JP3117697B2 - High frequency cooking device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention converts a commercial power supply to a high-frequency power supply by a frequency conversion unit, and supplies the high-frequency output to a magnetron via a step-up transformer. The present invention relates to a high-frequency heating / cooking apparatus for driving a slab.

(Prior Art) In this type of high-frequency heating cooking apparatus, for example, any one of components such as a step-up transformer, a voltage doubler rectifier circuit provided on the secondary side of the step-up transformer, and a magnetron driven by the doubler voltage rectifier circuit is used. If the operation becomes defective, a large current flows through the circuit, or on the contrary, the current drops abnormally, so that normal high-frequency heating cannot be performed. If the operation is continued in such a state, not only the quality of the cooking is deteriorated but also other normal circuit components are broken by the Joule heat due to the large current, and the like.

In order to cope with this, as shown in JP-A-1-298677, an abnormal voltage detection winding is provided on the secondary side of the step-up transformer, and the voltage detected by the abnormal voltage detection winding is out of an allowable range. Sometimes, the operation of the magnetron is stopped.

(Problems to be Solved by the Invention) However, in the above-mentioned publication, the abnormal voltage detection winding is provided on the secondary side of the step-up transformer. Moreover,
The induced voltage generated in the abnormal voltage detection winding determines indirectly whether the circuit from the secondary coil of the step-up transformer to the magnetron is in an abnormal or normal operating state. is there.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to provide a high-frequency heating apparatus that can reduce the size of a step-up transformer while reducing costs and increase the reliability of abnormality detection. It is to provide a cooking device.

[Structure of the Invention] (Means for Solving the Problems) A high-frequency heating and cooking device according to the present invention controls a conduction time width of a switching element to convert a commercial power frequency to a high frequency, and a frequency converter. A step-up transformer for boosting the AC output from the step-up transformer, and a magnetron connected to the secondary side of the step-up transformer, wherein an anode current detection circuit for detecting an anode current of the magnetron is provided, and the anode current detection circuit The operation of the magnetron is stopped when the current value detected by the method deviates from a preset allowable range.

When the magnetron is operated in a steady state, it receives the detection signal from the anode current detection circuit and controls the conduction time width of the switching element of the frequency conversion unit in a direction in which the anode current keeps a constant value. The upper limit value and the lower limit value are set.

(Operation) The anode current detection circuit detects the anode current of the magnetron. If the detected current value is within the allowable range, the circuit is operating normally, and the operation of the magnetron is continued. If the detected current value of the anode current detection circuit is out of the allowable range, one of the circuit components has malfunctioned, and the magnetron stops operating at the time of the detection. In this case, since the current of the circuit to be subjected to abnormality detection is directly detected by the anode current detection circuit, the reliability of abnormality detection is high. In addition, there is no need to provide an abnormal voltage detection winding on the secondary side of the step-up transformer, so that the size of the step-up transformer does not increase.

Also, the magnitude of the high frequency output of the magnetron is determined by the magnitude of the anode current, and the magnitude of the anode current is determined by the magnitude of the conduction time width of the switching element. The detection time signal from the converter controls the conduction time width of the switching element of the frequency conversion unit in the direction in which the anode current maintains a constant value, thereby preventing fluctuations in high-frequency output due to fluctuations in commercial power supply voltage. As a result, stable high-frequency heating becomes possible. In addition, the anode current detection circuit can be used for both abnormality detection and normal control, and the cost can be reduced from this aspect as well.

In this case, assuming that the conduction time width of the switching element is adjusted indefinitely in accordance with the fluctuation of the anode current value, the conduction time width of the switching element is kept within an appropriate range in order to maintain the anode current at a constant value even when an abnormality occurs. May be adjusted to exceed the limit, and the detection of a circuit abnormality may be delayed.

Therefore, when the magnetron is operated in a steady state, an upper limit value and a lower limit value are set for the conduction time width of the switching element, and when the abnormality occurs, the conduction time width is prevented from being adjusted beyond an appropriate range, and the abnormality of the circuit is prevented. This is to ensure detection.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Reference numeral 1 denotes a frequency converter for converting a commercial power supply frequency to a high frequency, a rectifier circuit 2 for full-wave rectifying an AC voltage of the commercial power supply connected to terminals t ₁ and t ₂ , and a DC voltage for smoothing the full-wave rectified voltage. And a filter 5 formed by a choke coil 3 and a capacitor 4.
An oscillating circuit for frequency conversion is composed of a primary winding 6a of the step-up transformer 6, a resonance capacitor 7, a switching transistor 8 and a diode 9 as switching elements, and a control circuit 10 controls the switching transistor 8 to turn on and off. As a result, a high-frequency current is generated in the primary winding 6a of the step-up transformer 6. As a result, in the magnetron drive unit 11, a high-frequency voltage is induced in, for example, two secondary windings 6b and 6c of the step-up transformer 6, and the high-frequency voltage induced in the secondary winding 6b is applied to the diode 12 and the smoothing voltage. The voltage is applied between the anode and the cathode of the magnetron 15 via the voltage doubler rectifier circuit 14 including the capacitor 13, and the voltage induced in the secondary winding 6c is applied to the cathode. Further, an anode current detection circuit 18 composed of a current transformer is provided in the current path on the anode side of the magnetron 15. On the other hand, the primary winding 6a of the step-up transformer 6 is connected in parallel to a conduction timing detection circuit 21 constituted by a voltage dividing circuit composed of resistors 19 and 20, and a terminal
In order to detect the magnitude of the commercial power supply voltage connected between t ₁ and t ₂ , a voltage detecting unit 24 configured by a voltage dividing resistor circuit including resistors 22 and 23 is connected to the DC output side of the rectifier circuit 2. Have been.

Next, a specific configuration of the control circuit 10 for controlling the on / off of the switching transistor 8 will be described with reference to FIG. The detection current Ia from the anode current detection circuit 18 is rectified and smoothed for one cycle by the current averaging circuit 25, and the signal of the average anode current value Iav is compared with the set value Vr by the error amplifier 26. Then, the difference signals S ₁ are supplied to the conduction timing determining circuit 27. The conduction timing determination circuit 27, the switching transistor provided for determining the conduction start time and the conduction time width 8 at a predetermined timing based on a voltage waveform signal S ₂ received from the conducting timing detection circuit 21 and outputs the base signal S _3. The base signal S ₃ is adapted to be supplied to the base of the switching transistor 8 through the AND gate 28. In this case, in order to prevent the conduction time width of the switching transistor 8 from being adjusted beyond the appropriate range, as shown in FIG. 3, the usable range of the commercial power supply voltage (in this embodiment, 80 V
An upper limit value Tmax and a lower limit value Tmin are provided for the conduction time width of the switching transistor 8 corresponding to the above range (120 V or less).

FIG. 3 is a characteristic diagram showing the relationship between the conduction time width of the switching transistor 8 and the commercial power supply voltage. According to FIG. 3, the conduction time width of the switching transistor 8 with respect to the commercial power supply voltage is uniquely determined. The conduction timing determining circuit 27 has a conduction time width of the switching transistor 8 corresponding to the commercial power supply voltage of 80 V and a commercial power supply voltage of 120 V
Are input as the upper limit value Tmax and the lower limit value Tmin, and the conduction timing determination circuit 27 outputs the difference signal S1 from the error amplifier 26.
, The conduction time width of the switching transistor 8 is set within the range of the lower limit value Tmin and the upper limit value Tmax, and the conduction timing of the switching transistor 8 is set based on the voltage waveform signal S ₂ from the conduction timing detection circuit 21.

On the other hand, the detection voltage Va from the voltage detection unit 24 is averaged by rectification and smoothing for one cycle by the voltage averaging circuit 29, and the average voltage value is provided to the voltage range comparator 30. . The voltage range comparator 30 determines from the input average voltage whether or not the commercial power supply voltage belongs to a usable range (in this embodiment, a range of 80 V or more and 120 V or less). adapted to the aND gate 28 to the non-conductive outputs a stop signal S _4.

The signal of the output signal of the current averaging circuit 25 (the average anode current value Iav obtained by averaging the anode current value Ia detected by the anode current detection circuit 18) is supplied to the A / D
The signal is also input to the conversion circuit 31, where it is converted to a digital signal and input to the microcomputer 32. The microcomputer 32 reads a signal of the average anode current value Iav according to a control program (see FIG. 4) described later, and the average anode current value Iav is set to a predetermined upper limit value Iav.
Range between max (see Fig. 5) and lower limit Imin (permissible range)
Entered with either is determined within, when outside the allowable range, because either the circuit component is in malfunction, and outputs a stop signal S ₅ of low level to the AND gate 28 at the detection point This is made non-conductive.

Next, the operation of the above configuration will be described. After the start of cooking, an oscillating current flows through an oscillating circuit including the primary winding 6a of the step-up transformer 6 and the resonance capacitor 7 by the on / off control of the switching transistor 8, and the high-frequency voltage induced in the primary winding 6a generated in this case. V ₁ and high frequency current
The state of the I ₁ shown in Figure 6. Such a high-frequency voltage V ₁ is further boosted by a boost transformer 6 and
It is supplied to 15 to drive this. In this frequency conversion operation, the conduction time width T ₁ of the switching transistor 8 is set.
The gate signals S ₁ to vary in accordance with the magnitude of the difference signals S ₁ is
The non-conduction time width T ₂ is determined by the energy stored in the inductance of the step-up transformer 6 and the size of the resonance capacitor 7 during the conduction time of the switching transistor 8. That non-conduction time of the switching transistor 8 and to a timing To a high-frequency current I ₁ becomes substantially zero, the point
To is also the start of conduction in the next cycle. The conduction timing determination circuit 27 always outputs the high frequency voltage from the timing detection circuit 21.
Receives a voltage waveform signal S ₂ of V _1, the voltage value Vo in the signal S _2, to determine the timing To a high-frequency current I ₁ becomes zero,
To obtain the timing of outputting the gate signal S _3.

On the other hand, during the oscillation operation of the magnetron 15, the anode current value Ia of the magnetron 15 is detected by the anode current detection circuit 18 and the anode current value Ia is averaged by the current averaging circuit 25.
The average anode current value Iav compared with a set value Vr by the error amplifier 26 outputs the difference signals S ₁ in accordance with the difference. This difference signal
S ₁ becomes a larger value as the commercial power supply voltage applied to the terminals t ₁ and t ₂ becomes higher, and the conduction timing determination circuit 27
As the difference signal S ₁ is larger switching transistors 8
The width of the conduction time to be shorter, to control the time width of the base signal S ₃ (see FIG. 3). As a result, the anode current is suppressed from being increased with an increase in the voltage. In other words, the anode current is controlled to decrease and increase in accordance with the level of the commercial power supply voltage, and the high-frequency output is made constant. You.

In parallel with this operation, the voltage range comparator 30 receives the detection voltage Va from the voltage detection unit 24 via the voltage averaging circuit 29, and the commercial power supply voltage falls out of the range of 80 V or more and 120 V or less. when that is cut off the aND gate 28 outputs a stop signal S _4, to stop the on-off operation of the switching transistors 8, it stops the operation of the magnetron 15. In this case, the lower limit of 80 V is an anode current of the magnetron 15 at a voltage lower than this, and the upper limit of 120 V
Is determined from the purpose of setting the upper limit of the withstand voltage of the magnetron 15.

FIG. 5 shows the change over time of the anodic current of the magnetron 15 after the start of cooking.
When the operation of 15 is unstable or when the secondary windings 6b and 6c of the step-up transformer 6 are short-circuited, the anode current does not increase so much even after the filament warm-up time of the magnetron 15 has elapsed. Further, for example, when a short circuit occurs between the anode and the cathode of the magnetron 15, the anode current becomes extremely large. In this way, paying attention to the fact that the anode current extremely increases or decreases when an abnormality occurs in the circuit, in this embodiment, the upper limit value Imax and the lower limit value Imin is set, and the above-described abnormality is detected based on whether or not the anode current falls within this range. This abnormality detection is performed by the microcomputer 32 in accordance with the control program shown in FIG. That is, the frequency converter 1
Is started (Step P1), and when cooking is started, after a lapse of a certain time (for example, 5 seconds) from the start of cooking until the anode current is stabilized, the anode current is detected by the anode current detection circuit 18 (Step P2, P3). At this time, the anode current value Ia detected by the anode current detection circuit 18 is calculated by a current averaging circuit.
The average anode current value Iav is read by the microcomputer 32 via the A / D conversion circuit 31. Then, it is determined whether or not the read average anode current value Iav is larger than the upper limit value Imax (step P4). So when we detect that,
By the microcomputer 32 to the non-conducting this by outputting a stop signal S ₅ of low level to the AND gate 28 stops the operation of the magnetron 15 (step P5).
On the other hand, if the average anode current value Iav is equal to or less than the upper limit value Imax,
The process proceeds to Step P6, and after a predetermined time (for example, 2 seconds), the average anode current value Iav is detected again (Step P7), and it is determined whether the average anode current value Iav is smaller than the lower limit value Imin (Step P8). . Here, if it is determined that the average anode current value Iav is smaller than the lower limit value Imin, the operation of the magnetron 15 becomes unstable or the secondary winding of the step-up transformer 6 is determined.
6b, the abnormality detection of the short circuit of 6c, at that time, and outputs a stop signal S ₅ of low level from the microcomputer 32 stops the operation of the magnetron 15 (step P9).
On the other hand, if it is determined in step P8 that the average anode current value Iav is equal to or more than the lower limit value Imin, the process returns to step P2,
The above operation is repeated. Thereby, during cooking, the average anode current value Iav is periodically checked, and when the average anode current value Iav deviates from the appropriate range (Imin to Imax),
That is, when the abnormality occurs, the operation of the magnetron 15 is stopped.

In this case, the current of the circuit to be subjected to abnormality detection is directly detected by the anode current detection circuit 18, so that the reliability of abnormality detection can be improved as compared with the above-described conventional configuration. In addition, since there is no need to provide an abnormal voltage detection winding on the secondary side of the step-up transformer 6, the step-up transformer 6 does not become large, and the cost can be reduced.

The magnitude of the high-frequency output of the magnetron 15 is determined by the magnitude of the anode current, and the magnitude of the anode current is determined by the magnitude of the conduction time width of the switching transistor 8. Is configured to control the conduction time width of the switching transistor 8 in such a direction that the anode current keeps a constant value in response to the detection signal from Stable high-frequency heating becomes possible. In addition, the anode current detection circuit 18 can be used for both abnormality detection and normal control, and the cost can be reduced in this aspect as well.

By the way, if it is assumed that the conduction time width of the switching transistor 8 is adjusted indefinitely in accordance with the fluctuation of the anode current value, the conduction time width of the switching transistor 8 is properly adjusted so as to keep the anode current at a constant value even when an abnormality occurs. The adjustment may be performed outside the range, and the abnormality detection of the circuit may be delayed.

In this regard, in this embodiment, as shown in FIG. 3, the conduction time width of the switching transistor 8 corresponds to the usable range of the commercial power supply voltage (in this embodiment, the range of 80 V or more and 120 V or less), and the upper limit value Tmax is set. And the lower limit value Tmin, it is possible to prevent the conduction time width from being adjusted beyond an appropriate range when an abnormality occurs, and it is possible to further increase the reliability of abnormality detection.

In this embodiment, the usable range of the commercial power supply voltage is
Although set to 80V or more and 120V or less, various modifications are possible, such as a configuration in which the magnetron 15 can be driven in the range of 80V or more and 260V or less so that it can be used for either 100V or 200V commercial power supply. It is.

[Effect of the Invention] As is clear from the above description, the present invention provides an anode current detection circuit for detecting an anode current of a magnetron, and a current value detected by the anode current detection circuit falls within a predetermined allowable range. Since the abnormality is detected based on whether or not there is, it is possible to enhance the reliability of the abnormality detection as compared with the related art in which the abnormality is detected by the induced voltage. Moreover,
Since there is no need to provide an abnormal voltage detection winding on the secondary side of the step-up transformer, the step-up transformer does not become large,
Cost can be reduced.

In this case, when the magnetron is stationary, the detection signal from the anode current detection circuit is received and the conduction time width of the switching element of the frequency conversion unit is controlled in a direction to maintain the anode current at a constant value. Fluctuations in high-frequency output due to fluctuations in power supply voltage can be prevented, and stable high-frequency heating can be performed. In addition, the anode current detection circuit can be used for both abnormality detection and normal control, and the cost can be reduced from this aspect as well.

Furthermore, since the upper and lower limits are set for the conduction time width of the switching element when the magnetron is steadily moved, it is possible to prevent the conduction time width of the switching element from being adjusted beyond an appropriate range when an abnormality occurs. Thus, the reliability of the abnormality detection can be further increased.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is an electric circuit diagram of a high-frequency cooking device, FIG. 2 is a block diagram showing details of a control circuit, and FIG. 3 is a commercial power supply voltage and a switching transistor. FIG. 4 is a flow chart showing an abnormality detection method, FIG. 5 is a diagram showing a change over time of the anode current, and FIG. 6 is a high-frequency voltage in the primary winding of the step-up transformer. FIG. 5 is a diagram showing a relationship between the high-frequency current and the current. In the drawing, 1 is a frequency converter, 5 is a filter, 6 is a step-up transformer, 7 is a capacitor for resonance, 8 is a switching transistor (switching element), 15 is a magnetron, 18
Is an anode current detection circuit, 24 is a voltage detection unit, 25 is a current averaging circuit, 26 is an error amplifier, 27 is a conduction timing determination circuit,
29 is a voltage averaging circuit, 30 is a voltage range comparator, and 32 is a microcomputer.

Continuation of front page (56) References JP-A-2-119090 (JP, A) JP-A-2-129894 (JP, A) JP-A-55-68532 (JP, A) JP-A-59-194378 (JP) JP-A-61-211987 (JP, A) JP-A-54-116848 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 6/68 330 F24C 7/02 355

Claims (1)

(57) [Claims] 1. A frequency converter for controlling a conduction time width of a switching element to convert a commercial power frequency to a high frequency, a boost transformer for boosting an AC output from the frequency converter, and a secondary side of the boost transformer. A magnetron connected to the magnetron; and an anode current detection circuit for detecting an anode current of the magnetron. When the magnetron is operated in a steady state, a detection signal from the anode current detection circuit is received, and the anode current has a constant value. Controlling the conduction time width of the switching element in a direction to maintain the upper limit value and the lower limit value of the conduction time width, and the current value detected by the anode current detection circuit is out of a predetermined allowable range. A high-frequency heating / cooking apparatus characterized in that the operation of the magnetron is sometimes stopped.