MIVAR (RADIO VAR) TELEVISORE 20" T49-B CHASSIS TV1454/1 + TV1413/1 + TV1416/2 INTERNAL VIEW.

MIVAR (RADIO VAR)  TELEVISORE 20" T49-B  CHASSIS  TV1454/1 +  TV1413/1 +  TV1416/2  Circuit arrangement for generating a sawtooth deflection current through a line deflection coil:

1. Circuit arrangement for generating a sawtooth deflection current flowing through a line deflection coil in an image display apparatus, which circuit arrangement comprises a deflection network including trace and retrace capacitor means coupling to said coil, and a first diode coupled to said retrace capacitor through which the deflection current flows during part of the trace interval, means for conveying the deflection current during the remainder of the trace interval including a second diode and a controllable switch coupled to said diode, said switch and second diode together being coupled in parallel with the first diode, the circuit arrangement further comprising an inductive element coupled to the switch, a third diode coupled to the deflection network and to said inductive element, a transformer having a core of a magnetic material and a winding, and a capacitor coupled to said winding and to the deflection network, characterized in that the inductive element is coupled via the third diode to the series combination of the above-mentioned series capacitor and part of the transformer winding less than all of said winding.

2. Circuit arrangement as claimed in claim 1, in which the inductive element comprises a winding, characterized in that the winding of the inductive element is wound on the transformer core.

3. Circuit arrangement as claimed in claim 1, characterized in that a first capacitor is coupled in parallel with the said part of the transformer winding and a second capacitor is coupled in parallel with the remainder of the winding, the ratio between the reactances of the said capacitors being equal to the ratio between the number of turns of the said parts of the winding.

4. Circuit arrangement as claimed in claim 1 in which the inductive element has a primary winding and a secondary winding which are coupled with one another, characterized in that the ratio of the number of turns of the secondary winding to that of the primary winding is substantially equal to ##EQU19## where m is the ratio of the turns number of the part of the transformer winding between the connection to the third diode and the series capacitor to the turns number of the entire winding, α is the ratio of the amplitude of the retrace voltage to the trace voltage, and δ_max is the value of that ratio of the conduction time of the switch to the line period which is associated with the maximum value of a voltage supply source which supplies energy to the circuit arrangement.

5. A circuit arrangement as claimed in claim 1 wherein said core has two limbs, a tapped transformer winding and at least one high-voltage winding wound on one limb, a primary winding and a secondary winding wound on the other limb, the ratio of the number of turns of the secondary winding to that of the primary winding being greater than the ratio of the number of turns of the part of the transformer winding between the tapping and an end adapted to be connected to a series capacitor to the number of turns of the entire winding and being less than 1.

Description:

The invention relates to a circuit arrangement for generating a sawtooth deflection current through a line deflection coil in an image display apparatus, which circuit arrangement comprises a deflection network including the deflection coil, a trace capacitor and a retrace capacitor and a first diode through which the deflection current flows during part of the trace interval whilst during the remainder of the trace interval this current flows through a second diode and a controllable switch, which switch and which second diode are connected in parallel with the first diode, the circuit arrangement further comprising an inductive element which is connected to the switch and is coupled to the deflection network via a third diode, and a transformer which has a core of a magnetic material and a winding of which is coupled, in series with a capacitor, to the deflection network.
Such a circuit arrangement is described in "IEEE Transactions on Broadcast and Television Receivers," August 1972, volume BTR-18, Nr. 3, pages 177 to 182, and is a combination of a line deflection circuit and a switched-mode supply voltage stabilizing circuit, the controllable switch being used to perform both the said functions. This known circuit arrangement has the advantage that it can be fed with an unstabilised supply voltage and is capable of supplying a satisfactorily stabilized deflection current, a stabilized high voltage and, if desired, auxiliary voltages, the stabilization being obtained by control of the conduction time of the swtich.
When such a circuit arrangement is to be designed, amongst other problems the three following ones arise. Firstly care must be taken to ensure that the maximum voltage set up across the switch (a transistor) during the retrace interval does not exceed the permissible limit value for this element. Secondly the variation of the conduction time of the transistor must be capable of accommodating the supply voltage variations to be expected. Thirdly the (stabilized) trace capacitor voltage applied to the deflection coil during the trace interval must be selectable at will, for with a given deflection coil this voltage determines the intensity of the deflection current produced.
The said problems are not independent of one another. If, for example, the trace voltage is low, the maximum collector voltage of the transistor also is low; it may be further reduced by making the conduction time of the transistor as short as possible. It will therefore be clear that several degrees of freedom are required. One degree of freedom is available to a certain extent, namely the transformation ratio between two windings of the inductive element, one winding being connected between a terminal of the supply voltage source and the junction point of the collector and the second diode, whilst the other winding, which is coupled to the first one, is connected to the third diode, for the choice of the said ratio enables a freer choice of the trace voltage. However, the two other problems, specifically that of maximum collector voltage, are not solved thereby.
It is an object of the present invention to provide a circuit arrangement having one more degree of freedom, permitting the maximum permissible collector voltage to be freely determined, and for this purpose the circuit arrangement according to the invention is characterized in that the inductive element is connected via the third diode to the series combination of the abovementioned series capacitor and part of the transformer winding.
The introduction of a new parameter not only enables the maximum collector voltage to be reduced without the trace voltage being affected but also proves to enable a larger range of supply voltage variations to be accommodated. Hence, the step according to the invention permits of designing a circuit arrangement in which conflicting requirements can simultaneously be satisfied.
In a possible embodiment in which the inductive element has a winding the circuit arrangement is characterized in that the winding of the inductive element is wound on the transformer core.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which
FIG. 1 is a circuit diagram showing schematically the basic elements of an embodiment of the circuit arrangement according to the invention,
FIG. 2 shows waveforms of voltages produced in said embodiment,
FIGS. 3a and 3b show graphs which may be used in the selection of the parameters, and
FIG. 4 is a circuit diagram of a modified part of the circuit arrangement of FIG. 1.
The circuit arrangement shown in FIG. 1 includes a driver stage Dr to which signals from a line oscillator, not shown, are applied and which delivers switching pulses to the base of a switching transistor Tr. One end of a primary winding L ₁ of a transformer T ₁ is connected to the collector of the transistor Tr, which is of the n-p-n type, the other end of the winding L ₁ being connected to the positive terminal of a direct-voltage source B to the negative terminal of which the emitter of the transistor Tr is connected. This negative terminal may be connected to the earth of the circuit arrangement.
A trace capacitor C _t is connected in series with a line deflection coil L _y of the image display apparatus, not shown further, of which the circuit arrangement of FIG. 1 forms part, the resulting series combination being shunted by a diode D ₁ having the conductive direction shown and by a retrace capacitor C _r . The capacitor C _r may alternatively be connected in parallel with the coil L _y . The said four elements represent the schematic circuit diagram including the basic elements of the deflection section only. This section may, for example, in known manner be provided with one or more transformers for mutual coupling of the elements, with devices for centering and linearity correction and the like.

A secondary winding L ₂ of the transformer T ₁ is connected to the anode of a diode D ₃ , and the anode of a diode D ₂ is connected to the junction point A of the elements D ₁ , C _r and L _y . The cathode of the diode D ₂ is connected to the collector of the transistor T _r whilst the cathode of the diode D ₃ is connected to a tapping Q on a winding L ₃ of a transformer T ₂ . One end of the winding L ₃ is connected to the point A, the other end being connected to earth via a capacitor C ₁ . The core of the transformer T ₂ carries further windings across which voltages are produced which serve as supply voltages for other components of the image display apparatus. FIG. 1 shows one of said windings, the windings L ₄ , which by means of a rectifier D ₄ produces a positive direct voltage across a smoothing capacitance C ₂ . One of said windings, for example the winding L ₄ , is the high voltage winding, so that the voltage set up across the capacitor C ₂ is the high voltage for the final accelerating anode of the display tube (not shown). The free ends of the windings L ₂ and L ₄ are connected to earth, and the winding senses of the windings shown are indicated in the Figure by polarity dots.

The operation of the circuit arrangement is similar to that described in the abovementioned paper and may be summarized as follows. During a first part of the line trace interval the diode D ₁ is conducting. The voltage across the capacitor C _t is applied to the deflection coil L _y through which a sawtooth deflection current i _y flows. At a given instant the transistor TR becomes conducting. When in about the middle of the trace interval the current i _y reverses direction the diode D ₁ is cut off, so that the current i _y then flows through the diode D ₂ and the transistor Tr. At the end of the trace interval the transistor Tr is cut off. As a result an oscillation, the retrace pulse, is produced across the capacitor C _r whilst the energy derived from the source B and stored in the winding L ₁ causes a current to flow through the diode D ₃ . When the voltage across the capacitor C _r has become zero again, the diode D ₁ becomes conducting: this is the beginning of a new trace interval. The diode D ₃ remains conducting until the transistor Tr is rendered conducting, the energy stored in the winding L ₂ being transferred to the winding L ₁ . Stabilisation is provided, for example, by feeding back the voltage across the capacitor C _t to the driver circuit Dr, in which a comparison stage and a modulator ensure that the conduction time of the transistor Tr is varied so that the said voltage and hence the amplitude of the deflection current remain constant. Compared with the known case in which the cathode of the diode D ₃ is connected to the point A instead of to the tapping Q operation is different, the difference being as follows. In the known case the current passed by the diode D ₃ flows to earth via the diode D ₁ during the first part of the trace interval. In the arrangement shown in FIG. 1, during this same part energy is stored in the series combination L ₃ , C ₁ . The voltage v _A across the capacitor C _r , the voltage v _c at the collector of the transistor T _r and the voltage v ₁ across the winding L ₁ are plotted against time in FIGS. 2 a, 2b and 2c respectively. The symbol T indicates the line period, τ ₁ indicates the retrace interval, τ ₂ that part of the period T in which the transistor Tr is non-conducting, and τ ₃ = δ T indicates the part of the period T in which this transistor is conducting. The number δ is the ratio between the time τ ₃ and the period T.
The voltage v _A consists of the retrace pulse of amplitude V during the time τ ₁ and is zero during the time τ ₂ . At the instant at which the transistor Tr is rendered conducting, i.e. the instant of transition t ₁ between τ ₂ and τ ₃ , the voltage v _C becomes substantially zero. Thus the volage V _B of the source B is set up across the winding L ₁ .
In the circuit arrangement of FIG. 1 two ratios are significant, namely the transformation ratio between the windings L ₁ and L ₂ , i.e. the ratio between the number of turns of the winding L ₁ and that of the winding L ₂ , which is equal to 1 : p, and the ratio of the turns number of the entire winding L ₃ and that of the part of this winding between the tapping Q and the end connected to the capacitor C ₁ , which ratio is 1 : m. First it will be assumed that the points Q and A coincide (m = 1).
During the time τ ₃ the voltage cross the winding L ₂ is equal to -pV _B . During the time τ ₁ the voltage v _c is equal to V/p + V _B . Let V _o be the direct voltage across the capacitor C _t , if the capacitance of this capacitor is large enough, or the direct voltage component of the voltage across this capacitor, if it has a comparatively small capacitance for the purpose of the S correction; in either case it is equal to the mean value of the voltage v _A , for no direct-voltage component can be set up across the coil L _y . The capacitor C ₁ has a large capacitance, so that a direct voltage equal to V _o is set up across it. The following equation applies: ##EQU1##
The mean value of the voltage across the winding L ₃ also is zero, so that the equation applies: ##EQU2## In this formula the integral can be substituted, Yielding V _o T = pV _B . τ ₃ , that is; V _o = pδ. V _B (1)
At given values of the ratios δ and p the diode D ₂ will conduct during the time τ ₁ . Because during this time the diode D ₃ is conducting, the windings L ₁ and L ₂ will be short-circuited by the diodes D ₂ and D ₃ , causing the retrace pulse across the capacitor C _r to be clipped and the deflection current to be distorted. U.S. Pat. Application No. 443,863 filed Feb. 19, 1974 describes steps for avoiding such an effect, for example by including in series with the diode D ₂ a transistor which is cut off during the time τ ₁ . A capacitor C ₃ is connected between the ends of the windings L ₁ and L ₂ or between tappings thereon for the purpose of preventing the occurrence of parasitic oscillations which may be produced by the leakage inductance between the said windings in a manner such that no line-frequency voltage is set up across the capacitor C ₃ . FIG. 1 shows the case where p <1.

The maximum value of the collector voltage v _c of the transistor is equal to ##EQU3## where α is the ratio V/V _o which depends upon the retrace ratio Z = τ1/T. The maximum value of V _c is obtained when V _B has its maximum value V _B max, for which δ has the value δ _min , for from the relationship (1) it follows that δ and V _B are inversely proportional to one another because the voltage V _o is maintained constant.
The voltage V _o can be chosen by choosing the ratio p, so that the deflection current _y is determined for a given deflection coil L _y . However, from the above it follows that the maximum value of the voltage V _c , which is highly critical for the transistor, is not controllable. Moreover, the relationship (1) can be written:
V _o = p δ _min . V _B max = p δ _max . V _B min, where V _B min is the minimum value of V _B for which δ = δ _max , and from which follows: ##EQU4## The ratio δ _min has its minimum value δ ₁ if the instant t ₁ coincides with the middle of the trace interval, and δ _max has its maximum value δ ₂ if the instant t ₁ coincides with the beginning t _o of the trace interval. Hence the above ratio cannot exceed 2, so that the arrangement cannot accommodate larger variations of the voltage V _B .
According to the invention the points A and Q do not coincide. The voltage across the winding L ₃ is equal to v _A - V _o so that the voltage v _Q in the point Q is equal to v _Q = V _o + m(v _A - V _o ) = mv _A + (1 - m) V _o . With the aid of the waveform of the voltage v _A of FIG. 2a the waveform of the voltage v ₁ across the winding L ₁ between the positive terminal of the source B and the collector of the transistor Tr can be plotted (FIG. 2c), allowing for the fact that the diode D ₃ is conducting during the times τ ₁ and τ ₂ .
Thus we have: ##EQU5## during time τ ₃ : v ₁ = - V _B . Writing the condition for the mean value of the voltage v ₁ being zero after some calculations yields. ##EQU6## The maximum value of the collector voltage v _c is ##EQU7## from which follows: ##EQU8## after substitution of the formula (2). It can be shown that this function steadily decreases with decrease of the ratio m. It is plotted in FIG. 3a for z = 0.2, from which follows α ≉ π/2z ≉ 7,8, and with δ _min = δ ₁ = 1/2 (1 - z) = 0.4. The Figure shows that by making m less than 1 a reduction of the maximum collector voltage is obtained and that this result is independent of the ratio p.
From the formula (2) the following relationship can be derived: ##EQU9## ##EQU10## This function also is independent of the ratio p and it increases as m decreases. It is plotted in FIG. 3b for δ _min = δ ₁ = 0.4 and δ _max = δ ₂ = 0.8 (Z = 0.2), so that the entire δ range is used, whilst the Figure shows that a larger range of supply voltage variations can be accommodated, for when m is less than 1 the ratio V _B max /V _B min exceeds 2.
Similarly to the preceding case, the voltage V _o can be determined by the choice of the ratio p. If the means described in the abovementioned U.S. Pat. Application No. 443,863 are to be dispensed with, it is found that an upper limit can be set to p. The diode D ₂ will just be conducting during the time δ ₁ if the lowest value of the voltage V _c which is found in practice, that is ##EQU11## is equal to the voltage V. In the above expression, according to the formula (2), ##EQU12## from which we can derive: ##EQU13##
The above will be explained by means of two numerical examples. If the voltage V _B can vary between 230 volts and 345 volts (with a mains voltage of 220 volts) V _B max /V _B min is less than 2, so this does not provide difficulty. If the transistor Tr is not capable of withstanding a voltage exceeding 1200 volts, it will be seen from FIG. 3a that m = 0.64. From the formula (2) it follows that ##EQU14## with δ _min = δ ₁ and ##EQU15## so that δ _max = 0.56 < δ ₂ . The formula (5) yields: ##EQU16## so that V _o = 0.87 times 161 = 140 volts.

If now the voltage V _B can vary between 115 volts and 345 volts (the mains voltage is 110 volts or 220 volts), then V _B max /V _B min = 3. FIG. 3b shows that m = 0.38, for which FIG. 3a yields V _c max = 2.9 times 345 = 1000 volts. Formula (2) yields: ##EQU17## whilst ##EQU18## so that V _o = 0.54 times 183 volts = 99 volts. Because m cannot be increased, a higher V _o if desired requires p to exceed 0.54, and hence the step according to the abovementiond Patent Application must be used.
Similarly to what is the case in U.S. Pat. Application No. 473,771, filed June 1, 1973, the cores of the transformers T ₁ and T ₂ of FIG. 1 may be one and the same core, that is to say the windings L ₁ , L ₂ and the winding L ₃ may be coupled to one another in spite of the fact that voltages of different waveforms are set up across the said windings. This is possible because the said voltage waveforms are not affected by the coupling, since the voltages V _o and V _B are "hard," that is to say they are externally impressed, and hence are not affected by the coupling. The currents flowing through the windings, however, are affected. In the lastmentioned Patent Application it is shown that the operation of the circuit arrangement is not adversely affected thereby, but on the contrary important advantages are obtained. It should be mentioned that instead of the tapping Q an additional winding may be wound on the same core as the winding L ₃ , which additional winding has a smaller number of turns than the winding L ₃ and is included between the cathode of the diode D ₃ and the junction point of L ₃ and the capacitor C ₁ .

Formula (5) shows that the ratio m should not be excessively small, because in this case the ratio p also is small, with the result that large currents flow on the secondary side of the transformer T ₁ . In addition, large currents then will flow through the leakage inductance of the said transformer, which gives rise to ringing at the instant t ₁ . Furthermore difficulties will arise in designing the abovementioned embodiment using a single transformer. If for these reasons the formula (5) is not complied with, that is to say if p is made greater than the preferred value p _max , the steps according to the abovementioned U.S. Pat. Application No. 443,863 have to be employed. This requires an additional transistor, which is expensive, or an additional diode, which does not prevent the production of a high V _c max, whilst it was the very purpose of using a low m to obtain a low V _c max.
In practice there is a leakage inductance between the two parts of the winding L ₃ . In FIG. 4, which shows only part of the circuit arrangement, this leakage inductance is shown as an inductance L ₅ between the point Q and an imaginary tapping Q' on the winding L ₃ . The inductance L ₅ prevents abrupt current transistions which in conjunction with the stray capacitances may give rise to ringing. This can be avoided by connecting a capacitor C ₄ between points A and Q and a capacitor C ₅ between the point Q and the junction point of the winding L ₃ and the capacitor C ₁ . If the ratio between the reactances of C ₄ and C ₅ is equal to that between the numbers of turns of the upper and lower parts of the winding L ₃ , no alternating voltage is set up across the inductance L ₅ so that no ringing can occur. The parallel connection of the capacitor C _r and of the network C ₄ , C ₅ together with the inductive components of the circuit arrangement results in a resonant frequency the period of which is about equal to twice the time τ ₁ .
Hereinbefore it has been assumed that the capacitance of the capacitor C ₁ is sufficiently large to enable the voltage across it to be regarded as constant (= V _o ). It should be mentioned that this is necessary only if one or more of the auxiliary voltages produced by means of windings of the transformer T ₂ are obtained by means of trace rectification.

MIVAR (RADIO VAR)  TELEVISORE 20" T49-B  CHASSIS  TV1454/1 +  TV1413/1 +  TV1416/2   Self-regulating deflection circuit with resistive diode biasing:
"A New Horizontal Output Deflection Circuit" by Peter L. Wessel,
A self-regulating deflection circuit includes a first inductor and switching transistor coupled across the unregulated voltage supply. A damper diode, retrace capacitor and second inductor are coupled in parallel, and the parallel combination is coupled across the transistor by a first rectifier poled to prevent current from flowing from the first inductor to the second inductor. A second rectifier is coupled between the first and second inductors for transferring energy from the first inductor to the second during the retrace interval. A control circuit coupled to the second inductor and to the base of the switching transistor controls the time during the first half of the trace interval during which the transistor conducts to allow energy to be stored in the first inductor. A storage capacitor is coupled in series with the second rectifier. Charge accumulation on the storage capacitor and resultant blocking of the second rectifier is prevented by a resistor coupled across the storage capacitor.

1. A self-regulating deflection circuit adapted to be energized from a source of unregulated direct voltage, said deflection circuit including
first inductance means;
controllable switch means including a unidirectional main current conducting path and a control electrode, said main current controlling path being serially coupled with said first inductance means across the source of unregulated direct voltage thereby forming a first series path for storing energy in said first inductance means during those intervals in which said main current conducting path is conductive;
first rectifier means;
a parallel combination of elements coupled by said first rectifier means across said main current conducting path, said parallel combination including second inductance means, damper diode means and retrace capacitance means, said first rectifier means being poled for current conduction in the same direction as said main current conducting path;
control means coupled with said second inductance means and with said control electrode for recurrently switching said main current conducting path for promoting current flow in said second inductance means during recurrent trace and retrace intervals and for maintaining the peak value of said current flow at a constant level;
second capacitance means;
second rectifier means coupled by said capacitance means with said parallel combination of elements and to a point on said first series path for transferring energy from said first inductance means to said parallel combination of elements during said retrace intervals;
wherein the improvement comprises
resistance means coupled with said second capacitance means for equalizing charge on said second capacitance means during said trace interval.
2. A circuit according to claim 1 wherein said resistance means is coupled in parallel with said second capacitance means. 3. A circuit according to claims 1 or 2 wherein said capacitance means is serially coupled with said second rectifier means. 4. A circuit according to claim 3 wherein said point on said first series path is a point along said first inductance means. 5. A circuit according to claim 4 wherein said point along said first inductance means is an end of said first inductance means. 6. A circuit according to claims 1 or 2 wherein said second rectifier means is coupled by said capacitance means with said second inductance means in said parallel combination of elements. 7. A circuit according to claims 1 or 2 wherein said second inductance means is a winding of a transformer and said second inductance means is paralleled by a deflection winding.

Description:

BACKGROUND OF THE INVENTION
This invention relates to self-regulating horizontal deflection circuits with diode steering in which one of the diodes is biased.

Horizontal deflection circuits are used in conjunction with television picture tubes in television display devices. Typically, the horizontal deflection circuit includes a magnetic winding associated with the picture tube and a switching circuit by which energy from a dc voltage source is coupled to the winding and its associated reactances. The switching circuit is synchronized with synchronizing signals associated with the information content of the video to be displayed on the picture tube. In order to avoid distorted images on the displayed raster, the size of the horizontal scanning line and the peak deflection or scanning current must be maintained constant over substantial periods of time.
Many conditions can cause the size of the horizontal scanning line to vary. If the direct energizing voltage for the horizontal deflection circuit varies, the scanning energy and hence the width of the horizontal scanning line may vary. It has in the past been customary to regulate the direct voltage applied to the horizontal deflection circuit by the use of a dissipative regulator. Requirements for low power consumption in television receivers is reducing the use of such dissipative regulators in favor of nondissipative types.
Another approach to regulating the scan width involves the use of a self-regulating deflection circuit, such as is described in the article "A New Horizontal Output Deflection Circuit" by Peter L. Wessel, which appeared in the IEEE Transactions on Broadcast and Television Receivers, August, 1972, Vol. BTR-18, No. 3, pages 117-182. The Wessel deflection circuit may be energized from an unregulated direct voltage, and uses a single switching transistor to perform the switching function for the horizontal deflection and for nondissipative switching regulation. In the Wessel circuit, the unregulated direct voltage is applied across the primary winding of a transformer by the switching transistor. The deflection winding, retrace capacitor and damper diode associated with the horizontal deflection are coupled across the collector-emitter path of the switching transistor by a first diode poled for conduction in the same direction as the collector-emitter path. A secondary winding of the transformer is coupled across the deflection winding by a second diode poled to conduct and transfer energy from the primary to the deflection winding during the retrace interval. It is desirable to eliminate the secondary winding, and thereby reduce the total number of windings.
A horizontal deflection circuit in which the secondary winding is eliminated is described in U.S. Pat. No. 3,906,307 issued Sept. 16, 1975 in the name of J. Van Hattum. However, in the Van Hattum arrangement, an additional inductor and capacitor are used. The necessity for the additional inductor negates the advantage of elimination of the secondary winding.

SUMMARY OF THE INVENTION
A self-regulating deflection circuit includes a first inductor and controllable switch serially coupled across a source of unregulated direct voltage to form a first series path for storing energy in the first inductance during the intervals in which the switch is conductive. A first rectifier couples a parallel combination of elements across the switch, the parallel combination including a second inductance, a damper diode and retrace capacitor. The first rectifier is poled for current conduction in the same direction as the switch. A control circuit coupled to the second inductance and with the switch recurrently operates the switch for promoting current flow in the second inductance during recurrent trace and retrace intervals, and maintains the peak value of the current flow at a constant level. A second rectifier is coupled by a second capacitance with the parallel combination of elements and to a point on the first series path for transferring energy from the first inductance to the parallel combination of elements during the retrace intervals. A resistance is coupled to the second capacitance for equalizing charge on the second capacitance during the trace interval.
DESCRIPTION OF THE DRAWING
FIG. 1 illustrates partially in block and partially in schematic form a portion of the deflection circuit of a television display device embodying the invention; and
FIG. 2 illustrates voltage-and current-time waveforms occurring in the arrangement of FIG. 1 during operation.
DESCRIPTION OF THE INVENTION
In FIG. 1, a power supply designated generally as 10 includes a rectifier represented by a diode 16 and a filter capacitor 18 coupled to terminals 12 and 14 adapted to be coupled to the alternating-current power mains. Unregulated direct voltage appearing across capacitor 18 energizes a horizontal deflection circuit designated generally as 20.
Deflection generator 20 includes an inductor 22 connected at one end to capacitor 18 and at the other end to the collector of an NPN switching transistor 24, the emitter of which is connected to ground. The cathode of a diode 26 is connected to the collector of transistor 24, and its anode is connected to the cathode of a damper diode 32, the anode of which is connected to ground. A retrace capacitor 28 is coupled in parallel with diode 32. A deflection winding 34 is serially coupled with an S-shaping capacitor 36, and the serial combination is coupled in parallel with capacitor 28. A primary winding 38a of a transformer 38 is coupled at a terminal 37 with the anode of diode 26. The other end of primary winding 38a is connected at a terminal 39 with one end of a storage capacitor 40, the other end of which is grounded. A high-voltage secondary winding 38b of transformer 38 has one end grounded and the other end connected to an ultor rectifier represented as a diode 44 for producing high voltage for application to the ultor of a kinescope, not shown. Another secondary winding 38c of transformer 38 has a grounded center-tap and the ends connected to rectifier diodes 46 and 48 for producing operating voltages for the low-voltage portions, not shown, of the television device.
A dc blocking capacitor 52 is serially connected with a diode 50, and the serial combination is coupled between the collector of transistor 24 and a point on winding 38a. The cathode of diode 50 is connected to winding 38a, and the anode is coupled to the collector of transistor 24. A resistor 54 has one end connected to capacitor 52 at a circuit point 56, and the other end is coupled to the end of capacitor 52 remote from point 56 so as to form a parallel connection.
A synchronized pulse-width modulator illustrated as a block 60 is coupled to capacitor 40 for sampling the voltage appearing thereacross. Modulator 60 receives horizontal synchronizing pulses illustrated as 64 at an input terminal A. Modulator 60 produces pulses in known manner, the time duration or width of which are controlled in response to the voltage across capacitor 40, and the pulses are applied by way of a conductor B to a driver circuit illustrated as a block 66. Driver 66 replicates or, if desired, shapes the pulses in a known manner and applies them to the base of switching transistor 24 to control its collector-emitter conduction in a switching manner.
The waveforms of FIG. 2 in the intervals T0-T5, T5-T10 and T10-T15 exemplify operation for low, correct, and excessive deflection energy, respectively. The interval T4-T10 is representative and will be used to describe details of the circuit operation.
In operation during the last half of the horizontal scanning or trace intervals preceding time T5, the collector-emitter path of transistor 24 is conductive, and current is increasing in inductor 22 as illustrated by waveform I22 of FIG. 2f in the interval following time T4. The current in inductor 22 flows through the collector-emitter path of transistor 24. During this same interval immediately following the time T4, which is the time of the center of the horizontal trace interval, current is flowing in deflection winding 34 as illustrated by waveform I34 of FIG. 2d, and is increasing under the impetus of the voltage on capacitor 36. The current in winding 34 flows through diode 26 and adds to the collector-emitter current flowing in transistor 24, as illustrated by waveform I24 of FIG. 2h. A current flows through winding 38a under the impetus of the voltage on capacitor 40, which current adds to the deflection current flowing through diode 26 and transistor 24. Winding 38a is in parallel with winding 34 and they may be viewed as being a single inductor through which a single current proportional to the deflection current flows. In the interval between times T4 and T5, diode 50 is reversed-biased by a voltage, poled as shown, on capacitor 52.
The deflection current and the current in inductor 22 continues to increase until a time such as T5 at which a horizontal synchronizing pulse 64 as illustrated in FIG. 2a is applied to modulator 60. Modulator 60 responds by producing a transition of voltage V60 on conductor B as illustrated in FIG. 2b. Voltage V60 causes driver 66 to render the collector-emitter path of transistor 24 nonconductive. This initiates the retrace interval, which extends from time T5 to T7. During the first portion T5-T6 of the retrace interval, winding 34 (together with winding 38a) transfers the energy stored in its magnetic field to capacitor 28 in a resonant manner, causing the voltage at circuit point 37 to rise as illustrated by V37 of FIG. 2c.

The voltage at terminal point 39 remains substantially unchanged during the retrace interval because of the filtering effect of capacitor 40. Consequently, the voltage at a point along winding 38a will rise during the retrace interval in an amount depending upon how remote the point is from circuit point 39. Thus, the voltage at the cathode of diode 50 will depend upon the exact point on winding 38a at which the cathode is connected.
When transistor 24 is rendered nonconductive at time T5, the voltage across inductor 22 rises so as to maintain the current of transistor 24 therefore rises and forces the current through capacitor 52 and forward-biased diode 50 to winding 38a and capacitor 40, resulting in an energy transfer thereto. The voltage across inductor 22 during the retrace interval determines the rate at which energy is transferred during this interval from winding 22 to winding 38a and the remainder of the deflection circuit. The voltage across winding 22 during this interval is the algebraic sum of the voltage which is then on capacitors 18, 40 and 52, the voltage produced by the inductance of winding 38a, and the forward voltage drop of diode 50. During this retrace interval, voltage is coupled from winding 38a to windings 38b and 38c for rectification and energization of the remainder of the television device.
The first half of the retrace interval ends at a time T6 as the current in windings 34 and 38a is reduced to zero and the voltage on retrace capacitor 28 peaks. Voltage V37 represents the voltage across the retrace capacitor. During the second half of the retrace interval, diode 50 continues to conduct a decreasing current as illustrated by I50 of FIG. 2i as energy is transferred to winding 38a and capacitor 40 from winding 22. Also during the second half of the retrace interval, the current in windings 34 and 38a reverses and increases to a peak at a time 27 as illustrated by I34. As the current in winding 34 increases to a peak in the negative direction, the voltage at circuit point 37 decreases towards zero as illustrated by V37 of FIG. 2c. The retrace interval ends at a time T7 as V37 reaches zero and damper diode 32 conducts.
During the first half T7-T9 of the following trace interval, the current in winding 34 decreases as its energy is transferred to capacitor 36. During a first portion T7-T8 of the trace interval, transistor 24 is maintained nonconductive. The remaining energy in winding 22 continues to cause current to flow through capacitor 52 and diode 50. The collector voltage VC24 of transistor 24 during this interval is maintained at a voltage equal to the algebraic sum of the voltage on capacitors 40 and 52, the voltage caused by winding 38a, and the forward junction potential of diode 50, as illustrated in FIG. 2e.
At a time T8, modulator 60 produces a gating pulse V60 which is coupled to transistor 24 to render it conductive. When transistor 24 becomes conductive, its collector goes to ground potential, coupling winding 22 across capacitor 18 to commence the energy storage portion of the deflection cycle. At the same time, the positive end of capacitor 52 is coupled to ground, placing a negative potential as illustrated by V56 of FIG. 2g on the anode of diode 50, which cuts it off. During the remainder of the trace interval, the increasing current in winding 22 flows through the collector-emitter path of transistor 24.
At a time T9, the deflection current in winding 34 reaches zero, and capacitor 36 has reached its maximum potential. Diode 32 becomes nonconductive. The voltage at junction point 37 rises until diode 26 becomes conductive, and current begins to flow through deflection winding 34 under the impetus of the voltage on capacitor 36. This current flows through diode 26 and the collector-emitter path of transistor 24, as illustrated by I24. The currents in windings 22 and 34 continue to increase until the end T10 of the deflection interval, at which time transistor 24 is rendered nonconductive to create a retrace voltage pulse at circuit point 37 and cause energy transfer from winding 22 to winding 38a.
In the interval between times T5 and T10, modulator 60 produces a gating pulse V60 rendering transistor 24 conductive at times during the first half of trace interval. During the interval T5-T8 in which transistor 24 is nonconductive, current in inductor 22 decreases and energy is transferred therefrom into winding 38a and capacitor 40. In the interval T8-T10 in which transistor 24 is conductive, current increases in winding 22 as it stores energy derived from the unregulated direct voltage. Time T8 is selected as that time which results in the peak value of current I22 being equal from one horizontal cycle to the net so as to maintain substantially the same transfer of energy from winding 22 to the deflection components in order to compensate for the losses during the deflection cycle. These losses include dissipative losses and energy transferred to the kinescope ultor.
In the event that the losses during successive deflection cycles exceed the energy transferred from inductor 22, less energy than desired will circulate through deflection system during each cycle, resulting in reduced raster width. The voltage across capacitor 40 will decrease as a result of this decreased energy and modulator 60 will produce a gating waveform V60 at a time T3 occurring earlier during the deflection cycle than corresponding time T8. This reduces the time T0-T3 in which current I22 decreases, and increases the interval T3-T5 in which voltage is applied to inductor 22 in a polarity to increase the current. Consequently, at a time T5 at the end of the deflection interval, the energy stored in the magnetic field of inductor 22, as measured by current I22, will exceed that at time T0. This results in an increased energy transfer which restores the circulating energy and the voltage across capacitor 40.
Similarly, when the loads on winding 38a decrease and the circulating energy increases, the voltage on capacitor 40 will increase, and modulator 60 will gate transistor 24 into conduction at a time T13 which is later relative to the deflection cycle than time T8. This allows a greater time T10-T13 in which current I22 can decrease and reduces the time T13-T15 in which the current can increase, thereby resulting in reduced current in inductor 22 at the end of the deflection cycle and reduced energy available for transfer to the deflection components, thereby restoring the voltage across capacitor 40 and maintaining the raster width. Time T13 at which transistor 24 is rendered conductive cannot be selected later than time T14 of the center of scan, because of the resulting raster distortion.
The point on winding 38a at which the cathode of diode 50 is connected may be selected at the end of winding 38a corresponding to circuit point 39. Substantial regulation results at all points along winding 38a to which the cathode of diode 50 may be connected. However, some changes in the waveforms occur. Current I222 of FIG. 2f represents the current in winding 22 when the cathode of diode 50 is coupled to circuit point 37, and current I250 of FIG. 2i represents the corresponding current in diode 50.

In the absence of resistor 54, the unidirectional current flow through capacitor 52 and diode 50 will tend to raise the voltage across capacitor 52 to a very high value in the polarity shown. If charge is allowed to accumulate on capacitor 52 in this manner, the voltage across capacitor will soon equal the maximum voltage which can occur at the collector of transistor 24, and diode 50 will cease to conduct during the retrace intervals, no energy will be transferred to the deflection components to compensate for the losses during the deflection cycle, and the circuit will cease to operate.
Resistor 54 is provided as a path for preventing accumulation of excess charge across capacitor 52. As the voltage across capacitor 52 increases, the rate at which charge is drained away through resistor 54 also increases. The end of resistor 52 remote from circuit point 56 can be coupled to any point of reference potential, such as B+ or ground, in order to achieve the desired discharge of capacitor 52. Reduced power dissipation results from coupling resistor 54 in parallel with capacitor 52, as illustrated in FIG. 1. With this arrangement, circuit point 56 takes on a negative potential during those portions of the horizontal scanning interval in which transistor 24 is conductive as illustrated by V56.
Other embodiments of the invention will be apparent to those skilled in the art. In particular, the positions of serially coupled diode 50 and capacitor 52 may be interchanged. Impedance-matching considerations may require either the collector of transistor 24 or the serial combination of diode 50 and capacitor 52 to be coupled to a tap on winding 22.

MIVAR (RADIO VAR)  TELEVISORE 20" T49-B  CHASSIS  TV1454/1 +  TV1413/1 +  TV1416/2  POWER SUPPLY COMBINED WITH BU134 BU109S TRANSISTOR HORIZONTAL DEFLECTION CIRCUIT, EXPLANATION AND CONCEPT VIEW.

A combination deflection circuit and switching mode power supply uses only a single switching element. Across certain diodes in this circuit is a stable voltage. A capacitor and a transformer primary are series coupled to each other and together parallel coupled across at least one of the diodes. A rectifier is coupled to the transformer secondary to provide power to other portions of a television set.








1. A line deflection circuit for generating from a direct voltage source a sawtooth current flowing through a deflection coil, said circuit comprising a parallel resonant circuit comprising said coil, a trace capacitor coupled to said coil, and a retrace capacitor coupled to said coil; a first diode coupled to said retrace capacitor, the deflection current flowing during a first part of the trace period through said first diode and during a second part of the trace period through a controllable switch, energy being applied from said direct voltage source during the trace period to a first winding arranged between said direct voltage source and the switch, and being applied through a second diode conducting during the retrace period from a second winding to the parallel resonant circuit which is connected to the switch through a third diode conducting during the second part of the trace period, at least one of the second and third diodes being shunted by the series arrangement of a capacitor and a primary winding of a current supply transformer, and means for rectifying coupled to said transformer for the direct current supply to other stages of the device. 2. A circuit as claimed in claim 1 wherein said switch comprises a transistor. 3. A circuit for generating from a direct voltage source a sawtooth current having trace and retrace periods through a deflection coil, said circuit comprising a trace capacitor, means for coupling said trace capacitor to said coil, a retrace capacitor coupled to said trace capacitor, diode coupled to said retrace capacitor, a first diode means coupled to said retrace capacitor for conveying said current during a first part of said trace period, a first winding having a first end means for coupling to said source and a second end, a controllable switch means coupled to said second end for conveying said current during a second part of said trace period, a second winding, a second diode means coupled between said first diode and said second winding for conducting during said retrace period, a third diode means coupled between said first diode and said switch for conducting during said second part of said trace period, and means for supplying direct current power comprising a transformer having primary and secondary windings, a capacitor series coupled to said primary, said primary and capacitor being parallel coupled to at least one of said second and third diodes, and a rectifier coupled to said secondary. 4. A circuit as claimed in claim 3 wherein said switch comprises a transistor.

Description:

The invention relates to a line deflection circuit for a device comprising a cathode-ray tube particularly a television receiver display tube, for generating a sawtooth current flowing through a deflection coil in which the deflection coil constitutes part of a parallel resonant circuit comprising also a trace capacitor, a retrace capacitor and a first diode, the deflection current flowing during a first part of the trace period through said first diode and during a second part of the trace period through a controllable switch, for example, a transistor, energy being applied from a direct voltage source during the trace period to a first winding arranged between said direct voltage source and the switch, and being applied through a second diode conducting during the retrace period from a second winding to the parallel resonant circuit which is connected to the switch through a third diode conducting during the second part of the trace period.

Such a circuit arrangement is known from "IEEE Transaction on Broadcast and Television Receivers", August 1972, vol. BTR-18, No. 3, pages 177 to 182. The known circuit arrangement is the combination of a transistorized line deflection stage for a television receiver and a stabilised switch mode power supply, whereby one single switching element, the above mentioned transistor is both the switching transistor and the line deflection transistor.

An object of the invention was to further develop this circuit arrangement. It was found that an alternating voltage is present at the above mentioned second and third diode, which voltage is stabilized. The object according to the invention was to utilize this available and unilaterally stabilized rectangular voltage in a particularly advantageous manner.

This object is solved in that in a line deflection circuit of the kind described in the preamble the second and/or third diode is shunted by the series arrangement of a capacitor and a primary winding of a current supply transformer serving via rectifying for the direct current supply to other stages of the device.

An embodiment of the invention is shown in the drawings and will be further described hereinafter.

FIG. 1 shows the circuit improved according to this invention.

FIG. 2 shows different voltage variations as a function of time.

For the description of FIG. 1 the description of the Figures of the previously cited known circuit may be essentially used as a reference. A transformer is denoted by T1, a primary winding is L1; it is connected through a coupling capacitor CK to a secondary winding L2. A direct voltage source is UB. Furthermore a winding L3 is provided on the transformer secondary side which may serve for the high voltage generation UH through the diode Db.

The switching transistor is TR; rectangular pulses with the line frequency and originating from a driver stage (not represented) are applied to this transistor. The entire circuit arrangement thus serves for generating a sawtooth current flowing through a deflection coil L. The deflection coil L is part of a parallel resonant circuit consisting of a retrace capacitor C2, the deflection coil L itself and a trace capacitor C3.

In the operative condition a first diode D2 which is parallel connected to the said resonant circuit conducts during a first part of the trace period and conveys the negative part of the deflection current I ₂ during the period from t1 to t3 (compare FIG. 2d). During this period the switching transistor TR is separated from the deflection circuit consisting of D2, L, C2, C3 by a third diode Dd biassed in the blocking direction.

At the instant t2 which is adjustable via the width of the rectangular pulses (compare FIG. 2f) at the base of TR, TR is rendered conducting. As a result a current can flow through L1 and TR which stores until the switch-off instant t4 the energy required for operating the circuit in L1. This energy is applied to the deflection circuit at the initiation of the retrace period t4 so as to compensate for losses. This energy storage is ended at the instant t1 of the new period.

Meanwhile the zero crossing of the deflection current occurs at instant t3. D2 is blocked. Due to the polarity change of the current I _L the third diode Dd becomes conducting and the deflection current may be taken over by the switching transistor TR. This current is superimposed uninterfered on the part of the collector current originating from the power supply function of TR.

Thus the deflection function of the circuit in addition to the power supply function is ensured. This function may be influenced by shifting the instant t2. The limits of the control range are at t1 and t3. By comparison, for example, of the voltage UA over the diode D2 in the retrace period with a reference voltage a control magnitude for t2 can be derived. A stabilisation of the deflection in case of mains voltage and beam current fluctuations is then possible.

It is often essential to provide further stages in the television display apparatus with a stabilized voltage. Conventionally such supply voltages are obtained by trace rectification on an auxiliary winding of the line transformer. In this circuit this simple possibility is not given due to the connection with the power supply function. As can be seen in FIG. 2a the secondary voltage US consists of a rectangular voltage on which the flyback pulse of the deflection circuit is superimposed. When the trace part of US is rectified no stabilized direct voltage can be obtained due to the duty cycle variations caused by the control since the value of the voltage US between the instants t ₂ and t ₄ depends on that of the voltage UB.

A flyback rectification is feasible in this case. However, due to the small conduction angle an inadmissibly high internal resistance of the obtained supply voltage is to be taken into account.

According to the invention a rectangular voltage present alternatively across the diodes D1 and D2, respectively is used. These voltages do not contain a flyback pulse FIG. 2c shows the voltage variation UN on the secondary side L5 of a transformer T2 introduced for potential separation. A primary winding L ₄ thereof is arranged in series with a capacitor C ₄ and this series arrangement shunts the diode D1. The capacitor C ₄ prevents a dc short circuit of the diode D1 by the winding L ₄ and has a capacitance which is large enough for preventing an influence upon the variation of UN. The voltage across the capacitor C ₄ is thus equal to the dc-component of the voltage across the capacitor C ₃ , which component is stabilised since the voltage UA is. The voltage across the winding L ₄ is equal to the difference between that across the diode D1 and that across the capacitor C ₄ , the first mentioned voltage being equal to U _A -U _S . The voltage UN across the winding LS, which winding has the indicated winding sense, has the variation shown in FIg. 2c and between the instants t _o and t ₂ it is equal to the stabilised dc-component of the voltage present across the capacitor C ₃ . The voltage UN is rectified with the aid of a diode DN and smoothed with the aid of a capacitor CN. The rectified voltage UL is applied to the parts of the apparatus using a low voltage which in this case are represented by a load resistor RL.

DN must have such a polarity that it conveys current during the time t _o -t ₂ . Then the rectified voltage is stabilised to the same extent as the deflection voltage. The conduction angle is large so that the internal impedance of the voltage source is low. The primary side L4 of the transformer T2 is connected to D1 as is shown in FIG. 1. D1 and DN are then conducting simultaneously so that the internal resistance of UN is further reduced. In the same manner the series arrangement of L4 and C4 in parallel with Dd is alternatively possible.

The transformer T2 may be formed with a relatively small core due to the high operating frequency. On account of the switching properties (Dd and D1 alternately conducting) the rectangular voltage cannot become larger than the direct voltage on CK (corresponds to the voltage UB). Overvoltages as a result of for example picture tube flash-overs are thus prevented.