FI63845C - SAETTING THE PICTURE IN THE HORIZONTAL AND OVER VERTICAL EQUIPMENT HOUSING THE PURPOSE OF THE VARIABLE FOCUSING SPEAKING SA MTOPPLING FOR THE GENOMATION OF THE SAFETY - Google Patents

Description

63845

The method of generating a variable focusing voltage depending on the horizontal and vertical deflection of the picture tube, and the connection for performing this method

The present invention is directed to a method of generating a variable focusing voltage depending on the horizontal and vertical deflection of a picture tube by summing the deflection dependent voltage to a static focusing voltage. The invention also relates to a connection by which this method is implemented.

The electron beam of the cathode ray tube is assembled on the image surface by means of an electric lens, the focal length of which depends on the focusing voltage used. Since the image surface of the cathode ray tube is almost planar, the greater the beam deflection angle, i.e., the farther from the center of the image surface the beam strikes. If the focusing voltage is independent of the deflection angle, a focusing error is caused when the beam deviates from the center of the image surface, which is in principle larger the larger the beam deflection angle. In practice, the farther the beam is from the horizontal and vertical axes of the image surface, the more disturbing the error.

If it is desired to avoid the above-mentioned focusing error, the focusing voltage must be dependent on the deflection angle, which means the so-called dynamic focusing. In this case, a higher voltage is applied to the edge areas of the image surface than to the center of the image surface.

It is known to use high voltage transistor circuits to implement a dynamic focusing voltage. The disadvantages of such connections are the high power consumption and the sensitivity to the spark discharges of the picture tube.

In order to avoid the disadvantages described above, the so-called focusing transformer connection, 2,63845 in which the horizontal deflection current is passed through the low-turn primary winding of the above-mentioned transformer. A low-capacitance capacitor is connected in parallel with the multiple secondary winding, the voltage of which is proportional to the integral of the deflection current and is thus in the shape of a parabola. This voltage is summed to the static focusing voltage to obtain a focusing voltage depending on the deflection angle. The disadvantage of the described coupling is the undesired effect on the S-equalizer and the linearity of the horizontal deflection current. Another disadvantage of the coupling described above is the independence of the dynamic focusing from the vertical deflection angle.

It is an object of the present invention to obviate the disadvantages described above. The method according to the invention is characterized by what is set forth in the appended claim 1, while the features of the connection according to the invention appear correspondingly from claim 5.

According to the invention, a transducer circuit is thus used in the prediction of the dynamic focusing voltage, by means of which the voltage depending on the deflection angle is summed to the static focusing voltage. The dependence of the voltage in question on both the vertical and horizontal deflection angles is inventively achieved by passing a current proportional to the vertical deflection through the control coil of the transducer and a voltage proportional to the horizontal deflection through the working coil.

The invention and its other features and advantages will now be described in more detail by way of example with reference to the accompanying drawings, in which Figure 1 schematically shows an essential part of a circuit according to the invention, Figure 2 shows curves related to the description of Figure 1, Figure 3 shows a possible embodiment of another circuit, Fig. 4 shows curve shapes related to the description of the circuit of Fig. 3, and Fig. 3 63845 Fig. 5 shows the variable part of the dynamic focusing voltage as a function of time.

In the connection, an auxiliary winding L 1 is wound around the core of the horizontal deflection transformer, from which a voltage proportional to the horizontal deflection is obtained. The ends of the auxiliary winding are connected together by the working windings of the transducer connected in series and the so-called via the primary winding L2 of the parabolic voltage transformer M2. The current in the control coil of the transducer is proportional to the vertical deflection current.

Since the horizontal deflection frequency is high compared to the vertical deflection frequency, it is worth considering the operation of the coupling in two parts. In the following, the operation is considered using the curves in Figure 1 and Figure 2. Let us first assume that the vertical deflection voltage and thus also the inductance L, p of the working windings of the transducer is constant.

Fig. 2A shows a horizontal deflection current IQ, the voltage UL1 generated by the auxiliary winding in Fig. 2b. The current caused by the voltage UL1 passing through the primary winding L2 of the parabolic transformer M2 generates a voltage at the terminals of the secondary winding of the parabolic transformer, which appears as a voltage across the diode (Fig. 2c). This voltage, when summed into the static focusing voltage, causes a focusing correction proportional to the horizontal deflection angle of the beam.

It can be shown that the value of the voltage UD 1 from peak to peak is approximately inversely proportional to the inductance L, p of the transducer. By introducing a signal proportional to the vertical deflection angle of the transducer control winding, the focusing voltage is also made dependent on the vertical deflection.

In order for the coupling shown not to cause significant feedback to the horizontal deflection, the core of the transducer must be very small, for example the EK 20 of a ferrite core.

63845

The voltage conversion ratio of the parallel transformer M2 must be large, e.g. 3700: 25 = 148. The integration capacitance is 170 pF, which consists of a capacitance of 150 pF of the capacitor and a switching capacitance of 20 pF. In order to achieve a sufficiently high parabolic voltage, the characteristic resonant frequency of the transformer must not be very much below the line frequency. The characteristic frequency is selected by means of winding turns, switching coefficient or integration capacitor.

In practice, it has been shown that the parabolic voltage is not completely symmetrical, which, however, does not significantly affect the resolution. The reasons for the asymmetry are the ohmic losses of the copper coils and the hysteresis of the ferrite core. In order to keep the effect of hysteresis small, the magnetic flux density of the ferrite core must not exceed about 0.18 T. At low control currents, the effect of hysteresis is greater than at large, but not disturbing.

In the example case, the working winding of the transducer is wound on the outer column of the ferrite body and has 40 turns of 0 0.25 mm copper wire. The control winding of the transducer has 1500 turns of 0 0.070 mm copper wire.

There is a requirement for the operation of the control circuit that the control current must not exceed the zero point during the image change, ie saturation of the upper and lower part of the image takes place with the same polarity. During crossing the zero point, the horizontal deflection degree would have a short load pause that would result in a slight oscillation of the resonant circuit formed by the S-correction capacitor and the deflection coil, which would cause a phase shift of the first upper lines. By means of the connection shown in Figure 3, the disadvantage described above has been avoided. By means of the connection, a triangular control current is formed from the vertical deflection voltage {curve 4a), which is shown in Fig. 4b.

5,63845

The connection works in such a way that only the other half of the vertical deflection voltage sweeping part (t ^ ~ t ^) controls the transistor T. The operation is implemented by means of a diode. The resistor dampens high-frequency oscillation in the degree of vertical deflection.

During the first part of the sweep (t1 - t2), including the return time of the previous sweep, the diode is in the closed state and the diode D2 conducts. Capacitor Cg is charged through a high-resistance resistor Rg, and an almost linear voltage acts across the capacitor. The operating point of the transistor T depends on the ratio of the resistor Rg to the resistor R 1. Through line capacitor C, a line frequency current is conducted to ground. In response

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The function of R is to dampen the oscillation due to the capacitor Cg and the inductance of the control coil. T is a small signal transistor.

The maximum collector current of transistor T is about 32 mA when using a typical 12 "High Resolution cathode ray tube. Under normal operating conditions, its instantaneous peak value is about 20 mA and the average power consumption of the control circuit is about 10 mA 0.12 W. The line frequency losses of the transducer are less than eo The total losses due to dynamic focusing are thus less than 0.2 W.

The parabolic voltage transformer is wound on a ferrite core EK 20 made of material FJ 321. The air gap has little effect on the parabolic voltage when the dispersion of the effective permeability is within the limits ^ u = 650 + 30%. The pre-magnetization carried out by means of a locking connection is small, i.e. approx. 1 mT. The lock connection locks the parabola to the minimum static focusing voltage, i.e. to a value corresponding to the center of the image.

The emitter resistor Rg of the transistor T is intended to accommodate a control current suitable for the air gap and the ferrite material. The length of the air gap should be about 20 in each column of the transducer. In this case, the ferrite core has an effective permeability after winding yU = 650. The effects of the + 30% dispersion of the permeability on the parabolic voltage can be compensated by adjusting the value of the resistor Rg in the range of about 120-270 Ω.

Figure 5 shows the dynamic focusing voltage as a function of time. For the sake of clarity, the difference between the horizontal deflection and the vertical deflection frequency has been drawn much smaller than the actual one.

In the example connection, a voltage proportional to the horizontal deflection is generated by means of an auxiliary winding of the horizontal deflection transformer. It is clear that it can also be formed in other ways, e.g. over a deflection coil or switch. Likewise, the current proportional to the vertical deflection is in principle obtained directly from the vertical deflection coil.

Claims (8)

1. A method of generating a variable focusing voltage depending on the horizontal and vertical deflection of a picture tube by summing a deflection-dependent voltage to a static focusing voltage, comprising a field frequency the dependent voltage is generated in a circuit which includes at least one working winding of the transducer (Τβ) and that a vertical deflection dependent current is applied to the transducer control winding (N 1) so that said horizontal deflection voltage will also depend on the vertical deflection . A method according to claim 1, wherein the voltage dependent on the horizontal deflection is generated by a so-called by means of a parabolic transformer (M2), to the primary (L1) of which a voltage proportional to the horizontal deviation is applied, characterized in that said voltage is applied to the transformer (1) via both working windings connected in series. Method according to Claim 1 or 2, characterized in that the voltage which depends on the horizontal deflection is taken out by means of an auxiliary winding (L ^) of the horizontal deflection transformer (M ^). Method according to Claim 3, characterized in that a non-directional triangular control current (Ic) is formed from the vertical deflection voltage, which is applied to the control winding (N 1) of the transducer. A circuit for generating a focusing voltage dependent on the horizontal and vertical deflection of a picture tube, the circuit comprising means (L 1, LT, M 2, R 2, R 2, C 1 -C 4) for generating a horizontally dependent voltage, which voltage is then summed to a static focusing voltage. , characterized in that said switching elements 8 63845 forming a horizontally deflection-dependent voltage comprise at least one working winding (LT) of the transducer (Tp), and that the control winding (N 1) of the transducer is connected to be controlled by a vertical deflection-dependent current. The circuit of claim 5, wherein the horizontal deflection dependent voltage generating means comprises a so-called a parallel transformer (M2), the primary winding (I ^) of which is connected to receive a signal directly or indirectly from a horizontal deflection coil, characterized in that the two working windings (LT) of the transducer are connected in series with said primary winding (1 ^). Coupling according to Claim 5 or 6, characterized in that the control winding (N 2) of the transducer (Τβ) is connected directly or indirectly to the vertical deflection coil. 7 63845 Coupling according to Claim 7, characterized in that means (T1, RjR1, D2 », C4-C8) are connected between the vertical deflection coil and the control winding (N1) of the transducer (T1) to form a unidirectional triangular current (Ic). vertical deflection. 63845 9