KR20020019774A - Dynamic focus circuit for computer monitor using current type transformer - Google Patents

Abstract

PURPOSE: A dynamic focus circuit for a monitor using a current type transformer is provided to control the effective current flowing through the primary coil of the transformer according to a horizontal frequency so as to induce a waveform with a specific amplitude to the secondary coil and apply the waveform to the dynamic focus terminal of a CRT. CONSTITUTION: A dynamic focus circuit for a monitor using a current type transformer includes a focus transformer(10), an S-shape correction part, and a vertical dynamic focus part(30). The focus transformer outputs a horizontal parabola waveform with a specific amplitude, which is induced by current flowing through the primary coil to the secondary coil. The S-shape correction part includes a plurality of correction capacitors that are turned on/off to select one of middle tabs of the primary coil of the focus transformer as a current path. The vertical dynamic focus part mixes the horizontal parabola waveform with a vertical parabola waveform output from a vertical output part(60).

Description

Dynamic focus circuit for computer monitor using current type transformer}

The present invention relates to a dynamic focus circuit for improving image focus of a multiscan monitor. More specifically, the present invention is effective by flowing a plurality of intermediate taps on the primary winding of the focus transformer and connecting the S-shaped compensation capacitors to the primary winding terminals of the focus transformer, respectively, according to the horizontal frequency. The present invention relates to a dynamic focus circuit for a monitor using a current transformer, in which a waveform of a constant amplitude is induced in a secondary winding and applied to a terminal for dynamic focus of a CRT.

In order to uniformly focus each part on the monitor screen, the focus voltage must be proportionally changed according to the mechanical distance from the CRT cathode to the CRT plane. The circuit that accomplishes this is called a dynamic focus circuit. A parabolic voltage waveform in a horizontal and vertical direction is synthesized and applied to a focus grid. This voltage varies with the CRT, but is about 300 to 600 Vpp horizontal and 150 to 250 Vpp vertical.

Conventional dynamic focus circuits are distinguished in several ways, depending on how the horizontal parabola is made. For example, there is a method using a transformer. A method of coupling a parabolic waveform at the rear of a deflection yoke (deflection coil) to a capacitor and amplifying it to a transformer is used. This circuit has the advantage that there is little waveform distortion and the circuit is simple because it uses the amplification effect of the focus transformer's 1st and 2nd turns ratio, while the waveform amplitude behind DY varies according to the horizontal frequency. There is a disadvantage in that frequency cannot be used. That is, it is not possible to compensate for the difference in amplitude according to the horizontal frequency, so it is not applicable to the monitor using a wide range of horizontal frequencies.

Another method is to use an amplification circuit using TR or the like. This is to double-integrate the horizontal pulse to generate a parabola waveform, and then amplify it to the necessary amount as an amplification circuit. In particular, most modern deflection processors have a built-in horizontal and vertical parabolic waveform generation circuit with adjustable amplitude and delay, which greatly simplifies the circuit. Output amplifiers mainly use cascade amplifiers and emitter-coupled buffers.

In this method, however, waveform distortion and delay are difficult to avoid because they require quite large amplification degrees. To compensate for this, cascade amplifiers and amplifying transformers are often used in combination, but the circuit is complicated and the cost is increased. In addition, it has a complicated configuration such as a horizontal parabolic waveform generating circuit, a delay compensation circuit, an amplifier circuit, an impedance matching circuit, and the like, thereby increasing the number of parts and increasing power consumption.

In the circuit according to the present invention, a focus circuit was devised by applying a current transformer. The basic operation principle is to connect the primary winding of the focus transformer in series with the deflection circuit and use the voltage induced in the secondary according to the amount of current.

In order to eliminate the amplitude difference between frequencies, which is a disadvantage of conventional transformer circuits, taps were connected to each terminal of the primary winding, and an S-shaped compensation circuit of a horizontal deflection circuit was connected to each terminal.

An object of the present invention is to draw a plurality of intermediate taps on the primary winding of the focus transformer, and connect the S-shaped compensation capacitors to the primary winding terminals of the focus transformer, respectively, so that an effective current flows in the primary winding of the transformer according to the horizontal frequency. It is to provide a dynamic focus circuit for a monitor using a current transformer, characterized in that by inducing the waveform of a constant amplitude in the secondary winding and applying it to the terminal for dynamic focus of the CRT.

1 is a block diagram of a dynamic focus circuit according to the present invention;

2 is a detailed circuit diagram of FIG.

<Description of Drawing>

Focus transformer section 10, first middle tap (a), second middle tap (b), third middle tap (c), primary winding start end (A), primary winding end (B), 2 Start end (C) of the secondary winding, the end (D) of the secondary winding, the S-shaped correction unit 20, the first capacitor (C6), the second capacitor (C7), the third capacitor (C8), the fourth capacitor (C9), fifth capacitor (C10), load capacitor (C2), switching elements (Q4, 5, 2, 6, 3), vertical dynamic focus unit 30, integrating means 32, amplifying means Q1 , Bypass capacitor (CH30), microprocessor 40, horizontal output unit 50, vertical output unit 60, flyback transformer (FBT) 70, cathode ray tube (CRT) 80,

The multi-scan type monitor has a circuit for compensating image linearity according to the horizontal frequency, which is called an S-shaped compensation circuit (or S compensation circuit). This S-shaped compensation circuit compensates the waveform of the horizontal deflection current by turning on / off the compensation capacitor for each horizontal frequency (horizontal parabolic waveform) region.

The present invention provides a plurality of intermediate taps on the primary winding of the focus transformer, and connects the S-shaped compensation capacitors to the primary winding terminals of the focus transformer to adjust the effective current flowing in the primary winding of the transformer according to the horizontal frequency. Thus, the basic concept is to induce a waveform of a constant amplitude in the secondary winding and apply it to the terminal for dynamic focus of the CRT.

Referring to FIG. 1, the dynamic focus circuit for a multi-scan monitor according to the present invention,

A plurality of intermediate taps (a, b, c) are formed in the primary winding to which the horizontal parabolic waveform output from the horizontal output unit 50 is applied, and a constant amplitude induced in the secondary winding from the current flowing in the primary winding A focus transformer unit 10 for applying a horizontal parabolic waveform to a flyback transformer (FBT) 70 of the CRT 80,

In order to adjust the current flowing in the primary winding of the focus transformer unit 10 in accordance with the frequency of the horizontal parabolic waveform, the control of the microprocessor 40 in accordance with the frequency region of the horizontal parabolic waveform of the focus transformer unit 10 S-shaped correction unit 20 including a plurality of compensation capacitors on or off so that one of the middle tap of the primary winding is selected as the current path

The horizontal parabolic waveform generated on the secondary side of the focus transformer section 10 is composed of a vertical dynamic focus section 30 which combines the vertical parabolic waveform output from the vertical output section 60.

Detailed description of each component and action will be described with reference to FIG.

The transformer used in the present invention has a structure in which a plurality of intermediate taps are provided on the primary windings and connected to the compensation capacitors of the S-shaped correction unit 20, respectively, and the insulated secondary windings are wound. To operate as a current transformer, each primary winding is extremely limited in one to three circuits and the secondary winding adjusts the number of turns according to the required voltage.

Specifically, the primary winding of the focus transformer unit 10 has a start end (A) and end (B) of the winding, between the first middle tap (a), the second middle tap (b), the first Three intermediate tabs c are formed.

The horizontal parabolic waveform output from the horizontal output unit 50 is applied to the first winding start end A of the focus transformer unit 10, and the first capacitor C6 of the S-shaped correction unit 20 is connected. The second capacitor C7 of the S-shaped correction unit 20 is connected to the first middle tab a, and the third capacitor C8 of the S-shaped correction unit 20 is connected to the second middle tab b. The fourth intermediate capacitor C9 of the S-shaped correction unit 20 is connected to the third intermediate tab c, and the fifth capacitor C10 of the S-shaped correction unit 20 is connected to the end B of the primary winding. ) Is connected.

In the present invention, the primary winding of the focus transformer unit 10 is the first middle tap once (1Turn), the second middle tap once (1T), the third middle tap twice (2T) from the start of the winding ), The fourth intermediate tap was wound twice (2T), and the secondary winding was wound 900 times (900T). In addition, a load capacitor C2 was connected to both ends C-D of the secondary winding.

Since the load capacitor C2 oscillates with a very large amplitude when the winding ratio of the focus transformer unit 10 is very large, the secondary voltage oscillates at a very large amplitude. The capacitance of the load capacitor C2 was 330pF. The smaller this value, the larger the secondary amplitude.

The compensating capacitor of the S-shaped correcting unit 20 is the first to fifth capacitors C6 to C10 turned on / off by the switching elements Q4, 5, 2, 6 and 3 driven by the microprocessor 40. Each capacitor is connected in series with the current path of the FET switched by the microprocessor MCU. The capacitance of each capacitor is set to decrease from the start end A to the end B of the primary winding.

On the other hand, the vertical dynamic focusing unit 30 is a means 32 for integrating the vertical parabolic waveform output from the vertical output unit 60, and the terminal C of the secondary winding of the focus transformer unit 10 by amplifying the integrated waveform. Means Q1 for applying to the.

Conventionally, the dynamic focus unit synthesizes a horizontal parabolic waveform and a vertical parabolic waveform. In the present invention, the waveform is synthesized by applying the amplified vertical parabolic waveform to the secondary bias of the focus transformer unit 10.

The parabolic waveform of the vertical component was used by directly integrating the waveform of the vertical deflection output by the integrating means 32 to simplify the circuit, and inverted and amplified it by the amplifying means Q1 and applied to the secondary side of the transformer 10. It was. The amplitude is about 150 ~ 250Vpp. To adjust the amplitude, change the series base resistance R3 or adjust the amplification degree (R1 / R7).

At the connection point of the amplifying means Q1 and the secondary winding, a capacitor CH30, which bypasses the horizontal parabolic waveform induced in the secondary winding to the vertical dynamic focus unit and prevents waveform distortion, is connected. The capacitance of CH30 is set to 1500pF, but it is sufficient to set the capacitance large enough so that waveform distortion does not occur.

The operation of the focus transformer unit 10 and the S-shaped correction unit 20 configured as described above will be described. First, when the frequency of the horizontal parabolic waveform is high, the FET is controlled by the MCU so that all capacitors except the fifth capacitor C10 of the S-shaped correction unit 20 are turned off. Therefore, the effective primary winding of the focus transformer unit 10 is 6T, which is the sum of the number of turns of each intermediate tap, so that the voltage amplification between the primary and secondary is maximum.

On the other hand, at low horizontal frequencies, all capacitors are controlled by the MCU so that the deflection current flowing in each primary winding increases in proportion to the capacitance of each capacitor. That is, at the low horizontal frequency, a large amount of deflection current flows toward C6, which has a large capacitance, and the effective primary winding becomes 1T between A-a and the influence of the remaining windings is insignificant.

Each capacitor in the S-shaped correction unit 20 is turned on / off according to the horizontal frequency, the higher the frequency is set so that the capacity of the capacitor is smaller. However, at the highest frequency, a coarse correction capacitor must be present, so a capacitor that does not need to be turned on / off is needed. This is C11. That is, at the highest frequency, all capacitors except C11 are turned off.

Due to this action, the voltage transformer is varied in the focus transformer section 10 in accordance with the frequency of the horizontal parabolic waveform, and a horizontal parabolic waveform having a constant amplitude can be obtained on the secondary side.

As described above, in the conventional focus transformer method, the difference in amplitude according to the horizontal frequency cannot be compensated, and thus it is not applicable to the monitor using a wide range of horizontal frequencies. However, according to the present invention, a separate additional circuit is not required. The difference in amplitude according to frequency can be effectively compensated. In addition, the complicated configuration of the waveform generation circuit, the delay compensation circuit, the amplifier circuit, the impedance matching circuit, and the like, which are necessary for the conventional TR amplifier method, is not necessary.

Claims (8)

As a dynamic focus circuit for multiscan monitors, A focus transformer is formed in the primary winding to which the horizontal parabola waveform outputted from the horizontal output unit is applied, and a horizontal parabolic waveform having a constant amplitude induced in the secondary winding from the current flowing in the primary winding to the CRT. Part 10, Primary winding of the focus transformer section 10 in accordance with the frequency region of the horizontal parabolic waveform by control of a microprocessor to adjust the current flowing in the primary winding of the focus transformer section 10 according to the frequency of the horizontal parabolic waveform. S-shaped correction unit 20, comprising a plurality of compensation capacitors that are turned on / off so that one of the middle tap of the selected as the current path, A dynamic focusing circuit for a monitor using a current transformer, comprising a vertical dynamic focusing unit for synthesizing a vertical parabolic waveform output from a vertical output unit with a horizontal parabolic waveform generated on a secondary side of the focus transformer unit 10. In claim 1, The primary winding of the focus transformer unit 10 has a start end and an end of a winding, and a first middle tap, a second middle tap, and a third middle tap are formed therebetween, and the S-shaped correction unit 20 The compensating capacitor is composed of first to fifth capacitors turned on / off by a switching element driven by a microprocessor. The horizontal parabola waveform output from the horizontal output unit is applied to the start of the primary winding of the focus transformer unit 10, and the first capacitor C6 of the S-shaped correction unit 20 is connected to the first intermediate tab. The second capacitor C7 of the magnetic correction unit 20 is connected, the third capacitor C8 of the S-shaped correction unit 20 is connected to the second middle tap, and the S-shaped correction unit ( The fourth capacitor (C9) of 20) is connected, and the fifth capacitor (C10) of the S-shaped correction unit 20 is connected to the end of the winding, characterized in that the dynamic focus circuit for a monitor using a current transformer. In claim 2, the primary winding of the focus transformer unit 10 is the first middle tap once, the second middle tap once, the third middle tap twice, the fourth middle tap twice from the start of the winding Winding, the secondary winding is characterized in that the winding 900 times, the dynamic focus circuit for a monitor using a current transformer. The method according to claim 2 or 3, characterized in that the load capacitor is connected to both ends of the secondary winding of the focus transformer unit 10, the dynamic focus circuit for a monitor using a current transformer. The method of claim 1, wherein the vertical dynamic focus unit Means for integrating the vertical parabolic waveform output from the vertical output section; And a means for amplifying the integrated waveform and applying it to the secondary winding of the focus transformer section (10). The current transformer according to claim 5, wherein a connecting means for amplifying the integrated waveform and the secondary winding is connected to a capacitor which bypasses the horizontal parabolic waveform induced in the secondary winding to not enter the vertical dynamic focus unit. Dynamic focus circuit for monitor using A focus transformer used in a dynamic focus circuit for a monitor configured as claimed in claim 1, The primary winding has a start end and an end of a winding, and a first middle tap, a second middle tap, and a third middle tap are formed therebetween, and the primary winding is formed according to the frequency region of the horizontal parabolic waveform by the control of a microprocessor. One of the intermediate taps of the winding is selected as the current path, and the focus transformer is characterized by applying a horizontal parabolic waveform of constant amplitude induced in the secondary winding from the current flowing in the primary winding to the CRT. The method of claim 7, wherein the primary winding is wound once from the winding start end, the first middle tap is wound once, the second middle tap is wound once, the third middle tap is wound twice, and the fourth middle tap is wound twice. Focus transformer, characterized in that the winding 900 times.