JP2001076861A - Cooking device - Google Patents

Abstract

(57) [Problem] To provide a high-frequency power supply with low loss and low cost. An IG having a primary coil (26a) between terminals of an AC power supply (22) and an energizing direction opposite to that of the primary coil (26a).
BT27 and 28 are connected in series, and IGBT27,
28, diodes 29 and 30 are connected in anti-parallel. The voltage detection circuit 35 is configured to apply the collector voltages of the IGBTs 27 and 28 to the common resistance voltage dividing circuit via diodes, respectively.
Extracts a resonance frequency component from the detection voltage Vb of the voltage detection circuit 35. The timing setting circuit 43 compares the output voltage Vh of the high-pass filter 40 with the reference voltage Va to
The ON timing of T27 and T28 is set, and the output control circuit 46 further sets the OFF timing. IGBT27
And 28 are driven by a common gate voltage Vg by a drive circuit 47.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating cooker for heating an object to be heated by applying a resonance current to a high-frequency transformer or an induction heating coil for driving microwave generating means.

[0002]

2. Description of the Related Art A heating cooker using microwave heating, such as a microwave oven, and a cooker using induction heating such as an electromagnetic cooker, an electric kettle, and a hot plate are excellent in convenience, safety, heat efficiency, and the like. And is widely spread. FIG.
Indicates an electrical configuration of a high-frequency power supply conventionally used in a microwave oven (a configuration called a so-called “quasi-E class”). Hereinafter, this will be briefly described.

In FIG. 13, a high-frequency power supply 1 includes a DC power supply circuit 5 having a diode bridge 2 composed of diodes 2a to 2d, a reactor 3, and a capacitor 4 as constituent elements. Then, by connecting an AC power supply 6 (for example, a commercial AC power supply) to the input terminal of the diode bridge 2, the AC voltage is rectified and smoothed, and a DC voltage is generated between both terminals of the capacitor 4.

A resonance circuit 9 in which a primary coil 7a of a high-frequency transformer 7 and a resonance capacitor 8 are connected in parallel between terminals of a capacitor 4, and an IG as a switching element
The collector and the emitter of the BT 10 are connected in series. Between the collector and emitter of the IGBT 10
A shunt circuit 14 in which a diode 11 is connected in anti-parallel and a capacitor 12 and a resistor 13 are connected in series.
Is connected. The control circuit 15 controls the shunt circuit 14
The timing at which the IGBT 10 is turned on is determined based on the resonance current detected by the method. The secondary coil 7b of the high-frequency transformer 7 has a rectifier circuit 16
Is connected to the magnetron 17 via the.

In the high-frequency power supply 1 having the above configuration, when the control circuit 15 switches the IGBT 10, a resonance current flows through the resonance circuit 9, and a high-frequency high voltage is generated in the secondary coil 7b by the resonance current. This high-frequency voltage is rectified by the rectifier circuit 16 and applied between the electrodes of the magnetron 17, thereby generating a microwave from the magnetron 17.

The means for obtaining the on-timing of the IGBT 10 includes, in addition to the configuration using the shunt circuit 14 described above,
Various configurations have been proposed, such as a configuration in which the collector-emitter voltage of the IGBT 10 is compared with the voltage across the capacitor 4.

[0007]

In the high-frequency power supply 1, when the voltage of the AC power supply 6 is in a positive half cycle, the current flowing from the AC power supply 6 passes through the diode 2a, the reactor 3, the capacitor 4, and the diode 2d. The capacitor 4 is charged by flowing through the capacitor 4. When the voltage of the AC power supply 6 is in the negative half cycle, the current flowing from the AC power supply 6 is the diode 2b, the reactor 3, the capacitor 4,
By flowing through the diode 2c, the capacitor 4
Charge. Therefore, in the DC power supply circuit 5, the charging current to the capacitor 4 always passes through two diodes, and if the forward voltage of the diode is VF,
A loss corresponding to approximately (2 × VF × charging current) occurs in the diode bridge 2.

The above-mentioned high-frequency cooking device widely used in general households has a maximum output of, for example, 1.3 kW in the case of a 100 V input, and is approximately (2 × 0.8 V) by applying the above-described formula. × 13A) = 20.8 W of loss has occurred. This loss is caused by the DC power supply circuit 5,
The loss (for example, 50 W) in the entire power unit including the high-frequency transformer 7, the IGBT 10, the diode 11, the rectifier circuit 16 and the like has reached 40%. For this reason, in addition to the IGBT 10 and the like, a large heat sink or a large cooling fan is required to cool the diode bridge 2 (diodes 2a to 2d), which is an obstacle to downsizing and price reduction of the cooking device. .

In order to reduce the loss of the high-frequency power supply 1, it is generally necessary to control the on-timing so that the switching element is turned on when the applied voltage is low. Even in this case, if the control circuit has a complicated configuration or uses expensive circuit components, it is not possible to reduce the price. Therefore, it is necessary to adopt a control circuit that takes into account the component level.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heating cooker provided with a high-frequency power supply which can achieve low loss and further lower the price.

[0011]

According to a first aspect of the present invention, there is provided a heating cooker, comprising: a resonance circuit comprising a high-frequency transformer for driving a microwave generation means and a resonance capacitor; First and second switching elements connected between the terminals of an AC power supply via the resonance circuit and connected in series in a state where the current supply directions are opposite to each other; and the first and second switching elements A first and a second rectifying element connected in anti-parallel to the first and second switching elements, respectively, and a voltage applied to the first or second switching element during a period in which the first and second switching elements are in an off state In order to detect a resonance voltage of the resonance circuit, a resonance voltage detecting means commonly provided for the first and second switching elements, and a detection of the resonance voltage detecting means. Filter means for extracting a resonance frequency component from a signal; timing setting means for setting on timings of the first and second switching elements based on an output signal of the filter means; and on timing set by the timing setting means Switching control means for controlling the first and second switching elements to be turned on in response to the control signal and turning off the first and second switching elements after a predetermined ON period has elapsed. And

According to this configuration, a current path through the first switching element and the second rectifier element and a current path opposite to the current path, and the second switching element and the first rectifier are provided. And a current path through the element is formed,
A current that is turned on and off is supplied from the AC power supply to the resonance circuit via any one of the current paths according to the voltage polarity of the AC power supply. That is, without converting the AC voltage to the DC voltage, in almost the entire cycle of the AC power supply voltage,
Current energy can be supplied from the AC power supply to the resonance circuit.

As a result, a rectifying circuit for rectifying the AC power supply voltage becomes unnecessary. For example, in a conventional configuration using a rectifier bridge circuit as a rectifier circuit, a current flowing from an AC power supply to a resonance circuit passes through two rectifier elements in the rectifier bridge circuit. Only passes through one of the rectifying elements. In other words, the number of rectifiers through which the current passes decreases,
The loss of the cooking device is reduced by the loss occurring in the rectifying element.

The timing setting means sets the on-timing of the first and second switching elements based on a resonance frequency component which is an AC component of the resonance voltage extracted by the filter means. Even if the low-frequency component of the resonance voltage fluctuates due to changes in the switching frequency, the effect of the fluctuation of the low-frequency component is eliminated, and the switching element is turned on at an appropriate timing to reduce the switching loss. can do. In addition, since the phase change of the resonance frequency component in the filter means is small, it is possible to set the ON timing more accurately.

Further, since the resonance voltage detecting means is provided commonly to the first and second switching elements instead of being provided separately, the structure can be simplified and the cost can be reduced. In addition, as described in claim 2, the above configuration can be similarly applied to a cooking device provided with a resonance circuit including an induction heating coil and a resonance capacitor.

Further, in a configuration provided with a resonance circuit including a high-frequency transformer for driving the microwave generation means and a resonance capacitor, the current flowing through the microwave generation means is defined by the third aspect. It is preferable to include an output current detecting means for detecting, and a phase variable means for changing a phase characteristic of the filter means based on a detection signal of the output current detecting means.

According to this configuration, the phase varying means changes the phase characteristic of the filter means based on the current flowing through the microwave generating means according to the state of the microwave generating means. Even when the resonance state of the resonance circuit changes, the ON timing of the switching element can be appropriately controlled.

For example, when the microwave generation operation of the microwave generation means is stopped at the time when the voltage amplitude of the AC power supply becomes small (in the case of a sine wave voltage, near zero crossing), the current flowing through the microwave generation means is smaller than during operation. And the resonance voltage waveform changes. By employing the above configuration, an appropriate on-timing can always be set according to the state (operating state / stop state or load state) of the microwave generating means, and the switching loss can be further reduced.

According to a fourth aspect of the present invention, there is provided an input current detecting means for detecting an input current from an AC power supply, and a phase variable for changing a phase characteristic of a filter means based on a detection signal of the input current detecting means. Means may be provided.

According to this configuration, by detecting the input current, it is possible to grasp that the resonance state of the resonance circuit has changed due to a change in the amplitude of the AC power supply or a change in the state of the microwave generation means accompanying the change, and the like. However, since the ON timing is appropriately controlled by changing the phase characteristic of the filter means according to the change, the switching loss can be further reduced.

In this case, it is desirable that the phase variable means changes the phase characteristic of the filter means while the first or second switching element is in the ON state. According to this configuration, the phase characteristic of the filter does not change during the period when the switching element is turned off and the resonance voltage is applied, that is, during the period when the resonance voltage detection signal is given to the filter. This eliminates the occurrence of a transient state in the means and prevents malfunction of the timing setting means.

Further, when driving the microwave generating means, the timing setting means sets the on-timing by comparing the output signal of the filter means with the reference signal. And
It is preferable to include an output current detecting means for detecting a current flowing through the microwave generating means, and a reference signal varying means for changing a level of the reference signal in a plurality of steps based on a detection signal of the output current detecting means.

According to this configuration, the reference signal varying means includes:
Since the level of the reference signal is changed based on the current flowing through the microwave generating means according to the state of the microwave generating means, the on-timing of the switching element is performed even when the resonance state of the resonance circuit changes due to the state of the microwave generating means. Can be appropriately controlled.

According to a seventh aspect of the present invention, there is provided an input current detecting means for detecting an input current from an AC power supply,
Reference signal varying means for changing the level of the reference signal in a plurality of steps based on the detection signal of the input current detecting means may be provided. According to this configuration also, when the resonance state of the resonance circuit changes due to the amplitude of the AC power supply and the state of the microwave generation unit associated therewith, the reference signal variable unit changes the level of the reference signal to appropriately control the on-timing. Therefore, the switching loss can be further reduced.

Further, the reference signal varying means may be configured to continuously change the level of the reference signal based on the detection signal of the output current detecting means (claim 8).
It is preferable that the level of the reference signal be continuously changed based on the detection signal of the input current detection means.

According to such a configuration, since the level of the reference signal does not suddenly change due to the change in the resonance state, it is possible to prevent a malfunction of the timing setting means, for example, a situation in which the ON timing is temporarily shifted. Further, timing control with higher accuracy can be performed as compared with a case where the level of the reference signal is changed in a plurality of stages.

In each of the above cases, as described in claim 10, the switching control means controls the on-period of the first and second switching elements according to the magnitude of the resonance voltage detected by the resonance voltage detection means. It is preferable to adopt a configuration in which control is performed to change. According to this configuration, for example, when the voltage amplitude of the AC power supply is small and the resonance voltage is low, the switching control unit can control the ON period to be long, so that the input power factor is improved. .

Further, as set forth in claim 11, a common connection point of the first and second switching elements is used as a ground terminal, and a resonance voltage detecting means is connected to a resistance voltage dividing circuit connected to the ground terminal. The first and second switching elements are connected in series in opposite directions so that the resonance voltage applied to the first or second switching element is applied to the resistance voltage dividing circuit, and the common connection point is connected to the resistance voltage dividing circuit. The first and second detection rectifiers may be connected to each other.

According to this configuration, the resonance voltage applied to the first or second switching element is applied to the common resistive voltage dividing circuit via the first or second detection rectifying element. Since the resonance voltage detecting means is constituted by low-cost circuit components such as a resistor and a rectifier, the cost can be reduced.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment in which the present invention is applied to a microwave oven will be described with reference to FIGS. FIG. 1 shows an electrical configuration of a high-frequency power supply 21 provided in a microwave oven. In FIG. 1, for example, commercial 100 V, 50 Hz (or 60 Hz)
One terminal of the AC power supply 22 is connected to a power supply bus 24a via a reactor 23, and the other terminal of the AC power supply 22 is connected to a power supply bus 24b.

A capacitor 25 is connected between the power supply buses 24a and 24b, and a primary coil 26a of a high frequency transformer 26 and an N-channel IGBT 27
And 28 (corresponding to the first and second switching elements in the present invention) are connected in series. in this case,
The collectors of the IGBTs 27 and 28 are connected to the primary coil 26a and the power supply bus 24b, respectively.
The emitters 28 are both connected to the ground terminal Ec. Diodes 29 and 30 (corresponding to the first and second rectifiers of the present invention) are connected in parallel between the collectors and the emitters of the IGBTs 27 and 28, respectively, with the collector side as the cathode.

A resonance capacitor 31 is connected in parallel with the primary coil 26a of the high-frequency transformer 26, thereby forming a resonance circuit 32. The secondary coil 26b of the high-frequency transformer 26 includes, for example, a rectifier circuit 3 that performs voltage doubler rectification.
3 through the magnetron 3 as a microwave generating means
4 are connected to the anode and cathode.

Voltage detection circuit 3 as resonance voltage detection means
Reference numeral 5 denotes a circuit configured to divide and detect a resonance voltage applied to the collectors of the IGBTs 27 and 28 with reference to the ground terminal Ec, and is provided in common with the IGBTs 27 and 28. have.

The voltage detection circuit 35 is specifically shown in FIG.
As shown in FIG.
6, 37 (corresponding to the first and second detection rectifiers in the present invention) and resistors 38, 39 (resistive voltage dividing circuit in the present invention) connected in series between the cathode and the ground terminal Ec. ). Diode 36, 3
The anode of 7 is connected to the collectors of IGBTs 27 and 28, respectively. The detection voltage Vb is equal to the resistance 38
And 39 are output from a common connection point.

High-pass filter 4 as filter means
Reference numeral 0 denotes a signal for cutting a low frequency component such as a commercial frequency (50 Hz or 60 Hz) from the detection voltage Vb of the voltage detection circuit 35 and extracting a resonance frequency component which is a high frequency component of, for example, about 30 kHz. As shown in FIG. 2, the high-pass filter 40 includes a capacitor 4 connected between the output terminal of the voltage detection circuit 35 and the ground terminal Ec.
1 and a resistor 42.

The timing setting circuit 43 as timing setting means is a circuit for setting the ON timing of the IGBTs 27 and 28 based on the output voltage Vh of the high-pass filter 40. The timing setting circuit 43 includes, as shown in FIG.
4, an output terminal thereof and a power supply terminal Vcc for control (for example, 5
V) and a pull-up resistor 45 connected between the pull-up resistor V. Here, the inverting input terminal of the comparator 44 is connected to the ground terminal Ec to apply the reference voltage Va.
(0 V), and the output voltage Vh from the high-pass filter 40 is supplied to the non-inverting input terminal.

Although not specifically shown, the output control circuit 46 serving as a switching control means falls from the high level (5 V) of the output signal St of the timing setting circuit 43 to the low level (0 V) (at the ON timing). (Equivalent) is used as a trigger to generate an oscillation signal of a predetermined switching frequency (for example, 30 kHz) by the oscillation circuit. The IGB depends on the frequency (cycle) of the oscillation signal at this time.
The off timing (that is, the on period) of T27 and T28 is set.

This oscillation signal is controlled by a microcomputer (not shown). That is, the microcomputer inputs an operation signal from a setting key for heating and cooking conditions provided on a front panel (not shown) of the microwave oven, and operates the magnetron 34 in response to a user operating the setting key. Judge the size of the output,
The frequency of the oscillation signal is controlled accordingly. Further, although not shown, the output control circuit 46 receives the detection voltage Vb from the voltage detection circuit 35, detects the magnitude (peak value), and controls the ON period to be long when the peak value is low. Configuration.

The drive circuit 47 receives the output signal Sc from the output control circuit 46 in which the ON timing and the OFF timing are set, and according to the output signal Sc, the IGBT 2
A common gate voltage Vg is output to the gates 7 and 28.

Next, the operation of the present embodiment will be described with reference to FIGS. FIG. 3 shows which side of the IGBT that performs a switching operation for causing a high-frequency current to flow through the resonance circuit 32 is substantially the same as the polarity of the voltage polarity of the AC power supply 22. The voltage polarity in this case refers to the power supply bus 24a with respect to the power supply bus 24b.
Means the voltage polarity of

As described above, IGBTs 27 and 28
Are supplied with a common gate signal and both are turned on and off at the same time. However, when the power supply voltage polarity is positive, the AC power supply 22 supplies the power supply bus 24a, the primary coil 26a, the IGB
A current flows through a path via T27, diode 30, and power supply bus 24b. At this time, since the collector-emitter of the IGBT 28 is reversely biased and biased by the diode 30, no current is supplied even when the IGBT 28 is in the ON state as an element. In other words, substantially IGB
The switching operation is performed by T27.

Conversely, when the polarity of the power supply voltage is negative, a current flows from the AC power supply 22 through a path through the power supply bus 24b, the IGBT 28, the diode 29, the primary coil 26a, and the power supply bus 24a, and the switching operation is substantially performed by the IGBT 28. Is performed. By performing such a switching operation, a quasi-class E inverter having a conventional configuration (see FIG. 13)
Unlike this, a circuit (such as a diode bridge) for full-wave rectification of the AC voltage of the AC power supply 22 is not required. And
Even with such a configuration, the operating principle of each of the positive and negative half-waves of the AC power supply 22 is basically the same as that of the conventional quasi-E inverter.

FIG. 4 shows a case where the magnetron 34 is oscillating (left) and a case where oscillation is stopped (right).
3 shows the waveforms of the respective parts in FIG. In each case, the AC voltage of the AC power supply 22 is positive, and the IGBT 2
7 shows a waveform when a switching operation is being performed. The oscillation of the magnetron 34 stops when the amplitude of the AC voltage of the AC power supply 22 decreases, that is, when it is near zero crossing. Here, for convenience, the voltage between the power supply buses 24a and 24b regardless of the presence or absence of oscillation. Are shown as positive voltage of the same magnitude.

The waveforms (a) to (g) shown in FIG. 4 respectively represent the following voltages, currents, and signals. Note that all the voltages and signals are based on the ground terminal Ec, and 0V of the signal corresponds to a low level and 5V corresponds to a high level.

4 (a): Current Ia flowing through primary coil 26a of high frequency transformer 26 FIG. 4 (b): Collector voltage Vc of IGBT 27 FIG. 4 (c): Detection voltage Vb of voltage detection circuit 35 FIG. : Output voltage Vh of high-pass filter 40 FIG. 4 (e): Output signal St of timing setting circuit 43 FIG. 4 (f): Output signal Sc of output control circuit 46 FIG. 4 (g): Gate voltage Vg of IGBTs 27 and 28

(Operation During Oscillation) Hereinafter, the magnetron 34
The operation when is oscillating will be described. Drive circuit 4
7 is a gate voltage V for turning on the IGBTs 27 and 28.
g, the current Ia of the primary coil 26a increases substantially linearly during the period when the IGBT 27 is in the energized state (before time t2 and after time t6 in FIG. 4). During this energization period, the collector voltage Vc of the IGBT 27 and the detection voltage Vb of the voltage detection circuit 35 are almost 0 V, and the output voltage Vh of the high-pass filter 40 has a substantially negative negative value. Therefore, the output signal St of the timing setting circuit 43 keeps a low level.

As described above, the length of the ON period is set by the microcomputer controlling the oscillation circuit in the output control circuit 46 in accordance with the key operation of the user or in accordance with the magnitude of the resonance voltage. Is done. At time t1, the output control circuit 46 ends the ON period and outputs the output signal S
When c is changed from the high level to the low level (corresponding to the off timing), the drive circuit 47 drives so that the gate voltage Vg becomes 0V. At this time, the gate voltage Vg gradually decreases due to the influence of the gate capacitance of the IGBTs 27 and 28,
When the voltage drops below the threshold voltage Vth at time t2, the IGBT 27 shifts from the on state to the off state.

When the IGBT 27 is turned off, the resonance circuit 32
, A resonance phenomenon occurs. That is, the primary coil 2
The current Ia flowing through 6a flows into the resonance capacitor 31 as a resonance current, and charges the resonance capacitor 31. By this charging, the collector voltage Vc of the IGBT 27 becomes 0 V
Rise from. At the same time, the current Ia decreases, and the collector voltage Vc reaches the maximum (for example, about 700 V) at a point in time when the current Ia changes from positive to negative (time t4).

Thereafter, the current Ia increases in the negative direction, and then begins to increase again in the positive direction after passing through the maximum value on the negative side.
When the current Ia reaches the maximum value on the negative side, the voltage between the terminals of the resonance capacitor 31 becomes almost 0 V, and the collector voltage V
c becomes substantially equal to the voltage between the power supply buses 24a and 24b. The collector voltage Vc continues to decrease while the current Ia is negative, and when the current Ia changes from negative to positive (time t
6) is minimum. In the case of the present embodiment, although the collector voltage Vc does not drop to 0 V, the IGBT 27 is turned on (energized state) at the time when the collector voltage Vc becomes minimum, so that the IGBT 27 starts energizing when the IGBT 27 starts energizing.
Short-circuit current flowing through the BT 27 and the diode 30 can be suppressed, and switching loss generated in the IGBT 27 and the diode 30 can be reduced.

The ON timing of the IGBT 27 is set as follows. That is, the voltage detection circuit 35
Outputs a detection voltage Vb by reducing the collector voltage Vc by resistance division. The high-pass filter 40 passes high-frequency components around the resonance frequency included in the detection voltage Vb and cuts low-frequency components around the frequency of the AC power supply, so that the output voltage Vh is substantially in phase with the detection voltage Vb. In addition, the waveform is shifted to the negative side.

The timing setting circuit 43 uses the comparator 44 to compare the output voltage Vh with the reference voltage Va of 0V. In FIG. 4, at time t5, the output voltage Vh changes from positive to negative, and the output signal St of the timing setting circuit 43 changes from high level to low level (ON timing).

The output control circuit 46 receives the ON timing from the timing setting circuit 43 and immediately outputs the output signal S
t is changed from a low level to a high level. At this time,
The drive circuit 47 drives so that the gate voltage Vg becomes a predetermined drive voltage. However, the gate voltage Vg gradually rises due to the influence of the gate capacitance of the IGBTs 27 and 28, and the gate voltage Vg eventually becomes the threshold voltage Vth at time t6. Then, the IGBT 27 is turned on. Even in an actual circuit, timing design is performed in consideration of a delay time (ΔT) from the on-timing to the IGBT 27 being turned on.

(Operation when Oscillation Stops) Next, the operation when the magnetron 34 stops oscillating will be described. In this case, since the high-frequency power supply 21 is in a lighter load state than during oscillation, the resonance state that occurs when the IGBT 27 is turned off is different from that during oscillation. The setting of the off-timing around times t11 to t13 in FIG. 4 is the same as that at the time of oscillation.

When the IGBT 27 is off and a resonance phenomenon occurs in the resonance circuit 32, the current Ia as a resonance current changes from positive to negative at time t14,
After passing through the negative maximum value, at time t17, the state changes from negative to positive again. At this time, the collector voltage Vc of the IGBT 27, which is the resonance voltage, is at a minimum, but has dropped to a negative voltage unlike at the time of transmission. The collector voltage Vc of this IGBT 27
Is negative, the diode 29 is in a conductive state, and its resonance voltage is applied between the collector and the emitter of the IGBT 28.

At this time, the timing setting circuit 43 sets the timing at which the output voltage Vh of the high-pass filter 40 matches the reference voltage Va (time t15) as described above, so that the IGBT 27 starts to operate at approximately ΔT
It is turned on at time t17 delayed by only a time. That is, when the magnetron 34 stops oscillating, I
The time (time t16) slightly deviates from the optimum time (time t16) when both collector voltages Vc of GBTs 27 and 28 become 0V.
It turns on at 17).

Even when the AC voltage of the AC power supply 22 is negative, a high-frequency current flows through the primary coil 26a of the high-frequency transformer 26 in the same manner by the switching operation of the IGBT 28. As a result, the magnetron 34 is driven in almost all cycles except the vicinity of the zero crossing of the AC voltage, and the object to be cooked in the heating chamber (not shown) is irradiated with microwaves to perform heating and cooking.

As described above, the high-frequency power supply 21 of the microwave oven shown in the present embodiment does not include a rectifier circuit for rectifying the AC power supply 22, and the high-frequency transformer 26 is connected between both terminals of the AC power supply 22. The primary coil 26 and IGBTs 27 and 28 in opposite directions are connected in series, and the IGBTs 27 and 28 are connected to diodes 29 and 3 respectively.
0 were connected in anti-parallel.

With this configuration, regardless of the voltage polarity of the AC power supply 22, a current path through which a high-frequency current capable of switching control is passed from the AC power supply 22 to the primary coil 26 is formed. Can operate on the same principle as the conventional quasi-class E inverter in each of the positive and negative half-wave periods. Also,
By connecting the emitters of the IGBTs 27 and 28 in common, it becomes possible to apply a common gate voltage Vg for driving, and the configuration and control can be simplified.

When this high-frequency power supply 21 is compared with the conventional high-frequency power supply 1 shown in FIG. 13, in the high-frequency power supply 1, a current flowing from the AC power supply to the resonance circuit passes through two diodes in the diode bridge 2. High frequency power supply 21
In this case, only one of the diodes 29 or 30 passes.

When the loss reduction effect in this case is estimated using a microwave oven (100 V input, maximum output 1.3 kW) widely used in general households and the like, the forward voltage V
Assuming that F is 0.8 V, the maximum is approximately (2 × 0.8 V × 13
A) The loss of 20.8 W can be reduced. This makes it possible to reduce the size of a radiator plate and a fan for cooling the elements such as the IGBTs 27 and 28 and the diodes 29 and 30, and to reduce the size and cost of the microwave oven itself.

Further, in this embodiment, the resonance voltage applied to the collectors of the IGBTs 27 and 28 is detected by the voltage detection circuit 35, and the low-frequency component is cut off from the detection voltage Vb by using the high-pass filter 40, and the high-pass The ON timing is set based on the voltage Vh including the resonance frequency component passed through the filter 40.

Therefore, even when the low-frequency component included in the resonance voltage changes due to a change in the voltage amplitude or switching frequency of the AC power supply 22, the on-timing does not largely shift, and the IGBTs 27 and 28 are not changed. When the collector voltage Vc becomes low, it can be surely turned on. This allows I
Short-circuit current flowing through the GBTs 27 and 28 and the diodes 29 and 30 is reduced, and switching loss can be reduced. Further, the voltage detection circuit 35 and the high-pass filter 4
At 0, since the phase change for the resonance frequency component is small, it is possible to set the ON timing more accurately.

Further, in the present embodiment, the voltage detection circuit 35
Are not provided separately for the IGBTs 27 and 28 but are provided in common, so that the configuration is simplified. Further, since expensive parts such as high-voltage capacitors are not used, the cost can be reduced.

The output control circuit 46 detects, based on the magnitude of the resonance voltage, a state in which the AC power supply voltage is near the zero crossing and the energy supply to the magnetron 34 is reduced. Since the control is performed so as to be longer, the input power factor can be increased.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In FIGS. 5 and 6, the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, different components will be described.

In FIG. 5, which shows the electrical configuration of the high-frequency power supply 48 provided in the microwave oven, an anode current (hereinafter, referred to as “current”) flowing through the magnetron 34 is provided between the positive output terminal of the rectifier circuit 33 and the anode of the magnetron 34. A current detector 49 for detecting the anode current) is provided. The peak hold circuit 50 holds the peak value of the anode current having the detected full-wave rectified waveform and outputs the detection signal Sa.
The current detector 49 and the peak hold circuit 50 constitute an anode current detection circuit 51 (corresponding to output current detection means in the present invention).

Phase variable circuit 52 as phase variable means
Changes the phase characteristic of the high-pass filter 40 based on the detection signal Sa from the anode current detection circuit 51, and has a specific circuit configuration shown in FIG. That is, the non-inverting input terminal of the open collector type comparator 53 is connected to the output terminal of the anode current detecting circuit 51, and the inverting input terminal is connected to the resistors 54 and 55 connected between the power supply terminal Vcc and the ground terminal Ec. Connected to a voltage dividing point of a voltage dividing circuit. The output terminal of the comparator 53 is connected to the output terminal of the high-pass filter 40 via the resistor 56.

When the magnetron 34 is oscillating, an anode current corresponding to its output flows, and the anode current detection circuit 51
Outputs a detection signal Sa having a level corresponding to the magnitude (peak value) of the anode current. On the other hand, when the oscillation of the magnetron 34 is stopped, the anode current hardly flows, and the detection signal Sa becomes an extremely small level. Therefore, the voltage (determination voltage) at the voltage dividing point in the phase variable circuit 52 is a predetermined voltage value that is lower than the level of the detection signal Sa when the magnetron 34 oscillates and higher than the level of the detection signal Sa when the oscillation stops. Is set in advance so that

Although not shown, a control circuit for operating the comparator 53 only during the ON period of the IGBTs 27 and 28 is added to the phase variable circuit 52. Therefore, when the IGBTs 27 and 28 are turned off and the positive detection voltage Vb is applied to the high-pass filter 40, the phase characteristics do not switch.

Next, the operation of the high-frequency power supply 48 having the above configuration will be described with reference to FIG. FIG. 7 shows waveforms of the respective parts when the magnetron 34 is oscillating (left) and when oscillation is stopped (right), similarly to FIG. 4 described above. Each of the waveforms is a waveform when the AC voltage of the AC power supply 22 has a positive polarity. Here, for convenience, the voltage between the power supply buses 24a and 24b is shown as a positive voltage of the same magnitude regardless of the presence or absence of oscillation.

(Operation during Oscillation) When the AC voltage amplitude of the AC power supply 22 is large to some extent, that is, not near zero crossing, the switching operation of the IGBT 27 causes the magnetron 34 to oscillate. At this time, since the detection signal Sa having a level higher than the determination voltage is output from the anode current detection circuit 51, the output transistor (not shown) in the comparator 53 is turned off, and the phase characteristic of the high-pass filter 40 is changed. The phase characteristics are the same as those in the first embodiment. Therefore, the waveform of each part in this case is the same as the waveform at the time of oscillation shown in FIG.

(Operation when Oscillation Stops) When the amplitude of the AC voltage of the AC power supply 22 is small, that is, near the zero crossing, the voltage is insufficient and the oscillation of the magnetron 34 stops. At this time, since the anode current detection circuit 51 outputs a detection signal Sa having a level lower than the determination voltage,
The output transistor in the comparator 53 is turned on,
The resistor 56 of the phase variable circuit 52 is connected in parallel to the resistor 42 constituting the high-pass filter 40. As a result, the cutoff frequency of the high-pass filter 40 increases, and the phase characteristics of the output voltage Vh with respect to the input voltage (detection voltage Vb) advance in the resonance frequency component.

In the waveforms of FIG. 7 and the above-mentioned FIG. 4 when the oscillation is stopped, times t11 to t14 and t16 represent the same time. 7 and 4, the current Ia, the collector voltage Vc, and the detection voltage Vb have the same waveform from time t11 to time t16. However, in this embodiment, since the phase of the output voltage Vh advances by Δθ, the timing (on timing) at which the output voltage Vh matches the reference voltage Va of 0 V in the timing setting circuit 43 is later than the time t15 shown in FIG. It is an early time (time ta). As a result, the IGBT 27 is turned on at a time t16 which is substantially delayed by ΔT from that time.

This time t16 is the time when the collector voltages Vc of the IGBTs 27 and 28 both become 0 V,
This is the optimum time point at which the switching loss is minimized when the GBTs 27 and 28 are turned on.

As described above, the high-frequency power supply 48 of the microwave oven shown in the present embodiment compares the anode current of the magnetron 34 detected by the anode current detection circuit 51 with the determination voltage to make the magnetron 34 oscillate. A phase variable circuit 52 for determining whether the oscillation is stopped or not, and varying the phase characteristic of the high-pass filter 40 according to the result is provided. Thus, even when the oscillation of the magnetron 34 is temporarily stopped, for example, during a period when the voltage amplitude of the AC power supply 22 is small, the collector voltage Vc of the IGBTs 27 and 28 is almost 0V.
And the switching loss can be further reduced as compared with the first embodiment.

During the off period of the IGBTs 27 and 28, that is, the period when the detection voltage Vb corresponding to the resonance voltage is applied to the high-pass filter 40,
Is not switched, the timing setting circuit 43 does not set an erroneous on-timing.

FIGS. 8 and 9 show the electrical configuration of a high-frequency power supply 57 according to a third embodiment of the present invention. The same components as those in FIGS. 5 and 6 in the second embodiment are the same. The code is attached.

The reference voltage variable circuit 58 as reference signal variable means changes the reference voltage Va of the timing setting circuit 59 in two stages in accordance with the detection signal Sa of the anode current detection circuit 51. Specifically, The circuit configuration is as shown in FIG. That is, the resistor 60 and the collector and the emitter of the NPN transistor 61 are connected in series between the power supply terminal Vcc and the ground terminal Ec.
The base 1 is connected to the output terminal of the anode current detection circuit 51 via a resistor 62 and to the ground terminal Ec via a resistor 63. Also, the transistor 61
Is connected to the inverting input terminal of the comparator 44 in the timing setting circuit 59, and the resistor 64
To the ground terminal Ec.

FIG. 10 shows the waveform of each part of the high-frequency power supply 57 shown in the same manner as FIG. 4 or FIG. 7, which will be described below. (Operation during Oscillation) When the magnetron 34 oscillates, the anode current detection circuit 51 outputs a detection signal Sa having a level corresponding to the magnitude of the anode current. Since the detection signal Sa at this time is higher than the forward voltage (approximately 0.7 V) between the base and the emitter of the transistor 61, the transistor 61 is turned on and almost 0 V is applied to the inverting input terminal of the comparator 44.
Is applied. Therefore, the waveform of each part in this case becomes the same as the waveform at the time of oscillation shown in FIG. 4 or FIG.

(Operation when Oscillation Stops) When the oscillation of the magnetron 34 is stopped, almost no anode current flows.
The detection signal Sa has an extremely small level. At this time, the transistor 61 is turned off, and a voltage obtained by dividing the control voltage of 5 V by the resistors 60 and 64 is supplied to the inverting input terminal of the comparator 44 as the reference voltage Va.

At this time, the time when the output signal St of the timing setting circuit 59 changes from the high level to the low level (on timing) is earlier than the on timing (time t15) when 0 V is used as the reference voltage Va. (Time ta). As a result, the IGBT 27 is turned on at a time t16 which is substantially delayed by ΔT from that time.

As described above, at time t16, IG
This is a point in time when both the collector voltages Vc of the BTs 27 and 28 become 0 V, and is an optimal point in time when the switching loss when the IGBTs 27 and 28 are turned on is minimized.

As described above, the high-frequency power supply 57 of the microwave oven shown in the present embodiment detects the anode current of the magnetron 34 by the anode current detection circuit 51, and controls the timing setting circuit 59 based on the detection signal Sa. Reference voltage Va
Is provided in two stages. As a result, the reference voltage Va for generating the optimum on-timing is used when the magnetron 34 oscillates and stops oscillating in different resonance states, so that the switching of the IGBTs 27 and 28 is performed as in the second embodiment. Loss can be further reduced.

FIG. 11 shows the electrical configuration of a high-frequency power supply 65 according to a fourth embodiment of the present invention. In FIG. 11, a current transformer 66 for detecting an input current is interposed between the AC power supply 22 and the capacitor 25, and the input current detected by the current transformer 66 is supplied to a rectifier circuit 67. Variable as the detection signal Sb after being rectified in
2 is output. The current transformer 66 and the rectifier circuit 67 constitute an input current detection circuit 68 (corresponding to input current detection means in the present invention).

In the above configuration, when the AC voltage amplitude of the AC power supply 22 is large to some extent, the switching operation of the IGBTs 27 and 28 causes the magnetron 34 to oscillate. Since the input current at this time is large, the detection signal Sb
Is higher than the judgment voltage of the phase variable circuit 52 (see FIG. 6), and the output transistor in the comparator 53 is turned off.

On the other hand, when the AC voltage amplitude of the AC power supply 22 is small, the voltage is insufficient and the magnetron 34 stops oscillating. At this time, since there is no load, the input current is extremely small, the level of the detection signal Sb becomes smaller than the determination voltage, and the output transistor in the comparator 53 is turned on.

Therefore, the high-frequency power supply 65 of the present embodiment operates at the same timing as the high-frequency power supply 48 of the second embodiment when the magnetron 34 is in the oscillation / oscillation stop state. The same effect as the example can be obtained.

FIG. 12 shows an electrical configuration of a high frequency power supply 69 according to a fifth embodiment of the present invention. The high-frequency power supply 69 includes the reference voltage variable circuit 58 described in the third embodiment in order to secure appropriate ON timing even when the magnetron 34 stops oscillating. The reference voltage Va of the timing setting circuit 59 is varied in two stages according to the level of the detection signal Sb from the input current detection circuit 68.

According to the present embodiment, the determination as to when the magnetron 34 is oscillating and when the oscillation is stopped is made based on the magnitude of the input current. In each case, the reference voltage Va for generating the optimum ON timing is used. Therefore, the switching loss can be reduced as in the third embodiment.

The present invention is not limited to the above embodiments, but can be modified or expanded as follows. The switching element is not limited to the IGBT but may be a power transistor, a MOSFET, or the like.

Although the first embodiment shows the case where the present invention is applied to a microwave oven, the present invention may be applied to a heating cooker utilizing induction heating such as an electromagnetic cooker, an electric cooker and a hot plate. That is, the coil forming the resonance circuit 32 may be an induction heating coil instead of the primary coil 26a of the high-frequency transformer 26. In the second and fourth embodiments, the phase variable circuit 52 varies the phase characteristic of the high-pass filter 40 in two steps, but may be configured to vary in multiple steps.

In the third and fifth embodiments, the reference voltage varying circuit 58 varies the reference voltage Va in two stages, but may be configured to vary in a plurality of stages.
The transistor 61 in the reference voltage variable circuit 58
The reference voltage Va applied to the comparator 44 in the timing setting circuit 59 is continuously varied by adjusting the resistance values of the resistors 60 and 62 to 64 and the levels of the detection signals Sa and Sb so that the comparator operates in the active region. May be configured.

According to this configuration, the reference voltage Va does not suddenly change stepwise even when the magnetron 34 transitions between the oscillation state and the oscillation stop state, and the timing setting circuit 59 malfunctions. For example, it is possible to prevent a situation where the ON timing is temporarily shifted. Further, finer control of the on-timing can be performed according to not only the oscillation state / oscillation stop state of the magnetron 34 but also the magnitude of the anode current.

[0094]

Since the present invention is as described above,
The following effects are obtained. According to the heating cooker according to claim 1 or 2, the on / off controlled current can be supplied from the AC power supply to the resonance circuit regardless of whether the voltage polarity of the AC power supply is positive or negative. A rectifier circuit for rectifying the rectifier becomes unnecessary, and the loss occurring in the rectifier circuit can be reduced.

In this case, the on-timing of the switching element is set based on the resonance frequency component which is an AC component of the resonance voltage, so that the influence of the low frequency component included in the resonance voltage can be eliminated, and the switching loss of the switching element can be reduced. Can be turned on at an appropriate timing to reduce the power consumption. Further, since the resonance voltage detecting means is provided commonly to the first and second switching elements,
The configuration can be simplified and the cost can be reduced.

According to the third aspect of the present invention, there is provided a cooking device comprising: an output current detecting means for detecting a current flowing through the microwave generating means; and a phase varying means for changing a phase characteristic of the filter means based on the detection signal. With this arrangement, even when the resonance state of the resonance circuit changes due to the state of the microwave generation means, the ON timing of the switching element can be appropriately controlled, and the switching loss can be further reduced.

According to the fourth aspect of the present invention, since the cooking device includes the input current detecting means for detecting the input current from the AC power supply and the phase varying means, the state of the microwave generating means is determined based on the input current. Thus, the ON timing of the switching element can be appropriately controlled, and the switching loss can be further reduced.

According to the fifth aspect of the present invention, since the phase variable means changes the phase characteristic of the filter means while the switching element is in the ON state, malfunction of the timing setting means can be prevented. .

According to the sixth aspect of the present invention, the on-timing is set by comparing the output signal of the filter means with the reference signal, and a plurality of levels of the reference signal are set based on the detection signal of the output current detection means. Since the reference signal varying means for changing the level is provided, the ON timing of the switching element can be appropriately controlled regardless of the state of the microwave generating means, and the switching loss can be further reduced.

According to the seventh aspect of the present invention, since the heating cooker is provided with the input current detecting means and the reference signal varying means, the ON timing of the switching element is appropriately determined according to the state of the microwave generating means based on the input current. , And the switching loss can be further reduced.

According to the heating cooker according to claim 8 or 9, since the level of the reference signal is continuously changed, the level of the reference signal does not suddenly change due to the change in the resonance state. Malfunction of the timing setting means can be prevented. Further, highly accurate timing control can be performed.

According to the tenth aspect of the present invention, the switching control means controls to change the ON period of the switching element in accordance with the magnitude of the detected resonance voltage. Can be improved.

According to the eleventh aspect of the present invention, the resonance voltage detecting means includes a resistor voltage dividing circuit provided commonly to the first and second switching elements, and the first and second detecting rectifying elements. Therefore, the configuration is simple and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an electrical configuration diagram of a high-frequency power supply according to a first embodiment of the present invention.

FIG. 2 is an electrical configuration diagram showing a main part of a high-frequency power supply.

FIG. 3 is a diagram showing a relationship between an AC power supply waveform and an IGBT switching operation.

FIG. 4 is a diagram showing waveforms of various parts when the magnetron oscillates and when the oscillation stops.

FIG. 5 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 6 is a diagram corresponding to FIG. 2;

FIG. 7 is a diagram corresponding to FIG. 4;

FIG. 8 is a view corresponding to FIG. 1, showing a third embodiment of the present invention.

FIG. 9 is a diagram corresponding to FIG. 2;

FIG. 10 is a diagram corresponding to FIG. 4;

FIG. 11 is a view corresponding to FIG. 1, showing a fourth embodiment of the present invention;

FIG. 12 is a view corresponding to FIG. 1, showing a fifth embodiment of the present invention;

FIG. 13 is a diagram corresponding to FIG. 1 showing a conventional technique.

[Explanation of symbols]

In the figure, 22 is an AC power supply, 26 is a high frequency transformer, 27 is an IGBT (first switching element), 28 is an IGBT
(Second switching element), 29 is a diode (first switching element).
Rectifier element), 30 is a diode (second rectifier element),
31 is a resonance capacitor, 32 is a resonance circuit, 34 is a magnetron (microwave generation means), 35 is a voltage detection circuit (resonance voltage detection means), 36 is a diode (first detection rectifier), and 37 is a diode (first detection rectifying element). 2 is a high-pass filter (filter means);
3, 59 are timing setting circuits (timing setting means), 46 is an output control circuit (switching control means),
51 is an anode current detection circuit (output current detection means), 52 is a phase variable circuit (phase variable means), 58 is a reference voltage variable circuit (reference signal variable means), and 68 is an input current detection circuit (input current detection means). is there.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference)

Claims (11)

[Claims] 1. A resonance circuit comprising a high-frequency transformer for driving a microwave generation means and a resonance capacitor, and a connection between terminals of an AC power supply via the resonance circuit and opposite directions of current flow. First and second switching elements connected in series in an oriented state, first and second rectifying elements connected in anti-parallel to the first and second switching elements, respectively, In order to detect a resonance voltage of the resonance circuit applied to the first or second switching element during a period in which the first and second switching elements are in an off state, the first and second switching elements are A resonance voltage detecting means provided in common with the filter means; a filter means for extracting a resonance frequency component from a detection signal of the resonance voltage detecting means; Timing setting means for setting on timing of the first and second switching elements based on a force signal; and turning on the first and second switching elements according to the on timing set by the timing setting means. And after the elapse of a predetermined ON period, the first
And a switching control means for controlling to turn off the second switching element. 2. A resonance circuit comprising an induction heating coil and a resonance capacitor, and connected in series between terminals of an AC power supply via the resonance circuit and in a state in which the current supply directions are opposite to each other. First and second switching elements, first and second rectifying elements connected in anti-parallel to the first and second switching elements, respectively, and the first and second switching elements. To detect a resonance voltage of the resonance circuit applied to the first or second switching element during a period in which the first and second switching elements are off. Voltage detecting means, filter means for extracting a resonance frequency component from a detection signal of the resonance voltage detecting means, and the first and the second signals based on an output signal of the filter means. Timing setting means for setting the on-timing of the second switching element; turning on the first and second switching elements in accordance with the on-timing set by the timing setting means; First
And a switching control means for controlling to turn off the second switching element. 3. An output current detecting means for detecting a current flowing through a microwave generating means, and a phase varying means for changing a phase characteristic of a filter means based on a detection signal of the output current detecting means. The cooking device according to claim 1, wherein 4. An input current detecting means for detecting an input current from an AC power supply, and a phase varying means for changing a phase characteristic of a filter means based on a detection signal of the input current detecting means. The cooking device according to claim 1, wherein 5. The cooking device according to claim 3, wherein the variable phase means changes the phase characteristic of the filter means while the first or second switching element is in an ON state. 6. The timing setting means is configured to set an on-timing by comparing an output signal of the filter means with a reference signal, and an output current detection means for detecting a current flowing through the microwave generation means. 2. The cooking device according to claim 1, further comprising a reference signal varying unit that changes a level of the reference signal in a plurality of steps based on a detection signal of the output current detection unit. 7. The timing setting means is configured to set an on-timing by comparing an output signal of the filter means with a reference signal, and an input current detecting means for detecting an input current from an AC power supply; 2. The cooking device according to claim 1, further comprising: a reference signal varying unit that changes a level of the reference signal in a plurality of steps based on a detection signal of the current detection unit. 8. The timing setting means is configured to set an on-timing by comparing an output signal of the filter means with a reference signal, and an output current detection means for detecting a current flowing through the microwave generation means. 2. The cooking device according to claim 1, further comprising a reference signal varying unit that continuously changes a level of the reference signal based on a detection signal of the output current detection unit. 9. The timing setting means is configured to set an on-timing by comparing an output signal of the filter means with a reference signal, and an input current detection means for detecting an input current from an AC power supply; 2. The cooking device according to claim 1, further comprising a reference signal varying unit that continuously changes a level of the reference signal based on a detection signal of the current detection unit. 10. The switching control means according to claim 1, wherein said switching control means is configured to control the first voltage in accordance with the magnitude of the resonance voltage detected by said resonance voltage detection means.
The heating cooker according to any one of claims 1 to 9, wherein control is performed so as to change an ON period of the second switching element. 11. A common connection point between the first and second switching elements is a ground terminal, a resonance voltage detecting means includes: a resistance voltage dividing circuit connected to the ground terminal; and the first or second switching. First and second connected in series in opposite directions so that a resonance voltage applied to the element is applied to the resistance voltage dividing circuit, and a common connection point thereof is connected to the resistance voltage dividing circuit. And a rectifying element for detecting the current.
A cooking device according to any one of claims 1 to 10.