FR2471102A1 - HORIZONTAL DEVIATION CIRCUIT CONTROLLED BY THE RETURN OF THE SPOT - Google Patents

Abstract

HORIZONTAL DEVIATION CIRCUIT CONTROLLED BY THE RETURN OF SPOT. THIS CIRCUIT 10, 14 INCLUDES IN ITS OUTPUT STAGE A RESONANT FIELD-EFFECT TRANSISTOR CIRCUIT 50 WHOSE HIGH-IMPEDANCE INPUT ELIMINATES THE NEED TO USE A PILOT TRANSFORMER SUCH AS THE HORIZONTAL PILOT STAGE CAN BE COUPLED DIRECTLY OUTPUT FLOOR AUDIT. ALSO, THE BILATERAL CONDUCTION CHARACTERISTICS OF THE COLLECTOR-SOURCE CHANNEL OF THE FIELD EFFECT TRANSISTOR ELIMINATES THE NEED TO USE A CONVENTIONAL MITIGATION DIODE. APPLICATION TO IMAGE DISPLAY DEVICES, SUCH AS CONTROL VIDEOS AND TELEVISION RECEIVERS.

Description

2471.02

  The invention relates to a circuit arrangement for producing a sawtooth current through a line deflection coil.

  in an image display apparatus such as a video receiver

  control or a television receiver.

  In a conventional image display apparatus, comprising a

  cathode ray tube, the horizontal deflection of the electron beam

  trons is produced by producing a periodic recurring sawtooth current in an inductive magnetic deflection coil. Ordinarily, such a deflection signal is produced using a horizontal output stage comprising an output transistor (which functions as an electronic switch), whose emitter-collector path is connected

  in series to the deflection coil and to a DC voltage source.

  The transistor is alternately controlled by a control stage controlled in turn by an oscillator, between its conducting state (or in circuit) and its non-conducting state (or off-circuit) in order to connect and disconnect in turn the DC power source and the deflection coil between them. Each time interval o the transistor of

  output is in circuit occupies approximately the second half of an in-

  horizontal sweep, and each time interval out of cir-

  bake coincides with about the first half of a scan interval plus a return interval of the spot. Due to the inductive nature

  of the deflection coil, the application of a fixed potential to this booster

  during the conductivity period of the output transistor or, if preferred, of the electronic switch, has the effect of producing a linear increase in the flow of current through the coil,

  in a sense. When the electronic switch is turned off or

  circuit, the current flowing in the coil stops growing and this is the beginning of a return interval. An attenuation diode, connected in parallel with this switch, passes the current of the coil

  during the first half of each line scan interval.

  During this period of time, a linear decreasing current flows

  in the reel but in the opposite direction.

  When the electronic switch is turned off at the end of a

  sweep interval to interrupt the rising current flowing through

  the coil, the magnetic field stored in the deflection coil is dis-

  and generates a relatively high amplitude spot return, or a spot return voltage pulse across the coil. This

ú4711,02

  -2 - return voltage is sometimes used to generate high voltage

  required for an anode of the cathode ray tube.

  According to the present invention, there is provided a resonant horizontal deflection circuit which comprises a field-effect transistor, which will be hereafter designated, for convenience, by the acronym TEF, in order to eliminate the use of a driver transformer or exciter, and thereby connect the horizontal excitation stage directly to the horizontal output stage. In addition, the bilateral conduction characteristics of the TEF channel - intensity source are exploited to eliminate the diode

  normally present in resonant circuits of

horizontal viation.

  The current flows through the deflection coil and the PET in one direction during the second half of each scan interval,

  while the remaining energy at the end of the return in said coil pro-

  current in the latter but in the opposite direction during the first half of each scan interval. At the end of each scan interval, the coil circulates a cosine current

  in a spot return capacitor.

  Therefore, it is an object of the present invention to provide a circuit for generating a sawtooth current through

  a horizontal deflection coil in an image display apparatus.

  Another object of the present invention is to provide a circuit

  fired to generate a sawtooth current through a coil of

  horizontal deflection in an image display device whose cir-

  fired output includes a field effect transistor (TEF).

  Furthermore, the present invention aims to provide a circuit

  fired to generate a sawtooth current through a coil of

  horizontal deflection in an image display device which does not

  does not stop the use of an attenuation diode.

  Finally, it is an object of the invention to provide a circuit for producing a sawtooth current through a horizontal deflection coil in an image display apparatus which does not require the use of a

  excitation transformer or driver.

  These different features of the present invention, as well as the benefits derived therefrom, will emerge clearly in the course of

  the following description, made with reference to the attached drawing, on

which:

{4 7 11 2

  FIGURE 1 is a horizontal deflection circuit diagram according to the prior art, which will serve to better demonstrate the advantages of the present invention;

  FIGURE 2 is a circuit diagram in accordance with the present invention.

  FIG. 3 represents different waveforms of signals used to explain the operation of the circuits shown on FIG.

Figures 1 and 2.

  Although specialists in this field are familiar with the

  In order to better understand the invention, it will be useful to first refer to FIG. 1, which shows a typical example of such a circuit known in the prior art.

  In the system shown in FIG. 1, the synoptic block 10 desires

  a horizontal oscillator for an image display device, for producing an alternating signal (more precisely a rectangular shaped signal) having a frequency equal to that of the horizontal analysis frequency of the display device; images. Preferably, oscillator 10 is of the non-servo type, and is subject to control

  automatically to ensure the maintenance of a synchronism pre-

  frequency and in phase between the synchronization pulses of the signal to be displayed and the scanning signal generated by this system, it is possible to produce a rectangular wave output of this oscillator 10 by any one of the many known arrangements of such circuits . The output signal of the oscillator 10 is applied to the input terminals of a driver stage or amplifier stage. An output terminal of the oscillator 10 is connected to ground, while the other is connected to the base of an NPN transistor 14. The emitter of this transistor 14 is set

  to ground and its collector is connected via the winding

  19 of a transformer 20 to the positive terminal 21 of a source

  this of DC working potential. The positive potential source 21 is connected to ground through a decoupling capacitor 22. The output of the stage p i 1 o t e is applied to the input of a horizontal output stage. One terminal of the secondary winding 23 of the transformer 20 is grounded, while the other is connected -4 -

  at the base of another NPN transistor 28 whose emitter is grounded.

  The collector of this transistor 28 is connected to a terminal of a magnetic deflection coil 33. The other terminal of this coil 33 is connected to the positive terminal 35 of a direct current source. Thanks to that

  provision, a serial circuit is realized which includes the source of potential

  positive electrode 35, the deflection coil 33 and the emitter-collector conductive path of the output transistor 28. The positive terminal 35

  is connected to the ground via a decoupling capacitor 36.

  An attenuation diode 38, shunted by the spot return capacitor 39, is connected between the upper terminal of the coil 33 and the ground. In other words, the cathode terminal of the diode 38 is connected directly to the upper terminal of the coil while the anode of the

  Attenuation diode is grounded.

  The primary winding 41 of a horizontal output transformer

  Tale 42 is connected in parallel with the coil 33. The high voltage secondary 43 is connected at its lower end to ground, and

  its upper end can be used to control a food

high voltage.

  To describe the operation of the scanning and high voltage generating system shown in Figure 1, reference should also be made to the voltage and current waveforms shown in Figure 3, which are present at different points in the circuit. Figure 1. There are eight waveforms in Figure 3, designated respectively by the letters A to H. The points of the circuit of Figure 1 o manifest themselves as

  voltages are designated by corresponding letters.

  The horizontal oscillator 10 produces at its output terminals a signal having the waveform A whose frequency is equal to the frequency

  horizontal scanning of the device or image display apparatus.

  This signal is applied between the base and the emitter of the transistor 14 to switch it alternately between its conductive state and its non-conductive state. More particularly, in response to each positive pulse component of waveform A, the base of transistor 14 is biased in the positive direction and brought to saturation. Current flows

  - therefore between the positive potential source 21 through the winding

  primary 19 and the collector-emitter path of the transistor 14 to achieve mass. Each negative pulse component of waveform A polarizes in reverse or negative direction the base-emitter junction

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  -5 - transistor 14, which makes the latter non-conductive and interrupts

  the flow of current between the collector and the emitter of this transistor.

  During the intervals where the transistor 14 is cut or not

  driver, his collector is at a positive potential in relation to

  to ground, while during the intervals when this transistor is con-

  driver his collector is effectively coupled to the transmitter, which

binds the collector to the ground.

  As a result, the waveform of the voltage produced at the collector is that represented by the waveform B of FIG. 3. This signal is then phase-shifted by 1800 with respect to the waveform A. The signal of Rectangular shape voltage of B waveform

  is transformed and transferred by the transformer 20 to the base of the tran-

  output sistor 28. The windings 19 and 23 of the transformer are formed in such a way that no phase inversion occurs between the primary and the secondary. In this way, the waveform of the voltage signal produced at the upper terminal of the secondary winding 23 is in phase with the signal obtained at the upper terminal of the primary winding 19. The signal applied to the base of the transistor 28 will appear in the form of waveform C of FIG. 3. For convenience in the drawing, the relative amplitudes of signals having A, B waveforms are not shown in FIG. and C. Each positive waveform pulse C is applied to the base-emitter junction of the transistor 28 and its magnitude is sufficient to bias this junction in the positive direction and turn the transistor 28 into its conducting state. The current is thus generated in the output circuit of transistor 28 and follows the path that goes from the source of

  positive potential 35 to ground through the coil 33 and the winding

  41, in parallel, then by the collector-emitter path of the transistor 28. Due to the inductive nature of the coil 33 and the primary 41, the amplitude of the current at the collector of this transistor 28 increases linearly, at from zero, as shown in waveform D in Figure 3. The current increases linearly, from

  zero, from the moment the transistor 28 is made conductive by the

  Positive voltage pulse of waveform C. Attenuation diode 38 can be neglected while transistor 28 is turned on because it is cut off by potential source 35 which makes its cathode positive with respect to its anode . The transistor 28 remains conductive and its current

24711 02

  of collector continues to increase linearly until the moment

  the waveform C goes from the positive state to the negative state. At this moment

  the base of the transistor 28 becomes negative with respect to the transmitter to the extent necessary to reverse the polarization of the base-emitter junction and cut the transistor 28, which terminates the flow

collector current.

  At the moment when the transistor 28 ceases to be conducting, the

  linearly increasing energy that flows through the coil and coil

  41 in the collector-emitter direction of transistor 28 ceases abruptly

  is lying. As soon as the increase of the current in the coil and the primary winding stops, the magnetic fields which form in the coil 33 and in the transformer 42 during the interval o occurs the increase of the current disappear. This dissipation of the magnetic fields induces a relatively high amplitude pulse of spot return in the coil 33 and in the primary 41. As indicated

  at the upper terminals of the coil and the primary winding by

  ground impulse, the spot return pulses are positive with respect to

  port to this ground, as indicated by the waveform E of FIG. 3. The waveform spot return voltage pulses E are amplified by the transformer 42 in order to produce higher potential pulses in the secondary winding 43. These potential pulses

  higher, for example, can be applied to a high-voltage rectifier.

  voltage to produce anode voltage for the image display device. At the end of each line scan interval, the magnetic fields being dissipated in the coil 33 and the primary winding 41 also produce a cosine-conduction current flowing in the spot return capacitor 39. This is represented by the shape current waveform F of Figure 3 during the first half of each spot return interval, designated by the t -t marks. During the second half of each spot return interval, namely during the period designated by the marks t2-t3, the current leaves the spot return capacitor 39 and enters the coil 33 and the primary winding 41. At time t3, the energy stored in the coil and the primary winding produces a linear decay current, which lasts about half of the line scan interval,

  this current coming out of the coil and the primary winding for

4,471 1 02

-7-

  pour the diode 38, as indicated by the waveform G of Figure 3.

  As shown in waveform D in Figure 3, the current

  flows from the positive potential source 35 through the bobbin

  33 and the primary winding 41 in a first direction during the second half of each scan interval, while the energy remaining at the end of the spot return in the coil and the primary winding

  ensures the flow of current through this coil 33 and rolls it

  primary education 41 but in the opposite direction during the first

  of the scan interval, as indicated by waveform G in Figure 3. During the scan interval, the current flowing in the coil is a combination of the currents flowing through transistor 28 and the diode d. attenuation 38, and during the return of the spot

  the coil current is cosine-fused since it is the same

  than the one flowing through the spot return condenser 39.

  Referring now to Figure 2, where it is shown

  a deflection circuit controlled by the return of the spot, produced according to

  In accordance with the principles of the present invention, it is seen that the elements

  similar are designated by identical reference numbers.

  If we examine in detail the circuit of Figure 2, we see that

  the synoptic block 10 also designates a conventional horizontal oscillator

  that, for example, that described above. The output signal of this

  Oscillator 10 is applied to the input terminals of a conventional driver stage.

  or an amplifier stage, an output terminal of this oscillator 10 is connected to the source 56 of negative potential, while the other output terminal is connected to the base of the NPN transistor 14 whose emitter is

  also connected to the source 56 of negative potential.

  The output of the driver stage is connected directly to the input of the horizontal output stage because the collector electrode of the

  transistor 14 is connected to the gate electrode of the FET transistor 50.

  The source electrode of the FET transistor 50 is connected to the source of po-

  negative current 56 and its collecting electrode is connected to a terminal of the primary winding 41 of the transformer 42. The upper terminal of the primary winding 41 is connected to a suitable source of positive potential 54. A plate of the capacitor 39 back of spot is also connected to the collector electrode of the field effect transistor TEF 50 as well as to the lower terminal of the primary winding 41. The collector of this TEF transistor 50 is also connected to a terminal of the magnetic deflection coil 33. The other terminal of this coil 33 is connected to a plate of the capacitor 52 of scanning whose other plate is

  connected to the source of negative potential 56.

  Thus, it can be seen that the present invention makes it possible to

  both the excitation transformer and the attenuation diode

  of the prior art. More specifically, the transformer 20 and the

  diode 38 have been eliminated from the conventional circuit layout represented -

Figure 1.

  Transformer Impedance Transformation Capability 20

  becomes useless because of the notoriously high impedance of

  field effect sistors, such as transistor TEF 50. The output of the

  The pilot unit can therefore be connected directly to the input of the horizontal output stage. Attenuation diode 38 and the transistor

  28, which together produce the two-way switching effect for

  the sawtooth coil current, are no longer necessary.

  res. The use of an attenuation diode is avoided because the collector-source channel of a TEF transistor is bilateral, instead of being one-sided like the collector-emitter path of a transistor. The field effect characteristics recalled above are well known to technicians in the field concerned. However, we will find all

  necessary information concerning the functional characteristics of

  field effect transistors, in particular by referring to the "Hand-

  book for Transistors "by John D. Lenk, Copyright 1976, published by Pren

  tice-Hall, Inc. The present invention operates essentially in the same way as

  the circuit of the prior art, shown in Figure 1 and described above.

  The only difference lies in the fact that, in the arrangement according to the invention, the TEF transistor 50 is used as a two-sided switch, while the NPN transistor 28 that it replaces can only function

  as a unilateral switch. This will make it easier to understand how

  circuit, assuming that the circuit is in the following conditions: the capacitors 39 and 52 have been previously charged to a level equal to that of the potential source 54, and the

  transistor TEF 50 has just been made conductive by a positive impulse

  This current is thus generated in the output circuit of the TEF 50 in the capacitor 52- "negative potential source 56 direction, and passes through the coil 33 and the channel.

24 7.11 02

- -

  source collector of the TEF transistor 50.

  The current flowing through the coil 33 continues to increase

  linear until the moment when the exit of the pilot stage passes from the

  positive state in the negative state. At this time, the TEF transistor 50 is

  switched off, which terminates the flow of current between the

  reader and the source of the transistor TEF 50.

  When this TEF transistor 50 is thus turned off or ceases to be conducting, the energy stored in the magnetic field of the coil 33 begins to flow through the spot return capacitor 39 to the negative potential source. 56. As soon as the transfer of energy between the coil 33 and the spot return capacitor 39 has ended, the direction of the current is reversed and it flows from the capacitor 39 through the primary winding 41 to reach the end of the current. firstly to the positive potential source 54, and secondly through the coil 33, to the capacitor 52, which generates the negative half of the spot return current. The voltage across the capacitor 39 then decreases to approximately equal to a diode drop

  (0.6 volts) below the voltage of the negative potential source 56.

  At this moment, the TEF transistor 56 begins to become conductive in the

  direction from its source electrode to its collector electrode. The-

  energy stored in the coil 33 is therefore transferred to the spot return capacitor 52. As soon as the transistor TEF 50 becomes conductive again

  thanks to the output of the pilot stage, the current flows in the direction

  milk through the collector-source channel of the field effect transistor

  , and the cycle described above is repeated.

  In summary, it can be seen that the current flows through the coil 33 and the TEF 50 field effect transistor in one direction for half of each line scan interval, while the energy

  which remains in the coil at the end of this scan produces a circular

  current flow through the coil 33 but in the opposite direction during the first half of each scan interval. At the of

  each line scan interval, the coil 33 determines the

  In this case, the waveform of the coil current is similar to the waveform of H of FIG. 3. During the scanning, the current is flowing. through the transistor TEF 50 (in both directions), whereas during the return of the spot this current is cosine-fused, since it is the same

? 471102

- 10 -

  current than that flowing through capacitor 39.

  From the foregoing, we can see that we have voluntarily

  avoid overloading-the description of the invention by an ex-

  details, or specific indications concerning

  such as polarization, synchronization and the like, expected

  that this is the knowledge which the spe-

  specialists in the art. It should also be emphasized that the partial mode

  particular embodiment of the invention shown and described here is not

  given as an illustration and in no way limits the scope of the

vention, or the invention itself.

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Claims (9)

  A circuit arrangement for producing a sawtooth current through a line deflection coil of an image display apparatus, which circuit arrangement is characterized by comprising:   (a) a source (10) of rectangular pulses, delivered to the   the horizontal lines of the image display device;   b) amplifier means (14) connected to an output terminal of the   said source of pulses; c) a field effect transistor (50) including gate, sink and source electrodes, connected to receive the output of said amplifier means (14) at its gate electrode, and d) a resonant circuit comprising a coil line deflector (33) connected between said collector electrode and said electrode of source.   2. Circuit arrangement for producing a sawtooth current   through a line deflection coil (33) in a display apparatus   image gallery, characterized in that it comprises:   a) a source (40) of rectangular pulses delivered to the   horizontal lines of the image display device; b) amplifier means (14) connected to receive the output of said pulse source; c) bi-directional switch means (50) connected to receive the output of said amplifier means, and d) a resonant circuit comprising the line deflection coil   (33) and connected to the output terminals of said bi-directional switch means nel (50).   3. A circuit arrangement according to Claim 2, characterized   in that said bi-directional switch means comprises a field effect transistor (50) connected to receive the output of said means   amplifier to its door electrode.   4. A circuit arrangement for producing a tooth current   sawing through a line deflection coil (33) of a   image recording, characterized in that it comprises: a) a source (10) of rectangular pulses delivered at the rate of the horizontal lines of said image display apparatus; b) bi-directional switch means (50) connected to receive said rectangular pulses, and 24711 02 - 12- -   c) a resonant circuit comprising the line deflection coil   (33) connected across said bi-directional switch means (50).   A circuit arrangement according to Claim 4, characterized in that said bi-directional switch means comprises a field effect transistor (50) connected to receive said pulses   rectangular to its door electrode.   6. A circuit arrangement according to any one of the   1, 2 or 4, characterized in that said resonant circuit further comprises a scanning capacitor (52) and a feedback capacitor of spot (39).   A circuit arrangement for producing a sawtooth current through a line deflection coil of an image display apparatus, characterized in that it comprises:   (a) a source (10) of rectangular pulses delivered to the   the horizontal lines of the image display device; b) amplifier means (14) connected to receive the output of said pulse source; c) a field effect transistor (50) including gate, sink and source electrodes, connected to receive the output of said amplifier means at its gate electrode, and d) a resonant circuit comprising a deflection coil of line (33), connected between the collecting electrode and the source electrode   of the field effect transistor (50).   8. A circuit arrangement for producing a sawtooth current through a line deflection coil of an image display apparatus, characterized in that it comprises: a) a source (10) of rectangular pulses at the rate of horizontal of said image display apparatus; b) a bi-directional switch (50) connected to receive said rectangular pulses, and c) a resonant circuit comprising said deflection coil of   line (33) connected to the output terminals of said bi-directional switch nel (50).   9. A circuit arrangement for producing a tooth current   sawing through a line deflection coil (33) of a display apparatus   image display, said coil being part of a resonant circuit, switch means applying a voltage to said deflection coil 2: 471 ZIGS - 13 -   during the scan interval and the spot return interval, which circuit is characterized in that said switch means comprises a field effect transistor (50).