JPS6161748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image distortion correction device for correcting so-called image distortion caused by changes in brightness and darkness of images in a television receiver using a cathode ray tube, and the present invention effectively corrects the distortion. The purpose is to provide an inexpensive device that can

In conventional television receivers, if a correction circuit is not used, depending on the content of the video signal, for example, when displaying a screen such as a white rectangle on a black background, the image tends to be distorted into a trapezoid. Ta. This is because the high voltage supplied to the cathode ray tube to display the white rectangle drops due to internal resistance of the flyback transformer, etc., and if the horizontal deflection power does not change, the deflection angle will widen as a result. This is caused by getting tired. In order to avoid this, it is necessary to improve the high voltage regulation or to externally correct the horizontal deflection current using a diode modulator system or the like.

However, all of the above methods result in larger, more complex, and more expensive devices, and are currently difficult to be adopted in general home television receivers.

The present invention basically makes it possible to correct image distortion caused by brightness changes in television receivers by adding very few elements, one diode and one capacitor, to the conventional horizontal deflection circuit. One embodiment of this will be described below with reference to the accompanying drawings.

In Figure 1, 1 is a horizontal deflection coil, 2 is an S
This is a correction capacitor. Note that 1 may also include a linearity coil. A first resonant capacitor 3 and a first damper diode 3 are connected in parallel to the horizontal deflection coil 1 and the S-shaped correction capacitor 2 connected in series. A connection point between the capacitor 3, the diode 4, and the capacitor 2 is grounded through a parallel circuit of a correction capacitor 5 and a second damper diode 6. The connection point between the capacitor 3, the diode 4, and the deflection coil 1 is connected to the +B power supply terminal through the primary winding of the flyback transformer 7, and is also connected to the collector terminal of the horizontal output transistor 8. The emitter of transistor 8 is grounded. 9 is a high voltage output circuit connected to the secondary side of the flyback transformer.

The operation of the above circuit will be explained below with reference to FIG.

FIG. 2 is an equivalent circuit representing the second half period of scanning by the horizontal deflection circuit. First, during the second half of the scan, the transistor 8 is conductive, so the charge stored in the capacitor 2 during the first half of the scan follows a loop a through the deflection coil 1, the transistor 8, and the diode 6, and is almost transferred to the deflection coil 1. Start passing a linearly increasing current. Also +B
A linearly increasing current flows from the power supply through the flyback transformer and transistor 8. Loop b represents this. These conditions persist until the transistor 8 becomes non-conducting and the current flowing through the deflection coil 1 is at its maximum.

FIG. 3 shows the operating state during the first half of the flyback period. At the beginning of the first half of the flyback period, the second
Although the transistor 8 shown in the figure becomes non-conductive,
The deflection coil 1 releases electromagnetic energy through a loop c formed by a capacitor 3 and a capacitor 2 in an attempt to keep the current flowing. This continues until the current flowing through the deflection coil becomes zero, and at the last timing of the first half of this flyback period, the electrostatic energy stored in the capacitor 3 is at its maximum, and the voltages across the capacitors 3 and 5 are at their maximum.

Figure 4 represents the second half of the flyback period. At the beginning of the second half of the flyback period, capacitor 3, where the voltage across both ends is maximum, tries to pass current through deflection coil 1, where current is minimum, and the loop formed by deflection coil 1, capacitor 2, and capacitor 3 A current is passed through the path e, and the voltage at the flow end of the capacitor 3 quickly returns to O. Further, through the series resonance loop f formed through the flyback transformer 7, capacitor 3, and capacitor 5, part of the charge stored in the capacitor 3 and capacitor 5 returns to the +B power supply through the flyback transformer 7.

FIG. 5 shows the state in the first half of scanning until transistor 8 is turned on. The deflection coil 1, which reaches its maximum current at the end of the flyback period, continues to flow a linearly decreasing current through the loop g formed by the capacitor 2 and the diode 4. Further, the charge remaining in the capacitor 5 returns to the power supply through a loop h formed by the diode 4 and the flyback transformer 7.

FIG. 6 shows the state after the transistor is turned on in the first half of scanning. Although the transistor turns on in the middle of the first half of the scan, there is no change in this loop, which continues to flow a linearly decreasing current through the loop i shown in the figure, which consists of the deflection coil 1, capacitor 2, and diode 4. However, a new loop j consisting of the flyback transformer 7 and the transistor 8 is formed and begins to conduct an increasing current directly. At the same time, almost all of the residual charge accumulated in the capacitor 5 is discharged through the loop k formed through the diode 4 and the transistor 8.

By repeating the above-described processes from FIG. 2 to FIG. 6, a short tooth-shaped deflection current flows through the deflection coil 1, and horizontal deflection scanning is performed.

In this state, as long as the load on the secondary side of the flyback transformer 7 is constant, there is no change, and there is no change in the amount of charge from the flyback transformer 7 to the resonance capacitor 3, and therefore there is no change in the horizontal scanning width. There is no change.

However, when the load on the secondary side becomes heavy, that is, when a large amount of high-voltage output current flows on the secondary side, the current in loop f in FIG. 4 increases.

This situation is shown in FIGS. 7 and 8. In FIG. 7, I ₁ represents the output current of the high voltage output circuit, and I ₂ represents the circuit current from the contact point of the capacitor 3 and the deflection coil 1 to the point connected to the flyback transformer 7. Further, V represents the voltage of the flyback pulse. The dotted line in the figure is the part that does not play a major role in the latter half of the flyback period.

I ₁ and I ₂ shown in FIGS. 8 and 7 are idealized representations of how they change when the load on the high-voltage output circuit is light and heavy. Further, V is shown in FIG. 8a to show the timing at which these events occur. When the load is small, I ₁ (Fig. 8b) flows in a pulsed manner only for a certain period in the latter half of the flyback period, but when the load becomes heavy, the peak value of the pulse increases as shown in Fig. 8c. flows as a peak current that increases depending on the weight of the load. This current is originally supplied by the charges of capacitors 3 and 5 via the flyback transformer 7, and as can be seen from the I ₂ waveform in this state, the I ₂ in the latter half of the flyback period is The peak value of is low when the load is light, as shown in FIG. 8d, and becomes high when the load is heavy, as shown in FIG. 8e. As a result, the total amount of charge accumulated in capacitor 3 during the flyback period is inevitably large when the load is light and small when the load is heavy, and the deflection power is large when the load is light and is small when the load is heavy. Sometimes it gets smaller. Therefore, the horizontal deflection amplitude is large when the load is light, that is, when the picture tube screen is dark on average in one horizontal scanning period, and it is large when the load is heavy, that is, when the picture tube screen is bright on average in one horizontal scanning period. It becomes smaller during the scanning period.

FIG. 9 shows another embodiment, in which the operation is the same except that the parallel circuit of diode 6 and capacitor 5 is placed on the flyback transformer side. Note that in both embodiments, other switching elements may be used as the transistor 8.

As described above, the present invention connects a first capacitor and a second damper diode in parallel to a series circuit of a horizontal deflection coil and an S-shaped correction capacitor, and connects a second damper diode in series to this parallel-connected circuit. A parallel circuit of a diode and a second capacitor is connected such that the polarity of the second damper diode is the same as that of the first damper diode, and a switching element is connected to both ends of this entire series circuit. This system is characterized by applying a DC power supply voltage through the primary winding of a flyback transformer, and can effectively correct distortion of cathode ray tube images with a simple configuration that requires only the addition of a diode and a capacitor. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an image distortion correction device according to an embodiment of the present invention, FIG. 2, FIG. 3, FIG. 4, and FIG.
6 and 7 are equivalent circuit diagrams for explaining the same device, FIG. 8 a, b, c, d, and e are waveform diagrams for explaining the same device, and FIG. 9 is an equivalent circuit diagram for explaining the same device. FIG. 2 is a circuit diagram of an image distortion correction device in an example. 1... Deflection coil, 2... S-shaped correction capacitor, 3, 5... Capacitor, 4, 6... Diode, 8... Transistor, 7... Flyback transformer.

Claims (1)

[Claims] 1 A first capacitor and a first damper diode are each connected in parallel to a series circuit of a horizontal deflection coil and an S-shaped correction capacitor, and a second damper diode and a second capacitor are connected in series to this parallel-connected circuit. Connect a parallel circuit with the second damper diode so that the polarity of the second damper diode is the same as that of the first damper diode, connect a switching element to both ends of this whole series circuit, and connect a switching element to the flyback transformer. An image distortion correction device characterized in that a DC power supply voltage is applied through a primary winding.