JPS60250589A - 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 present 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 the leakage transmission 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 transmission. 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 cope with low-power cooking such as defrosting and stewing.

However, such output control by turning on and off electricity (in units of several tens of seconds) alternates between maximum output (full power) and zero output, which may affect the quality of cooking. Although this is not inherently desirable, 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. Continuous control was very difficult.

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 actually starts oscillating when the power is turned on.

There is a delay in the preheating time of the heater, making it difficult to properly control the output.

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.

(Object of the invention) This invention was made in view of the above circumstances.
The purpose of this is to create an excellent cooking device that can perform continuous and appropriate output control, thereby making it possible to cook food with good results, and also making it possible to reduce the size and size of the entire cooking device. Our goal is to provide the following.

[Summary of the invention]

This invention connects the primary winding of a transformer to the output end of a rectifier circuit that rectifies AC power supply voltage, and connects a magnetron to the secondary winding of this transformer via a voltage doubler rectifier circuit consisting of a capacitor and a diode. Furthermore, a switching element is connected to the primary winding circuit of the transformer, and this switching element is turned on and off by an output control circuit. In other words, a rectifier circuit, a transformer, and a switching element constitute a high-frequency inverter, and this high-frequency inverter supplies power to the magnetron.By employing this high-frequency inverter, it is possible to achieve continuous and appropriate output control and to reduce the size and size of the transformer. This makes each possible.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a commercial AC power supply, and this power supply 1 has a diode bridge 2. Choke coil for noise removal 3. A primary winding 6a of the transformer 6 is connected via a rectifier circuit 5 comprising a smoothing capacitor 4 and a rectifier circuit 5. and,
- The next winding 68 circuit includes a switching element such as an NP
The collector and emitter of the N-type transistor 7 are connected. 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 comprising a capacitor 9 and a diode 101. Note that the anode of the magnetron 11 is grounded,
The heater (cathode) is connected to the power source 1 via a heater transformer 13.

That is, the rectifier circuit 5 and I.Landistav constitute a high frequency inverter.

In this case, in order to reduce the leakage inductance of the transformer 6 as much as possible, the transformer 6 is constructed as shown in FIG. 3. That is, the primary winding 16a (solid line in the figure) with a small number of turns 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 placed on top of it via insulating paper. It is wrapped (rolled in one layer, not overlapping). moreover,
- The next winding 6a is divided into a plurality of mutually parallel windings.

Therefore, an output control circuit 20 is connected to the power source 1ull.゛This output control circuit 20 includes a DC power supply circuit 30 which is a constant voltage power supply, and an output setting circuit 401 connected to the DC power supply lines P and N of this DC power supply circuit 30.
Shooting circuit 50. It consists of a drive circuit 100.

Here, as shown in FIG. 4, the DC power supply circuit 30 has a primary winding 31a connected to the power supply 1 and two secondary windings aib and 3ic. 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. It consists of a smoothing capacitor 37, DC power lines P and N to which the voltage across the smoothing capacitor 37 is supplied, a terminal 30a connected to the common connection point of the rectifier circuits 32 and 33, and the terminal 30a is connected to the emitter of the transistor 7. connected to. 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 30a, 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.

The oscillation circuit 50 includes a main oscillation circuit 80 as shown in FIG.
．． It consists of a pulse width determining circuit 90 that changes the pulse width of the oscillation output of the main oscillation circuit 80 according to the setting value of the output setting circuit 40, and an output terminal 50a to which the output of this pulse width determining circuit 90 is supplied. For example, if the frequency is 2
It emits a pulse signal of 0Kt-1z and a width corresponding to the setting value of the output setting circuit 40.

The main oscillation circuit 80 includes a resistor 81 to which a DC power supply voltage is applied.
．． 82 and capacitor 83, a series circuit of resistors 84 and 85 to which DC power supply voltage is applied, and capacitor 8.
3 and the voltage generated at the interconnection point of the resistor 84.85, and the output terminal is connected to the resistor 84.85 through the resistor 86.
comparator 87, resistor 81.82 connected to the interconnection point of
This is a monostable multivibrator circuit consisting of a diode 88 connected between the interconnection point of and the output terminal of the comparator 87, and outputs the voltage of the capacitor 83.

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 two output voltages of the main oscillation circuit 80. a comparator (operational amplifier) 93 that compares the , a resistor 94 connected between the positive power supply line P and the output terminal of the comparator 93 , a comparator 93 and the output terminal 50
It consists of a resistor 95 connected between a and a.

On the other hand, as shown in FIG.
00a, an output terminal 100b connected to the base of the transistor 7, a resistor 101 to which a DC power supply voltage is applied,
102. A series circuit between the collector and emitter of the NPN transistor 103 and the resistors 104 and 105, a series circuit between the collector and emitter of the resistor 106 and the NPN transistor 107 to which the DC power supply voltage is applied, and a PNP circuit to which the DC power supply voltage is applied. Between emitter and collector of transistor 1゜08, resistor 109, diode 110
．． The base of the transistor 103 is connected to the input terminal 100a, the base of the transistor 107 is connected to the interconnection point of the resistors 104 and 105, and the base of the transistor 108 is connected to the interconnection point of the resistors 104 and 105. The base of transistor 111 is connected to the interconnection point of resistors 101 and 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. Then, the interconnection point between the resistor 109 and the diode 110 is connected to the output terminal 1oob. That is, the transistor 7 is turned on and off according to the output of the oscillation circuit 50, and when the voltage at the input terminal 190a becomes a high level, a high level voltage is generated at the output terminal 100b.
The transistor 7 is turned on.

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

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

When the main oscillation 9 circuit 80 generates the DC power supply voltage, if the output 5 of the comparator 87 is a fault “1'°, the resistor 84
．． As the voltage 6 at the interconnection point 85 reaches a high level due to the voltage division of the resistor 84.85, the capacitor 83 is charged and its voltage v7 gradually rises. Therefore, the output V5 of the comparator 87 initially becomes logic "1", and then inverts to logic TO11 when the voltage 7 of the capacitor 83 exceeds the level of the voltage V6.Then, the voltage 7 of the capacitor 83 becomes the voltage 1. When the voltage drops to the level of 6, the output Vll of the comparator 87 becomes logic "1" again, and the capacitor 83 is charged. That is, capacitor 8
3 voltage V7 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 logic "ON" if the voltage V7 is higher than the voltage V8, and logic "111!" if the voltage V7 becomes lower than the voltage "6". l
becomes. The output of the comparator 93 is generated as ■9 at the output terminal 50C, and when the output ■9 is a logic "1°", the transistor 7 is turned on by the driving circuit 100.

Next, the operation of the high frequency inverter and its peripheral parts will be explained with reference to FIGS. 8 and 9.

Now, when transistor 7 turns on (timing to)
, the collector current IC of the transistor 7 increases in a sawtooth waveform. When the collector current 1c increases, a voltage proportional to the number of turns 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 400 OV). In this way, the operating voltage Vm is applied to the magnetron 11, the current Is flows, and the magnetron 11 operates in oscillation. In addition,
The current 1 m gradually decreases because the charge in the capacitor 9 is discharged.

When the transistor 7 is turned off at timing t1), a voltage Vce is generated between the collector and emitter of the transistor 7. When the voltage Vce is generated, a voltage is generated in the secondary winding 6b of the transformer 6, and a current id flows through the diode 10 to the capacitor 9, so that the capacitor 9 is charged. In this case, when charging of the capacitor 9 is completed and the current 1d flowing through the capacitor 9 becomes zero, the voltage Vce becomes low level in response.

Then, when the transistor 7 is turned on (timing t2
), the voltage Vce becomes zero, and the collector current IC
flows, the above operation is repeated, and the magnetron 11 operates in oscillation.

In addition, in FIG. 8, the current 1 flowing through the capacitor 9
The timing at which d becomes zero and the timing at which transistor 7 turns on happen to be the same.

Therefore, if the variable resistor 40r of the output setting circuit 40 is adjusted to increase its resistance value, the pulse width and the determination circuit 90
The level of the voltage v4 decreases at , the logic "1" period of the output 5 of the oscillation circuit 50 becomes shorter, and the on/off duty of the transistor 7 becomes smaller (the on period becomes shorter).Then, the current flowing through the magnetron 11 ) The effective value of m becomes smaller, and the oscillation output of the magnetron 11 can be lowered (FIG. 9).In other words, the output can be changed continuously.

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 the voltage V4 gradually increases at the start of cooking (when the power is turned on). As a result, the on-period of the transistor 7 is short at first, and gradually becomes longer, thereby making it possible to gradually increase the output.

In this way, power is supplied to the magnetron 11 using a high-frequency inverter, so the output can be controlled continuously, and an output of several hundred watts can be instantaneously added during low-power cooking such as defrosting or stewing. There is no problem of cooking, and you can always cook to a good quality. Moreover, by adopting a high-frequency inverter, it is no longer necessary to use a leakage transformer like in the past (transformer 6 is lightweight and small), making it possible to make the entire cooker lighter and smaller. 5
01h / 60 H1).

In addition, since the heater power of the magnetron 11 is obtained independently by the heater transformer 13, the operating voltage is always applied to the magnetron 11 after the heater has finished preheating, which results in a time delay in the oscillation operation of the magnetron 11. Appropriate output can be obtained without causing any problems. In particular, 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 6, protecting various devices. can do.

By the way, when configuring a high frequency inverter, it is common to provide a resonant capacitor on the primary side of the transformer 6, and add a resonant circuit (for example, voltage resonant type) consisting of this resonant capacitor and the reactance of the transformer 6. In that case, a regeneration diode (damper diode) is connected between the collector and emitter of transistor 7, and when transistor 7 is on, the energy stored in the inductance of transformer 6 due to resonance is transferred to the regeneration current. The regenerative current must be passed through the regenerative diode to prevent an abnormal spike voltage from being applied to the transistor 7, but this results in an inconvenience in that the efficiency is reduced by the amount of the regenerative current.

In contrast, the present invention does not configure a complete resonant circuit, but only when the transistor is off, the capacitor 9 of the voltage doubler rectifier circuit
is used as a resonant capacitor, and at this time, the energy of the inductance of the transformer 6 is released by charging the capacitor 9 passed through the diode 10. Furthermore, the transformer 6 is configured as shown in Fig. 3. Therefore, when the transistor 7 is turned on, no abnormal spike voltage is applied to the transistor 7, and no regenerative current flows, thereby improving efficiency. Furthermore, since there is no regenerative current, the transistor 7 can have a small current capacity, and the loss of the transistor 7 can also be small. Furthermore, a resonant capacitor and a damper diode are not required, so the structure can be simplified, and this can greatly contribute to reducing the weight and size of the entire cooking device. In particular, when a resonant circuit is provided as described above, it is necessary to provide a feedback circuit from the high frequency inverter to the oscillation circuit in order to prevent irregular oscillation of the resonant circuit, and to trigger the oscillation circuit by the feedback signal. According to , since there is no resonant circuit, there is no need for a feedback circuit or a trigger circuit, and as a result, there is no need for a resonant capacitor or damper diode, and the configuration can be greatly simplified.
Accordingly, lower costs are possible. Moreover, when a resonant fence circuit is used, the variable range of output cannot be made as wide as that, but according to the present invention, since there is no resonant circuit, the variable range of output can be greatly expanded, and the optimum heating conditions can be set for each type of cooking. can be ensured.

It should be noted that 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 carry out continuous and accurate output control, which makes it possible to cook food with good results, and furthermore, it is possible to reduce the size and size of the entire cooking device. We can provide you with 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 schematic diagram of a transformer in an embodiment of the invention.
FIG. 4 is a specific configuration diagram of the direct current and power supply circuit in the same embodiment, FIG. 5 is a specific configuration diagram of the oscillation circuit in the same embodiment, and FIG. 6 is a specific configuration diagram of the drive circuit in the same example. This is a block diagram and a time chart for explaining the operation of the first unit and its surrounding areas. DESCRIPTION OF SYMBOLS 1... Commercial AC power supply, 5... Rectifier circuit, 6... Transformer, 7... NPN type transistor (switching element), 9... Capacitor, 10... Diode,
11... Magnetron, 20... Output control circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Denkon □□ Figure 3 C Figure 4, 30 Figure 6 Figure 7 Figure 8 Figure 9

Claims (2)

[Claims] (1) A rectifier circuit connected to an AC power source, a transformer with a primary winding connected to the output end of this rectifier circuit, and a voltage doubler rectifier circuit consisting of a capacitor and a diode in the secondary winding of this transformer. 1. A cooking appliance comprising: a magnetron connected through a magnetron; a switching element inserted into and connected to a primary winding circuit of the transformer; and an output control circuit that turns on and off the switching element. (2) The 1i11 processor according to claim 1, wherein the output control circuit controls the output by changing the on/off duty of the switching element according to the output setting value.