Power Supply For Driving Magnetron

Abstract

A compact power supply for driving a magnetron to oscillation used for an electronic cooking range. A transformer having a three-legged magnetic core with at least primary, secondary and tertiary windings. The primary winding is divided into two halves, each wound on a separate leg of the core and switching means are provided for changing the direction of the magnetic flux produced by one half of the winding with respect to the other half. The secondary winding is linked by the flux from each half of the primary winding and is arranged to selectively provide the magnetron with high voltage in accordance with the position of the switching means. The tertiary winding, which is arranged to provide voltage to the magnetron heater, is linked to the flux produced by only one of the halves of the primary winding winding regardless of the position of the switching means.

Description

This invention relates to a power supply for driving a magnetron to oscillation, particularly to such a power supply of compact size suitable for use in an electronic cooking range in which food is cooked by high frequency energy produced by the magnetron oscillator.

This invention will be described in detail hereunder with reference to the accompanying drawings, in which;

FIG. 1 is a connection diagram of the conventional power supply for a magnetron oscillator;

FIG. 2 is a schematic diagram of the main transformer used in the power supply shown in FIG. 1;

FIGS. 3 to 6 are connection diagrams of different embodiments of the device of this invention;

FIGS. 7 to 10 are schematic diagrams showing the basic features of the transformers used in the device of this invention; and

FIGS. 11 to 14 are schematic diagrams showing the operation of the transformers.

Referring to FIG. 1 which shows a circuit diagram of the conventional power supply, index T.sub.1 designates a leakage transformer used as the main transformer. As shown in FIG. 2, the main transformer comprises a primary coil 1 and secondary Coil 2 wound on the center leg of a core 5, a pair of magnetic leakage paths 6 provided therebetween. Terminals 7, 8 are provided at the ends of the primary coil 1 and terminals 9, 10 for the secondary coil 2. Index T.sub.2 denotes a transformer for supplying power to a magnetron for heating the cathode; Mg, the magnetron; D, a rectifier; C, a capacitor; MS, contacts of a magnetic contactor; MSC the magnetic coil of the same contactor, and SW a push-button switch. Numerals 11, 12 designate terminals to which power lines are to be connected. By depressing the push-button switch SW and thereby closing the contacts MS, the primary winding 1 of the transformer T.sub.1 is energized. In the secondary circuit of the transformer, the magnetron Mg and the rectifier D are connected in parallel but in the opposite directions. This parallel connection is connected in series with the capacitor C. Primary winding 3 of another transformer T.sub.2 is also connected to the terminals 11, 12, while secondary winding 4 of the same transformer is connected to the cathode heater of the magnetron. Thus, two transformers are required for the operation of the magnetron oscillator. If two transformers are combined into one by providing the conventional main transformer with a third winding for the cathode heater, the third winding also will be energized or de-energized according to the closing or opening of the contacts MS. Therefore, a voltage will be imposed on the anode of the magnetron before the cathode has been sufficiently heated to emit ample electrons, resulting in generation of high voltage pulses due to an abnormal oscillation. Thus, it is impossible to incorporate the heater transformer into the main transformer in the conventional device.

The object of this invention is to provide a compact and unexpensive power supply for a magnetron oscillator, which includes a single transformer having both functions of the above-mentioned main transformer and the heater transformer.

With the power supply of this invention, the secondary high voltage circuit is controlled simply by a switching operation of the magnetic contactor, while the heater circuit is maintained alive. Further, this invention provides an additional advantage that if the door of the oven is opened during the operation, the magnetron oscillator is stopped with high reliability, thus assuredly preventing leakage of the harmful high frequency wave.

In order to achieve the above-mentioned object, the power supply for a magnetron oscillator of this invention comprises a transformer which has a three-legged magnetic core, a pair of halves of the primary winding, each of the pair being wound on each of the outer legs of the core, a secondary winding wound on the center leg of the core for providing the magnetron with a high voltage and a third winding wound on either one of the outer legs of the core for providing the cathode of the magnetron with heating power, and switching means connected with said halves of the primary winding so as to be able to change the direction of the magnetic flux produced by one of said half primary windings in relation to that by the other half primary winding while said halves of the primary winding are connected in parallel.

Now, the power supply of this invention will be described in connection with various embodiments of the invention. Referring to FIGS. 3 to 14, reference numerals 101, 101' designate the respective halves of the primary winding, and 102 a secondary winding. It will be noted in the arrangements shown in FIGS. 8 and 9 that the secondary winding consists of two equal parts. Reference numeral 103 designates a third winding for supplying power to a cathode heater, 104 a fourth winding, 105 the core of the transformer, and 106 bypath cores forming magnetic leakage paths. Terminals 109, 110 are to be connected across the load circuit which includes a magnetron Mg, a rectifier D connected, in parallel and in the opposite direction, with the magnetron, and a capacitor C connected in series with the parallel connection of the magnetron and the rectifier.

The operation of the power supply of this invention will be described hereunder in reference with FIGS. 3, 7, 11 and 12. Assuming that the contacts MS of the magnetic contactor normally connect the coil terminal 107 with the terminal 108' and the terminal 108 with the terminal 107' as shown in the FIG. 3; the half primary windings 101, 101' are energized in mutually opposite directions, upon the application of the rated voltage to the terminals 115, 116, so that the magnetic fluxes .phi..sub.1, and .phi..sub.1 ', produced by the windings 101 and 101' mutually cancel in the center leg and only a small voltage corresponding to the difference .vertline..phi..sub.1 - .phi..sub.1 '.vertline. is induced in the secondary winding 102. If it is so designed that fluxes .phi..sub.1 and .phi..sub.1 ' are exactly equal, no voltage will be induced in the winding 102. Then, if the switch SW is depressed to changeover the contacts MS so as to connect the terminal 107 with 107' and terminal 108 with 108', the windings 101 and 101' will be energized in the same direction. Accordingly, the fluxes .phi..sub.1 and .phi..sub.1 ' are mutually added in the center leg as shown in FIG. 11 and a voltage corresponding to .vertline..phi..sub.1 + .phi..sub.1 '.vertline. is induced in the secondary winding 102. Namely, a voltage sufficiently high for causing the magnetron to oscillate is induced in the winding 102. In FIG. 11, indexes .phi..sub.2, .phi..sub.2 ' designate leakage fluxes which are produced when the load current flows through the secondary winding 102. It will be seen from FIGS. 11 and 12 that a voltage of substantially constant amplitude is induced in the third coil 103 by the flux .phi..sub.1 regardless of the switched position of the contacts MS. Therefore, the heater of the magnetron cathode is kept energized regardless of the manner of connection of two half primary windings. In other words, the magnetron can be driven to oscillation or brought to rest, while the cathode is kept heated by a substantially constant power.

A similar result is obtained using a transformer constructed as shown either in FIG. 8 or 9.

Another embodiment of this invention will be described hereunder with reference to FIGS. 4, 10, 13 and 14. It is assumed that rated voltage is being applied to the terminals 115, 116 and the pushbutton switch SW is not yet depressed. As the contacts MS connect the terminal 107' with 116 and terminal 108 with 108' as shown in FIG. 4, the half primary windings 101, 101' are energized in mutually opposite directions. Thus, the fluxes .phi..sub.1 and .phi..sub.1 ' produced respectively by the windings 101 and 101' cancels each other in the center leg of the magnetic core as shown in FIG. 14. A voltage is induced in the third winding 103 and therefore the heating current flows through the winding 103. As this heating current produces a magnetic flux .phi..sub.H in the direction opposite to that of the flux .phi..sub.1, a further current flows through the half primary winding 101 to produce a counter magnetic .phi..sub.1H and to cancel the flux .phi..sub.1. As the half primary windings 101 and 101' are connected in series, the same additional current flows through the winding 101', producing an additional flux .phi.'.sub.1H which circulates through the center leg of the core. It will be noted that a fourth winding 104 is wound on the center leg. Terminals 113 and 114 are connected with each other by additional contacts of the same contactor when the push-button switch SW is not yet depressed. Therefore, a current flows through the winding 104 to produce a counter magnetic flux .phi..sub.4 so as to cancel the flux .phi.'.sub.1H. As will be clear from the above description, no voltage is induced in the secondary winding 102 before the push-button switch SW is depressed. Upon pushing the switch SW to energize the magnetic coil MSC, the contacts are switched so as to connect the terminal 108 with 107' and the terminal 108' with 116 and further to open the terminals 113 and 114 of the fourth winding 104. In this state, magnetic fluxes in the core assume the disposition as shown in FIG. 13. Thus, the fluxes .phi..sub.1 and .phi..sub.1 ' produced by the primary windings are added together in the center leg of the core. Meanwhile, a voltage is induced in the third winding 103 to allow a current to flow through the cathode heater of the magnetron. This heating current produces the magnetic flux .phi..sub.H in the direction opposite to that of the flux .phi..sub.1, the said flux .phi..sub.H in turn inducing a counter flux .phi..sub.1H which is maintained by an additional current in the winding 101. As the half primary windings 101 and 101' are connected in series, a flux .phi..sub.1H ' corresponding to .phi..sub.1H is produced by the winding 101' and it flows through the center leg of the core. Therefore, the total flux in the center leg mounts to .phi..sub.1 + .phi..sub.1 ' + .phi..sub.1H - .phi..sub.H + .phi..sub.1H ' .apprxeq. .phi..sub.1 + .phi..sub.1 ' + .phi..sub.1H '. Thus, a high voltage sufficient to drive the magnetron is induced in the secondary winding 102. Upon the energization of the magnetron, the load current produces fluxes .phi..sub.2 and .phi..sub.2 ' which flow through the leakage paths 106. As will be clear from the above description, the third winding 103 always produces a voltage of a substantially constant amplitude regardless of the position of the contacts. Therefore, the magnetron can be driven or stopped, while the cathode is kept heated. It will be understood that the fourth winding may not necessarily be a separate winding but may be provided as a part or an extension of the secondary winding.

FIG. 5 shows a further embodiment of this invention. In this embodiment, the structure and the operation of the transformer are similar to those described in connection with FIG. 4. A special feature of this embodiment is the fact that door switches which are interlocked with the oven door are connected in series with the normally-open contacts of the magnetic contactor. With this arrangement, it is ensured that the oscillation of the magnetron stops if the oven door is opened during the operation, thereby preventing the radiation of the high frequency wave out of the oven. It will be clear that a similar effect is obtained with a single door switch connected with either one of the normally-open contacts. Further, if an additional door switch is connected in series with the magnetic coil MSC of the magnetic contactor, the interlocked stoppage of the oscillation is still more assured, as the contacts MS are switched so as to nullify the secondary voltage.

In a still further embodiment of this invention as shown in FIG. 6, the door switch is connected across the terminals 113 and 114 of the fourth winding 104. This door switch is opened or closed respectively according to the closing or opening of the door. The other constituents of the device shown in FIG. 6 are the same as those shown in FIG. 4. If the door is opened and the door switch is closed during the operation, a magneto-motive force is produced so as to cancel the flux in the center leg. Thus, the voltage induced in the secondary winding 102 is reduced to stop the oscillation of the magnetron, thereby preventing leakage of the high frequency wave.

Claims

1. A power supply for a magnetron oscillator comprising a transformer having a three legged magnetic core, a primary winding divided into halves, each half being wound on one of the outer legs of the core, a secondary winding wound on the center leg of the core for providing the magnetron with high voltage and a third winding wound on either one of the outer legs of the core for providing the cathode of the magnetron with heating power, and switching means connected with said halves of the primary winding to change the direction of the magnetic flux produced by one of said half primary windings in relation to that produced by the other half primary winding while said halves of the primary winding are connected in parallel so that said third winding can be always energized to produce a constant output power irrespective of energization or

2. A power supply for a magnetron oscillator comprising a transformer which has a three-legged magnetic core, a primary winding divided into halves, each half being wound on one of the outer legs of the core, a secondary winding divided into halves, each half being wound on one of the outer legs of the core, said halves of the secondary winding being connected in series, the secondary winding providing the magnetron with high voltage, and a third winding wound on either one of the outer legs of the core for providing the cathode of the magnetron with heating power; and switching means connected with said halves of the primary winding to change the direction of the magnetic flux produced by one of said half primary windings in relation to that produced by the other half primary winding while said halves of the primary winding are connected in parallel so that said third winding can be always energized to produce a constant output power irrespective of energization or de-energization of said secondary

3. A power supply for a magnetron oscillator comprising a transformer which has a three-legged magnetic core, a magnetic bypath being provided between the center leg and each outer leg dividing the center leg of said transformer into two equal sections, a primary winding divided into halves, each half being wound on each of the two sections of the center leg of the core, a secondary winding divided into halves, each half being wound on one of the two sections of the center leg of the core, said halves of the secondary winding being connected in series, the secondary winding providing the magnetron with high voltage, and a third winding wound on either one of the two sections of the center leg of the core for providing the cathode of the magnetron with heating power; and switching means connected with said halves of the primary winding to change the direction of the magnetic flux produced by one of said half primary windings in relation to that produced by the other half primary winding while said halves of the primary winding are connected in parallel so that said third winding can be always energized to produce a constant output power irrespective of energization or de-energization of said secondary

4. A power supply for a magnetron oscillator comprising a transformer which has a three-legged magnetic core, a pair of halves of the primary winding, each of the pair being wound on each of the outer legs of the core, a secondary winding wound on the center leg of the core for providing the magnetron with a high voltage, a third winding wound on either one of the outer legs of the core for providing the cathode of the magnetron with a heating power, and a fourth winding wound on the center leg of the core; a first switching means connected with said halves of primary winding so as to be able to change the direction of the magnetic flux produced by one of said half primary windings in relation to that by the other half primary winding while said halves of primary winding are connected in series; and a second switching means connected across the terminals of the fourth winding, said second switching means being so interlocked with said first switching means that when the fluxes due to said half primary windings cancel each other in the center leg of the core, the fourth winding is closed, and when the fluxes due to said half primary windings are

5. A power supply for a magnetron oscillator as defined in claim 4, which is adapted so that at least one normally-open contact of said first switching means is connected in series with a door switch which is opened

6. A power supply for a magnetron oscillator as defined in claim 4, which is adapted so that a door switch which is closed when the door is opened is connected across the fourth winding.