JPH0287874A - High voltage/focus voltage generating circuit - Google Patents

Abstract

PURPOSE:To easily execute a focus adjustment without causing the deterioration of reliability of other circuit and a CRT by connecting newly a voltage source to a part whose voltage is a little lower than a focus voltage on the way of a bleeder resistance, and boosting the focus voltage by the new voltage source, when the focus voltage is insufficient. CONSTITUTION:The bleeder resistance 2 is provided on the output terminal of a high voltage generating circuit 1 containing the flyback transformer 14 of a CRT display. Also, the title circuit is provided with a focus adjusting voltage generating circuit 6 having a variable voltage source 17 for controlling an output voltage so that a voltage fetched from a focus voltage output terminal from which a voltage being lower than a voltage 4 required for a focus on the way of the resistance becomes a target voltage. In such a manner, the focus can be adjusted easily and stably, and also, the deterioration of reliability of other circuit, etc., is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a high voltage/focus voltage generation circuit for a CRT display using electrostatic focusing.

(Prior Art) Generally, there are two methods for focusing a CRT display: an electrostatic method and an electromagnetic method. And generally direct view type CR
T-displays use an electrostatic method, while projection CRT displays use an electromagnetic method.

Now, in a general direct view type CRT display, as shown in FIG. 4, the high voltage generating circuit 1 has a switching transistor 11
, a damper diode 12, a resonant capacitor 13, and a flyback transformer 14. Then, a tap is taken out from the middle of the secondary winding of the flyback transformer 14, the voltage is divided by the bleeder resistor 2, and the focus voltage (Er) is 4.
I am getting . However, with this method, the pulses generated in the secondary winding change as the high voltage load changes, so the focus voltage 4 cannot be maintained at a constant ratio with respect to the high voltage (Eh) 3.

Therefore, as shown in Fig. 5, there is a method of connecting the bleeder resistor 2 directly to the output of the high voltage generation circuit 1 and dividing the high voltage 3 to obtain the focus voltage (E').
Although the power consumption of the wave bleeder resistor 2 increases compared to the circuit shown in the figure, a relatively stable focus voltage 4 can be obtained.

Recently, large direct-view CRT displays have been manufactured, and when used as a monitor, the focus must be good to maximize the image quality. The problem here is that you have to adjust the focus while looking at the screen.

If it is a small set, you can adjust it while looking at the screen if there is a focus adjustment volume 21 for the bleeder resistor 2 on the side of the set. However, to adjust the focus adjustment volume 21 on the side, you need to bend your elbow slightly, so the width of the set is slightly longer than the distance from your eyes to your elbow.
In a set larger than about 0 cm, it becomes difficult to see the side opposite to the focus adjustment volume 21, making it difficult to make proper adjustments. Therefore, it is necessary to bring the focus adjustment volume 21 to the front.

However, considering the shape of the CRT display, the circuits are placed relatively toward the rear of the set. Therefore, the bleeder resistor 2 will be installed at a location away from the circuit. Here, the bleeder resistor 2 is relatively large due to its withstand voltage and power consumption, and is difficult to install because it is integrated with the flyback transformer 14 using a high voltage cable.

Also, the high voltage cable becomes long, which leads to various circuits, leads to the high impedance focus voltage 4, and when you consider the effects on various circuits when discharge occurs, it is not a very good structure. .

(Problems to be Solved by the Invention) In the above-described configuration in which the focus adjustment volume is brought to the front, problems may arise in terms of reliability of the circuitry, etc., even if focus can be easily adjusted.

Furthermore, there is a possibility that the focus voltage may vary due to dielectricity. Moreover, placing a large bleeder resistor at the front imposes structural constraints.

Therefore, the present invention has been made in view of the two circumstances, and is capable of generating a high voltage/focus voltage that can be easily and stably focused without causing a decrease in the reliability of other circuits. The purpose is to provide circuits.

[Structure of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention provides a high voltage generation circuit including a flyback transformer that outputs high voltage for a CRT display, and an output terminal of this high voltage generation circuit. A bleeder resistor is connected to the bleeder resistor, a focus voltage output end is connected to a part of the bleeder resistor where a voltage lower than the voltage required for focusing can be extracted, and an output end is connected to the part of the bleeder resistor to output the focus voltage. The present invention is characterized by comprising a focus adjustment voltage generation circuit having a variable voltage source that controls the output voltage so that the voltage taken out at the end becomes the voltage necessary for focusing.

(Function) With the above means, the point where the focus voltage is taken out from the bleeder resistor is fixed to be taken out from a point slightly lower than the required voltage, the focus adjustment volume is eliminated, and a new voltage source is connected in the middle of the bleeder resistor.

The voltage source can then be controlled from the front. As a result, the insufficient focus voltage can be raised to the required focus voltage by increasing the amount with a new voltage source.

(Example) An example of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a damper diode 12 and a resonant capacitor 13 are connected in parallel between the emitter and collector of a switching transistor 11 of a high voltage generating circuit 1 of a CRT display. Grounded. The transistor 11
The collector of the transformer 14 is connected to one end of the primary winding of a flyback transformer 4, and the other end of the transformer 14 is connected to the emitter of a control element 53 consisting of a transistor and grounded via a capacitor 56. The control element 53 has a collector connected to the +vb power supply and a base connected to the comparator 52.
connected to the output end of the A non-inverting input terminal of this comparator 52 is connected to a variable voltage source 51. The anode of a diode 16 is connected to the secondary winding of the flyback transformer 14, and a high voltage voltage (
Eh) 3 is taken out. The cathode of the diode 16 is connected to a resistor 54 whose midpoint is connected to the inverting input of a comparator 52 .

Further, the cathode of the diode 16 is connected to a resistor 22°23.
It is grounded through a bleeder resistor 2 consisting of 24, and a focus voltage (E') is applied to the connection point between these resistors 22 and 23.
4 is taken out. The connection point between the resistors 23 and 24 is connected to the cathode of a diode 68 and is grounded via a capacitor 66. The anode of this diode 68 is connected to the secondary winding of a flyback transformer 64, and one end of the primary winding of this flyback transformer 64 is connected to the collector of the switching transistor 61, and the collector and emitter of this transistor 61 are connected to each other. A damper diode 62 and a resonant capacitor 63 are connected in parallel between them.

The emitter of this transistor 61 is grounded.

The other end of the primary winding of the flyback transformer 64 is grounded via a capacitor 75 and a transistor 73.
The emitter of this transistor 73 is connected to a resistor 74.

The collector of the transistor 73 is connected to the +vb power supply, and the base is connected to the output terminal of the comparator 72. This comparator 72 has a non-inverting input terminal connected to the variable voltage source 71,
The inverting input terminal is connected to the midpoint of the resistor 74. The comparator 52. A circuit including a control element 53 and a resistor 54 constitutes a high voltage stabilizing circuit 5, and the transistors 61. A circuit including the flyback transformer 64 constitutes the focus adjustment voltage generation circuit 6, and includes the variable voltage source 71, the comparator 72. A circuit including the resistor 74 and the resistor 74 constitutes the control circuit 7.

That is, a display that requires high precision in focus also requires high precision in other parts. Therefore, a high voltage stabilizing circuit 5 is provided to control the power supply voltage 15 of the high voltage generating circuit 1 so that fluctuations in the high voltage (Eh) 3 due to high voltage load fluctuations are reduced. The control is performed by comparing the high voltage 3 divided by a resistor 54 with a variable voltage source 51 (for example, a constant voltage power source divided by a volumetric volume) by a comparator 52, and controlling the control element 53 based on the comparison to control the power supply voltage 15. This is done by changing the .

The focus voltage (Ef) 4 is extracted by dividing the high voltage 3 using a bleeder resistor 2, but the voltage extracted here is made slightly lower than the required voltage. For example, if the voltage required for focusing is 30% of the high voltage 3, then the bleeder resistor 2
The value of resistor 22 is 75% of the total, and the remaining resistor 23.
The values of 24 are combined to 25% so that the value of high voltage 3 is 25%. The output of the focus adjustment voltage generation circuit 6 is connected to the connection point between the resistors 23 and 24. The output voltage 67 of the focus adjustment voltage generation circuit 6 changes depending on the power supply voltage 65,
Since the power supply voltage 65 is changed by the control circuit 7, the output voltage 67 of the focus adjustment voltage circuit 6 is ultimately controlled by the control circuit 7. As the focus adjustment voltage generation circuit 6, for example, one having the same configuration as the high voltage generation circuit 1 is used. (The capacitor 66 is for rectification and is a CR in the high voltage generation circuit 1.
It is a substitute for the capacity at T. ) The control circuit 7 has almost the same configuration as the high-voltage stabilizing circuit 5, and instead of the resistor 54 that divides the high voltage 3, the output is divided by a resistor 74 and is supplied to the comparator 72. Thereby, the voltage of the input power supply voltage 65 of the focus adjustment voltage generation circuit 6 can be controlled by the voltage of the variable voltage source 71, and furthermore, the output voltage 67 can also be controlled.

When the input power supply voltage 65 of the focus adjustment voltage generation circuit 6 is low, the pulse generated on the secondary side of the flyback transformer 64 is small and if it does not reach the voltage divided by the bleeder resistor 2, the output voltage 67 will be lower than the bleeder resistor 2. The voltage is divided by . For example, resistor 23 in bleeder resistor 2
If the values of and 24 are set to 15% and 10% of the total, the output voltage will be 6.
7 cannot be less than 10% of the high voltage 3. When the output voltage 67 exceeds that voltage, the high voltage voltage 3 and the output voltage 6
Focus voltage 4, which is obtained by dividing voltage 7 by resistors 22 and 23, also increases. When the output voltage 67 becomes 16% of the high voltage 3, the focus voltage 4 becomes 30% of the high voltage 3, and focus is achieved. In other words, the focus can be adjusted by adjusting the voltage of the variable voltage source 71.

The output voltage 67 of the focus adjustment voltage generation circuit 6 is lower than the high voltage 3, and the load is high with the bleeder resistor 2, so the load current is small and the power consumption is also low. Furthermore, since there is no load fluctuation, a stable voltage can be obtained as long as there is no change in the switching period of the switching transistor 61. Furthermore, the high voltage generating circuit 1 does not have to have a high rating.

FIG. 2 shows another embodiment of the invention. The only difference from the circuit shown in FIG. 1 is what the control circuit 7 controls. In FIG. 2, a divided voltage of the output voltage 67 of the focus adjustment voltage generation circuit 6 is input from the bleeder resistor 2 to the comparator 72 instead of the divided voltage of the output voltage of the control circuit 7. With this, a stable focus voltage can be obtained even when the switching period of the switching transistor 61 changes in a CRT display that can input signals with different horizontal frequencies.

FIG. 3 is also another embodiment of the present invention. The variable voltage source 71 of the control circuit 7 in the circuit shown in FIG. 2 is a voltage divided by a resistor 54 of the high voltage 3 and the impedance reduced by a buffer 55, which can be varied by a volume. In this case, even if the high voltage 3 fluctuates due to load fluctuations, the output voltage 67 of the focus adjustment voltage generation circuit 6 is controlled to change in proportion to it, so the focus voltage 4 is more stable relative to the high voltage 3. Keep a constant ratio.

As can be seen from the above embodiments, the focus can be adjusted by changing the voltage of the variable voltage source 71.

Since the voltage of the variable voltage source 71 can be set to a low voltage, when the variable voltage source 71 is configured as a volume, the power consumption of the volume is small, so a small size can be used, and it can be easily attached to the front. If the volume value is reduced, the influence of induction from other circuits will be reduced, and since it is a DC voltage, there will be no induction to other circuits.

Furthermore, since the focus voltage is not supplied independently from the focus adjustment voltage generation circuit 6, but is connected to the high voltage voltage 3 through the bleeder resistor 2, the focus adjustment voltage generation circuit 6 may stop. However, a certain amount of voltage is supplied to the focus. Therefore, CRT
There is no risk that the entire high voltage will be applied between the anode and the focus electrode, causing discharge and deterioration of the electrode.

[Effects of the Invention] As explained above, according to the high voltage/focus voltage generating circuit of the present invention, a focus adjustment function can be easily provided in front of the display without causing a decrease in the reliability of other circuits or CRTs. This has the advantage that focus can be easily adjusted.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the high voltage/focus voltage generating circuit of the present invention, FIGS. 2 and 3 are circuit diagrams showing other embodiments of the high voltage/focus voltage generating circuit of the present invention, and FIG. 5 and 5 are configuration diagrams of conventional high voltage/focus voltage generation circuits, respectively. 1... High voltage generation circuit, 2... Bleeder resistance, 3...
... High voltage, 4... Focus voltage, 6... Focus adjustment voltage generation circuit, 7... Control circuit, 7]...
・Variable voltage source. Applicant's Representative Patent Attorney Takehiko Suzue

Claims (1)

[Claims] A high voltage generation circuit including a flyback transformer that outputs the high voltage of the CRT display, a bleeder resistor connected to the output terminal of this high voltage generation circuit, and a place in the middle of this bleeder resistor where a voltage lower than the voltage required for focusing can be extracted. a focus voltage output terminal connected to the bleeder resistor, and a variable voltage source having an output terminal connected to the middle of the bleeder resistor and controlling the output voltage so that the voltage taken out to the focus voltage output terminal becomes a voltage necessary for focusing. 1. A high voltage/focus voltage generation circuit comprising: a focus adjustment voltage generation circuit.