JPH0432191A - High frequency heat-cooking apparatus - Google Patents

Abstract

PURPOSE:To protect a switching element of a frequency converter from an abnormal voltage generated at the time of unstable operation of a magnetron so as to employ the switching element having an allowable voltage lower than conventional by detecting a voltage applied to the switching element, and bringing the operation of the magnetron into a halt in the case where the detected voltage exceeds a preset allowable value. CONSTITUTION:IN order to detect a voltage applied to a switching transistor 8, two resistances 31, 32 are connected in parallel to a resonance capacitor 7, thus constituting a voltage detection unit 33 of the resistances 31, 32. A voltage Vb detected by the voltage detection unit 33, i.e., a detection voltage Vb output from a resonance connecting point between the resistances 31, 32 is compared with a reference voltage Vmax corresponding to an allowable voltage of the switching transistor 8 in an overvoltage detection circuit 34. If the detection voltage Vb exceeds the reference voltage Vmax, the overvoltage detection circuit 34 inputs a stop signal S5 of a low level into an AND gate 28 to thus deenergize the AND gate 28, thereby bringing operation of a magnetron 15 into a halt.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a high-frequency cooking device equipped with a frequency converter that converts a commercial power source into a high-frequency power source.

(Prior Art) This type of high-frequency cooking device converts commercial power into high-frequency power using a frequency converter, and supplies the high-frequency output to a magnetron via a step-up transformer.
The magnetron is operated in oscillation to heat food at high frequency. This device has the advantage that by controlling the conduction time width of the switching element of the frequency conversion section, the high frequency output (heating temperature) of the magnetron can be adjusted according to the content of the cooking.

(Problem to be Solved by the Invention) By the way, at the beginning of the oscillation operation of the magnetron, the anode temperature and anode voltage are changing and are not stable, so the operation of the magnetron tends to become unstable. In this case, when the operation of the magnetron becomes unstable, the anode current repeatedly flows and stops flowing, generating an abnormal voltage in the voltage doubler rectifier circuit on the secondary side of the step-up transformer. This phenomenon occurs constantly when the ability of the magnetron's filament to generate electrons decreases.

A similar abnormal voltage is also generated when a discharge phenomenon occurs in the voltage doubler rectifier circuit. When such an abnormal voltage occurs, its influence spreads to the switching element of the frequency converter provided on the primary side of the step-up transformer, and the abnormal voltage is also applied to this switching element. For this reason,
The switching element must have a large allowable voltage that can withstand the above abnormal voltage, and accordingly,
It has the disadvantage of high cost. Moreover, repeating unstable magnetron operation over and over again damages the filament and shortens the magnetron's lifespan. It also puts excessive stress on circuit components such as switching elements, reducing the lifespan and reliability of the circuit. This will result in damage.

The present invention has been made in consideration of these circumstances, and its purpose is to protect the switching element of the frequency converter from abnormal voltages that occur when the magnetron operates unstablely, and also to protect the switching element of the frequency converter from abnormal voltages that occur when the magnetron operates unstablely. An object of the present invention is to provide a high-frequency heating cooking device that can employ switching elements, reduce costs, and improve the life and reliability of the magnetron and circuit.

[Configuration of the Invention (Means for Solving the Problems) The high-frequency heating cooking device of the present invention includes a frequency conversion section that converts a commercial power supply frequency into a high frequency by controlling the conduction time width of a switching element, and this frequency conversion section. A step-up transformer that steps up the AC output from the step-up transformer and a magnetron connected to the secondary side of the step-up transformer is provided with a voltage detection section that detects the voltage applied to the switching element. The magnetron is configured to stop operating when the voltage detected by the magnetron exceeds a preset tolerance value.

In this case, after stopping the operation of the magnetron, the magnetron may be restarted after a certain period of time has elapsed.

Furthermore, when the number of times the magnetron stops operating reaches a preset number, the magnetron may not be restarted.

(Function) During operation of the magnetron, the voltage applied to the switching element is detected by the voltage detection section, and if the detected voltage of the voltage detection section exceeds a preset allowable value due to unstable operation of the magnetron, etc. Sometimes the magnetron stops working. Thereby, the switching element can be protected from abnormal voltage, and the unstable operating state of the magnetron can be minimized, so that the magnetron and the circuit can be protected.

In this case, if you stop the magnetron and then restart the magnetron after a certain period of time has passed,
In the unlikely event that an abnormal voltage is incorrectly detected due to noise, etc., or the magnetron's operation becomes temporarily unstable, the magnetron will automatically restart and continue operating once it returns to normal. This makes it possible to eliminate the effects of false detection and temporary unstable operation.

Further, when the number of times the magnetron stops operating reaches a preset number, the magnetron is not restarted after that, thereby avoiding a situation where the magnetron repeats restarting and stopping needlessly when an abnormality occurs.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 is a frequency conversion unit that converts the commercial power supply frequency to a high frequency, and includes a rectifier circuit 2 that full-wave rectifies the AC voltage of the commercial power supply connected to terminals i+ and i2, and smoothes the full-wave rectified voltage to obtain a DC voltage. The filter 5 includes a choke coil 3 and a capacitor 4. The oscillation circuit for frequency conversion is composed of a primary winding 6a of a step-up transformer 6, a resonant capacitor 7, a switching transistor 8 and a diode 9 as switching elements, and a control circuit 10 controls the switching transistor 8 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 transmitted to the diode 12 and the smoothing capacitor 13
The magnetron 15 is connected through a voltage doubler rectifier circuit 14 consisting of
A voltage is applied between the anode and the cathode of the secondary winding 6c, and a voltage induced in the secondary winding 6c is applied to the cathode. Furthermore, an anode current detection circuit 18 consisting of a current transformer is provided in the current conduction path on the anode side of the magnetron 15. on the other hand,
A conduction timing detection circuit 21 constituted by a voltage dividing circuit including resistors 19 and 20 is connected in parallel to the primary winding 6a of the step-up transformer 6, and a conduction timing detection circuit 21 is connected in parallel to the primary winding 6a of the step-up transformer 6. In order to detect the magnitude, a power supply voltage detection section 24 constituted by a voltage dividing resistor circuit including resistors 22 and 23 is connected to the DC output side of the rectifier circuit 2.

Next, a specific configuration of the control circuit 10 for controlling the switching transistor 8 on and off will be described with reference to FIG. 2. The detected current Ia from the anode current detection circuit 18 is rectified and smoothed for one cycle by the current averaging circuit 25, and the average anode current value I
The av signal is compared with a set value Vr by an error amplifier 26. The difference signal S1 is then supplied to the conduction timing determining circuit 27. This conduction timing determining circuit 2
7 is for determining the conduction start time and conduction time width of the switching transistor 8, and outputs a base signal S3 at a predetermined timing based on the voltage waveform signal S2 received from the conduction timing detection circuit 21. . This base signal S is supplied to the base of the switching transistor 8 via the AND gate 28.

On the other hand, the detected voltage Va from the power supply voltage detection section 24 is
The voltage is averaged by being rectified and smoothed for one period by the voltage averaging circuit 29, and the average voltage value is provided to the voltage range comparator 30. This voltage range comparator 30 determines whether the commercial power supply voltage belongs to the usable range (in this embodiment, the range of 80 V or more and 120 V or less) from the input average voltage, and if it is outside the range, it will be set to low level. A stop signal S4 is output to the AND gate 28 to make it non-conductive.

In order to detect the voltage applied to the switching transistor 8, two resistors 31 and 32 are connected in parallel with the resonant capacitor 7, as shown in figure 'M1, and a voltage from these resistors 31 and 32 is connected. A voltage detection section 33 is configured. The voltage vb1 detected by the voltage detecting section 33, that is, the detected voltage vb output from the common connection point between both resistors 31 and 32, is applied to the allowable voltage of the switching transistor 8 in the overvoltage detecting circuit 34 (see FIG. 2). (see FIG. 5), and when the detected voltage vb exceeds the reference voltage VlaX, a low level stop signal S is sent from the overvoltage detection circuit 34 to the AND gate 28. By outputting the signal and making it non-conductive, the operation of the magnetron 15 is stopped. In this case, the overvoltage detection circuit 34 outputs the stop signal S for a certain period of time (for example, about 10 seconds), and then outputs the stop signal S.
, the output of the magnetron 15 is stopped and the magnetron 15 is restarted. When the number of times the magnetron 15 stops operating reaches a preset number (for example, five times), the overvoltage detection circuit 34 thereafter outputs the stop signal S until the power switch (not shown) is turned off. The output continues, and the magnetron 15 is not operated again thereafter.

Next, the operation of the above configuration will be explained. After the start of cooking, an oscillating current flows through the oscillating circuit consisting of the primary winding 6a of the step-up transformer 6 and the resonant capacitor 7 by on/off control of the switching transistor 8. FIG. 4 shows the state of V1 and the high frequency current 11. Such a high frequency voltage v1 is further boosted by the step-up transformer 6 and supplied to the magnetron 15 to drive it. In this frequency conversion operation, the conduction time width T1 of the switching transistor 8 is forcibly controlled by a gate signal s1 in accordance with the magnitude of the commercial power supply voltage, which will be described later.
The non-conduction time width T2 is determined by the energy stored in the inductance of the step-up transformer 6 during the conduction time of the switching transistor 8 and the size of the resonance capacitor 7. That is, the non-conduction time of the switching transistor 8 is set until the timing To when the high frequency current 11 becomes approximately zero, and this time To is also the time when the next period of conduction starts. The conduction timing determining circuit 27 constantly receives the voltage waveform signal s2 of the high frequency voltage v1 from the timing detecting circuit 21, and detects the high frequency current according to the voltage value Vo in this signal S2.

Determine the timing To at which the gate signal S,
The timing to output is obtained.

On the other hand, during the oscillation operation of the magnetron 15, the anode current detection circuit 18 detects the anode current value Ia of the magnetron 15, and this anode current value! a is averaged by a current averaging circuit 25, and the average anode current value Iav is averaged by an error amplifier 26.
It compares it with the set value Vr and outputs a difference signal S1 according to the difference. This difference signal S1 increases in value as the commercial power supply voltage applied to the terminals j+ and t2 increases, and the conduction timing determining circuit 27 sets the conduction time width of the switching transistor 8 to become shorter as the difference signal S1 increases. , controls the time width of the base signal S4 (see FIG. 3). This prevents the anode current from increasing as the voltage increases.In other words, the anode current is controlled to decrease and increase as the commercial power supply voltage increases, and the high-frequency output is kept constant. Ru.

Further, in parallel with this operation, the voltage range comparator 30 converts the detected voltage Va from the power supply voltage detection section 24 into the voltage averaging circuit 2.
9, and the commercial power supply voltage is 80V or higher 12
When it is out of the range of 0 V or less, a stop signal S4 is output to cut off the AND gate 28, stop the on/off operation of the switching transistor 8, and stop the operation of the magnetron 15. In this case, the lower limit value of 8 ov is determined because if the voltage is lower than this, the anode current of the magnetron 15 will become excessive, and the upper limit value of 120 V is determined to be the upper limit of the withstand voltage of the magnetron 15.

By the way, at the beginning of the oscillation operation of the magnetron 15, the anode temperature and anode voltage are changing and are not stable.
The operation of the magnetron 15 tends to become unstable. In this case, when the operation of the magnetron 15 becomes unstable, the anode current repeatedly flows and stops flowing, and an abnormal voltage is generated in the voltage doubler rectifier circuit 14 on the secondary side of the step-up transformer 6. This phenomenon constantly occurs when the ability of the filament of the magnetron 15 to generate electrons decreases. Further, when a discharge phenomenon occurs in the voltage doubler rectifier circuit 14, a similar abnormal voltage is generated. When such an abnormal voltage occurs, its influence spreads to the switching transistor 8 of the frequency converter 1 provided on the primary side of the step-up transformer 6, and the abnormal voltage is also applied to this switching transistor 8 ( (See Figure 5).

Therefore, in this embodiment, during the operation of the magnetron 15, the voltage applied to the switching transistor 8 is detected by the voltage detecting section 33, and the detected voltage vb is detected by the overvoltage detecting circuit 34. When the detected voltage vb exceeds the reference voltage Vwax (in other words, when an abnormal voltage occurs), the overvoltage detection circuit 34 outputs a low-level stop signal. By outputting S to the AND gate 28 and making it non-conductive, the operation of the magnetron 15 is stopped. As a result, the switching transistor 8 can be protected from abnormal voltage, and the unstable operating state of the magnetron 15 can be minimized, and the magnetron 15 and the circuit can be protected, and their lifespan and reliability can be increased. You can improve your sexuality. However, since almost no abnormal voltage is applied to the switching transistor 8, it is possible to use a switching transistor 8 with a lower allowable voltage than the conventional switching transistor 8, and it is also possible to reduce costs.

In this case, the overvoltage detection circuit 34 outputs the stop signal S.

After outputting the stop signal S for a certain period of time (for example, about 10 seconds), the output of the stop signal S is stopped, the AND gate 28 is made conductive, and the magnetron 15 is restarted. As a result, even if an abnormal voltage is incorrectly detected due to noise, etc., or the operation of the magnetron 15 becomes temporarily unstable, the magnetron 15 can be automatically restarted and returned to a normal state. This allows the operation to continue, eliminates the effects of false detection and temporary unstable operation, and further improves the reliability of the operation.

Then, when the number of times the magnetron 15 stops operating reaches a preset number (for example, five times), from then on,
The overvoltage detection circuit 34 continues to output the stop signal S until a power switch (not shown) is turned off. As a result, the AND gate 28 is maintained in a non-conductive state, and the magnetron 15 is not operated again thereafter, but is completely stopped. Therefore, it is possible to avoid a situation in which the magnetron 15 repeatedly restarts and stops uselessly when an abnormality occurs.

In this example, the usable range of commercial power supply voltage is 8.
Although it is set to 0V or more and 120V or less, it can be set to 8V so that it can be used with either 100V or 200V commercial power supply.
The magnetron 15 may be configured to be able to be driven within a range of 0V to 260V.

In addition, the present invention provides the magnetron 15 when an abnormal voltage occurs.
Various modifications are possible, such as changing the operation stop time and the number of operation stops as appropriate.

[Effects of the Invention] As is clear from the above description, the present invention includes a voltage detection unit that detects the voltage applied to the switching element of the frequency conversion unit, and the voltage detected by the voltage detection unit is set in advance. Since the magnetron is configured to stop operating when the specified tolerance value is exceeded, it is possible to protect the switching element from abnormal voltage, and it is also possible to use a switching element with a lower allowable voltage than before, which reduces the The cost can be reduced, and the unstable operating state of the magnetron can be minimized, the magnetron and circuits can be protected, and their lifespan and reliability can be improved.

In this case, if you stop the magnetron and then restart the magnetron after a certain period of time has passed,
In the unlikely event that an abnormal voltage is incorrectly detected due to noise, etc., or the magnetron's operation becomes temporarily unstable, the magnetron will automatically restart and continue operating once it returns to normal. This makes it possible to eliminate the effects of false detection and temporary unstable operation, further improving operational reliability.

Further, when the number of times the magnetron stops operating reaches a preset number, the magnetron is not restarted after that, thereby avoiding a situation where the magnetron repeats restarting and stopping needlessly when an abnormality occurs.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention. Fig. 1 is an electric circuit diagram of the high-frequency heating cooking device, Fig. 2 is a block diagram showing details of the control circuit, and Fig. 3 is a diagram showing the commercial power supply voltage and switching transistors. Figure 4 is a diagram showing the relationship between the high-frequency voltage and high-frequency current in the primary winding of the step-up transformer, and Figure 5 is the change over time in the voltage applied to the switching transistor. FIG. In the drawing, 1 is a frequency conversion section, 6 is a step-up transformer, 7 is a resonant capacitor, 8 is a switching transistor (switching element), 15 is a magnetron, 18 is an anode current detection circuit, 24 is a power supply voltage detection section, and 25 is a current An averaging circuit, 26 an error amplifier, 27 a conduction timing determining circuit, 29 a voltage averaging circuit, 30 a voltage range comparator, 33
34 is a voltage detection section, and 34 is an overvoltage detection circuit. Continuity @ width (11s) Figure V. Figure Figure

Claims (1)

[Claims] 1. A frequency converter that converts a commercial power supply frequency into a high frequency by controlling the conduction time width of a switching element, a step-up transformer that steps up the AC output from this frequency converter, and a step-up transformer that controls the conduction time width of a switching element. In a high-frequency heating cooking device equipped with a magnetron connected to a secondary side, a voltage detection unit is provided to detect the voltage applied to the switching element, and the voltage detected by the voltage detection unit is set to a preset tolerance value. 1. A high-frequency heating and cooking apparatus, characterized in that the magnetron is configured to stop operating when the temperature exceeds the above-mentioned temperature. 2. The high-frequency heating cooking device according to claim 1, wherein the magnetron is restarted after a predetermined period of time has elapsed after the magnetron has stopped operating. 3. The high-frequency heating cooking apparatus according to claim 2, wherein the magnetron is not restarted after the number of times the magnetron has stopped operating has reached a preset number of times.