JP2000115567A - Control circuit for crt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control circuit which can apply larger DC voltage to both ends of a horizontal deflection coil and can reduce a cost. SOLUTION: A positive voltage generation circuit 10 generates positive DC voltage +V1 based on +B voltage to apply to one end side of the horizontal deflection coil LH. In a case when a horizontal deflection frequency fh is 130 kHz, a negative voltage generation circuit 20 generates negative DC voltage -V2 based on +B voltage to apply to the other end side of the coil LH. The control circuit 10 is formed of the circuit 10 and the circuit 20. Thus, voltage to apply to the horizontal deflection coil is easily boosted corresponding to raising of the frequency of the horizontal deflection frequency, thereby higher displaying resolution is suitably realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a CRT, and more particularly, to a CRT which can apply a large DC voltage to both ends of a horizontal deflection coil and can reduce the cost.
The present invention relates to an RT control circuit. In particular, when the horizontal deflection frequency is 30
This is useful for a multi-scan display device that changes in the range of about kHz to 130 kHz.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of an example of a conventional high voltage generating circuit for a CRT including a control circuit. In the CRT high voltage generation circuit 500, the flyback transformer FBT
A first end of the primary winding T1 is connected to a control circuit 10a that generates a positive DC voltage + V1 based on the + B voltage. The + B voltage is, for example, + 200V. The control circuit 10a includes an FET 11 and a freewheeling diode 12
, A smoothing reactor 13 and a smoothing capacitor 14. The control circuit 10a receives the horizontal deflection frequency f from the microcomputer 30.
The control signal S1 corresponding to h is input. The horizontal deflection frequency fh is set within a range of 30 to 110 kHz. As a result, the FET 11 of the control circuit 10a
The period during which the B voltage is intermittent (ON period, OFF period) is P
WM (Pulse Width Modulation) modulation is performed to generate a positive DC voltage + V1 corresponding to the horizontal deflection frequency fh. Generally, as the horizontal deflection frequency fh increases, a larger positive DC voltage + V1 is generated. For example, when the horizontal deflection frequency fh is 30 kHz, the positive DC voltage + V1
= + 50V. Further, when the horizontal deflection frequency fh is 110
At kHz, the positive DC voltage is + V1 = + 180V.

A horizontal output circuit H for generating a flyback pulse during a retrace time of the horizontal scanning of the electron beam is connected to a second end of the primary winding T1 of the flyback transformer FBT. That is, by the switching operation of the transistor Q1 by the horizontal synchronization pulse Ph and the function of the resonance circuit, the horizontal deflection coil LH
, A horizontal deflection current is supplied, and the electron beam is horizontally scanned. The positive DC voltage + V1 is applied between the terminals of the horizontal deflection coil LH via the primary winding T1. Thereby, the horizontal size of the screen is appropriately controlled according to the horizontal deflection frequency fh.

A first end of a secondary winding T2 of the flyback transformer FBT is connected to an anode A of a CRT via a high voltage rectifier diode D1. The output-side capacitance Cf of the high-voltage rectifier diode D1 is the capacitance of the flyback transformer FBT and the capacitance of the CRT. The second end of the secondary winding T2 of the flyback transformer FBT is grounded via a parallel circuit of a resistor R4 and a capacitor C2. Also, ACL (Autom
The control voltage is output for atic contrast limit.

[0005]

The above conventional control circuit 1
0a, it is necessary to generate a larger positive DC voltage + V1 as the horizontal deflection frequency fh increases,
Since the upper limit of the positive DC voltage + V1 depends on the + B voltage,
There is a problem that it is difficult to cope with a very high horizontal deflection frequency. That is, conventionally, it has not been possible to sufficiently cope with a demand for a higher horizontal deflection frequency fh for achieving a higher display resolution. For example, the upper limit of the positive DC voltage + V1 that can be generated when the + B voltage is +200 V is +180 V
Therefore, it was not possible to cope with a horizontal deflection frequency of 130 kHz at which + V1 had to be increased to about +250 V. It is also conceivable to increase the + B voltage (for example, to increase the + B voltage to about +270 V) in accordance with the required value of the positive DC voltage, but a + B voltage source (not shown)
In addition, an expensive element having excellent withstand voltage must be used as a circuit element of the control circuit 10a, which causes a new problem that the cost increases. SUMMARY OF THE INVENTION It is an object of the present invention to provide a CRT control circuit capable of applying a large DC voltage to both ends of a horizontal deflection coil and reducing the cost.

[0006]

According to a first aspect, the present invention is a CRT control circuit for applying a DC voltage to both ends of a horizontal deflection coil of a CRT, wherein the control circuit generates a positive DC voltage based on a + B voltage. A positive voltage generation circuit that generates and applies the voltage to one end of the horizontal deflection coil; and a negative voltage generation circuit that generates a negative DC voltage based on the + B voltage and applies the voltage to the other end of the horizontal deflection coil. A CRT control circuit is provided. In the CRT control circuit according to the first aspect, the positive DC voltage generated based on the + B voltage is applied to one end of the horizontal deflection coil, and the negative DC voltage generated based on the + B voltage is applied to the horizontal deflection coil. Is applied to the other end of the horizontal deflection coil, a DC voltage that is the sum of the magnitude of the positive DC voltage and the magnitude of the negative DC voltage is applied between the terminals of the horizontal deflection coil. Therefore, even if an inexpensive element with a low withstand voltage is adopted as a circuit element of the positive voltage generation circuit and the negative voltage generation circuit to reduce the value of the generated voltage,
A sufficiently large DC voltage can be applied between the terminals of the horizontal deflection coil. Also, since both the positive DC voltage and the negative DC voltage are generated based on the + B voltage, a dedicated power supply (negative power supply) for generating the negative DC voltage is not required, and the circuit configuration is simplified. Cost can be reduced.

According to a second aspect, the present invention provides a C
In the RT control circuit, the negative voltage generating circuit applies either a ground potential or the negative DC voltage to the other end of the horizontal deflection coil in accordance with a horizontal deflection frequency. A control circuit is provided. The second
In the CRT control circuit according to the above aspect, when a sufficient DC voltage can be applied to the horizontal deflection coil only by the positive DC voltage generated by the positive voltage generation circuit (generally, when the horizontal deflection frequency is relatively low), By applying a ground potential to the other end of the horizontal deflection coil, the operation of the negative voltage generation circuit can be stopped, and power consumption can be suppressed. Also,
When the DC voltage applied to the horizontal deflection coil is insufficient with only the positive DC voltage by the positive voltage generation circuit (generally when the horizontal deflection frequency is relatively high), a negative voltage is generated at the other end of the horizontal deflection coil. By applying a negative DC voltage generated by the circuit, a sufficient DC voltage can be applied between the terminals of the horizontal deflection coil to the horizontal deflection coil.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited by this. FIG. 1 is a circuit diagram of a CRT high-voltage generation circuit including a control circuit according to an embodiment of the present invention. In the CRT high-voltage generation circuit 100,
The control circuit 101 for applying a DC voltage to the horizontal deflection coil LH of the CRT includes a positive voltage generation circuit 10 and a negative voltage generation circuit 20. The positive voltage generation circuit 10
The internal configuration of negative voltage generation circuit 20 will be described later in detail in the order in which the overall configuration of the circuit is described.

The primary winding T of the flyback transformer FBT
1 has a positive DC voltage + V based on the + B voltage.
1 is connected. The + B voltage is, for example, + 200V. The positive voltage generation circuit 10 includes an FET 11, a freewheeling diode 12,
This is a DC chopper circuit including a smoothing reactor 13 and a smoothing capacitor 14 (this configuration is basically the same as the conventional control circuit 10a shown in FIG. 2). A control signal S1 corresponding to the horizontal deflection frequency fh is input from the microcomputer 30 to the positive voltage generation circuit 10. That is, the FET 11 of the positive voltage generation circuit 10
During which + B voltage is intermittent (ON period, OFF period)
Is subjected to PWM modulation to generate a positive DC voltage + V1 corresponding to the horizontal deflection frequency fh. In general, as the horizontal deflection frequency fh increases, the larger positive DC voltage + V
1 is generated. The flyback transformer FBT 1
The second end of the next winding T1 has a horizontal output circuit H for generating a flyback pulse during a retrace time of the horizontal scanning of the electron beam.
Is connected. That is, by the switching operation of the transistor Q1 by the horizontal synchronization pulse Ph and the function of the resonance circuit, a horizontal deflection current is supplied to the horizontal deflection coil LH via the capacitor C, and the electron beam is horizontally scanned.

The horizontal deflection frequency fh is 130 kHz at the other end of the horizontal deflection coil LH (one end of the capacitor C).
z, a negative DC voltage −V based on the + B voltage
2 is connected. The negative voltage generating circuit 20 includes a DC chopper circuit 200 including an FET 21, a freewheel diode 22, a smoothing reactor 23, and a smoothing capacitor 24, and an output from the DC chopper circuit 200 in response to a switching signal Sc from the microcomputer 30. Switch 201 for selectively inputting either negative DC voltage -V2 or ground potential
It is composed of The negative voltage generation circuit 20 includes:
Only when the horizontal deflection frequency fh is 130 kHz, the control signal S2 is input from the microcomputer 30.

Next, the operation of the control circuit 101 will be described. (1) When the horizontal deflection frequency fh is 30 to 110 kHz, the changeover switch 201
The ground potential is selectively input in response to the control signal Sc from the controller (in the drawing, the switching state is indicated by a solid line). At this time, only the positive DC voltage + V1 is applied from the positive voltage generation circuit 20 to the horizontal deflection coil LH (the negative DC voltage -V2).
Is not applied). For example, if the horizontal deflection frequency fh is 30
kHz, a positive DC voltage + is applied to the horizontal deflection coil LH.
V1 = + 50 V is applied. Also, the horizontal deflection frequency f
When h is 110 kHz, a positive DC voltage + V1 = + 180 V is applied to the horizontal deflection coil LH. Thereby, the horizontal size of the screen is appropriately controlled according to the horizontal deflection frequency fh. (2) When the horizontal deflection frequency fh is 130 kHz, the changeover switch 201 selectively inputs the negative DC voltage -V2 according to the control signal Sc from the microcomputer 30 (the switching state is indicated by a dotted line in the figure). ). At this time,
The positive voltage generating circuit 1 is provided at one end of the horizontal deflection coil LH.
A positive DC voltage + V1 from 0 is applied, and a negative DC voltage -V2 is applied from the negative voltage generation circuit 20 to the other end of the horizontal deflection coil LH. Thus, the DC voltage | V1 | + | V2 is applied between the terminals of the horizontal deflection coil LH.
| Is applied. For example, between the terminals of the horizontal deflection coil LH, a DC voltage of 250 V which is a potential difference between a positive DC voltage + V1 = + 180 V and a negative DC voltage −V2 = −70 V
Is applied. Thereby, the horizontal size of the screen is appropriately controlled. According to the above control circuit 101, when the applied voltage is insufficient just by applying the positive DC voltage + V1 generated by the positive voltage generation circuit 10 to one end of the horizontal deflection coil LH (when the horizontal deflection frequency fh is 130 kHz). Time), the negative voltage generating circuit 2 is connected to the other end of the horizontal deflection coil LH.
By applying the negative DC voltage -V2 generated by 0, a sufficiently large DC voltage can be applied between the terminals of the horizontal deflection coil LH. Further, the positive voltage generation circuit 10
In addition, since an inexpensive element having a low withstand voltage can be adopted as a circuit element of the negative voltage generation circuit, the cost can be reduced.

According to the control circuit for a CRT of the present invention, the positive DC voltage generated by the positive voltage generating circuit and the negative DC voltage generated by the negative voltage generating circuit are connected between the terminals of the horizontal deflection coil. DC voltage corresponding to the sum of the magnitudes of the horizontal deflection coils can be applied to the horizontal deflection coil even if an inexpensive circuit element having a low withstand voltage is used for each voltage generating circuit. . Therefore, the voltage applied to the horizontal deflection coil can be easily increased in response to the increase in the horizontal deflection frequency, and a higher display resolution can be suitably realized.

[Brief description of the drawings]

FIG. 1 illustrates a C including a control circuit according to an embodiment of the present invention.
FIG. 3 is a circuit diagram of a high-voltage generation circuit for RT.

FIG. 2 is a circuit diagram of a CRT high-voltage generation circuit including an example of a conventional control circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 positive voltage generating circuit 11, 21 FET 12, 22 freewheeling diode 13, 23 smoothing reactor 14, 24 smoothing capacitor 20 negative voltage generating circuit 30 microcomputer 100 high voltage generating circuit for CRT 200 DC chopper circuit 201 changeover switch LH horizontal deflection coil

Claims (2)

[Claims] 1. A CRT control circuit for applying a DC voltage to both ends of a horizontal deflection coil of a CRT, wherein the CRT control circuit generates a positive DC voltage based on + B voltage and applies a positive voltage to one end of the horizontal deflection coil. Generating circuit and the + B
A CRT control circuit, comprising: a negative voltage generation circuit that generates a negative DC voltage based on the voltage and applies the DC voltage to the other end of the horizontal deflection coil. 2. The CRT control circuit according to claim 1, wherein said negative voltage generating circuit is connected to a ground potential or said negative DC voltage at the other end of said horizontal deflection coil in accordance with a horizontal deflection frequency. C characterized by applying
RT control circuit.