JPH0531347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a linearity correction circuit in a horizontal deflection output circuit of a multi-scanning cathode ray tube, which can accommodate various different horizontal frequencies.

[Conventional technology]

Conventionally, displays connected to industrial computer terminals, personal computers, etc. have different horizontal frequencies depending on the computer of each company.
Each uses a dedicated display.
The horizontal frequency used varies by company, but approximately
The horizontal frequency range is 24kHz to 80kHz, which is higher than the horizontal frequency of 15.75kHz (NTSC system) for normal consumer televisions, and it covers a wide range.

Multi-scan cathode ray tubes allow a single device to support models from different companies with different horizontal frequencies.

Incidentally, the horizontal deflection output circuit of a cathode ray tube generally uses a method in which a sawtooth wave current is passed through the horizontal winding of a deflection coil. In order to deflect the raster left and right, it is best to periodically flow this deflection current through the deflection coil, but in an actual circuit it is difficult to flow a linear sawtooth wave current through the deflection coil. This is due to the influence of the direct current resistance of the deflection coil, the saturation voltage of the transistor, the forward voltage drop of the damper diode, the resistance of other lead wires, and the efficiency of the flyback transformer, and the sawtooth wave current increases exponentially. Because of this, the left side of the raster tends to stretch and the right side tends to shrink. In this way, conventional horizontal deflection output circuits suffer from poor linearity, but in conventional single horizontal frequency cathode ray tubes, linearity correction consists of a saturable reactor biased with a DC magnetic field in series with the deflection coil. A coil (hereinafter referred to as a linearity coil) is connected, and by utilizing the fact that the self-inductance changes depending on the degree of saturation of the deflection current flowing through it at each point, the deflection current is made small at the beginning of the scan and becomes large at the end. and corrected it.

Also, when using a silicon diode as a damper diode, since the internal resistance at the beginning of current flow is large, the damper diode is connected to the wound terminal of the horizontal output transformer to correct its linearity (hereinafter referred to as winding). (referred to as correction).

[Problem to be solved by the invention]

However, in multi-scan cathode ray tubes that can handle signals with various horizontal frequencies with a single device, the power supply voltage must be varied according to the horizontal frequency to achieve appropriate horizontal deflection, so conventional linear The gender correction method has some drawbacks.

For example, some deflectors have a horizontal frequency of 15k
When changing from Hz to 80kHz, the power supply voltage is changed from about 35V to 180V depending on the horizontal frequency. When the horizontal frequency is low, the power supply voltage is also low, so the influence of the saturation voltage of the damper diode and horizontal output transistor becomes large and linearity deteriorates. Similar to conventional single-frequency cathode ray tubes, the influence can be reduced by correction using a linearity coil, winding correction using a choke coil or flyback transformer at the connection point of the damper diode, and the like.

The characteristics of the linearity coil can be fixed or changed by adjusting the variable magnet.
This controls linearity correction, but it is not practical because it needs to be varied according to the horizontal frequency. Further, correction by winding the damper diode connection point is inconvenient because the winding correction voltage varies depending on the power supply voltage. This is because at a high horizontal frequency, the winding correction voltage becomes high and the loss increases. For this reason, if correction by winding is performed, it will have an adverse effect at high horizontal frequencies.

Therefore, an object of the present invention is to provide a horizontal deflection linearity correction circuit that is optimal for multi-scan cathode ray tubes and can not only perform linearity correction at low horizontal frequencies, but also prevent the adverse effects of winding correction at high horizontal frequencies. Our goal is to provide the following.

[Means to solve the problem]

The horizontal deflection linearity correction circuit according to the present invention is used in a horizontal deflection output circuit of a multi-scan cathode ray tube that performs horizontal deflection using a power supply voltage that changes depending on the horizontal frequency. A switching circuit in which the series connection circuit of the first and second diodes and the horizontal deflection yoke are connected in parallel, and which is turned on by the detection signal of the horizontal frequency detection circuit which outputs the detection signal when the horizontal frequency is below a predetermined frequency. A first winding of a step-up transformer is connected between the transistor and the connection point of the first and second diodes forming the series connection circuit, and a damper diode is connected to the connection point of the horizontal output transistor and the flyback transformer. and a parallel circuit of a resonant capacitor, and the path of the current flowing through the first winding of the step-up transformer is switched by the on/off operation of the switching transistor. When the horizontal frequency is below a predetermined frequency, the linearity is corrected by a switching operation that boosts the potential at the connection point between the second winding of the step-up transformer and the damper diode.

[Effect]

According to the horizontal deflection linearity correction circuit according to the present invention, the switching circuit provided in the horizontal deflection output circuit works to boost the potential at the anode side connection point of the damper diode when the horizontal frequency is below a predetermined frequency,
When the predetermined frequency is exceeded, the step-up is stopped, so that linearity correction equivalent to the conventional winding correction can be performed at low horizontal frequencies, and the winding at high horizontal frequencies that occurs in the conventional method can be corrected. Loss due to correction can be prevented.

〔Example〕

Next, embodiments of the horizontal deflection linearity correction circuit according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a horizontal deflection output circuit diagram showing an embodiment of the horizontal deflection linearity correction circuit according to the present invention.
In FIG. 1, reference numeral 10 indicates a horizontal drive circuit for driving the horizontal output transistor _Q11 , and a current of a magnitude necessary for the horizontal output transistor _Q11 to sufficiently saturate the horizontal oscillator output signal in the previous stage of this circuit is designated by reference numeral 10. The drive current waveform is amplified to a maximum of 100 kHz, and is configured to shape the drive current waveform. The emitter of the horizontal output transistor _Q11 is grounded via the primary winding _L11 of the flyback transformer, and is also connected to the anode of the diode _D21 in the switching circuit 20 and the secondary winding L of the step-up transformer _T20 . Connect to one end of ₂₂ ,
Furthermore, it is also connected to one end of the deflection yoke L _Y.

The collector of the horizontal output transistor Q ₁₁ is the cathode of the damper diode D ₁ , the resonant capacitor C ₁
and DC blocking capacitor C _S , and switching circuit 2
It is connected to each cathode of diodes D ₂₂ and D ₂₃ in 0, and also connected to a power supply circuit 40 that changes according to the horizontal frequency. The DC blocking capacitor C _S , the linearity coil L _S and the deflection yoke L _Y are connected in series. The anode of the damper diode _D1 and one end of the resonant capacitor _C1 are connected to the other end of the secondary winding _L22 of the step-up transformer _T20 . One end of the primary winding L ₂₁ of the step-up transformer T ₂₀ is connected to the anode of the diode D ₂₂ and the cathode of the diode D ₂₁ , and the other end of the primary winding L ₂₁ is connected to the anode of the diode D ₂₃ and the cathode of the diode D 21. It is connected to the cathode of diode _D24 and to the collector of switching transistor _Q21 . Diode D ₂₄
The anode of is grounded. The emitter of the switching transistor _Q21 is grounded, and the horizontal frequency detection circuit 30 is connected to the base. Horizontal frequency detection circuit 3
0 detects the horizontal frequency, outputs an on signal that turns on the transistor _Q21 when the frequency is below a predetermined frequency, and outputs an off signal when the frequency exceeds the predetermined frequency.

Next, the operation of the circuit of this embodiment configured as described above will be explained. In a multi-scan cathode ray tube, appropriate horizontal deflection must be achieved by varying the power supply voltage according to the horizontal frequency. This point will be briefly explained below.

Generally, the relationship between the sawtooth wave current i flowing through the horizontal deflection yoke and the voltage v generated across the deflection yoke is expressed by the following equation.

v=-Ldi/dt (1) where L is the inductance value of the deflection yoke. By integrating the above equation, the following equation is obtained.

i=-V _DC /Lt (2) Here, V _DC is the DC voltage applied to the deflection yoke. The peak value i _p of the sawtooth wave current is expressed by the following equation.

i _p =-V _DC /Lt _H (3) Here, t _H is the horizontal deflection scanning period, that is, the reciprocal of the horizontal deflection frequency f _H . Angle δ of deflection due to the deflection yoke of the electron beam scanning inside the cathode ray tube
is determined by δ=√i _p …(4). Substituting equation (3) into equation (4) gives |δ|=V _DC /√Lt _H (5).

According to equation (5), the angle of deflection of the electron beam, that is, the deflection angle δ, becomes smaller as the horizontal frequency (1/t _H becomes higher), and the horizontal amplitude becomes smaller. It turns out that the power supply voltage must be increased.

If the horizontal frequency f _H changes from 15kHz to 80kHz, the power supply voltage is changed accordingly. The power supply circuit 40 in FIG. 1 detects the horizontal frequency,
A voltage V _cc corresponding to the horizontal frequency is supplied to the horizontal deflection output circuit.

In FIG. 1, a case where the horizontal frequency detection circuit 30 outputs an on signal, that is, a case where the frequency is below a predetermined frequency will be described first. What is the predetermined frequency?
Below that frequency, linearity distortion due to internal resistance at the beginning of current flow in the damper diode cannot be ignored, and here it is 32kHz.
Below this horizontal frequency, the power supply voltage is typically below 70V, and if the voltage drop across the diode is 1.5V, it will have an impact of 2-5%. At frequencies higher than that, the effect is less than 2% and can be ignored. Of course,
Since the voltage changes depending on the inductance of the deflection yoke used, the size of the screen, etc., the optimum value of the predetermined frequency can be arbitrarily determined depending on the device to which it is applied.

Now, when the switching transistor _Q21 becomes conductive due to the ON signal of the horizontal frequency detection circuit 30,
As a result, the primary winding L ₂₁ of the step-up transformer T ₂₀ becomes
Grounded via transistor _Q21 . Therefore,
A current path of horizontal output transistor Q ₁₁ , diode D ₂₁ , winding L ₂₁ , and transistor Q ₂₁ is formed,
Due to the on/off operation of the horizontal output transistor Q ₁₁ , the voltage according to the turns ratio of the step-up transformer T ₂₀ changes to 2.
induced in the secondary winding L ₂₂ . That is, the connection point of damper diode D ₁ is horizontal output transistor Q ₁₁
The potential is higher than the emitter potential of , and a correction equivalent to the conventional winding correction is performed. When the power supply voltage V _cc is low, the influence of the saturation voltage of the horizontal output transistor Q ₁₁ and the forward voltage drop of the damper diode is large, and the linearity _deteriorates . This can be improved by boost correction.

When the horizontal frequency exceeds the predetermined frequency of 32 kHz, the output voltage V _cc of the power supply circuit 40 is a high voltage according to the horizontal frequency, so the linearity distortion due to the effect of the voltage drop of the damper diode is The size is negligible. On the other hand, the effect of increased loss due to boost correction due to higher voltage is greater, so if this predetermined frequency is exceeded,
It is better not to perform boost correction, which corresponds to conventional winding correction.

Therefore, the horizontal frequency detection circuit 30 operates to output an off signal when the predetermined frequency is exceeded. This causes switching transistor _Q21 to be cut off. At this time, the current of damper diode D ₁ and resonant capacitor C ₁ is 2
During the period when the current flows through the secondary winding L ₂₂ , the current path of the diode D ₂₁ → primary coil L ₂₁ → diode D ₂₃ and the current path of the diode D ₂₄ → primary coil L ₂₁ → diode D ₂₂ are changed due to the coupling of the transformer. Current is consumed via the current path. For this reason, the step-up transformer
No voltage is induced in the secondary winding L ₂₂ of T ₂₀ , and the anode connection point of the damper diode D ₁ has the same potential as the emitter of the horizontal output transistor Q ₁₁ .
No boosting correction, which corresponds to conventional winding correction, is performed. Linearity correction is achieved simply by adjusting the linearity coil L _S or by adjusting the DC blocking capacitor C _S (adjustment circuit not shown).

The horizontal deflection output circuit that operates as described above and has the switching circuit 20 shown by the dashed-dotted line in FIG. 1 enables linearity correction over a wide horizontal frequency range.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention, the switching circuit is configured so that a boost correction circuit similar to the conventional winding correction operates in the horizontal deflection output circuit below a predetermined frequency. Even when the power supply voltage changes depending on the frequency because a single device, such as a cathode ray tube, receives various horizontal frequencies, linearity correction can be effectively performed.

At a horizontal frequency lower than a predetermined frequency, the power supply voltage is low, so the effect of the forward voltage drop at the beginning of the current flow in the damper diode becomes relatively large, and deterioration of linearity becomes a problem. However, the switching circuit according to the present invention works to boost the potential at the connection point on the anode side of the damper diode, so-called winding correction, so that linearity is corrected.

At a horizontal frequency higher than the predetermined frequency, the power supply voltage becomes high, and the linearity distortion due to the voltage drop of the damper diode is relatively negligible, and the switching circuit according to the present invention works to stop the boost correction. Therefore, the problem that the winding correction voltage becomes high and the loss increases that occurs in the conventional method can be solved.

Therefore, according to the present invention, it is possible to effectively correct the linearity of the horizontal deflection output circuit over a wide range of horizontal frequencies.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a horizontal deflection linearity correction circuit according to the present invention. 10...Horizontal drive circuit, 20...Switching circuit, 3
0...Horizontal frequency detection circuit, 40...Power supply circuit,
Q ₁₁ ... Horizontal output transistor, L ₁₁ ... Primary winding of flyback transformer, D ₁ ... Damper diode, C ₁ ... Resonance capacitor, C _S ... DC blocking capacitor, L _S linearity coil, L _Y ...
Deflection yoke, T ₂₀ ... Step-up transformer, L ₂₁ ... Primary winding of step-up transformer, L ₂₂ ... Secondary winding of step-up transformer, Q ₂₁ ... Switching transistor, D ₂₁ , D ₂₂ , _D23 , _D24 ...Diode.

Claims (1)

[Claims] 1. In a horizontal deflection output circuit for a multi-scan cathode ray tube that performs horizontal deflection using a power supply voltage that changes according to the horizontal frequency, a first and second transistor is connected between the collector and emitter of the horizontal output transistor. A series connection circuit of diodes and a horizontal deflection yoke are each connected in parallel, and the switching transistor is connected in series by the detection signal of a horizontal frequency detection circuit that outputs a detection signal when the horizontal frequency is below a predetermined frequency. A first winding of a step-up transformer is connected between the connection point of the first and second diodes forming the circuit, and a damper diode and a resonant capacitor are connected in parallel to the connection point of the horizontal output transistor and the flyback transformer. A second winding of the step-up transformer is connected between the step-up transformer and the circuit, and the path of the current flowing through the first winding of the step-up transformer is switched by the on/off operation of the switching transistor, so that a horizontal frequency is set at a predetermined level. A horizontal deflection linearity correction circuit characterized in that the circuit is configured to correct linearity by a switching operation of boosting the potential at a connection point between the second winding of the step-up transformer and the damper diode when the voltage is below the frequency. .