US2613334A - Electrical system - Google Patents

Description

Oct. 7, 1952 c. F. oTls ET Al.

ELECTRICAL SYSTEM Filed Jan. 18, 1952 lNvENToRs CH/IRLS E 07/5 BY Ul/)5mn H. .STH/9K5 MMV.:

ATTOR Patented Oct. 7, 1952 Charles F.

t Philadelphia, Pa., assgnorsto,` Philco Corporai i f tion, Philadelphia, Pa., a corporation o'i RembU A Sylvania.

This invention relatesto electrical systems and more particularly, to improved `electromagnetic systems of the type `commonlyused4 for deilecting the beam of av catlioderaytubeadapted to prof duce a television image. "j j j l In theirusual form;A electromagnetic deflection systems for the beam of a cathode-ray tube comprise a scanning' yokeindutorwhichsurrounds a portion of the tube` infc'ooperative relationship with the cathddeH-ray beam,'a source ofa deflection signal forenergizingthe yoke, and a coupling systemby whichthe source is coupled to the yoke in proneA impedance matching relationship.

The energy source for the electromagnetic denection system` generallyv comprises a multigrid electron discharge tube of thebeam tetrode or pentode type, such-"tubesibeing used because of their large power sensitivity; Tubes of these types are characterized by relatively `high plate resistance values. Whereasin Iits usual form, the scanning yoke `thas" an impedance which isrelatively small., Iri vvorder toachieve a satisfactory` impedance match, the coupling element between source and yokejis 'thusjnecessarily a step-down i coupling element. Thefcoupling element generfally takesjthe formgof atransformer the input and output windings of vvvhiczh are appropriately related as to their numbers of `turns, to produce the desired impedance ratio. `In one form, the

transformer maybe an autotransformer having a single winding `With appropriate taps, to which taps the source vandthe yoke are connected.

Mostefficient energy transfer occurs when the coupling betweenthe sourcejandyoke is unity.`

the scanning cycle, is returned to its initial position. These movements of the beam maybe produced by applying a signal of suitable Waveform to the source, e. g., a sawtooth signal which, at

the end of the Scanning period. cuts off the source for atleast a part of the flyback period and causes a collapse of the magneticfleld in the coupling transformer and the. deflection yoke.- The energy which has been stored in the transformer and nppiieationianuaryis,1952,seria1n0.2s7,i4s `s claims. (ci. 31a-27). t

yoke'duringA theVscan'ning cycle may 'bfdissipated to a greater or lesser extentby means of "a suitably poled damping tube.

energy isrecove'red, foi-example, by -means` ofa so-called boost"circuit`-which converts-'the magnetic field energy into additional Supply` energy for the source. -Sucha boost circuit may take the;l

form of acapacitor coupled in series "with'avrectierwhichusually isf the damper tubeabove referred to.` This series combination is "connected in shunt with thel yoke insofar as'yoke currents are concerned,` and in series vWiththe anode supplyof the source tube insofar as direct-voltages are concerned.

Because of the leakage inductancereferred td' above, the boost circuit -is tunable to recoverall of'v the energy stored in the' deflection system at the end of the deflection cycle'.l y This unrecovered energy hasbeen' found to Produce spuriousoscillations or` ringing currents in ythetransformerV windingsfTh'ese' spuriousoscillations are undesirable from twostandp'oints. `First, they may be radiatedfiom the "circuits in which they ap?- peanf causinglfi interference in the' nearby radio and television equipment. Secondly, 4tlieserlnging currents: are` coupled topthelanode 'of the tube constituting--the source, and vvary tlieanode` potential duringthe Vflybaclr period. In practice, these spurious oscillations may have ysufllcient 4amplitude to cause theanode toassume periodicallyl a. considerablyfnegative potential "with `:respect to,` theY screen grid of Vthe tube,` and mayk even cause the anode; to assume a negative `po-` tential `with respect tothe cathode `of the tube s It hasloeen found thatfwhen thepotental of' the anode of a beam tetrode or pentode undergoes i variations ofthe above type, -the negative 'voltage gradient between thegscreen grid V,and the `anode may -bringgabout furtherspurious oscillations of thetype known as transit-timeoscillations, and

more especially, asBarkhausen-Kurz or Gill-v y Morrell ,v oscillations. l These oscllational whose frequencyisa function o f thegeometry of.' the tube, the tube electrodepotentialsand the external circuitry associated with the tube, may occur over a wide range of frequencies-.fof theorder of4 Such highire.-

fifty tothousands of ina/sec. quency 'currents have associatedwith them elec- 4tromagn'etic,Waves which `are ,readily radiated bythe tube4 and `its associated .circuits to surrounding circuits of the-cathode-ray'tube, e. gl.

te the videdcircuitsof the receiver. Unless spe-,-

cial precautions are taken;y these'radiatio'ns may overload the video-signal systemof `the receiver,` and degrade the image seen upon the screen of Preferably; this Y I In some instances, the

,pendicular to the :direction of scanning, and

points of which lines usually occurnear the start of the scanninglines;l r

1t nasfbeenfproposodto'euminate tnsetansit- `time oscillations by modifying the structure' of the tube serving asy the scanning signal source.` i' Such a procedure, however, considerably increases v the cost of the tube and has been found to be not effective forall circuit arrangements:-

y' 1 ,',Another proposalV has 'been to shieldv `,c iarefully Athe circuits in lwhich the transit-time oscillations are likely to arise. While shielding may' reduce l image degradation by attenuating the radiated. Waves, itis an expensive expedient, particularly y in assembly -lineproluction- Furthermore; since shieldingI does nothing to eliminate the transittime. oscillations themselves, the loss. of energy n repreysen'fl''therebyV reduces the efficiency ofthe v scanningacircuit. o j p v -f w v y l,It hasalso beenvproposed ,to preventthese os- V cillationsbyreducing the screen-'grid yoltag'e of the source Ytube during the ybaclc Vperiod. However,this' ymethod requires A'auxiliary equipment, .thefoperationrof which.` must be carefully syn.- c hroni'zed-in order, that` the screen grid potential is,reducedto-theproper .value attlie proper time. It is'anobject of the inventionto provide an animproved magnetic deflectionA scanningcirrcuitq-ini-Iwhich spurioussignals are reducedv to a tolerable value Aor eliminated.

' `A further i obj ect ofthe inventionislto provide anj improvedmagnetic` deflection scanning circuitf-injuwhich radiationoi .spurious signals is `reduced -.to.a; .tolerable f ,value or eliminated.V

A f specific: -object of :the inventionY is -.to pro-' vide an; -,.improved magnetic fdeflection scanning circuit which is, substantially'ffree from transittime"-cscillatio-ns.jl 1

g A2 still further vobject oftheinventionisto provideuangimproved magnetic deflection scanning circuit characterized by.. siinplicityri'o'f? circuitry and 4lovmicost.VIK A 1 According-to the invention, the .foregoing obr jects arefachieved, invanelectromagnetic deflection systemvof `the above-describedA type; by providinga' low impedance Apath. for the ringing cury rents,' lfrom the-anodeI o'f the 4tube serving as a deflection-'energy source tothe damping orv boost componeiitff-the deilection circuit.` By'means of"theilow` impedance `pathso provided, variations-bf-the 'anode potentialrwhich normally occuatfthefrequency or frequencies ofthernging currents generatedfbe'cause of the 'shockexcitationloffthefleakageinductance in the cou-,p pling transformer, arediminishedgf The anode lhas "a low impedance at theA frequencyof the nother object of the invention' istofprovide ringing currents and lhas la high impedance at the scanning frequency.

The invention will be described in greater detail with reference to the appended ldrawing forming part of the specification, the single' iigure of which is a schematic diagram of a magnetic denection system `embodying ythe invention.

,Referring .tothe drawing,V the ldeflection systern there shown comprises a source tube I0, an

ioy

autotransformer I2,'and ya yoke 32. -Tube I6 comprisesl'fa cathode I4, a control grid I6, a screen grid'IIB and an anode 20. (Although tube l0 is speciicallyV shown as a beam tetrode, it is ap- L'parentithat'the source tube'rnay be a pentode or Vother.,multi-element tube.) The control grid I6 is energized by .a vsuitableA sourceof scanning potentiall (not shown), said source Vproviding a scanning signal of generally sawtooth waveform in accordance with Well-known practice.

Approximate operating potentials are .applied` to the control grid I6 and the screen grid I8 from a sourcel .(notshown).`V f o 'Iheautotransformer I 2 comprises three wind-` ing sections, 22, 24 and 426, connected in series. The anode Ill of vacuum tubevr I0 is connected to the -junction 30 of sections 22 and 24, whereby the windingI sections 24 and 26 together serve as an output coupling impedance for the tube I0,

whereas theyoke 3 2 is connected to the junction 64 of ..sections y24 and 26, whereby the 'yoke is coupled to the winding 2,6.- In accordance with well-known practice, the turns ratio of the winding sections 24 and 26 is so selected that a desired impedance match between the tube I0 and the yoke 32 is eilected.

Winding'section 22 ...is the usual high voltage winding lhaving a terminal 28 which may be con` nectedl't'o la suitablerectiersystem (not shown) for supplyingan accelerating potential for the beam'of the cathode-ray tube.

The anode 20 of tube I0 is supplied from ka suitab1e.D.`C. source. 4(not shown), introduced at Br'terminal V44, and connected through a voltage boost circuit comprising a diode 36 and a boost capacitor 46. Diode 36 has .itscathode 38 connected vto' the junction 34 and its anode 42 connected to'thef'Btjterminal 44. Capacitor 46 inte'rconnects lthe anode 42 of tube 36 and the termin'al '.46 of thewinding 26..

In the normal operation of the scanning circuit,

energy, is storedduring the scanning period of thebeain in the transformer 'l2 and the yoke 32. At the endof the 'scanning period the amplitude of thefrsawtooth'voltage applied to grid I-6 undergoesfa'sudden change, with the result that the anode current of source-tube III isl suddenly cut on. This current'` cut-off causes Vthe magnetic field of 'transformer I2 to collapse. The collaps-- ing magnetic field induces a voltage across the winding sections/'of the transformer, of such polarity as to place terminal 28 lof winding section 22 at a high posi-tive potential with respect to tion of the Winding section 26 and the yoke 32.`

Anjadditional partl of the energy existing in the transformera and the yokeaz at the end of the hasta scanning vperiodis vaccordingly' fsupplliClf-i '61.151

capacitor 46. This energy charges rthecapacitor 46 in a direction such that the yvoltage there-4 across is in additive series relationship to the voltage at,B1+. so that the anode 20 oftubeif;

is thereby energized at a totalvvoltagegequal to the sum of the B-lvoltageand the voltagejacross capacitor46.

Because of the leakage inductance of the transformer winding sections, al1 of the stored energy is not'recovered by thehigh voltage system cou'-u pled to winding section 22, and by"the.boosftlcirfl cuit. The remaining part of theenergy causes ringing currents to be set up in theresonant sys,- 1

tem constituted by the aforementioned leakage y inductance and the distributed capacitance'` as,`

sociatedwith the. transformer windings', which ringing currents flow in winding`24.y It has been found that these ringing currents are normally` of suilicient magnitude to cause the anode 20 of tube l to be periodicallydriven .to a. potential considerably negative with respect to screen grid I8. The ringing currents are of sufficiently long duration so that the'periodic lowering of the` potential of the anode of tube l0 continues until conduction in the tube l0 is again initiated by the sawtooth wave appliedto the control lgrid I6.

generating transit-timeoscillations inthe tube,`

I0 vare fulfilled.

l In accordance with the inventionithese transittime oscillations are substantially.,.suppressed by insuring that the anode 20 does not assume an excessively negative Vpotential with respect to screen grid I 8 during the conduction period of tube lil. This result is accomplished in accordance with the invention by means of an auxiliary path coupled between the winding sections of vthe transformer I2 and the dampingrdiodeSB. This auxiliary path is so constituted that it provides a low impedance to the ringing currents, shunting them to alternating current ground potential through the diodev 36, while" nevertheless providing `a high impedance `path for thescan ning currents in the transforrr'ierj,` As show irgin the drawing, this path` isan electrical network 56 which comprises a capacitor 50 and an inductor 52 connected in series, and which is connected between the junction of the transformer and diode cathode 38. Preferably this path is series resonant at the frequency of the ringing currents so as to provide a desirably low impedance at the ringing frequency, and a desirably high impedance at the scanning frequency. In a typical arrangement, in which the ringing currents in winding section 24 have a frequency of the order of 220 kc./s., the capacitor 50 may have a value of 56 micromicrofarads and the inductor 52 may have a value of 9.5 milliA henries.

In some instances, the inductor 52 may store sufcient energy to produce ringing currents of its own and thereby partially nullify the suppressive action of the path shunting the winding lsection 24. In accordance with afurther feature Iof the invention, these ringing currents in the inductor 52 are attenuated by means of a damping resistor 54, which, as shown, is connected in l shunt with inductor 52, but which, as is well known to those skilled in the art, may be connected in series with capacitor 50 and inductor 52.

` thirty thousand Lohrfns;

Thelvalueof the d ductor `and is fselectedV so/that the `impedance of the network 56, remains suiiiciently flow toV preventthe` ringing currents `induced inthe transvformer:windings fromcontin'uinglfor a time be-V i I0 begins to; `conduct."` Typicalva1ues` for resistor54in a network 56 which embogdiesan inductorjand capacitor ofV the values given `abo fe, rangrejjfrom ten thousandxto tionwith a'"transformer systemhavingga `selfresonant frequency of the order of220-kc-l/s. *as* above specifically described. When ringing cur-f rents of frequency 'other than `that specifically described "are induced, the values Vof Vthe kcapacitor"5ll, inductor-52 and resistor 54 aremodied appropriate1y,"as` will be readilylapparent to those ski1ledin`the1art. The `precedingdiscussion has assumedrthe existence of spurious ringing', currents at only one frequency. In some instances, the transformer I2 mayfexhbit a plurality of such. ringing curn` rents, each occurring at a dferentfrequency, in

which Acase additional-4 sriesereslonant circuits (not shown) conforming to'fthe characteristics of .network 56, mayY be connected between junctions 30 andf34, each suchseries-resonant circuitbeu ing tuned to thefrequency ofgone of thesaid ringing currents.4 A 1, l

While the network .56 has ,been shownf to be connected across the wholegof the-winding "24, `in some instancesit has been :found that satisfactory" suppression ofthe ringingk currents in the wind'- ing section 24' maybe eifectedby connecting the network 56 between thejunction 30, orthe junction 34,and a-tap-on winding section 24 intermejunctions 30 andvv 34, orlbetween a tap on winding section 22 and; a tap on winding diate to the section 24. d i i i l While Werhave-described ourunvention by means Vofspecific examples andin specific embodiments, we do not wishwto-be limited thereto, for obvious modiiicationswill occur to those skilled in theart without departingfrom the spiritandscopeof thei vention. Y F `i 1. A magnetic deection system comprising a pulse signal source operating at a given repetition rate, a transformer comprising a plurality of winding elements connected in series and susceptible toringing currents at a frequency different from said repetition rate, means to couple said winding elements to said source as a load therefor, a deection element coupled to one of `said winding elements, means to damp oscillations in said one winding element, vand means to suppress ringing currents in another of said winding elements, said last-named. means comprising a network shunting a portion of said other winding element, said network having a low impedance at the said frequency of said ring-r ing currents and a high impedance at a frequency corresponding to said repetition rate.

2. A magnetic deflection system as claimed in claim 1, inwhich said means to damp oscillations in said one winding section comprises a unidirectional electrical conductor. and in which said means to suppress ringing currents in another of said winding sections comprisesan electrical network, one terminal of which is connected to ping resistor fdeter mined by the amount of energystored in theinf- Ihe above-noted values Vfor capacitor 5U, in` l diictinji. and resistor 54 are given .in comico-

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