JPH063991B2 - Magnetron drive power supply - Google Patents

Description

The present invention relates to a magnetron driving power source, and more particularly to a magnetron driving power source suitable for driving a non-linear load such as a magnetron used as a microwave source of a microwave oven.

[Conventional technology]

Conventional magnetron power supplies, such as microwave ovens,
For example, Electronic Technology Vol. 20, No. 3 (Showa 53) p. 34-
45 is a circuit for applying a DC voltage of a magnetron by rectifying a commercial AC voltage with a transformer and then rectifying it with a half-wave voltage doubler rectifier circuit on the secondary side of the transformer, and controlling the output power of the transformer. This is a method in which the energization phase of a bidirectional controllable switch directly connected to the primary side is controlled.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technique, the transformer of the magnetron power source of the microwave oven is operated at the commercial frequency, so that the transformer is large and heavy, and the commercial frequency is 50 Hz.
It was necessary to design separately for 60Hz. Furthermore, when the applied voltage between the anode and cathode of the load magnetron exceeds the cutoff voltage, the anode current begins to flow, and the anode current directly increases with the increase of the applied voltage, and microwave output can be obtained. It has a characteristic that an abnormal oscillation is caused when it reaches to a point where the microwave output cannot be obtained, and this abnormal oscillation remarkably shortens the life of the magnetron. Moreover, the cutoff voltage of the magnetron is, for example, about 4 kV, and this value changes depending on the temperature of the magnetron, and fluctuates by several 100V during normal operation. However, in the prior art, since no consideration is given to such a case where the power supply voltage and the cutoff voltage of the magnetron fluctuate, the anode current exceeds the critical value and abnormal oscillation occurs when the power supply voltage rises or the cutoff voltage falls. In addition, when the power supply voltage is decreased or the cutoff voltage is increased, the applied voltage of the magnetron does not exceed the cutoff voltage, and microwave output is hardly obtained. In order to solve this problem with conventional technology, the transformer winding ratio should be set to a value at which the applied voltage of the magnetron becomes equal to or higher than the cutoff voltage even when the power supply voltage reaches the minimum value, and the anode current is detected when the power supply voltage rises. It is possible to prevent abnormal oscillation by turning off the bidirectional control switch before reaching the critical value.However, in this case, a means for detecting the anode current is required and the bidirectional control is possible. There is a problem that the control circuit of the control switch becomes complicated.

The object of the present invention can be applied to a microwave oven power source in which the transformer is made smaller and lighter, and the microwave required by a simple control circuit does not need to detect the anode current even when the power source voltage and the cutoff voltage of the magnetron change. Optimal use for magnetron power supplies in microwave ovens with stable output, good control characteristics against power supply voltage fluctuations, and economical to supply stable voltage power to nonlinear loads such as magnetrons with a simple circuit To provide a power supply for driving a magnetron.

[Means for solving problems]

The present invention realizes downsizing and weight reduction of a transformer by turning on and off a controllable switch of a primary winding of a transformer and a circuit of a controllable switch connected in series to a DC power supply at high frequency and using the transformer at high frequency. However, pay attention to the following points.

There is a method of supplying electric power to the magnetron by a current source as a method of supplying the electric power required for the magnetron even when the power supply voltage and the cutoff voltage of the magnetron are changed by a magnetron power supply of a microwave oven. For example, on
In the off-chopper method, the energy of the DC power supply is stored as the excitation energy of the transformer during the ON period of the controllable switch of the primary winding and the controllable switch circuit connected in series to the DC power supply, and the transformer is stored during the OFF period of the controllable switch. Since the excitation energy is supplied to the magnetron as a current source by controlling the excitation current of the transformer by changing the on / off duty of the controllable switch even when the power supply voltage fluctuates, the required power is generated without causing abnormal oscillation. Can be supplied to. However, since the output power of the on / off chopper method is proportional to the square of the product of the power supply voltage and the on / off duty of the controllable switch, when constant power is output when the power supply voltage changes, the on / off duty and power supply voltage are inversely proportional. Therefore, it is necessary to give the control circuit of the controllable switch a non-linear characteristic, and the control circuit has a complicated configuration. On the other hand, in the ON / ON chopa system, the output voltage is proportional to the ON / OFF duty of the controllable switch, but since the output voltage of a value proportional to the power supply voltage is applied to the magnetron, abnormal oscillation occurs when the power supply voltage fluctuates. Occurs or the applied voltage does not exceed the cutoff voltage, and the microwave output cannot be obtained.

In view of the above, an object of the present invention is to provide a series circuit of a primary winding of a transformer connected to a DC power source and a controllable switch,
A secondary voltage of the transformer is connected to the secondary winding of the transformer while connecting a first voltage source for outputting a voltage having a value proportional to a power supply voltage generated in the secondary winding during the ON period of the controllable switch. In the winding, the exciting energy from the power source is stored in the exciting inductance of the transformer during the ON period of the controllable switch, and then the stored energy is supplied by using the exciting inductance of the transformer as a current source during the OFF period of the controllable switch. While connecting the second voltage source,
By adopting a configuration in which a load is connected to the series circuit of the first voltage source and the second voltage source, the characteristics of the on / off chopper method and the on / on chopper method are combined, and the voltage value of the DC power source is further provided. This is achieved by providing a voltage detecting means for detecting the voltage and a control means for controlling the controllable switch based on the detection voltage of the voltage detecting means.

[Action]

According to the present invention, a first voltage source that outputs a voltage proportional to a power source voltage and a second voltage source that is supplied with energy from the current source after the energy of the power source is stored in a current source are connected in series. Since the sum of the output values is applied to the load, the on / off duty of the controllable switch is changed when the power supply voltage fluctuates, and the energy stored in the current source to the second voltage source together with the first voltage source is changed. By controlling, the fluctuation of the output voltage of the first voltage source is compensated for by adjusting the output voltage of the second voltage source, so that the load can be supplied with stable power of a desired voltage.

Further, since the controllable switch is controlled by the input power (DC power supply voltage), it is possible to cope with the change in the cutoff voltage or the input voltage of the magnetron, which is the load,
It can always supply stable power to the magnetron.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 is a block diagram showing a first embodiment of a switching power supply according to the present invention. In FIG. 1, 10 is a DC power supply, 20 is a transformer, 30 is a controllable switch, 40 is a control circuit for the controllable switch 30, and the DC power supply 10 has a primary winding of the transformer 20 and a series circuit of the controllable switch 30. Are connected.

Reference numeral 50 is a first voltage source, 60 is a second voltage source, and 70 is a load.
0 and the second voltage source 60 are connected, and the load 70 is grounded in the series circuit of the first voltage source 50 and the second voltage source 60. In the following, the same reference numerals denote the same or corresponding parts throughout the drawings.

FIG. 2 is an example of operation waveforms of each part of FIG. The circuit operation of FIG. 1 will be described with reference to FIG. As shown by the solid line in FIG. 2, the first voltage source 50 connected to the secondary winding of the transformer 20 has the DC power supply 1 during the ON period of the controllable switch 30.
Transformer 2 proportional to voltage of 0 and turns ratio of transformer 20
The voltage generated in the next winding is output as the output voltage. A second voltage source 60 connected to the secondary winding of one transformer 20
Outputs a voltage generated by accumulating the exciting energy during the OFF period of the controllable switch 30 using the exciting energy by the exciting current stored in the exciting inductance of the transformer 20 by the DC power supply 10 during the ON period of the controllable switch 30 as the current source. Output as voltage. Transformer 2 shown in FIG.
The shaded portion of the waveform of the exciting current of 0 represents the amount of charge accumulated in the second voltage source 60. The load 70 connected to the series circuit of the first current source 50 and the second current source 60 is supplied with the power of the sum of the output voltage of the first current source 50 and the output voltage of the second current source 60. To do. In this case, the control circuit 40 changes the on / off duty of the controllable switch 30 to make the power of the output voltage supplied to the load 70 variable.

When the voltage of the DC power supply 10 rises as indicated by the broken line in FIG. 2 when the power supply voltage changes (broken line I), the control circuit 40 reduces the on / off duty of the controllable switch 30, The exciting energy is reduced by the exciting current of the transformer 20, and the output voltage of the second voltage source 60 that uses this exciting energy as a current source is lowered to reduce the first voltage source 5
By compensating for the increase in the output voltage proportional to the power supply voltage of 0, the power having a stable voltage is supplied to the load 70.
When the voltage of the DC power supply 10 drops (broken line II),
The ON / OFF duty of the controllable switch 30 is increased to increase the excitation energy due to the excitation current of the transformer 20, thereby increasing the output voltage of the second voltage source 60 and increasing the output voltage of the first voltage source 50. By compensating for the decrease, electric power having a stable output voltage is supplied to the load 70.

FIG. 3 is a circuit diagram of a magnetron power supply showing a second embodiment of the switching current according to the present invention. In FIG. 3, 21 is a primary winding of the transformer 20, 22 is also a secondary winding, and the polarities of the primary winding 21 and the secondary winding 22 are indicated by dots. 31 is a transistor forming the controllable switch 30,
Reference numeral 32 is also a drive circuit for the transistor 31. The collector of the transistor 31 is connected to the positive side of the DC power supply 10 via the primary winding 21 of the transformer 20, and the emitter of the transistor 31 is connected to the negative side of the DC power supply 10. Reference numeral 51 is a first diode forming the first voltage source 50, and 52 is a first diode.
Capacitor, 61 is a second diode forming the second voltage source 60, 62 is also a second capacitor, 71 is a magnetron forming a load 70, and 72 is also a magnetron 7
1 heater power supply. The anode of the diode 51 and the cathode of the diode 61 are connected to one end of the secondary winding 22 of the transformer 20, and one end of the capacitor 52 and one end of the capacitor 62 are connected to the other end of the secondary winding 22 of the transformer 20. The cathode of the diode 51 and the anode (ground) of the magnetron 71 are connected to the other end of the capacitor 52, and the anode of the diode 61 and the cathode of the magnetron 71 are connected to the other end of the capacitor 62.

4 (a) and 4 (b) are equivalent circuit diagrams in which the transistor 31 of FIG. 3 is in the on and off states, respectively. In FIGS. 4 (a) and 4 (b), 25 is the exciting inductance of the transformer 20. The circuit operation when the transistor 31 in FIG. 3 is turned on and off will be described with reference to FIGS. 4 (a) and 4 (b). When the transistor 31 shown in FIG. 4 (a) is turned on, the first voltage source 50 forming the first voltage source 50 is formed.
The diode 51 is turned on to charge the first capacitor 52 with the current in the direction of the arrow by the DC power source 10, and the magnetron 71 forming the load 70 is charged with the charging voltage of the capacitor 52 and the second capacitor forming the second voltage source. Power is supplied by applying a voltage that is the sum of the voltages of 62. Further, when this is turned on, the excitation energy by the excitation current in the direction of the arrow is stored in the excitation inductance 25 of the transformer 20 by the DC power supply 10. On the other hand, when the transistor 31 shown in FIG. 4 (b) is off, a counter electromotive force is generated in the secondary winding 22 of the transformer 20.
The second diode 61 forming the voltage source 60 is turned on to charge the second capacitor 62 with the exciting energy stored in the exciting inductance 25 at the time of turning on in FIG. Electric power is supplied to the magnetron 71 by applying a voltage that is the sum of the charging voltages of the first capacitor 52 and the second capacitor 62. In this case, the control circuit 4
0 drives the transistor 31 via the drive circuit 32 with on / off duty determined by the voltage of the DC power supply 10 and the reference output power supplied to the magnetron 71. Further, when the voltage of the DC power source 10 fluctuates, the above-mentioned FIG. 1 and FIG.
By controlling the on / off duty of the transistor 31 in the same manner as in the illustrated embodiment, the excitation voltage is controlled together with the secondary voltage of the transformer 20 to change the charging voltage of the capacitor 62 together with the capacitor 51, and the applied voltage of the magnetron 71 is changed. A predetermined output power is supplied while suppressing fluctuation.

FIG. 5 is an example of operation waveforms of each part of FIG. The circuit operation of the magnetron 71 shown in FIG. 3 including a change in the cutoff voltage will be described with reference to FIG. As indicated by the solid line in FIG. 5, the DC power supply 10 operates each part of the transistor 31 during the on / off period. When the cutoff voltage of the magnetron 71 fluctuates and the cutoff voltage rises as shown by the broken line in FIG. 5 (broken line I), the discharge charge amount of the anode current, that is, the capacitor 62 decreases. The charging voltage of the capacitor 62 during the off period of the transistor 31 in the operation cycle rises as illustrated. When the cutoff voltage decreases (broken line II), the anode current, that is, the amount of discharged charge of the capacitor 62 increases, so that the capacitor 6 in the OFF period of the transistor 31 in the next operation cycle is increased.
The charging voltage of 2 drops as shown. In this way, the charging voltage of the capacitor 62 changes according to the change of the cutoff voltage of the magnetron 71, and the applied voltage to the magnetron 71, which is the sum of the voltage of the capacitor 52 and the charging voltage of the capacitor 62, changes, so that the anode current is uncontrolled. Fluctuations can be suppressed. The relationship among the output power P, the DC power supply voltage E, the cutoff voltage Ec of the magnetron, and the on / off duty ρ of the transistor in this case is as follows with respect to the switching frequency f of the transistor, the turns ratio n of the transformer, and the magnetizing inductance L of the transformer. It becomes an expression.

6 (a) and 6 (b) are characteristic examples of FIG. 3 obtained from the above equations, respectively, and the solid line in FIG. 6 (a) indicates the on / off duty of the transistor 31 with respect to the fluctuation of the voltage of the DC power supply 10. Fig. 6 (b) shows the constant output power control characteristic of the magnetron 71
FIG. 5 is a characteristic diagram of output power when there is no control with respect to variations in the cutoff voltage. The broken line in FIG. 6 (a) shows the characteristics of the conventional on / off chopper method. The constant output power control characteristic of the on / off duty when the voltage of the conventional on / off chopper type DC power source changes as shown by the broken line in FIG. 6 (a) is non-linear, while the DC line in FIG. The control characteristic of the constant output power P of the on / off duty ρ of the transistor 31 when the voltage E of the power source 10 fluctuates becomes a substantially linear characteristic. Also, the magnetron 7 of FIG. 3 shown in FIG. 6 (b).
The characteristic of the output power P when the cutoff voltage Ec of 1 changes is almost flat, and the influence of the change of the cutoff voltage is small.

As described above, in the embodiment shown in FIG. 3, the series circuit of the secondary winding 22 and the first diode 51, which are connected in the polarity that makes the transistor 31 conductive during the ON period and forms the current path to the first capacitor 52. Is connected in parallel to the first capacitor 52 to configure the first current source 50, and is connected to the second capacitor 62 in a polarity that forms a current path by conducting during the off period of the transistor 31. A series circuit of the secondary winding 22 and the second diode 61 is connected in parallel to the second capacitor 62 to configure the second voltage source 60, and the first capacitor 52 and the second capacitor 62 are connected. By connecting the series circuit in parallel to the magnetron 71, a stable voltage is supplied even when the power supply voltage and the cutoff voltage of the magnetron are changed with a simple circuit structure. It is possible to obtain a micro-wave output of.

FIG. 7 is a circuit diagram of a magnetron power supply showing a third embodiment of the switching power supply according to the present invention. In FIG. 7, reference numeral 23 denotes a tertiary winding of the transformer 20, the polarity of which is indicated by dots. The embodiment shown in FIG. 7 is different from the embodiment shown in FIG. 3 in that the winding for extracting the excitation energy of the transformer 20 is used as a current source for the second voltage source 60 constituted by the first diode 61 and the second capacitor 62. The secondary winding 23 is provided separately from the secondary winding 22. The circuit operation and characteristics of this embodiment are similar to those of FIG.

FIG. 8 is a circuit diagram of a magnetron power supply showing a fourth embodiment of the switching power supply according to the present invention. In FIG. 8, 11 is a commercial AC power supply, 12 is a rectifying circuit (rectifying bridge), and 13 is a power supply capacitor, which constitutes the DC power supply 1. In the embodiment of FIG. 8, the voltage of the DC power supply 1 of FIG. 3 is obtained as a rectified voltage obtained by full-wave or half-wave rectifying the AC voltage of the commercial AC power supply 11 by the rectifier circuit 12, and the rectified voltage between the power supply capacitors 13 is used. By controlling the ON / OFF duty of the transistor 31 via the drive circuit 32 by the control circuit 40 according to the instantaneous value, a predetermined microwave output of the magnetron 71 can be obtained. Its circuit operation and characteristics are the third
It is similar to the figure.

FIG. 9 is a circuit diagram of a microwave oven showing a fifth embodiment of the switching power supply according to the present invention. In FIG. 9, 1 is an AC outlet, 2 is a fuse, 3 is a power switch, 4 is a powered switch, 5 is a door switch, 6 is a control power transformer, 7 is a rectifier circuit, 8 is a constant voltage circuit, and 9 is It is a cooling fan. The circuit operation and characteristics of FIG. 9 are similar to those of FIG.

〔The invention's effect〕

As described above, according to the switching power supply of the present invention, not only is it possible to reduce the size and weight of a transformer by applying it to a magnetron power supply of a microwave oven at high frequencies,
Since the duty control characteristic is almost linear to the fluctuation of the power supply voltage and the characteristic fluctuation of the nonlinear load such as magnetron has a small effect on the output power, the power supply voltage and the magnetron can be cut with a simple circuit configuration. Even when the off-voltage fluctuates, there is an effect that a stable voltage output can be obtained by supplying a stable voltage power to the magnetron.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a switching power supply according to the present invention, FIG. 2 is an example of operation waveforms of respective parts of FIG. 1, and FIG. 3 is a second embodiment of a switching power supply according to the present invention. The circuit diagrams shown in FIGS. 4 (a) and 4 (b) are equivalent circuit diagrams of the on / off state of the transistor of FIG. 3, respectively, and FIG. 5 is an example of operation waveforms of respective parts of FIG. 3, and FIG. 6 (a). ) And (b) are examples of constant duty output power control characteristics when the power supply voltage fluctuates, uncontrolled output power characteristics when the cutoff voltage fluctuates, and FIG. 7 shows a third example of the switching power supply according to the present invention. FIG. 8 is a circuit diagram showing the fourth embodiment, FIG. 8 is a circuit diagram showing the fourth embodiment, and FIG. 9 is a circuit diagram showing the fifth embodiment. 10 ... DC power supply, 20 ... Transformer, 21 ... Primary winding, 2
2 ... Secondary winding, 30 ... Controllable switch, 31 ... Transistor, 40 ... Control circuit, 50 ... First voltage source, 51 ... First diode, 52 ... First capacitor, 60 ... Second
Voltage source, 61 ... Second diode, 62 ... Second capacitor, 70 ... Load, 71 ... Magnetron.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-51-121163 (JP, A) JP-A-59-159667 (JP, A) JP-A-58-150300 (JP, A) JP-A-50- 135518 (JP, A) JP 54-148219 (JP, A) JP 57-207919 (JP, A) JP 60-190164 (JP, A) Actual development 57-104782 (JP, U) Actually open 57-163189 (JP, U) Actually open 59-189483 (JP, U) Actually open 52-8112 (JP, U) Special public Sho 58-22942 (JP, B2)

Claims (1)

[Claims] 1. A transformer having a primary winding and a secondary winding, a controllable switch connected in series to the primary winding, and a commercial AC voltage obtained by full-wave rectification or half-wave rectification. The rectified voltage is applied across the power supply capacitor and
A rectifier circuit that is applied to a series circuit of the secondary winding and the controllable switch, and a first rectifier circuit that is connected to the secondary winding and that outputs a voltage generated in the secondary winding during an ON period of the controllable switch
Voltage source, a second voltage source connected in series to the first voltage source for storing the excitation energy of the transformer during an off period of the controllable switch, and connected to the first and second voltage sources. And a voltage detecting means for detecting an instantaneous value of a rectified voltage applied across the power supply capacitor, and the controllable switch when the instantaneous value of the rectified voltage detected by the voltage detecting means is large. Is a control means for decreasing the on-duty of, and increasing the on-duty when the instantaneous value is small. Here, E: instantaneous value of rectified voltage applied to both ends of power supply capacitor Ec: cutoff voltage of magnetron P: output power value of magnetron n: turns ratio of transformer f: switching frequency of controllable switch L: transformer A magnetron driving power supply, characterized in that it is provided with a control means which is determined by an exciting inductance formula.