US3302060A - Control system for regulating the current in a magnetron tube - Google Patents

Control system for regulating the current in a magnetron tube Download PDF

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Publication number
US3302060A
US3302060A US380374A US38037464A US3302060A US 3302060 A US3302060 A US 3302060A US 380374 A US380374 A US 380374A US 38037464 A US38037464 A US 38037464A US 3302060 A US3302060 A US 3302060A
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United States
Prior art keywords
magnetron
control
current
coil
circuit
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Expired - Lifetime
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US380374A
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English (en)
Inventor
Blok Lourens
Johannes Frederik Maria V Dijk
Kots Johan Theo
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/66—Circuits
    • H05B6/666—Safety circuits
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/10—Regulating voltage or current 
    • G05F1/46—Regulating voltage or current  wherein the variable actually regulated by the final control device is DC
    • G05F1/56—Regulating voltage or current  wherein the variable actually regulated by the final control device is DC using semiconductor devices in series with the load as final control devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02—Electrodes; Magnetic control means; Screens
    • H01J23/10—Magnet systems for directing or deflecting the discharge along a desired path, e.g. a spiral path
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/50—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field
    • H01J25/52—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode
    • H01J25/58—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode having a number of resonators; having a composite resonator, e.g. a helix
    • H01J25/587—Multi-cavity magnetrons
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B9/00—Generation of oscillations using transit-time effects
    • H03B9/01—Generation of oscillations using transit-time effects using discharge tubes
    • H03B9/10—Generation of oscillations using transit-time effects using discharge tubes using a magnetron

Definitions

  • the supply circuit of the magnetron generator includes a control-circuit of a control-device.
  • the output circuit of the control-device is connected to a magnet coil of the magnet system of the magnetron.
  • the control-device governs the energizing current through the magnet coil so as to stabilize the magnetron direct current.
  • the supply circuit includes acontrol-switch for switching the magnetron on and 0E.
  • the invention has for an object to provide in such a magnetron generator a simplification of the magnetron structure and a particularly simple control-device wherein the reliability of operation and the lifetime of the magnetron are improved.
  • the magnet system of the magnetron comprises an electromagnet having a magnet coil constructed as a separate control-coil and that of the magnet coil.
  • the control-device further comprises a permanent magnet, the magnetic field of which supports an auxiliary control-circuit which, when the magnetron is switched on by means of the control-switch, supplies an auxiliary energizing current decreasing with time for the magnet coil constructed as a control-coil.
  • FIG. 1 shows a detail diagram of a magnetron generator according to the invention.
  • FIG. 2 shows the construction of a magnetron according to the invention
  • FIG. 3 shows a, time diagram for explaining the operation of the magnetron generator shown in FIG. 1.
  • the magnetron generator shown in FIG. 1 comprises a magnetron 1 of, for example, 2 kw. for producing ultra high-frequency oscillations having .a Wavelength of 12 cms.
  • the anode and the cathode of the magnetron 1 are connected to the output terminals of a rectifier 2, which is in turn connected to the terminals of a source of threephase alternating-voltage.
  • the magnetron generator forms part of .a high-frequency heating furnace (not shown).
  • the supply circuit includes a control-switch 3 for switching the magnetron on and off.
  • the magnetron generator shown comprises a controldevice 4 comprising a control-circuit 5 connected to the direct-current supply circuit of the magnetron 1.
  • the output circuit of the control-device 4 is connected to a field coil 6 of the magnet system of the magnetron 1.
  • the energizing current of the field coil, and hence the magnetic field of the magnetron 1 is governed by the control device 4.
  • the magnet system of the magnetron 1 is formed, as will be explained more fully with reference to FIG. 2, by the magnet coil 6, constructed as a separate control-coil, together with a permanent magnet 7, shown diagrammatically in FIG. 1, the magnetic fields of said members supporting each other.
  • the control-circuit 5 of the control-device 4 is formed by a series resistor 8 included in the DC. supply circuit of the magnetron 1. Coupled to resistor 8 is a smoothing filter for smoothing ripple voltages, comprising a series resistor 9 and a capacitor 10.
  • the capacitor is connected through a comparatively high series resistor 11 to the base electrode of a transistor 12 connected as a comparison device and including a Zener diode 13 in its emitter circuit.
  • the base electrode of the transistor 12 is connected through a base-emitter resistor 14 to the emitter electrode.
  • the supply voltage of the transistor 12 is derived from a full-wave rectifier comprising diodes 16, 17 connected via a transformer 15 to the AC. supply and a smoothing capacitor 18, connected to the output circuit of the rectifier.
  • the emitter circuit of the transistor 12 is traversed by an emitter current, the value of which is proportional to the difference in the voltage across the smoothing capacitor 10 and the Zener voltage.
  • the value of the emitter current is substantially independent of the temperature over a considerable temperature range since the base-emitter voltage of the transistor 12 and the Zener voltage have temperature coefficients of opposite polarities.
  • the emitter current of the transistor 12 is amplified in a two-stage D.C. amplifier comprising transistors 19, 20.
  • the amplified emitter current of the transistor 12 is supplied to the magnet coil 6 included in the collector circuit of the transistor 20.
  • the transistor 19 comprises in its emitter circuit a feedback resistor 21 and the transistors 19, 20 are provided with stabilizing resistors 22, 23, respectively, connected to the base electrodes.
  • the control-device 4 described above provides, Iby stabilisation of the magnetron direct current, an effective reduction of variations occurring in the power supplied by the magnetron 1. If the magnetron direct current increases, the increase in the voltage of the capacitor 10 will produce an increase in the emitter current of the transistor 12. In turn, the energizing current through the magnet coil 6 increases, resulting in an increase in the magnetic field of the magnetron 1, the latter increase counteracting the increase in the magnetron direct current.
  • a decrease in the magnetron direct current causes a decrease in the magnetic field which, in turn, counteracts the decrease of the magnetron direct current.
  • Variations of the power supplied by the magnetron which may amount to many hundreds of watts, are reduced to a few tens of watts.
  • this control provides a reduction of variations of the output power of the magnetron of many hundreds of watts by means of a control-device 4 adapted to provide a power of 30 watts, so that the control-device 4 is particularly simple. Furthermore, it is even possible to equip the control-device with transistors, as is indicated in the embodiment shown, whereas on the other hand the structure of the magnetron 1 is considerably simplified.
  • FIG. 2 shows in detail the structure of the magnetron 1.
  • the magnetron tube is provided in known manner with a control cathode 25, an anode 26 surrounding the cathode, resonant cavities formed by radial partitions 27, and pole pieces 28 for concentrating the magnetic field in the space between the cathode 25 and the anode 26.
  • magnetron cathode is cooled by air by means of cooling vanes 29.
  • the anode of the magnetron is cooled by water.
  • the magnetron tube is surrounded by a magnetic circuit comprising two permanent magnets 30, lying each on one side of the magnetron tube and consisting for example of high-grade magnet steel on the basis of aluminum-cobalt-nickel, if desired with titanium the so-called ticonal or else ceramic permanent magnetic material with a non-cubic crystal structure for example consisting of polyoxides of barium and iron with hexagonal crystal structure (so-called Ferroxdure (magnadur)
  • Ferroxdure magnadur
  • the magnetic field produced by the permanent magnets 30 is guided by means of a soft-iron magnet yoke 31 towards the pole pieces 28 in the magnetron tube.
  • the magnetron comprises a magnet coil 6 constructed as a separate control-coil which is connected to the output circuit of the control-device 4.
  • the magnet circuit further comprises a soft-iron core 32 which is arranged in a radial direction with respect to the magnetron tube and supplies, upon energisation, a magnetic field through the magnetron tube in the same direction as the magnetic field of the two permanent magnets 30.
  • the axial arrangement of the magnet coil 6 with respect to the magnetron 1 ensures that substantially the Whole field of the magnet coil 6 is guided through the magnetron tube, in contrast to a different arrangement of the magnet coil 6. If, for example, the magnet coil 6 were arranged to surround the permanent magnets 30, the field of the magnet coil 6 would extend for the major part as a leakage field beyond the magnetron tube owing to the low permeability of the permanent magnetic material (,u abou-t 4).
  • a simple and rugged structure of the magnetron 1 is achieved wherein a magnet coil 6 of small size and a comparatively small number of turns may suffice.
  • a very high control-sensitivity is obtained so that variations of the output power of the magnetron 1 of many hundreds of watts may be reduced to acceptable limits by means of a control-device of 30 watts.
  • the device so far described provided excellent results, but from elaborate experiments it was found that the lifetime of the magnetron 1 did not come I up to the expectations, which had to be ascribed to a transient peak current occurring across the magnetron 1 when switched on and producing an overload thereof.
  • the magnetic field of the magnetron is supplied only by the permanent magnets 30.
  • the permanent magnet-s supply only a fraction of the required magnetic field so that initially the magnetron direct current has a maximum value until, after a time lag determined by the time constant of the control-device 4, the magnetic field of the magnetron 1 is brought to its normal value by the energisation of the magnet coil 6.
  • the time constant of the control-device 4 in the embodiment shown is mainly determined by the time constant of the smoothing filter 9, 16 and the value of the magnet coil 6.
  • the magnetron direct current has the variation indicated by curve a.
  • the magnetron direct current has a maximum value (for example three times its normal value).
  • the control-device 4 becomes operative after a time lag determined by the time constant of the control-device, at which time the magnetron direct cu rent is brought to its normal value I Whilst the advantages obtained are maintained, said difiiculty is obviated in accordance with the invention iia simple manner by providing the control-device 4 (of FIG. 1) with an auxiliary control-circuit 33, which supplies, when the magnetron 1 is switched on, an auxiliary energizing current decreasing with delay for the magnet coil 6 constructed as a control-coil.
  • the auxiliary control-circuit 33 is formed by a capacitor 35 connected through a switching contact 34 to the output circuit of the rectifier 16, 17 and connected by means of a series resistor 36 through a second pair of input terminals 37, 38 to the input circuit of the transistor amplifier 19.
  • Contact 34 is coupled :to the switch 3 so that when the control-switch 3 is open, the switching contact 34 is closed and the capacitor 35 is charged to the full supply voltage of the rectifier 16, 17.
  • an auxiliary control-current passes to the base electrode of the transistor 19, said current producing, subsequent to amplification in the transistors 19, 20, a maximum energizing current through the magnet coil 6. Then the magnetic field of the magnetron 1 composed of the magnetic field of the permanent magnet 7 and the magnetic field of the magnet coil 6- has a maximum value.
  • the magnetic field of the magnetron will decrease gradually from a maximum value, so that the magnetron direct current will gradually increase until by the operation of the control-device 4 the magnetron direct current is stabilised on its desired value via the control-circuit 5.
  • the control exercised by the auxiliary circuit 33 is taken over by the control-circuit 5 and the auxiliary control-circuit 33 no longer affects the control-process.
  • the time constant of the auxiliary control-circuit which is determined by the time constant of capacitor 35 and resistor 36, is a factor 7 times greater than that of the overall control-device.
  • the time diagram of FIG. 3 illustrates the magnetron direct current at the closure of the control-switch 3.
  • the magnetron direct current follows the path indicated by the curve b.
  • the magnetron direct current gradually rises from a minimum value at the switchingn instant T to the desired value. Peak currents through the magnetron 1, which would shorten the useful life of the magnetron 1, as stated above, do not appear in the device according to the invention. Instead, when the magnetron is switched on direct current will gradually rise to the desired value, which results in a prolongation of the lifetime of the magnetron 1 in intermittent operation.
  • the switching contact 34 might be constructed so that, when the control-switch 3 is actuated, the switching contact 34 is closed prior to the switching-on instant, thereby charging the capacitor 35, whereas at the switching-on instant the switching contact 34 is opened like in the device shown. All of these embodiments have the feature that when the magnetron generator 1 is switched on, an auxiliary energizing current which decreases with time lag passes through the magnet coil 6.
  • a control system for regulating the current in a magnetron tube comprising, means for establishing a magnetic field in said tube comprising a permanent magnet and an electromagnet having a field coil, voltage supply means for energizing said tube and said field coil, first control means for varying the current in said field coil as a function of the magnetron tube current, said first control means having a given time constant which determines its response time, switching means for apply- 69 ing the energy of said voltage'supply means to said magnetron tube, and second control means responsive 6 to the closure of said switching means for supplying to said field coil a gradually decreasing current.
  • said second control means has a time constant which is greater than the time constant of said first control means so that upon energization of said tube the rate of buildup of the current supplied to said field coil by said first control means is greater than the rate of decrease of the current supplied to said field coil by said second control means.
  • said switching means further comprises a switch contact arranged to open upon the application of said supply energy to said magnetron tube by said switching means, and wherein said second control means comprises a capacitor, a source of direct voltage, a charge path including said switch contact interconnecting said direct voltage source and said capacitor, and a discharge path for said capacitor which includes resistance means.
  • said first control means comprises a resistor connected in series with the magnetron tube, a low pass filter across said resistor, a transistor having a base electrode and an emitter electrode, a Zener diode connected in series with said emitter, a second resistor connected in series between the output of said filter and said base electrode, a transistor direct current amplifier having an input circuit and an output circuit and means for coupling said output circuit to said field coil to supply current thereto, means for coupling said emitter electrode to said input circuit so that the transistor emitter current is supplied to said direct current amplifier for controlling the current supplied to said field coil, and means for coupling the output of said second control means to the input circuit of said direct current amplifier.
  • said second control means includes an energy storage element which has a time constant greater than said given time constant whereby the current supplied to said field coil by said second control means decreases in an exponential manner.
  • HERMAN KARL SAALBACH Primary Examiner.
  • P. L. GENSLER Assistant Examiner.
  • the control-device furthercomprises a permanent magnet, the magnetic field of which supports an auxiliary control-circuit which, when the magnetron is switched on by means of the control-switch, supplies an auxiliary energizing current decreasing with time. for the magnet coil constructed as a control-coil.” and insert instead net coil constructed as a separate control-coil and a permanent magnet, the magnetic field of which supports that of the magnet coil.
  • the controldevice further comprises an auxiliary control-circuit which, when the magnetron is switched on by means of the controlswitch, supplies an auxiliary energizing current decreasing with time for, the magnet coil constructed as a control-coil. column 5, line 40, for "central” read control Signed and sealed this 17th day of, October 1967.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
  • Microwave Tubes (AREA)
US380374A 1963-07-17 1964-07-06 Control system for regulating the current in a magnetron tube Expired - Lifetime US3302060A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL63295449A NL142560B (nl) 1963-07-17 1963-07-17 Magnetrongenerator voor hoogfrequentverhitting.

Publications (1)

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US3302060A true US3302060A (en) 1967-01-31

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US380374A Expired - Lifetime US3302060A (en) 1963-07-17 1964-07-06 Control system for regulating the current in a magnetron tube

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US (1) US3302060A (enrdf_load_stackoverflow)
AT (1) AT247912B (enrdf_load_stackoverflow)
BE (1) BE650596A (enrdf_load_stackoverflow)
CH (1) CH433462A (enrdf_load_stackoverflow)
DE (1) DE1491382B2 (enrdf_load_stackoverflow)
DK (1) DK116948B (enrdf_load_stackoverflow)
ES (1) ES302122A1 (enrdf_load_stackoverflow)
GB (1) GB1066646A (enrdf_load_stackoverflow)
NL (2) NL142560B (enrdf_load_stackoverflow)
SE (1) SE332239B (enrdf_load_stackoverflow)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3392308A (en) * 1965-05-25 1968-07-09 Varian Associates Crossed field tube having a pair of permanent magnets of different magn etomotive force
US3514566A (en) * 1968-08-26 1970-05-26 Raytheon Co Adjustable voltage transformer for microwave oven apparatus
US3523170A (en) * 1967-10-27 1970-08-04 Technology Instr Corp Of Calif Control system for microwave heater apparatus
US3535483A (en) * 1967-02-10 1970-10-20 Krupp Gmbh Microwave heating apparatus
US3614505A (en) * 1969-07-10 1971-10-19 Tokyo Shibaura Electric Co Packaged magnetron
US3723806A (en) * 1971-04-07 1973-03-27 Int Standard Electric Corp Adjustable stable power supply for continuous wave magnetron
US4100463A (en) * 1975-11-05 1978-07-11 Hitachi, Ltd. Magnetron, power supply, and fan integral assembly
US4223195A (en) * 1978-08-04 1980-09-16 Robertshaw Controls Company Pulse transformer
US4395659A (en) * 1980-03-10 1983-07-26 Toshiba Electric Equipment Corporation Power supply device
US4504767A (en) * 1982-09-07 1985-03-12 Litton Systems, Inc. Magnetron mode detector
US20050184063A1 (en) * 2004-02-20 2005-08-25 Samsung Electronics Co.,Ltd. Microwave oven

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2296764A (en) * 1939-05-27 1942-09-22 Rca Corp Magnetic flux regulator
US2450629A (en) * 1944-03-14 1948-10-05 Gen Electric Ultra high frequency magnetron generator
US2523684A (en) * 1946-07-13 1950-09-26 Rca Corp Stabilized oscillator system
US2648772A (en) * 1949-02-15 1953-08-11 Raytheon Mfg Co Magnetron control circuits
GB717001A (en) * 1951-04-14 1954-10-20 Csf Improvements in or relating to magnetrons
US2979671A (en) * 1959-02-27 1961-04-11 Raytheon Co Magnetron current control systems

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2296764A (en) * 1939-05-27 1942-09-22 Rca Corp Magnetic flux regulator
US2450629A (en) * 1944-03-14 1948-10-05 Gen Electric Ultra high frequency magnetron generator
US2523684A (en) * 1946-07-13 1950-09-26 Rca Corp Stabilized oscillator system
US2648772A (en) * 1949-02-15 1953-08-11 Raytheon Mfg Co Magnetron control circuits
GB717001A (en) * 1951-04-14 1954-10-20 Csf Improvements in or relating to magnetrons
US2979671A (en) * 1959-02-27 1961-04-11 Raytheon Co Magnetron current control systems

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3392308A (en) * 1965-05-25 1968-07-09 Varian Associates Crossed field tube having a pair of permanent magnets of different magn etomotive force
US3535483A (en) * 1967-02-10 1970-10-20 Krupp Gmbh Microwave heating apparatus
US3523170A (en) * 1967-10-27 1970-08-04 Technology Instr Corp Of Calif Control system for microwave heater apparatus
US3514566A (en) * 1968-08-26 1970-05-26 Raytheon Co Adjustable voltage transformer for microwave oven apparatus
US3614505A (en) * 1969-07-10 1971-10-19 Tokyo Shibaura Electric Co Packaged magnetron
US3723806A (en) * 1971-04-07 1973-03-27 Int Standard Electric Corp Adjustable stable power supply for continuous wave magnetron
US4100463A (en) * 1975-11-05 1978-07-11 Hitachi, Ltd. Magnetron, power supply, and fan integral assembly
US4223195A (en) * 1978-08-04 1980-09-16 Robertshaw Controls Company Pulse transformer
US4395659A (en) * 1980-03-10 1983-07-26 Toshiba Electric Equipment Corporation Power supply device
US4504767A (en) * 1982-09-07 1985-03-12 Litton Systems, Inc. Magnetron mode detector
US20050184063A1 (en) * 2004-02-20 2005-08-25 Samsung Electronics Co.,Ltd. Microwave oven
US7026589B2 (en) * 2004-02-20 2006-04-11 Samsung Electronics Co., Ltd. Microwave oven

Also Published As

Publication number Publication date
DK116948B (da) 1970-03-02
SE332239B (enrdf_load_stackoverflow) 1971-02-01
NL295449A (enrdf_load_stackoverflow)
DE1491382B2 (de) 1972-05-18
DE1491382A1 (de) 1969-04-10
GB1066646A (en) 1967-04-26
BE650596A (enrdf_load_stackoverflow) 1965-01-15
ES302122A1 (es) 1965-01-16
AT247912B (de) 1966-07-11
NL142560B (nl) 1974-06-17
CH433462A (de) 1967-04-15

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