MXPA99005593A - High voltage system - Google Patents

Abstract

A sample of the high voltage retrace pulse is modeled across the series connection of a coil and low voltage winding of the flyback transformer. The AC current of the high voltage winding is fed through the coil in order to obtain the same retrace voltage shape as across the high voltage winding. Thus in this manner modeled high voltage retrace pulse is rectified by a diode and a charge capacitor. The rectified voltage is loaded by the beam current by a load resistor. The loading produces excellent tracking between the high voltage and the high voltage sample.

Description

HIGH VOLTAGE SYSTEM Background of the Invention Field of the Invention This invention relates to a high voltage system for color television receivers, display monitors and projectors with cathode ray tubes, and in particular to a high voltage system that indirectly tracks the anode voltage or final accelerator of the cathode ray tubes. Prior Art Variations in the final accelerator voltage adversely affect the performance of the deflection circuits. The high-voltage generator of the final accelerator voltage exhibits an internal impedance that decreases it as the image tube produces a greater beam current. Frame aspiration is a form of deflection distortion produced by variations in the final accelerator voltage of the cathode ray tubes used in color television receivers, display monitors and projectors. The frame aspiration causes the horizontal width of the frame to shrink and expand according to the variations of the final accelerator voltage. Other manifestations of reduced performance are reduced peak brightness and an efficient focus to high beam currents. It is common practice to generate the high voltage or final accelerator voltage in a return transformer that is part of a horizontal deflection circuit. The amplitude of the retrace pulse voltage across a primary winding and through the retrace capacitor is constant due to the regulated supply voltage B + and the retrace time and frequency of uniform lines. The patch pulse voltage can be considered as a voltage source for high voltage generation due to the large amount of circulating energy during the retrace interval in the deflection circuit and in the primary winding. High voltage generation and rectification is usually achieved in a split diode configuration. A secondary high voltage winding is divided into several winding sections. The high voltage diodes are coupled between the winding sections and between an upper terminal of the high voltage winding and the high voltage terminal of the return transformer. The retrace voltage is transformed by the ratio of turns of the return transformer to have a very high secondary retrace pulse voltage, for example 30 kV peak. The high-voltage rectifiers conduct during the voltage peaks and charge the capacitor formed by the colloidal graphite of the image tube to the final accelerator voltage. The capacitance of colloidal graphite is commonly from 1500 pF to 2500 pF, depending on the size and type of the imaging tube. The final accelerator voltage is charged by the beam current of the image tube. The average beam current is commonly between 0 and 2 mA with peaks up to 20 mA. The return transformer, and in particular the split windings, are constructed to obtain a tuning of harmonics that lead to producing a call in the split windings. Tuning to non-harmonic produces a high-voltage pulse with a more square waveform. The result is an increased conduction type of the diodes and in turn a lower high voltage source impedance. The high voltage source impedance shows a strong non-linearity at low beam currents, between 0 and 0.5 mA. As a result, the differential reduction of the high voltage is greater at low beam currents than at high beam currents. The deflection sensitivity is a function of the final accelerator voltage and therefore, depends on the high voltage. The non-linear high voltage source impedance produces undesirable variations in the screen performance, such as the frame size. It is known that to obtain a detection voltage of the high voltage generator a sample of the voltage is taken through a dissipating resistor. Then, the detection voltage is supplied to a high-voltage control circuit or used to limit the beam current (ABL) to correct the frame aspiration via an East-West correction circuit. Nevertheless, the variation in the detection voltage is proportional to the beam current, but not to the high voltage. This produces a bad patch aspiration correction because the East-West correction circuit does not consider the non-linearity of the high voltage, which is linear, or the high-voltage control circuit. This produces no precise results in the high-voltage regulation or the East-West correction because the charge of the focus and the G2 electrodes still depend on the beam current. Another disadvantage of using the heatsink resistor is that the damage to the imaging tube that can occur is a poor connection between the heatsink resistor and the high voltage circuit. A separate second resistor resistor can be used, specifically to sample only the high voltage. However, this approach is expensive and consumes too much energy. U.S. Patent Serial Number 4,827, 194, discloses a configuration for providing an envelope detector circuit for detecting the amplitude variation of the sample voltage pulses having amplitudes that vary in accordance with the load of the final throttle terminal. The envelope detector develops a size control signal that tracks variations in the final accelerator voltage. Subsequently, the size control signal is coupled to a modulating means for modulating the scanning current in a manner that regulates the size of the frame. The ratio of high voltage to beam current has a non-linear relationship. For example, at low beam currents, the high voltage source impedance shows strong non-linearity. Also, as illustrated in Figure 3 of the applicant, there is a greater differential decrease in high voltage at low beam currents than at higher beam currents. The sample pulse generating means of the applicant generates sample pulses that vary in a corresponding non-linear manner relative to the variations in the beam current load so that the sample pulses track the high voltage pulses. . Subsequently, another means that responds to the sample pulses of non-linear variation generates a correction voltage. Thus, the correction voltage, which can be supplied to a frame correction means as set forth in the appended claims, considers this non-linear relationship. Nowhere in U.S. Patent Serial Number 4,827, 194 is there shown the recognition that high voltage pulses vary in a non-linear manner relative to the beam current load, where the load The beam current can vary in a range of high and low beam current levels. Therefore, this reference does not take any steps to treat the high voltage of non-linear variation. Brief description of the invention Sampling high voltage is necessary for an adequate correction. It is desirable to take a high voltage sample under conditions of similar high voltage loads for plot correction and high voltage regulation. It is also desirable to sample the high voltage in an economical manner without major energy requirements. In accordance with a configuration of the invention, the high voltage is reproduced accurately under similar beam current load conditions of the final accelerator voltage. A switched output circuit and a return transformer are coupled to generate high voltage pulses. High voltage pulses tend to be adversely affected by the beam current load. The generated sample pulses track the high voltage pulses in form and magnitude. A correction voltage is generated that responds to the sample pulse and the correction voltage tracks the final accelerator voltage. The correction voltage is used to correct the frame distortion. In accordance with another aspect of the invention, to avoid additional loading of the correction voltage, a high-voltage system additionally comprises a means for transforming the impedance. The impedance transformation means can be used to activate the frame correction means. This provides compensation for voltage variations due to temperature variations. DETAILED DESCRIPTION OF THE INVENTION Figure 1 illustrates a high voltage generator and a high voltage system, in accordance with the prior art; Figure 2 illustrates useful waveforms to explain the operation of the circuit of Figure 1; Figure 3 illustrates the high voltage against the beam current and the source impedance against the beam current of the circuit of Figure 1; Figure 4 illustrates a high voltage generator and a high voltage system, which presents an aspect of the invention; Figures 5A-5C illustrate waveforms useful for explaining the operation of the circuit in Figure 4; Figures 6A-6C illustrate waveforms useful for explaining the operation of the circuit in Figure 4; Figures 7A-7B illustrate waveforms useful for explaining the operation of the circuit in Figure 4; and, Figure 8 illustrates a high voltage generator and a high voltage system, including another aspect of the invention.

Figure 1 illustrates a return transformer, which is part of a horizontal detion circuit, commonly used to generate the high voltage or final accelerator. The amplitude of the retrace pulse voltage V1 through the primary winding W1 and through the retrace capacitor C1 is constant due to the regulated supply voltage B +, and to the uniform line frequency fH and the retrace time tr. The voltage V1 is the voltage source for the generation of the high voltage due to the large amount of circulating energy during the retrace interval tr in the detion circuit and in the winding W1. Generally a split diode configuration is used for high voltage generation and rectification. The high voltage secondary winding is divided into several sections, shown in Figure 1 as windings W2a, W2b and W2c. The high voltage diodes are coupled between the winding sections and between the upper terminal of winding W2c and the high voltage terminal of the return transformer. The retrace pulse voltage V1 of 1000V peak is transformed by the N turns ratio of 30 between windings W1 and W2 to obtain a secondary retrace pulse voltage of 30 kV peak. The high-voltage rectifiers conduct during the voltage peaks and charge the capacitor formed by the colloidal graphite of the image tube to the final accelerator voltage of 30 kV. The capacitance of the colloidal graphite is from 1500 pF to 2500 pF depending on the type and size of the image tube. The final accelerator voltage is charged by the beam current of the image tube. The average beam current is commonly between 0 and 2 mA, with peaks up to 20 mA. The return transformer and, in particular, the windings W2a, W2b and W2c are constructed to obtain a tuning of harmonics to the 3rd or 5th or 7th harmonic of the fundamental frequency of the retrace pulse voltage V1. The tuning to harmonics nones produces a pulse of high voltage of more square wave form. The square-wave voltage pulse increases the driving time of the diodes and, therefore, reduces the impedance of the high-voltage source. Figure 2 illustrates waveforms with a predominance of the 7th harmonic. Figure 3 shows the relation of high voltage versus beam current and the ratio of source impedance to beam current of the circuit of Figure 1. The impedance of the high voltage source shows a strong non-linearity at low beam currents, between 0 and 0.5 mA. Figure 3 also shows that the differential decrement of the high voltage is greater at low beam currents than at high beam currents. Referring again to Figure 1, the low side of the high voltage winding W2a is connected to an integration capacitor C2 and to a current source resistor R 1. The high voltage charging current becomes a voltage drop through the current source resistor R1. Then, the voltage is used to limit the beam current (ABL) and to correct the frame aspiration via the East-West correction circuit. Figure 4 shows the high voltage system according to the invention. The primary side of the return transformer is similar to the circuit of the. Figure 1 . The waveforms of Figure 2 and the impedance and high voltage (HV) characteristics for Figure 3 are also applicable to the circuit of Figure 4. The high-voltage retrace pulse voltage V2 shown in the waveforms was measured by placing a capacitive probe near the upper face of the return transformer. The W3 heater winding is used as a voltage source for the high voltage reproductive circuit. The coil L1 and the damper resistor R2 represent the leakage inductance transformed between the primary winding W1 and the high voltage winding W2. The DC blocking capacitor C2 connects the coil L1 to the low side of the high voltage winding W2. The alternating current 1, which consists of the harmonic current called nons in the windings W2a, W2b, and W2c and the high voltage charging current, modulates the voltage across the coil L1 and the heating winding W3 forming the pulse voltage of High voltage equivalent delay V4. Figure 5 shows the voltage waveform discharged from the high voltage equivalent retrace pulse voltage V4 at different beam currents. The alternating current i 1 and the high voltage retrace pulse voltage V2 are also shown. The high voltage equivalent retrace pulse voltage V4 is measured by connecting the anode of D1 directly to the dotted side of the heater winding W3. The tuning of the high voltage equivalent retrace pulse voltage V4 is similar to the high voltage retrace pulse voltage V2. At low beam currents, the shape is equivalent to that shown in Figure 2. At higher beam currents, the portions of the 3rd and 5th harmonics are visible in the center of the retrace. The modulation to higher beam currents is produced by the horizontal and vertical extinction intervals of the image tube, during which the beam current is cut off. The high voltage equivalent retrace pulse voltage V4 is rectified by diode D 1. The charge capacitor C3 represents the colloidal graphite capacitor of the high voltage reproductive circuit. The current ¡3 is equal to the beam current discharged by the colloidal graphite capacitor. As can be seen in Figure 4, the equivalent circuit is connected in series with the high-voltage circuit. The alternating current circuit is completed by the current blocking capacitor C2 and the direct current circuit by the resistor R3 (it is assumed that the ABL load is depreciably small). The current blocking capacitor C2 couples the high voltage winding W2 and the heating winding W3. The high amplitude call current 1 modulates the voltage across coil L1 so that a sum of voltages through heater winding W3 and coil L1 is equal to the high voltage retrace pulse voltage V2. Resistor R3 closes the direct current path between the high voltage generator (rectifiers and high voltage windings) and the low voltage generator (heater winding W3, coil L1, diode D1 and load capacitor C3). The charge current, which is the direct current component of the current 3, flows from the ground through the heater winding W3, the coil L1, the diode D1, the resistor R3, the windings W2a, W2b, and W2c and the anode-cathode path of the image tube, not shown. Thus, the current 3 is equal to the beam current and therefore, the charge capacitor C3 is charged in a manner similar to the colloidal graphite capacitor. The high-voltage reproducing circuit produces a correction voltage V5 which is derived from a sample of modeled high-voltage pulse, which is rectified and charged by the current beam current. The two steps that form the high-voltage equivalent retrace pulse voltage V4 and the load by the current 3, produce an excellent tracking between the high voltage and the correction voltage V5. Tests performed on a SELECO 1 10 ° color television chassis, using an ELDOR return transformer type 1 182.0857, and incorporating a high voltage system in accordance with the configurations of the invention taught herein, showed a tracking error of less than 2. per thousandth. Figure 4 shows that the correction voltage V5 serves as an input to the East-West correction circuit. The frame aspiration correction is provided by coupling the East-West circuit to the high-voltage reproductive circuit. The operation of a convenient example of an East-West circuit is described in more detail in U.S. Patent Serial No. 5,399, 945 to Haferl. The additional load of the correction voltage V5 can be avoided by using an impedance converter follower, Q1, to activate the East-West frame correction circuit for frame aspiration compensation or to control a high voltage generator. The emitting base diode of the follower emitter Q 1 compensates for direct voltage variations against the temperature of the diode D1. Figure 6 shows waveforms of the voltages, the high voltage retrace pulse voltage V2, the high voltage equivalent retrace pulse voltage V4 and the current 2 at different beam currents. The high voltage equivalent retrace pulse V4 is charged by diode D1. The series impedance formed by the coil L1 and the damper resistor R2 produces an amplitude limitation of the high voltage equivalent retrace pulse voltage V4. In addition to the amplitude limitation, the shape of the high voltage equivalent retrace pulse voltage V4 is equivalent to that of the high voltage retrace pulse voltage V2. The amplitude of the high voltage equivalent retrace pulse voltage V4 is increased during the conduction time of the current 2. The shape of the high voltage retrace pulse voltage V2 shows the same increase. This is caused by the energy stored in coil L1 for the high voltage equivalent retrace pulse voltage V4 and by the energy stored in the leakage inductance of the return transformer for the high voltage retrace pulse voltage V2. By comparison with the waveforms of Figure 5, it can be noted that the conduction time and the shape of the current i2 is approximately the same as the charging portion of the current I 1. The alternating current 1 consists of two portions of current. The first current portion is the zero beam current call current, as shown in Figure 5a. The second portion is the charging current. The alternating current i 1, including both current portions, is shown in Figures 5b and 5c. At a zero-beam current, the circuit is still charged by a current of 0.05 mA flowing through the resistor resistor. Figure 7 shows the retracement or low voltage V3 through the heater winding W3 which acts as a voltage source for the high voltage reproducing circuit. The current 2 and the high voltage retrace pulse voltage V2 are also shown. The shape of the low voltage V3 does not change when the beam current is increased. Figure 7 shows that the low voltage V3 does not track the high voltage retrace pulse voltage V2. As a consequence, the low voltage V3 does not track the high voltage equivalent retrace pulse voltage V4, because the high voltage retrace pulse voltage V2 and the high voltage equivalent retrace pulse voltage V4 are the same. . The peak voltage of the non-charged high voltage equivalent retrace pulse voltage V4, as shown in Figure 5, is also larger than the peak voltage of the low voltage V3 due to the energy stored in the coil L1 generated by the current of call i 1. Therefore, the low voltage V3 does not trace in magnitude to the high voltage equivalent retrace pulse voltage V4. The tuning of the high voltage retrace pulse occurs from the leakage inductance between the windings W2 and W1 and the capacitance between the windings. The measured leakage inductance (W1 in short circuit and W2 directly polarized by 0.3 mA via 330 k-Ohm) of the return transformer is 50 mH. The equivalent circuit and the high voltage circuit are charger by the beam current. Accordingly, the leakage inductance is transformed by the winding ratio of the winding W2 to the heating winding W3 to obtain the value of the coil L1. This value of the coil L1 must be doubled because the energy stored in L1 by the calling portion of the current I is charged by the load current I 2 and the load portion of the current I 1. Thus, the calculation of L1 is as indicated below: L1 = 2 X 50 mH / 1500 = 67 μH. The damper resistor R2 limits the call voltage through L1 and serves to track fine tuning. The resistor R3 acts as a current voltage converter to obtain the voltage ABL. R3 also isolates the current blocking capacitor C2 from the load capacitor C3. The load capacitor C3 is selected for better suction compensation. The value of the charge capacitor C3 is generally smaller than the capacitance of the colloidal graphite transformed to obtain a faster response time of the correction voltage. Correction voltage V5. This compensates for the rather long time constant of frame size variations. Figure 8 illustrates a high voltage system that includes another aspect of the invention. Figure 8 shows the correction voltage V5 correction voltage that serves as an input to a high voltage regulator. The high-voltage circuit is similar to the circuit of Figure 4. The waveforms of Figures 2, 3, 5, 6, and 7 are also applicable to Figure 8. The operation of a convenient example of a high-voltage regulator Voltage is described in greater detail in the United States Patent Serial Number 5,266,871 to Haferl.

Claims (9)

1. CLAIMS 1. A high voltage system, comprising: a switched output circuit and a return transformer (FBT) coupled to generate high voltage pulses (V2), said high voltage pulses establish a final accelerator voltage tends to be adversely affected by the beam current charge; characterized by means (W3, L1, R2) coupled to said return transformer and responding to a return pulse to generate sample pulses (V4) that tracks such high voltage pulses with beam current load in form and magnitude. , said sample pulse generating means comprise a series impedance network, characterized in that said impedance network comprises an inductor (L1) and a resistor (R2); and, means (R3, C3, D1) to generate a correction voltage (V5) that responds to such sample pulses that track said final accelerator voltage.
2. 2. The circuit of claim 1, characterized in that said correction voltage generation means comprises a rectifier (D1).
3. The circuit of claim 2, characterized in that said correction voltage generation means further comprises a filter (L1, R2) coupled to an output of said rectifier.
4. 4. The circuit of claim 1, further comprising means (C2) for coupling said alternating current network in alternating current to such a high voltage winding.
5. 5. The circuit of claim 1, further comprising means (Q1) for transforming an impedance responsive to said correction voltage generation means and coupled to said frame correction means. The circuit of claim 5, characterized in that said transformation means comprise a transistor, 7. The circuit of claim 5, characterized in that said transformation means compensate for temperature variations due to voltage variations in said generation means. of correction voltage. 8. A high-voltage system, comprising: a horizontal output circuit and a return transformer (FBT) having a primary winding (W1), a high voltage winding (W2) and a low voltage winding (W3), said horizontal output circuit and such a return transformer coupled to generate high voltage pulses (V2) establishing a final accelerator voltage that tends to be adversely affected by beam current loading; characterized by means (L 1, R2) including an impedance coupled to such a low voltage winding to generate sample pulses (V4) that correspond in shape and are proportional in magnitude to said high voltage pulses; means (C2) for coupling said impedance in alternating current to said high voltage winding; means (D 1) for generating a rectified voltage responsive to such sample pulses tracking said final accelerator voltage; means (R3) for coupling said rectified voltage in direct current to said high voltage winding; and, means (East-West) to correct the distortion of the frame that responds to said rectified voltage. The circuit of claim 8, characterized in that said alternating current coupling means comprise a capacitor (C2). The circuit of claim 8, characterized in that said rectified voltage generating means comprises a rectifier (D 1) and a filter (L1, R2). eleven . The circuit of claim 8, characterized in that said direct current coupling means comprise a resistor (R3). 12. A high voltage system, comprising: a switched output circuit and a pulse transformer (FBT) coupled to generate high voltage pulses (V2) that establish a final accelerator voltage, said high voltage pulses vary from In a non-linear manner with respect to variations in the beam current load, such variations in the beam current load occur in a range that ranges between high and low beam current levels; characterized by means (W3, L1, R2) coupled to such a pulse transformer and responding to pulses therein to generate sample pulses (V4) which vary in a corresponding non-linear manner in relation to variations in the beam current charge which track such high voltage variant pulses; and means (R3, C3, D1) that respond to such high voltage variant pulses to generate a correction voltage (V5) that tracks such high voltage variant pulses in said range of beam current levels. The circuit of claim 12, characterized in that said correction voltage generating means further comprises means (R3) for charging said sample pulse generating means by such beam current. The circuit of claim 13, characterized in that said load means is a resistor (R3) coupled to a low end of a high voltage winding (W2) of said pulse transformer (FBT). 15. The circuit of claim 12, further comprising means (East-West) for correcting the frame distortion responsive to said correction voltage. 16. The circuit of claim 15, characterized in that said frame correction means comprise an East-West correction circuit. The circuit of claim 1, characterized in that said frame correction means comprise a high voltage regulator. The circuit of claim 1, characterized in that said frame correction means comprise a high-voltage regulator and an East-West correction circuit. 9. The circuit of claim 15, characterized in that said frame distortion is weft aspiration. 20. The circuit of claim 12, characterized in that said means for generating sample pulses comprises an inductor (L1). twenty-one . The circuit of claim 1 3, characterized in that said sample pulse generating means comprise a low voltage pulse source (W3) and a capacitor (C2). 22. The circuit of claim 12, further comprising means for limiting the beam current responsive to said correction voltage. 23. A high-voltage system, comprising: a horizontal output circuit and a return transformer (FBT) having a primary winding (W1), a high voltage winding (W2) and a low voltage winding source (W3), said horizontal output circuit and such return transformer coupled to generate high voltage pulses ( V2) establishing a final accelerator voltage that tends to be adversely affected by beam current loading; characterized by means (L1, R2) including an impedance coupled to such a low voltage pulse source to generate sample pulses (V4) that correspond in shape and are proportional in magnitude to said high voltage pulses; means (C2) for coupling said impedance in alternating current to said high voltage winding; means (D1) for generating a rectified voltage responsive to such sample pulses tracking said final accelerator voltage; means (R3) for coupling said rectified voltage in direct current to said high voltage winding; and, means (East-West) to correct the distortion of the frame that responds to said rectified voltage. RESU MEN A sample of the high voltage retrace pulse is modeled through the series connection of a coil and a low voltage winding of the return transformer. The alternating current of the high-voltage winding is fed through the coil to obtain the same form of the retrace voltage as through the high-voltage winding. Thus, the high voltage retrace pulse modeled in this manner is rectified by a diode and a load capacitor. The rectified voltage is charged by the beam current through a load resistor. The load produces an excellent tracking between the high voltage and the high voltage sample.