter circuit consisting of a rectifier circuit, a switching element, a transformer, etc., and connected to an AC power supply;
Two of the transformers in this inverter circuit. A magnetron whose anode and cathode are connected via a voltage doubler rectifier circuit consisting of a capacitor and a diode is connected to the secondary side of the transformer of the inverter circuit; power means and said ins. A cooking appliance characterized by comprising: an output control circuit that performs output control by turning on and off a switching element of a converter circuit, and maintains the output below a certain value for a predetermined period of time when the power is turned on. (2) The cooking appliance according to claim 1, wherein the constant power means is turned on by a constant voltage circuit. (3) The constant power means is characterized in that the capacitor of the voltage doubler rectifier circuit is divided into a pair of series capacitors, and both ends of one of the capacitors are connected to the heater of the magnetron. A cooking appliance according to claim 1.