JP2552717B2 - Focus voltage adjustment circuit for cathode ray tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focus voltage adjusting circuit for a cathode ray tube (hereinafter referred to as “CRT”), and particularly to a focus voltage for obtaining an optimum focus point of a magnetic field focusing CRT. Regarding the adjustment circuit.

[Conventional technology]

Conventionally, as a magnetic field focusing CRT, one having an electrode structure including a cathode, a plurality of grids and an anode is known.

However, conventionally, as a focus voltage adjusting circuit in this type of CRT, for example, one having a configuration shown in FIG. 2 is known. That is, in FIG.
Reference numeral 10 denotes a CRT, the electrode structure of which is composed of a cathode K, grids G ₁ , G ₂ , G ₃ and an anode A. Further, reference numeral 12 indicates a flyback transformer. A power supply voltage + B is applied at one end to a primary winding L ₁ of the transformer 12, and a horizontal drive pulse is applied to a transistor Tr, a deflection yoke DY, a DC blocking capacitor. C ₁ is connected to be supplied via the resonance capacitor C ₂ . D ₁ is a damper diode.

On the other hand, the secondary winding of the flyback transformer 12 has the first
Consisting of winding L _2-1 and second wire winding L _2-2 , the first winding L
_2-1 is connected to supply the anode voltage to the anode A of the CRT 10 via the diode D ₂ . The second winding L _2-2 is connected to the grid G of the CRT 10 via the diode D ₃ , the smoothing capacitor C ₃ , the fixed resistor R ₁ and the sliding resistor R _2.
2 and G ₃ are connected to supply the grid voltage, respectively. The cathode K of the CRT 10 is configured to supply a video signal.

Therefore, in such a circuit configuration, the deflection yoke DY is driven on the primary side of the flyback transformer 12 by supplying the horizontal drive pulse from the transistor Tr, and at the same time, the resonance capacitor C ₂ A flyback pulse that resonates with the deflection yoke DY is generated, and this flyback pulse is supplied to the primary winding L ₁ of the flyback transformer 12, and the first winding L ₂₋ of the secondary winding thereof is supplied. _The required anode voltage of ₁ can be obtained. Therefore, the anode voltage obtained at the first winding L _2-1 is rectified by the diode D ₂ and applied to the anode A of the CRT 10.

On the other hand, the voltage boosted by the second winding L _2-2 for the focus voltage of the flyback transformer 12 is rectified by the diode D ₃ , smoothed by the smoothing capacitor C ₃ , and slightly higher than the required focus voltage. And apply this voltage to a fixed resistor R ₁
And a sliding resistor R ₂ divide the voltage to obtain a focus voltage from the sliding terminal of the sliding resistor R ₂ , supply it to the focus grid G _{3 of the} CRT 10, and modulate it with the video signal applied to the cathode K. Configured to control the focused electron beam.

However, in this type of CRT10, it is generally adopted to apply a horizontal retrace pulse to the low voltage part of the high voltage winding in order to make the high voltage constant. Then, the focus voltage extracted from the intermediate tap of the high voltage winding tends to change. Here, in this case, in order to obtain the optimum focus point of the CRT 10, for example, a method of changing the flyback pulse width by the flyback transformer 12 or changing the power supply voltage has been proposed.

[Problems to be Solved by the Invention]

However, the former method of changing the flyback pulse width has a drawback that not only cannot smooth adjustment because the handling voltage is high, but also the adjustment width cannot be sufficiently achieved.

Further, in the case of adopting the method of changing the power supply voltage, not only power loss occurs, but also the deflection dimension of the CRT 10 varies, and the brightness changes and the like, which makes it impossible to reproduce an appropriate image.

However, focus adjustment of a CRT is generally performed by adjusting the grid voltage. this is,
The focus principle of the image of the CRT is the magnetic field formed by the potential difference between the cathode voltage and the grid voltage, which causes electrons emitted from the cathode electrode at an appropriate speed to be generated according to the potential difference between the multiple grid electrodes through which the electrons pass. The lens is set so that it is appropriately deflected and focused on the screen of the CRT. Therefore, conventionally, focus adjustment is performed by adjusting the grid voltage to obtain the required resolution.

However, due to variations in the structure of the CRT, even if the potential difference between the grid electrodes is adjusted, some CRTs may not obtain the specified high resolution. In particular, in the case of a CRT that requires a small size and high resolution, such as an electronic viewfinder used in a video camera, a high voltage cannot be obtained because of the power source built into the video camera, that is, a battery power source, and therefore, it is not specified. There is a strong tendency that the high resolution of is not obtained.

In the case of the small CRT for electronic viewfinder,
When adjusting the focus, first the CRT is adjusted with the power supply for adjustment before it is installed in the video camera, and after adjustment, it is driven by the power supply (battery etc.) built into the video camera, so there is a potential difference between the drive power supply and the adjustment power supply. In some cases, readjustment is required. Therefore, for this type of CRT,
Instead of focus adjustment by adjusting the grid voltage, CR
There is also one in which T is manufactured accurately and the grid voltage is not adjusted. However, in such a CRT, the number of grid electrodes is limited to two, and fine adjustment of the voltage at the grid power supply is impossible.

Further, in the case of the small CRT in which the number of grid electrodes is limited to two as described above, the brightness adjustment is performed by adjusting the potential difference between the cathode electrode and the grid electrode. For this reason,
For example, when the grid voltage is adjusted to adjust the focus of the CRT, the brightness also changes.

Therefore, an object of the present invention is to supply a flyback pulse derived from a flyback transformer as a cathode voltage and a grid voltage of a CRT (cathode ray tube),
By variably setting the DC voltage obtained by rectifying a part of the flyback pulse, the potential difference between the cathode voltage and the grid voltage and the anode voltage is relatively variably adjusted to adjust the optimum focus point. It is an object of the present invention to provide a focus voltage adjusting circuit for a cathode ray tube which can be achieved with a simple circuit configuration easily and without causing power loss.

[Means for solving the problem]

A focus voltage adjusting circuit for a cathode ray tube according to the present invention,
The horizontal drive pulse is supplied to the flyback transformer, and the flyback pulse derived from this flyback transformer is rectified and smoothed to be supplied as the cathode voltage, grid voltage and anode voltage of the cathode ray tube. In the voltage supply circuit, a DC load is fixed to a reference potential point of a first winding of a flyback transformer that generates a first flyback pulse that is supplied to obtain an anode voltage of the cathode ray tube, and a cathode and a grid of the cathode ray tube are fixed. By adjusting the DC potential with respect to the reference potential point of the second winding or the third winding of the flyback transformer that generates the second or third flyback pulse supplied to Both of the grid voltages are changed together in parallel, and the cathode voltage and It is characterized in that the potential difference of the anode voltage with respect to both the grid voltage and the grid voltage is adjusted relatively.

[Action]

According to the focus voltage adjusting circuit of the cathode ray tube (CRT) of the present invention, the anode voltage supplied to the CRT changes due to the change of the flyback pulse on the primary side of the flyback transformer, and the focus adjustment of the CRT is inappropriate. In that case, the first winding for obtaining a constant voltage to be supplied to the CT anode is provided on the secondary side of the flyback transformer,
By providing the second and third windings that obtain the voltage to be supplied to the cathode and grid of the CRT, and adjusting the voltage derived from these windings, the cathode voltage and grid voltage relative to the anode voltage are always correct. The optimum focus point of the CRT can be easily obtained by maintaining the optimum state.

〔Example〕

An embodiment of a focus voltage adjusting circuit for a cathode ray tube (CRT) according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of an essential part showing an embodiment of a focus voltage adjusting circuit of a CRT according to the present invention. For convenience of explanation, the same components as those of the conventional circuit configuration shown in FIG. 2 will be described with the same reference numerals.

However, in the circuit shown in Fig. 1, the magnetic field focusing CR
T10 comprises a cathode K, a first grid G ₁ , a second grid G ₂ and an anode A, respectively. The primary winding L ₁ of the flyback transformer 12 has a transistor Tr for supplying a horizontal drive pulse, a deflection yoke DY, a DC blocking capacitor C ₁ , a resonance capacitor C ₂ and a damper diode.
D ₁ is connected.

As the secondary winding of the flyback transformer 12,
The first winding L ₈ and the second winding L ₇ are provided separately.
One end of the first winding L ₈ is grounded to a common ground potential point (reference potential point) on the secondary side that is insulated from the primary side, and the other end is a voltage rectifier consisting of a diode D ₁₁ and a smoothing capacitor C _11. The circuit is connected and this output is applied to the anode A of the CRT 10 as the anode voltage.

On the other hand, the second winding L ₇ has a diode D ₁₀ , a bleeder resistor R ₁₀ , a smoothing capacitor C ₁₀ and a bleeder resistor R _10.
A voltage rectifier circuit consisting of ₁₁ is connected. In addition, winding
L ₃ is a heater winding of the cathode K in the CRT 10.

The second winding L ₇ is a floating winding and fixes the middle tap of the bleeder resistor R ₁₀ to a required potential, while supplying the middle tap of the bleeder resistor R _{11 to} the cathode K for brightness adjustment. The circuit is configured to The negative side of the rectified voltage applied to the bleeder resistor R ₁₁ is supplied as the first grid G ₁ voltage, and the positive side is supplied as the second grid G ₂ voltage. . Furthermore, coupling capacitors
A video signal is supplied to the cathode K of the CRT 10 via C ₁₂ .

In the focus voltage adjusting circuit of the present invention configured as described above, the flyback transformer is insulated from the primary side.
Since the second winding L ₇ on the secondary side of 12 is a floating winding, by changing the intermediate tap position of the bleeder resistor R ₁₀ , a common ground potential (reference potential) on the secondary side is obtained. The entire potential of the second winding L ₇ from changes. As a result, the potentials of the cathode K, the first grid G _1, and the second grid G ₂ connected to the second winding L ₇ are changed in parallel, and a constant high potential is maintained from the common ground potential on the secondary side. It changes relative to the fixed potential of the anode A, and the potentials of the cathode K, the first grid G ₁ and the second grid G ₂ are substantially fixed, and the focus voltage is adjusted by adjusting the anode potential. It is equivalent to making an adjustment.

In this case, the luminance adjustment, the bleeder resistor R _11,
This is performed by adjusting the potential difference between the cathode K and the first grid G ₁ and the second grid G _2, and even if the intermediate tap position of the bleeder resistor R ₁₀ is changed, this potential difference does not change, and the brightness is reduced. The focus voltage can be adjusted regardless of the modulation characteristics.

〔The invention's effect〕

The cathode ray tube (CRT) according to the present invention configured as described above
According to the focus voltage adjusting circuit of (1), both the cathode voltage and the grid voltage with respect to the anode voltage are always kept in proper states, and the optimum focus point of the CRT can be easily obtained. That is, according to the circuit of the above-described embodiment, the anode A is connected and fixed to the first winding L ₈ having a predetermined constant voltage with respect to the reference potential point (secondary side ground potential point), and Bleeder resistor R provided for winding L ₇
By changing the positions of the ₁₀ intermediate taps, the DC potentials of the cathode, the first grid, and the second grid with respect to the reference point are changed in parallel with the anode voltage, so that regardless of the brightness and modulation characteristics of the CRT. The optimum focus voltage can be obtained by changing the relative potential difference among the anode voltage, the cathode voltage, and the first grid voltage.

Therefore, in the present invention, since the focus adjustment is performed by changing the reference potential point on the low voltage side, relatively inexpensive parts can be used as compared with the case of directly changing the high voltage anode voltage. The advantage is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a focus voltage adjusting circuit of a cathode ray tube (CRT) according to the present invention, and FIG. 2 is a circuit showing an example of a configuration of a focus voltage adjusting circuit of a conventional cathode ray tube (CRT). It is a figure. 10 …… Cathode ray tube (CRT), 12 …… Flyback transformer K …… Cathode, G ₁ , G ₂ …… Grid A …… Anode, L ₁ …… Primary side winding L ₃ …… Heater winding , L ₇ ...... 2nd winding L ₈ ...... 1st winding, Tr ...... Transistor D ₁ ...... Damper diode, DY ...... Deflection yoke C ₁ ...... DC blocking capacitor, C ₂ ...... Resonance capacitor D ₁₀ , D ₁₁ ...... Rectifying diode, C ₁₀ , C ₁₁ …… Smoothing capacitor C ₁₂ …… Coupling capacitor, R ₁₀ , R ₁₁ …… Bleeder resistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-98970 (JP, A) JP-A-54-82121 (JP, A) Actually open Sho-53-119822 (JP, U) Actual-open Sho-61- 95163 (JP, U) JP 58-20436 (JP, B2) JP 62-30368 (JP, Y2) JP 60-25176 (JP, Y2)

Claims (1)

(57) [Claims] 1. A horizontal drive pulse is supplied to a flyback transformer, and the flyback pulse derived from this flyback transformer is rectified and smoothed to be supplied as a cathode voltage, a grid voltage and an anode voltage of a cathode ray tube. In the configured voltage supply circuit for the cathode ray tube, the DC load is fixed to the reference potential point of the first winding of the flyback transformer that generates the first flyback pulse that is supplied to obtain the anode voltage of the cathode ray tube, and the cathode wire is fixed. By adjusting the DC potential with respect to the reference potential point of the second winding or the third winding of the flyback transformer that generates the second or third flyback pulse supplied to the cathode and grid of the tube, the anode electrode is adjusted. On the contrary, both the cathode voltage and the grid voltage are changed together in parallel, A focus voltage adjusting circuit for a cathode ray tube, characterized in that a potential difference of an anode voltage with respect to both a sword voltage and a grid voltage is adjusted relatively.