DE2246967B2 - PROCEDURE FOR STARTING A MAGNETRON, IN PARTICULAR FOR MICROWAVE OVEN, AND CIRCUIT FOR CARRYING OUT THE PROCEDURE - Google Patents

Description

2. Circuit for carrying out the method This object is according to the invention according to claim 1, characterized in that solves that automatically about three seconds to five seconds of the connection between the voltage source 20 announce after switching on the primary winding of the (74) and the primary winding (84 ) of the high-voltage high-voltage transformer to the voltage-conditioning transformer (82) automatic timer supply to the primary winding is interrupted for a period of medium (126, 128) to generate the stated 0.1 to 0.4 seconds.
Interruption of the voltage supply to the primary It turns out that the filament of the cathode of the winding of the high-voltage transformer is attached to the magnetron generator after the initial placement. heating during the interruption of the voltage

3. Circuit according to claim 2, characterized in that it remains sufficiently warm so that after re-identifying that the automatic timer use the power supply to the magnetron means one can start immediately with a main on / off switch (80) in the power line and the Schwin series in the connection between the voltages in the desired oscillation state (74) and the primary winding (84) of the set.

High voltage transformer lying time- A magnetron start circuit to carry out

switches (126,128) included. of the above procedure is thereby

characterized that in the connection between the

35 voltage source and the primary winding of the high voltage transformer automatic time switch means for generating said interruption of the

The invention relates to a method for supplying voltage to the primary winding of high-voltage commissioning a magnetron, in particular for voltage transformer are arranged. In particular Microwave ovens, in which of the secondary 40, the automatic time switch means contain one with Winding the primary side to a voltage source a main on / off switch in series in the connection connectable high-voltage transformer between the voltage source and the primary winding Magnetron is supplied with a voltage such that lying time switch.

an automatic change during the start cycle

the voltage supply to the magnetron brought about 45 explained in more detail with reference to the drawing. It

will. The invention also relates to a shows

Circuit for performing such a F i g. 1 is a circuit diagram of a magnetron starter

driving. tur.g,

When switching on magnetron generators via Fig. 2, the current-voltage characteristic of a Ma-

a circuit such as that in US patent 50 gnetron generator,

96 342, the difficulty arises, FIG. 3, the voltage curve over time

that the vibrations of the magnetron are not in which the operation of a magnetron generator

desired oscillation mode, especially the rr.it start circuit,

Use η mode, but in a vibration Fig. 4 is a diagrammatic view of a micro-

Higher order mode, which is characterized by high frequency 55

sequences and high voltages. FIG. 5 shows a view of the operating state shown in FIG. 4, however, leads to a microwave oven in vertical section and FIG
Unstable operation and the high temperatures, F i g. 6 is a side view of one of the magnetron generators used in the illustrated, which occur in the cathode-microwave oven shorten the service life and make an early switch-off necessary. Gnctronstartschallung let a microwave oven 10 in From the German patent 9 73 333 it is described in connection with FIGS. It is known that the desired oscillations of a magnetic generator 12 generated microwave frequencies are brought about by the induction of 2450 MHz, which corresponds to a wavelength of about fcoperation in the space briefly described at the beginning of 65.12.5 cm. For the purposes of the manner carried out by the connec- tion, the description of the magnetron for high voltage trans-

includes lengths of 30 cm to 1 mm. Rectangular conductive walls 14 delimit a heating space 16 with an access opening closed by a door 18 operated by a handle 20 can be.

A switch panel 22 is arranged adjacent to the access opening, behind which the magnetron generator is located and the high voltage source. The switch panel 22 carries a 5-line-time timer

40: 1 to 50: 1 used. A full-wave voltage doubler circuit 88 is connected in series with the secondary winding 86 to generate the strong electrical To generate fields for the cathode 90 of the magnetron 12, the housing 54 at 92 is earthed are required. The cathode is usually a directly heated cathode, for example a thoriated tungsten cathode that has been carbonized. To increase the electron emission temperatures

24 and a timer 26 for a longer i ° reach, an alternating voltage of about Period of, for example, 30 minutes. On the 3.0 volt by means of a few turns of the secondary control panel a switch-on button 28, a switch-off button 30 and a light switch 32 are also arranged.

The Magne'ron generator 12 is generated with the high winding 86 α and applied directly to the filament.

The above in connection with FIG. 6 loading

12 bi f ie

g g

voltage source and with electrical control elements 15 written magnetron generator 12 also has a bd di general dh d Blk 34 Ahl Hhl 94 lh in the area

connected, which are indicated generally by the block 34. The microwave energy is from the Geiierator by an antenna or probe 36 disposed within a dielectric flap 38 is fed to a rectangular HohJleiterabschnitt 40, which is used to generate the energy of the desired Frequency in room 16. The waveguide 40 is at one end through a wall 42 short-circuited and open at the inner end 44. the

A number of cavity resonators 94 arranged around the cathode 90 in the circumferential direction is. The high frequency oscillations are from the generator 12 through a coupling loop 96 with the Antenna or probe coupled.

The full-wave voltage doubler circuit 88 has diodes 98 and 100 and capacitors 102 and 104. In operation, when the end of secondary winding 86 connected to line 106

briefly open. The _D

Energy can be connected through any known per se, is positively polarized, current through the halves, for example by an impeller 46 with a conductor diode 100 to the capacitor 104 on the

Charge input peak voltage of a certain value. The semiconductor diode 98 remains idle di Li

conductive. In the next half-period, the line

Fig.6 shows an example of a Magnelron generator 12. A conductive housing 54, which the anode is formed with a number of on the circumference

Number of blades 48, which are driven by a motor 50, are effectively distributed. That too

The item to be heated or treated is on one

dielectric plate 52 within the space 16 3 <> device 108 positive, so that no current through the diode

stored. 100 can flow. The capacitor 102 is on the

'~' Input peak voltage charged when the

Diode 98 is conductive. The rectified overall

"", _O _ .. _e . output voltage at the anode and cathode of the magnet

arranged cavity resonators as well as with one with 35 trongenerators 12 is the sum of the charges or filamentized central cathode - approximately equal to twice the voltage of each allowed. In the case of the magnetic field generator 56, this capacitor 102 and 104. But it can also Embodiment is permanent magnets, other rectifier circuits are used, wherein the magnetic field through the parts 58 and 60 eg half-way voltage doubler as well is formed. A substantially U-shaped holding 40 voltage tripler or quadruple. Natural rung or a housing 62 surrounds the magnets and is borrowed, since the magnetron generator 12 is an im forms the magnetic circuit. The antenna or probe 36 and the dome-shaped Part 38 protrude from the housing 62. The high voltage leads 64 and 66 are 45 positive.

with the high-voltage circuit through a high- With regard to certain extremely high empty-

frequency-shielded bypass capacitor, current overvoltages that occur when the main switch is closed, which is located within a box-shaped part and which is up to 12 to 15 kV. This component is attached to a plate when the full Netzsoan-70 is put on, which in turn is attached to the housing 62 5o voltage to the line to the primary winding 84 preferably : -l vKt.1.:— ""t> u * u _or , now.hr ,, "r, r. ·; «^,» Rr. loitor ^ stepwise with a suitable resistor 110 connected in series, which is initially switched on. An electromagnetic relay 112 provides for

, να »« u ... -.v ..... w ... ^ w _b -.- the simultaneous closing and opening of this part

High-frequency oscillations generated heat from the circuit of the primary winding at the contacts

is an essentially unidirectional organ, receive rectification for part of each period, when the anode with respect to the cathode

is cooling fins 72 have contact rr.with the conductive Housing 54, so that rapid cooling, for example by means of circulated air, can be achieved can around the inside of the device through the

_conduct

Reference is made to FIG. 1 for a description of the mode of operation. An AC power source 74 in Form of a conventional AC voltage network is through connecting lines 76 and 78 with the High-voltage circuit coupled via a hand-operated on and off switch 80. A Stray reactance transformer 82 is connected with its primary winding 84 to the Nctzleitungcn. the 86 i i d Piäikl i

114 and 116 by means of a contact piece 118. When the contacts open, a resistor is used 110, which has a value of 10 ohms, for example, an additional resistance value during the first Start period level switched on. Various relay actuators 112 can be provided for example an RC circuit with a semiconductor diode resistor and a capacitor or other suitable means to enable the mooring

Secondary winding 86 is completely connected to the primary winding 65 · full line voltages during the initial

• ■ ■ · · ■ ■ ■ · - ··> ...: - λ ι.-: j-., »..R ι:" ι u; " _f " i, alinorinfl (. RW SrhaiMinp gradually

Ductively coupled and usually in the case of step-up transformers, used in such a device has a turns ratio of

borrowed switch-on period of the circuit takes place in stages.

With reference to FIG. 2 look at the processes -

Hch of the start cycle described in the previously known manner. When the main switch 80 is closed, the voltage at the anode and the cathode reaches a point A, which can be, for example, in the range from 7 to 8 kV. The current-voltage characteristic for the magnetron is indicated by line 120 . When the cathode filament is heated, the generator begins to conduct current, the voltage dropping to point B. Line 122 indicates the high order mode of vibration which may have a frequency of about 4420 MHz, which is much higher than the 2450 MHz required for normal operation of the microwave oven. The further operation of the generator in the higher frequency mode with the correspondingly much higher voltages results in an extremely short service life for the cathode and an unstable mode of operation. It is therefore necessary to jump to a desirable operating mode, as indicated for example by line 124 and point C. In one embodiment, it has been determined that if there is a momentary interruption in the start cycle e.g. B. is provided by an automatic delay timer 126, which operates a switch 128 , the voltage on the magnetron generator does not immediately drop to zero and the filament remains hot enough to bring about the conduction state when the full line voltages are reapplied. The momentary interruption in the start cycle has led to a jump to a new operating level if the interruption takes place after a time of about 3 to 5 seconds after the circuit was energized. The duration of the momentary interruption is characteristically on the order of 0.1 to 0.4 seconds before the full mains voltage is reapplied.

In Fig. 3 shows the fog behavior of a magnetron with a starting circuit of the type proposed here. In this representation, the vibrations at the respective voltage values are plotted over time. Initially, the voltage values from point A reach a point indicated by the letter B at which the waveform 132 of a steady state of oscillation is obtained. Continued operation at this high voltage level only leads to overheating of the cathode and a shortened service life of the generator. The instantaneous interruption indicated by peak 130 yields waveform 134 at the new, lower voltage level indicated at point C. The constant oscillations at this voltage level represent the desired operating mode with simultaneous stability and a longer service life. The operating point remains at this point until the high-voltage circuit is removed again by opening the main switch 80, for example at the end of the working period or in the event of a power failure will.

For this purpose 3 sheets of drawings

Claims (1)

O. a certain time program between patent claims: taps of the secondary winding of the high- 1. The procedure for commissioning a Ma voltage transformer is switched over,
gnetrons, in particular for microwave ovens, at It has been shown that when starting up which of the secondary winding of a primary 5 of a magnetron generator in this way the desired oscillation state that can be connected to a voltage source, for example in the high-voltage transformer, the magnetron π-mode does not reach with certainty is, and that a voltage is supplied in such a way that during a considerable circuit effort due to the end of the start cycle an automatic change taps of the secondary winding of the high voltage voltage supply to the magnetron induction transformer and the switching means is performed, characterized, required. that automatically about 3 seconds to 5 seconds. The object is to be achieved by the invention after switching on the primary winding of the high denier, a method that was briefly described at the beginning Voltage transformer to the voltage source type to start up a magnetron in such a way form the voltage supply to the primary winding on a 15 that with simple circuitry with Interrupted for a period of 0.1 to 0.4 seconds, the desired oscillation will. status is reached when switching on.