JPH065187U - High frequency heating device - Google Patents

Abstract

(57) [Summary] [Structure] A full-wave voltage doubler rectifier circuit 9 or a secondary winding is provided on the secondary winding 8b of the high-voltage transformer 8 that constitutes an inverter circuit.
Half-wave voltage doubler rectifier circuits 9a and 9b are connected to 8b and 8c, respectively, and switching elements 5a and 5b in the inverter circuit are alternately conducted to form full-wave voltage doubler rectifier circuit 9 or half-wave voltage doubler rectifier circuit 9a. , 9b alternately supply the anode current to the magnetron 10 and control the switching elements 5a, 5b at an operation cycle which is more than twice the resonance cycle of the inverter circuit. [Effect] The anode current is supplied to the magnetron almost constantly, and the magnetron is operated for about 100% of the operation cycle.
The peak value of the anode current is kept sufficiently low with respect to the rating to prevent the occurrence of the moding phenomenon and also the loss of switching elements and the generation of switching noise.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a high frequency heating apparatus having a current resonance type half bridge circuit for energizing a magnetron by alternately connecting two switching elements.

[0002]

[Prior art]

 The current resonance type half bridge circuit has been conventionally applied to various switching power supplies, and it is also considered to be applied to a high frequency heating device using a magnetron power supply as a load.

FIG. 4 shows an example of a circuit in which a half-bridge inverter circuit is applied to a conventional magnetron power supply having a half-wave voltage doubler rectifier circuit (see FIG. 6 of Japanese Patent Laid-Open No. 4-87291), and each part in this circuit. The main waveforms of are shown in FIG.

In this example, the commercial power supply 1 is rectified and smoothed by the diode 2 and the capacitor 3 to form a direct current power supply, which is converted to a high frequency power supply as follows by alternately turning on the switching elements 5a and 5b. , Is driving the magnetron 10.

In the operation of this example, when the switching element 5a is turned on, as shown in FIG. 5, it has a resonance period determined by the inductance of the primary winding 8a of the high voltage transformer 8 and the resonance capacitors 7a, 7b. The resonance current iL1 flows through the primary winding 8a, and a similar current also flows through the switching element 5a.

When the switching element 5a is turned off at the time when this current becomes zero, the diode 6a becomes conductive and the resonance current iL1 flows through the primary winding 8a of the high-voltage transformer 8 in the opposite direction to the above.

When the switching element 5b is turned on this time when the current of the diode 6a becomes zero, the resonance current iL1 flows through the primary winding 8a in the opposite state to that when the switching element 5a is turned on.

Similarly, when the switching element 5b is turned off at the time when this current becomes zero, the diode 6b becomes conductive and the primary winding 8a of the high-voltage transformer 8 has the switching element 5b turned on. The resonance current iL1 flows in the opposite direction.

When the current of the diode 6b becomes zero, the switching element 5a is turned on again, and the above operation is repeated thereafter.

Therefore, when the polarities of the primary winding 8a and the secondary winding 8b of the high-voltage transformer 8 are as shown in the figure, the period in which a positive current flows through the magnetron 10 in the primary winding 8a as shown in FIG. That is, the positive current iL1 flows during the period in which the switching element 5a is on and the period in which the diode 6a is conducting, and outputs microwaves.

[0011]

[Problems to be solved by the device]

 However, in this case, the magnetron 10 can be oscillated only for about half of the operation cycle T, and in order to obtain a high output from the magnetron 10 with one magnetron 10, it is inevitable. A method of increasing the peak value of the anode current iL1 of the magnetron 10 and increasing the anode current iL1 of the magnetron 10 to increase the power is considered.

However, in order to achieve the high output of the magnetron 10, the peak value of the anode current iL1 is raised to approach the above-mentioned rated peak value. Normally, the rated peak value of the anode current iL1 is 1.2A to 1. If the magnetron 10 of about 4 A easily exceeds the rated temperature, and if the rated peak value is exceeded in the worst case, the moding phenomenon is likely to occur and there is a risk of accelerating the deterioration of the magnetron 10.

On the other hand, one microwave oven is equipped with two magnetrons, and the two magnetrons are simultaneously driven to cause either magnetron to constantly oscillate, as if one magnetron continuously oscillates. It is also considered that the output of the microwave oven is increased by such a state (see Japanese Patent Laid-Open No. 4-62786).

However, in the case of using two magnetrons, there is a drawback that the cost of parts increases and the main body of the microwave oven also becomes large.

[0015]

[Means for Solving the Problems]

 The present invention has been made in order to solve the above-mentioned problems, and includes a first switching element and a second switching element connected in series to a DC power source, and a first switching element connected in anti-parallel to each of these switching elements. One diode and a second diode, a first resonant capacitor and a second resonant capacitor connected in series to the DC power supply, and a high-voltage transformer connected to the connection point of these capacitors and the connection point of both switching elements. An inverter circuit composed of a primary winding, a single or multiple secondary windings wound around the secondary side of the high-voltage transformer, and a full-wave voltage doubler rectifier circuit connected to the output of the single secondary winding. And a magnetron connected to each of the above-mentioned half-wave voltage doubler rectifier circuits connected to each of the outputs. In operation period of more than 2 times the resonance period of the aforementioned inverter circuit for supplying the anode current to emissions at a control circuit for controlling the above two switching elements is obtained by constituting the control circuit of the high-frequency heating apparatus.

[0016]

[Action]

 By alternately connecting the switching elements in this manner, the anode current is almost always supplied to the magnetron from the full-wave voltage doubler rectifier circuit or the half-wave voltage doubler rectifier circuit connected to each secondary winding of the high-voltage transformer. Since the operating cycle of both switching elements can be set to more than twice the resonant cycle of the inverter circuit, the anode current can flow to the magnetron for a period of maximum 100% of the operating cycle. Keep the peak current value sufficiently lower than the rating.

[0017]

【Example】

 An embodiment of the present invention will be described below.

FIG. 1A shows a control circuit diagram of a high frequency heating apparatus according to the present invention, and FIG. 1B shows a control circuit diagram of a high frequency heating apparatus according to another embodiment of the present invention.

In FIG. 1A, reference numeral 1 is a commercial power source, and a full-wave rectifier circuit 2 is connected to both ends of the commercial power source 1, and a rectifying / smoothing capacitor 3 and a choke coil 4 are connected to its output. .

Reference numerals 5 a and 5 b respectively denote a series connection body of a first switching element and a second switching element which are transistors and are connected in parallel to the capacitor 3.

Reference numerals 6a and 6b denote series-connected bodies composed of a first diode and a second diode, which are connected in reverse parallel to the first switching element 5a and the second switching element 5b, respectively.

Reference numerals 7 a and 7 b denote a series connection body including a first resonance capacitor and a second resonance capacitor, which are connected to the DC power supply 1.

Reference numeral 8 denotes a high-voltage transformer, which includes a primary winding 8a, a secondary winding 8b, and a secondary winding 8c. The connection point between the first switching element 5a and the second switching element 5b and the first resonant capacitor The primary winding 8a is connected between the connection point between the 7a and the second capacitor 7b.

Further, the secondary winding 8b and the secondary winding 8c of the high voltage transformer 8 are connected to each other in opposite polarities.

Reference numerals 9a and 9b denote a first half-wave voltage doubling circuit and a second half-wave voltage rectifying circuit, respectively, which are composed of a capacitor and a diode. Connected to line 8c.

Reference numeral 10 denotes a magnetron, which is connected to each of the secondary windings 8 b and 8 c of the high voltage transformer 8 described above.

Reference numeral 11 denotes a control circuit for controlling the first switching element 5a and the second switching element 5b with an operation cycle that is at least twice the resonance cycle of the inverter circuit, the output of which is the first switching element. 5a and the second switching element 5b are connected to the respective bases.

FIG. 1B is a circuit diagram according to another embodiment of the present invention. The difference from the circuit shown in FIG. 1A is that the secondary winding 8b of the high voltage transformer 8 is one. A full-wave voltage doubler rectifier circuit 9 composed of capacitors 9a and 9b and a diode is connected to the secondary winding 8b, and the full-wave voltage doubler rectifier circuit 9 is connected to the magnetron 10. FIG. 2 shows current waveforms of main parts of the circuits shown in FIGS. 1 (a) and 1 (b). The circuit operation will be described below with reference to FIGS. 1 (a), 1 (b) and 2. However, it is assumed that the capacitors in the half-wave voltage doubler rectifier circuits 9a and 9b and the full-wave voltage doubler rectifier circuit 9 in the figure have already been charged with the polarities shown during normal operation.

First, when the switching element 5a is turned on in FIG. 1A, the resonance current iL1 is almost in the path of the capacitor 3 → switching element 5a → primary winding 8a → resonance capacitor 7b → capacitor 3 as shown in FIG. It flows in a sine wave.

At this time, a voltage having a positive direction in the black circle is induced in the secondary winding 8b, so that the induced voltage is applied to the magnetron 10 by the capacitor voltage in the half-wave voltage doubler rectifier circuit 9a. The voltage to which the pressure is added is applied, whereby the magnetron 10 oscillates and the anode current i MG flows.

On the other hand, in the secondary winding 8c, a voltage whose positive direction is the same as that of the black circle is generated, so that the capacitor in the half-wave voltage doubler rectifier circuit 9b is charged.

When the switching element 5a is turned off when the resonance current iL1 flowing through the switching element 5a becomes zero, the direction of the current is changed, so that the diode 6a becomes conductive and the capacitor 3 → resonance capacitor 7b → primary winding 8a → The resonance current iL1 flows through the path from the diode 6a to the capacitor 3.

Since the direction of the current flowing through the primary winding 8a is reversed, the voltage induced in the secondary winding 8b is negative in the direction of the black circle, which is the opposite of the above, and the voltage inside the half-wave voltage doubler rectifier circuit 9a Charge the capacitors.

Furthermore, since a voltage in which the direction of the black circle is also negative is induced in the secondary winding 8c, the capacitor voltage in the half-wave voltage doubler rectifier circuit 9b is added to this and applied to the magnetron 10. Then, the anode current iMG flows.

When the current of the diode 6a becomes zero, the switching element 5b is turned on this time.

The resonance current iL1 flows through the path of the capacitor 3 → resonance capacitor 7a → primary winding 8a → switching element 5b → capacitor 3.

Since the direction of the current flowing through the primary winding 8a is the same as when the diode 6a is conducting, the anode current iMG also flows from the secondary winding 8c to the magnetron 10 in this case as well.

When the switching element 5b is turned off when the current flowing through the switching element 5b becomes zero, the diode 6b becomes conductive and the capacitor 3 → the diode 6b → the primary winding 8
The resonance current iL1 flows through the path of a → resonance capacitor 7a → capacitor 3.

Since the direction of the current flowing through the primary winding 8a is the same as when the switching element 5a is on, the anode current iMG flows from the secondary winding 8b to the magnetron 10.

When the resonance current iL1 flowing through the diode 6b becomes zero, the switching element 5a is turned on again, and the above operation is repeated thereafter.

In the case of varying the output here, as shown in FIG. 4, switching is performed from when the current of the diode 6a becomes zero to when the switching element 5b is turned on and when the current of the diode 6b becomes zero. A blanking time TB is provided before turning on the element 5a.

As described above, the maximum output is obtained when the switching elements 5a and 5b are alternately turned on for each resonance cycle of the circuit to set the blanking time to zero. Since the average value of the anode current iMG of the magnetron 10 decreases as the operating period of 5a and 5b is lengthened, the output can be narrowed.

On the other hand, when the switching element 5a is turned on in FIG. 1B, the resonance current iL1 is almost in the path of the capacitor 3 → the switching element 5a → the primary winding 8a → the resonant capacitor 7b → the capacitor 3 as shown in FIG. It flows in a sine wave.

At this time, a voltage having a positive direction in the black circle is induced in the secondary winding 8b, so that the capacitor 9a is charged and the voltage of the capacitor 9a and the voltage of the capacitor 9b are added. A voltage is applied to the magnetron 10, which causes the magnetron 10 to vibrate and the anode current iMG to flow.

When the switching element 5a is turned off when the resonance current iL1 flowing through the switching element 5a becomes zero, the direction of the current is changed, so that the diode 6a becomes conductive and the capacitor 3 → resonance capacitor 7b → primary winding 8a → The resonance current iL1 flows through the path from the diode 6a to the capacitor 3.

Since the direction of the current flowing through the primary winding 8a is reversed, the voltage induced in the secondary winding 8b is opposite to that in the previous case, the direction of the black circle is negative, and the capacitor 9b is charged and Similarly, the voltage of the capacitor 9b and the voltage of the capacitor 9a are added and applied to the magnetron 10, and the anode current iMG flows.

When the current of the diode 6a becomes zero, the switching element 5b is turned on this time.

The resonance current iL1 flows through the path of the capacitor 3 → resonance capacitor 7a → primary winding 8a → switching element 5b → capacitor 3.

Since the direction of the current flowing through the primary winding 8a is the same as when the diode 6a is conducting, the capacitor 9b is charged and the anode current iMG also flows through the magnetron 10. When the switching element 5b is turned off when the current flowing through the switching element 5b becomes zero, the diode 6b becomes conductive and the resonance current iL1 flows through the path of capacitor 3 → diode 6b → primary winding 8a → resonance capacitor 7a → capacitor 3. .

Since the direction of the current flowing through the primary winding 8a is the same as when the switching element 5a is on, the capacitor 9a is charged and the anode current iMG flows through the magnetron 10 as well.

When the resonance current iL1 flowing through the diode 6b becomes zero, the switching element 5a is turned on again, and the above operation is repeated thereafter.

When the output is varied, the blanking time TB is adjusted and the average value of the anode current iMG is adjusted.

[0053]

[Effect of device]

 As described above, according to the present invention, the switching elements are alternately turned on to supply the anode current to the magnetron at almost the same time, and the operation cycle of the switching elements can be made twice or more the resonance cycle of the inverter circuit. As a result, the magnetron can be operated in a period close to 100% of the operating period, and the peak value of the above-mentioned anode current can be suppressed sufficiently lower than the rating, so that the conventional modding phenomenon does not occur. Moreover, it is possible to provide a high-frequency heating device that can supply a highly reliable power supply and that suppresses loss of switching elements and the like and generation of switching noise.

[Brief description of drawings]

FIG. 1 is a control circuit diagram of a high-frequency heating device showing an embodiment of the present invention.

FIG. 2 is a main current waveform diagram of each part in FIG.

FIG. 3 is a current waveform diagram for explaining an output control state of the magnetron.

FIG. 4 is a control circuit diagram of a high-frequency heating device in a conventional example.

FIG. 5 is a main current waveform diagram of each part in FIG.

[Explanation of symbols]

 5a 1st switching element 5b 2nd switching element 6a 1st diode 6b 2nd diode 7a 1st resonance capacitor 7b 2nd resonance capacitor 8 High voltage transformer 9 Full wave voltage doubler rectifier circuit 9a First half wave voltage doubler rectifier circuit 9a Second Half-wave voltage doubler rectifier circuit 10 Magnetron 11 Control circuit

Claims (2)

[Scope of utility model registration request] 1. A DC power source (2, 3, 4) and a high-voltage transformer
(8), a series connection body of the first switching element (5a) and the second switching element (5b) connected to the DC power supply, and a first switching element and a second switching element of the series connection body, respectively. A first diode (6a) and a second diode (6b) connected in antiparallel, and a series connection body of the first resonance capacitor (7a) and the second resonance capacitor (7b) connected to the DC power supply, and The primary winding (8a) of the high-voltage transformer connected to the connection point of the first resonance capacitor and the second resonance capacitor of the series connection body and the connection point of the first switching element and the second switching element
An inverter circuit composed of, a first half-wave voltage rectifier circuit (9a) and a second half-wave voltage that are respectively connected to the secondary winding (8b) and the secondary winding (8c) of the high-voltage transformer. A rectifier circuit (9b), a magnetron (10) connected to the first half-wave voltage doubler rectifier circuit and the second half-wave voltage doubler rectifier circuit and energized by both circuits, and the first switching element and A control circuit for controlling the two switching elements with an operation cycle that is at least twice the resonance cycle of the inverter circuit.
(11) A high-frequency heating device comprising: 2. A DC power source (2, 3, 4) and a high voltage transformer
(8), a series connection body of the first switching element (5a) and the second switching element (5b) connected to the DC power supply, and a first switching element and a second switching element of the series connection body, respectively. A first diode (6a) and a second diode (6b) connected in antiparallel, and a series connection body of the first resonance capacitor (7a) and the second resonance capacitor (7b) connected to the DC power supply, and The primary winding (8a) of the high-voltage transformer connected to the connection point of the first resonance capacitor and the second resonance capacitor of the series connection body and the connection point of the first switching element and the second switching element
An inverter circuit composed of: a full-wave voltage doubler rectifier circuit (9) connected to the secondary winding (8b) of the high-voltage transformer;
A magnetron (10) connected to the output of the full-wave voltage doubler rectifier circuit and energized by this circuit, and the operation cycle of the first switching element and the second switching element is at least twice the resonance cycle of the inverter circuit. A high-frequency heating device comprising a control circuit (11) controlled by the.