US3714495A - Circuit arrangement including an auxiliary coil for generating a magnetic field periodically varying with time and being adjustable in amplitude - Google Patents

Circuit arrangement including an auxiliary coil for generating a magnetic field periodically varying with time and being adjustable in amplitude Download PDF

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US3714495A
US3714495A US00043369A US3714495DA US3714495A US 3714495 A US3714495 A US 3714495A US 00043369 A US00043369 A US 00043369A US 3714495D A US3714495D A US 3714495DA US 3714495 A US3714495 A US 3714495A
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coil
circuit
current
coupled
auxiliary coil
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US00043369A
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A Boekhorst
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/16—Picture reproducers using cathode ray tubes
    • H04N9/28—Arrangements for convergence or focusing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
    • H04N3/22—Circuits for controlling dimensions, shape or centering of picture on screen
    • H04N3/23—Distortion correction, e.g. for pincushion distortion correction, S-correction
    • H04N3/233—Distortion correction, e.g. for pincushion distortion correction, S-correction using active elements

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  • a circuit for clamping a magnetic field, such as a [2]] Appl. No.1 43,369 television convergence field has a main coil with AC. current applied to it for generating part of the field.
  • An auxiliar coil is wound on the same core and has 30 F A l I P I D I Y orelgn pp on y a a applied to it a DC current that has a value equal to June 7, Netherlands the average of the urrent Therefore an ex.
  • the invention relates to a circuit arrangement including a coil for generating a magnetic field periodically varying with time and being adjustable in amplitude, which coil is wound on a core of magnetic material through which an alternating current flows.
  • the dynamic convergence may be adjusted by means of potentiometers which are provided at the input of the said amplifiers so that the amplitudes of the parabola currents of line and field frequency and of the sawtooth currents can be adjusted. This is effected after the convergence has been adjusted statically, that is to say, in the center of the displayed picture, by means of permanent magnets. The levels at which the input voltage of each amplifier is clamped are adjustable. After controlling the dynamic convergence the static convergence may be recontrolled if necessary if a shift as a result of the dynamic convergence has taken place.
  • the alternating current and the direct current component thereof flowing through this coil may therefore be fairly low.
  • the arrangement according to the said United Kingdom patent specification has the following drawbacks. Firstly, the amplifiers and the relevant convergence coils must be DC-coupled, which is not always. possible or desirable. Secondly, the amplifiers for the convergence of line frequency must be able to supply a great power.
  • the first-mentioned drawback may of course be aliminated by displacing the clampingcircuit to the output of the amplifiers. In such a case, however, the said great power must no longer be dissipated by the amplifiers but by the clamping circuits.
  • the invention is based on the recognition of the fact that the desired clamping action is effected in a different manner and to this end the arrangement according to the invention is characterized in that in order to set an extreme value of the field at a fixed level the current flowing through the coil is provided by two amplifiers substantially adjusted in class B, an auxiliary coil being arranged in series with either of the two amplifiers, a smoothing capacitor being provided so that exclusively a direct current flows through said auxiliary coil, which current is the mean value of the current flowing through the lastmentioned amplifier, the auxiliary coil being wound on the same core and in the same winding sense as the first-mentioned coil and having a higher inductance than the first-mentioned coil, and the ratio of the turns on the two coils being determined by the level at which" the extreme value of the field must be set and by the form as a function of time of the field.
  • circuit arrangement according to the invention need not be limited to its use for convergence purposes. In fact, such an arrangement may advantageously be used in all those cases wherein a magnetic field is a periodical function of time and an extreme value ofwhich must be set at a given level.
  • FIG. 1 shows an arrangement according to the invention
  • FIG. 2a shows a current waveform which occurs in the arrangement according to FIG. 1 and which is the integral of the waveform shown in FIG. 2b,
  • FIG. 3 shows an electromagnet which is present in the arrangement according to FIG. 1
  • FIG. 4 shows the shape of induction fields generated therein
  • FIG. shows a current wave which is the combination of that according to FIG. 2a and a sawtooth wave
  • FIG. 6, 7 and 8 show arrangements which are suitable with the current wave according to FIG. 5.
  • terminal 1 is, for example, a terminal of the capacitor for the so-called S-correction on which a parabola voltage is produced, while terminal 2 may be a point on a winding on the line output transformer.
  • Terminals 1 and 2 are connected by means of a capacitor 3 of low capacitance and resistor 4, capacitor 3 being shunted by the series arrangement of a resistor 5 of fixed value and an adjustable resistor 6.
  • the junction of elements 3, 4 and 6 is connected to earth through a potentiometer 7 and a resistor 8.
  • the wiper on potentiometer 7 is connected to the wiper on a further potentiometer 9 whose ends are connected to earth through two resistors 10 and 10' of equal value.
  • the junction of potentiometer 9 and resistor 10 is connected to the bases of two transistors 11 and 12. These transistors, which are of opposite polarity, constitute a complementary pair, the bases and emitters being interconnected together.
  • Transistor 12, which is of the pnp-type, is shown at the bottom of the Figure. Its collector is connected to a negative supply line V while transistor 11, which is of the npn-type, is.connected through a coil 13 to a positive supply line +V Coil 13 is shunted by means of a resistor 14.
  • the collector of transistor 11 is decoupled for line frequency voltages by means of a capacitor 15 which may be optionally connected to earth or to either of the lines +V,, and V Elements l3, l4 and 15 may alternatively be incorporated in the collector line of transistor 12.
  • the common point of the emitters of transistors 11 and 12 drives via a capacitor 16 a current through the coil 17 for the horizontal dynamic convergence, the other end of which coil is connected to earth.
  • the series network of a capacitor 18 and a resistor 19 is arranged in parallel with coil 17.
  • Coils 13 and 17 are wound on the same core of magnetic material and serve for the convergence of the electron beam which must impinge upon red phosphor dots provided on the screen of the picture display tube.
  • the junction of potentiometer 9 and resistor 10' is connected to the bases of two transistors 11 and 12 and corresponding elements 13' and 19' inclusive are connected which serve for the green convergence.
  • the parabola voltage on terminal 1 is differentiated by the network comprising capacitor 3 and resistors 4, 7 and 8, so that a sawtooth voltage increasing with time is produced on the junction of these elements.
  • This voltage is added to the pulsatory voltage originating from the terminal 2 and part of the voltage obtained in this manner drives amplifiers 11, 12 and 11' and 12'.
  • variable resistor 6 The amplitude of the pulsatory voltage which is applied to both amplifiers can be adjusted by means of variable resistor 6.
  • Variable resistor 6 therefore ensures the adjustment of the amplitude of the sawtooth convergence current.
  • By displacing the wiper on potentiometer 7 the amplitude of the combined control voltage is adjusted. If the wiper on potentiometer 9 is displaced, the combined current which flows through one convergence coil is increased while the current flowing through the other coil is decreased by the same value.
  • the amplitudes of the convergence currents for red and for green may therefore be varied by means of potentiometer 7 in the same direction and by means of potentiometer 9 in the opposite direction so that the convergence can be controlled satisfactorily in a simple manner.
  • FIG. 2a shows the waveform as a function of time of the current i which flows through one of the convergence coils, for example, coil 17, it being assumed that there is no sawtooth component. Since the current i flowing through the coil cannot include a direct current component, the current waveform shown in FIG. 2a is situated around the zero line in such a manner that the mean value of the current is zero, the positive part being provided by transistor 11 and the negative part being provided by transistor 12.
  • Current i of FIG. 2a is, as a function of time, the integral of the sawtooth function of FIG. 2b, the interval 2, t H being a full line period.
  • I The peak-to-peak value of the current flowing during the scan period and corresponding to a given position of the control members described is referred to as I.
  • the peak value above the value indicated by I follows from the ratio of the flyback period relative to the line period of the waveform shown in FIG. 2b and may hereinafter be left out of consideration. It is then possible to calculate the mean value I, of current i as a function of I. In fact, the mathematical expressions of the two parabola parts of FIG. 2a can be derived with the aid of the sawtooth function of FIG. 2b. The origin of the time axis is chosen at the instant when current i has reached its negative maximum. The result of the calculation is that the mean value of the overall current i is equal to [/2 if percent of the overall line period has been chosen for the flyback period.
  • the negative maximum occurs in the middle of the line scan period, that is to say, at an instant when only the static convergence should be active. In other words, this maximum should be at zero. If in addition, the peak-to-peak value I of the parabola current flowing during the scan period varies, the negative maximum I/2 likewise varies, which means that the convergence varies in the middle of all horizontal lines when the convergence is adjusted on either side of these lines. It is therefore desirable to adjust the said negative maximum at a fixed level in some manner or other, which was also the purpose in the United Kingdom patent specification referred to. In addition this level must be zero in order that the field generated by current i in the convergence coil is zero in the middle of the horizontal lines, the convergence being adjusted statically so that the static and dynamic convergence are independent of each other.
  • the peak-to-peak amplitude I is, for example, 300 mA.
  • This value is determined by the inductance of coil 17 which in turn is determined by the admissible voltage which the transistors can stand and by the value of the supply voltages.
  • a clamping circuit provided behind capacitor 16 should therefore be able to provide [/2 150 mA.
  • the said transistors must be able to provide this amount of 150 mA.
  • the power taken from the supply must amount to 0.15 X 40 6 W for the direct current component alone.
  • the object of the step according to the invention is to reduce this considerable and useless loss ofpower.
  • FIG. 3 diagrammatically shows an electromagnet by means of which the red convergence is established.
  • Coils 13 and 17 are wound on a U-shaped core of magnetic material, coil 13 having more turns than coil 17.
  • the coil 20 for the vertical convergence is wound on the same core, which core is, however, associated with a circuit arrangement other than the relevant one.
  • windings l3 and 17 are wound in such a sense that an increase of the induction field which is generated by the current flowing in one winding corresponds to an increase of the field which is generated by the current flowing in the other winding. Since an induction field is proportional to the current which flows through the relevant coil, the field generated by coil 17 is the combination of a sawtooth and a parabola field, while the field generated by coil 13 is a direct current field.
  • the induction field generated by this coil assumes the shape which is shown by curve B in FIG. 4 and wherein field B, becomes negative and reaches a maximum negative value around the middle of one line scan period.
  • the direct current which flows through coil 13 is equal to the mean value of the pulsatory current flowing through transistor 11, that is to say, every time between the instants t and t t and t, etc. in FIG. 2a.
  • This mean value is of course equal to the mean value of the current which flows through transistor 12 between the instants t, and etc. in FIG. 2a.
  • This mean value t can be calculated by means of the simple waveform referred to in this case. It is found that the ratio i li between the absolute value-of the maximum current i,,,,,,, and direct current i as a function of the flyback ratio is the following:
  • coil 13 produces an induction field B2 which is positive due to the abo ve mentioned winding serge of both coils and which is equal to the absolute value of th rfiafiti Ii um ofTrfiiliiiori d'ieId BT TITresultant induction field which is produced in the electromagnet is shown by B3 in FIG. 4.
  • Direct current field B compensates to the negative maximum value of alternating current field B, so that the extreme value of field B is zero.
  • the amplitude of the parabola current is adjusted to a higher value, so that the induction field B becomes larger, the negative maximum thereof increases as well.
  • the direct current flowing through the transistors 11 and 12 increases proportionally thereto and the extreme value of the then resultant induction field remains zero.
  • the desired clamping action is therefore effected and is independent of the amplitude of the convergence current, but is only dependent on the waveform and on the clamping level, in this case zero.
  • this resistor is not critical so that it may have a fixed value. This is only possible because the resistance of coil 13 is not negligibly low, but is in the order of I Ohms. Thus a distribution of the direct current flowing through transistors 11 and 12 occurs between coil 13 and damping resistor 14 so that the number of turns on coil 13 must be more than the number calculated above.
  • the clamping action described is draws only a small amount of power and this may be explained as follows. If the peak-to-peak amplitude of the convergence current is 300 mA, the negative maximum value thereof is 150 mA if this current is purely parabolic. If the direct current flowing through transistors 11 and 12 is, for example, 3 times smaller than the negative maximum value of the current flowing through coil 17, that is to say if this direct current has an intensity of approximately 50 mA, then the power taken from the supply is only 0.05 X 40 2 W due to the direct current component. This is a considerable economy relative to the previously found Figure of 6 W and hence transistors may be used for transistors 11 and 12 which are suitable for lower powers, which may be considered to be an advantage of the arrangement according to the present invention.
  • the series network of capacitor 18 and the resistor 19 of relatively low value, which is arranged in parallel with coil 17, has for its object to add a pulsatory voltage to the parabola current flowing though transistors 11 and 12, which causes a further reduction of the dissipation in the transistors.
  • a similar result may alternatively be achieved with the aid of series arrangements of a coil and a capacitor.
  • the voltages on terminals 1 and 2 are proportional to the deflection current flowing through the line deflection coils.
  • This current is not constant for each line, but varies as a result of, for example, the correction of the so-called East-West pin cushion distortion.
  • this line deflection current is alternatively possible for this line deflection current to vary as a result of variations in the mains voltage.
  • a known step of stabilizing the width of the displayed picture in this case is done by causing the EHT generated in the line deflection circuit and required for the final anode of the picture display tube to vary by the same percentage as the mains voltage and to cause the deflection current to vary by half the percentage. It is evident that the variation in the convergence current must be proportional to that of the deflection current if the convergence is to be satisfactory in any area on the screen of the picture display tube.
  • FIG. 1 functions as desired when the current flowing through coils 17 is purely parabolic or when at least the sawtooth component is small. However, if this component is rendered comparatively large with the aid of resistor 6, the ratio of the inductance of coils 13 and 17 no longer corresponds to the new mean value i of the current which now flows through transistors 11 and 12.
  • FIG. 5 shows the broken line curve representing the sum of a parabola waveform and a sawtooth waveform increasing with time, the parabola component being the same as that in FIG. 2a.
  • FIG. 6a shows in a simplified form an arrangement for the convergence of one electron gun by which the effect described is compensated.
  • Positive and negative pulses are applied to the ends of a linear potentiometer 6' which pulses originate, for example, from a winding 21 of the line output transformer and thus a pulsatory voltage is derived from the wiper thereof, which voltage is variable in both amplitude and polarity.
  • This voltage is added across resistor 10 to a sawtooth voltage originating from potentiometer 7 and the voltage thus obtained is applied to the bases of transistors 11 and 12.
  • Both ends ofa linear potentiometer 22 are connected to a positive auxiliary supply voltage which is higher than +V while the wiper thereof is connected through a resistor 23 to the collector of transistor 11.
  • both potentiometers 6' and 22 are coupled mechanically. If both wipers are positioned at one end of the respective potentiometers, the sawtooth current component flowing through coil 17 becomes maximum, while the direct current originating from the auxiliary supply voltage and flowing through the parallel arrangement of coil 13 and resistor 14 is then at a maximum, namely in the direction opposite to that of the collector current of transistor 11. This direct current is at a minimum when both wipers are positioned in the middle, that is to say, when there does not flow any sawtooth current component.
  • FIG. 6b shows a modification wherein only one potentiometer 6' is used. In this case winding 21 has a central tapping which is connected to the auxiliary supply voltage.
  • Coil 24 is'wound on the same core as coils 13 and 17 and a direct current flows therethrough which is substantially proportional to the magnitude of the sawtooth current component through coil 17 by means of either two mechanically coupled linear potentiometers (FIG. 7a) or a single potentiometer (FIG. 7b).
  • the winding sense of coil 24 in both cases is such that the induction field generated thereby is reduced relative to that of coil 13.
  • the end of coil 24 not connected to earth is decoupled for the line frequency in the Example of FIG. 7b by means of a capacitor.
  • coil 24 may be driven by a separation transistor.
  • the coil for the vertical convergence may be used both for coil 24 and for coil 13.
  • a transistor ensuring the alternating current amplification for the vertical convergence may be used.
  • FIG. 8 shows a further embodiment.
  • the damping resistor 14 varies as a function of the magnitude of the sawtooth current component through coil 17.
  • resistor 14 is formed as the series arrangement of a resistor 14 of fixed value and a linear potentiometer 14" whose wiper is mechanically coupled to that of potentiometer 6' and both ends of which are connected to resister 14', while a resistor is incorporated in series with coil 13.
  • both wipers are positioned in the middle, a sawtooth current component does not flow through coil 17 while the direct current through coil 13 is at a maximum, As soon as the sawtooth current component does flow through coil 17, the direct current through coil 13 is reduced to substantially the same extent, which is desirable.
  • R and R are referred to as the values of resistors 14' and of the total resistance of potentiometer 17", respectively, if x is the value of the resistor situated between the wiper thereof and its lower end in FIG. 8 and if R is the resistance of the series arrangement of coil 13 and resistor 25, the current i flowing through coil 13 then is:
  • i is the collector current of transistor 11.
  • Resistance x is proportional to the angle of rotation of potentiometers 14" and 6'.
  • the current flowing through coil 13 is therefore a function of angle 4: with a maximum for d) maxl2 wherein 4), is the maximum of 4), that is to say, for the angle at which no pulsatory control voltage is applied to transistors 11 and 12.
  • Resistor 14, potentiometer 14" and resistor 25 a voltages so that the current through coil 13 varies little.
  • the resistance of the series arrangement of resistor 14' and 14" of FIG. 8 is of the same order as that of the resistive part of the impedance of coil 13, a
  • thermistor having a negative temperature coefficient may be chosen for resistor 25 in the embodiment according to FIG. 8, so that said variation may be compensated to a sufficient extent.
  • NTC negative temperature coefficient
  • transistors are used as amplifier elements.
  • the principle of the invention is not affected if different known amplifier elements are used such as, for example, electron valves or field effect transistors.
  • the field-of application of the circuit arrangement according to the invention need not be limited to convergence circuits but may be used in all cases where an extreme value of periodically varying magnetic field must be adjusted at a certain level.
  • a circuit comprising a magnetic core; a main coil wound on said core; means for providing an alternating current to said coil comprising a pair of linear amplifiers coupled thereto, whereby said coilgenerates a time varying magnetic field; and means for clamping an extreme value of said field to a selected level comprising a first auxiliary coil wound on said core in the same sense as said main coil and being coupled in series with one of said amplifiers, and a capacitor coupled in parallel with said auxiliary coil, whereby only direct current flows there through, the value of said direct current being the mean value of said alternating current, said auxiliary coil having a higher inductance than said main coil, the turns ratio therebet-ween being a function of said level and the waveform of said time varying field.
  • auxiliary coil comprises an internal resistance and said main coil field varies in accordance with a parabola function and further comprising a damping resistor coupled in parallel with said auxiliary coil, whereby a reduction in the current therethrough is caused, and 2.5n S r 5 3n, wherein r equals said ratio, and n equals the amount of said reduction.
  • a circuit as claimed in claim 4 further comprising a pair of mechanically coupled linear potentiometer means for adjusting the amplitudes of said parabola and compensating currents respectively.
  • a circuit as claimed in claim 6 further comprising a pair of linear mechanically coupled potentiometer means for adjusting the amplitudes of the currents in said second auxiliary coil and said sawtooth current.
  • auxiliary coil comprises an internal resistance
  • said main coil field varies in accordance with the sum of a sawtooth and parabola function
  • thermistor coupled in series with said auxiliary coil
  • series circuit including a fixed and a variable resistor, said series circuit being coupled in parallel with said auxiliary coil and thermistor
  • potentiometer means mechanically coupled to said variable resistor for adjusting the amplitude of said sawtooth function current.
  • a circuit as claimed in claim 1 further comprising a series circuit including a low value resistor and a capacitor, said series circuit being parallel coupled to said main coil.
  • a circuit as claimed in claim 1 further comprising a series circuit including a coil and a capacitor, said series circuit being parallel coupled to said main coil.
  • a circuit as claimed in claim 1 wherein said main coil comprises a radial convergence coil of a color cathode ray tube for converging one of the electron beams therein.

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  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US00043369A 1969-06-07 1970-06-04 Circuit arrangement including an auxiliary coil for generating a magnetic field periodically varying with time and being adjustable in amplitude Expired - Lifetime US3714495A (en)

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Application Number Priority Date Filing Date Title
NL6908715A NL6908715A (de) 1969-06-07 1969-06-07
NL7003282A NL7003282A (de) 1969-06-07 1970-03-07

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US (1) US3714495A (de)
AT (1) AT303846B (de)
AU (1) AU1589170A (de)
BE (1) BE751588A (de)
DE (1) DE2027895A1 (de)
ES (1) ES380450A1 (de)
FR (1) FR2045906A1 (de)
GB (1) GB1311184A (de)
NL (2) NL6908715A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6657840B2 (en) * 2000-09-21 2003-12-02 Benq Corporation Protecting circuit of horizontal transistor
US6686688B2 (en) * 1999-12-22 2004-02-03 Kabushiki Kaisha Toshiba Color cathode-ray tube apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4849652A (en) * 1986-12-01 1989-07-18 U.S. Philips Corporation Circuit for producing a periodic, essentially parabolic signal

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3258642A (en) * 1963-08-05 1966-06-28 Electron beam convergence apparatus
US3382400A (en) * 1965-02-26 1968-05-07 Sylvania Electric Prod Convergence circuit
US3586902A (en) * 1968-07-30 1971-06-22 Fernseh Gmbh Vertical deflection arrangement in a color television system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3258642A (en) * 1963-08-05 1966-06-28 Electron beam convergence apparatus
US3382400A (en) * 1965-02-26 1968-05-07 Sylvania Electric Prod Convergence circuit
US3586902A (en) * 1968-07-30 1971-06-22 Fernseh Gmbh Vertical deflection arrangement in a color television system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6686688B2 (en) * 1999-12-22 2004-02-03 Kabushiki Kaisha Toshiba Color cathode-ray tube apparatus
US6657840B2 (en) * 2000-09-21 2003-12-02 Benq Corporation Protecting circuit of horizontal transistor

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BE751588A (fr) 1970-12-07
DE2027895A1 (de) 1970-12-23
AU1589170A (en) 1971-12-09
FR2045906A1 (de) 1971-03-05
NL6908715A (de) 1970-12-09
AT303846B (de) 1972-12-11
GB1311184A (en) 1973-03-21
NL7003282A (de) 1971-09-09
ES380450A1 (es) 1973-04-01

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