JPH0314863Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) The present invention relates to a high voltage generation circuit for CRT of an electromagnetic deflection CRT monitor device, and more specifically, the secondary winding or winding of the winding is used in a non-resonant mode. This paper relates to improvements in high voltage generation circuits for CRTs using flyback transformers.

(Prior Art) Conventionally, in a CRT horizontal deflection high voltage generation circuit using a flyback transformer having a non-resonant winding, when adjusting the high output voltage or no-load voltage, the deflection coil or main output transistor is ,
This was done by adjusting the capacitance of a low-voltage resonant capacitor connected in parallel to a damper diode. FIG. 2 is an electrical configuration diagram showing a conventional example of such a high voltage generating circuit for CRT.

The output of the AC oscillator (specifically, the horizontal drive pulse generation circuit) OS drives the drive transformer _T1 ,
The transistor _Q1 is driven by an AC voltage signal induced in the secondary winding _of the drive transformer T1. and,
The transistor _Q1 drives a flyback transformer _T2 . A DC voltage _E1 is applied to one end of the flyback transformer _T2 , and a transistor _Q1
flyback transformer every time the
Current flows intermittently through _T2 to perform boost operation.

The flyback transformer T ₂ has its own coil L ₁ ~
It consists of a series circuit of _L4 , of which _L4 is a secondary winding for boosting voltage, that is, a winding.

DC power extracted from the power source E ₂ (+12V as an example) is supplied to the connection point A between the coils L ₁ and L ₂ via the choke coil L ₅ and the diode D ₁ . During the scanning period, _D1 conducts and supplies power, charging the capacitor C _E1 , and storing a value (+18V, for example) that is slightly higher than _E2 as _E1 .
This _E1 serves as a power source for deflection and high voltage generation for the entire circuit. Horizontal deflection/high voltage generation circuits including such boost circuits are well known. On the other hand, the collector of transistor Q ₁ is connected to the connection point B between coils L ₂ and L ₃ in the flyback transformer, and the damper diode D ₂ is connected to a point slightly wound up from that point, that is, the connection between coils L ₃ and L ₄ . Connected to point C. A method of canceling the forward potential drop of the damper diode by connecting the damper diode D ₂ to a point slightly higher than the main transistor is known. on the other hand,
Point C in the flyback transformer and the boosted power supply E ₁ at the bottom end are connected via the DC cutoff capacitor C ₁
A series circuit including deflection coils (horizontal deflection coils wound around the deflection yoke DY) L ₆ , L ₆ ', a linearity correction coil L ₇ , and an amplitude adjustment coil L ₈ is connected between the two.

When the transistor _Q1 is repeatedly turned on and off in such a configuration, a flyback pulse as shown in the figure is generated at one end of the coil _L4 each time the transistor _Q1 is turned off. This flyback pulse is
After the DC component is cut off by capacitor _C2 , it enters Kotscroft circuit D _A for voltage doubler rectification and is rectified at high voltage. A varistor ZNR for output voltage stabilization is connected between the output stage of the Kotskucroft circuit D _A and ground via a current detection resistor R _S to clamp the output voltage V _O to a constant value. The voltage rectified by the Kotscroft circuit D _A is smoothed by a smoothing capacitor C ₃ and then applied to the anode (not shown) of the CRT as an output V _O.

(Problem to be solved by the invention) In conventional circuits of this type, when adjusting the output voltage or no-load output voltage _VO , the primary winding of the flyback transformer and the deflection coil are used as described above. The capacitance of the low voltage side resonant capacitor Ct connected in parallel with was adjusted. This changes the self-resonant frequency of the circuit, which is determined primarily by the deflection coil and the capacitor Ct, and therefore the width of the flyback pulse, i.e. the retrace time width of the horizontal deflection, resulting in a change in the flyback pulse versus supply voltage. The step-up ratio of the peak value of is now changing.

When adjusting the resonant capacitor Ct, its capacitance value is a relatively large value of about 10 to 30 nF, so
It is not possible to adjust with a variable capacitor or trimmer capacitor. It is necessary to prepare multiple capacitors in advance and combine these capacitors as necessary to obtain the specified capacity, or to add capacitors each time by soldering until the specified capacity is reached. Ta. According to the former method, unused capacitors are wasted, and according to the latter method, operation is troublesome. Therefore, this method of adjusting the output voltage by changing the capacitance of the resonant capacitor is not suitable for applications that do not require high precision in screen dimensions, such as ordinary home television sets and CRT monitors for computer terminals. Often not used.

In CRTs used for this type of application, the horizontal amplitude and linearity are matched at best, and the high voltage output is left at the voltage value due to various variations. However, when dimensional accuracy of the screen is required, precise deflection must be performed while keeping the voltage applied to the anode of the CRT constant. In such a case, the flyback circuit as a whole must keep the amplitude of the current flowing through the deflection coil constant, so the flyback circuit can only operate in a fixed manner by obtaining power from a constant voltage power supply. Can not. Therefore, the shunt regulator type must be used as the high voltage generation and stabilization circuit installed in parallel, despite the large power loss. In the circuit shown in Figure 2, the varistor ZNR plays this role. When using a ZNR as a shunt regulator, it is necessary to provide the circuit with enough power supply capacity to allow an appropriate current to flow through the ZNR, and if sufficient current is not passed, the desired stabilizing effect cannot be obtained. Conversely, if too much current is applied
The steady state power loss of ZNR increases, leading to deterioration of ZNR characteristics and shortening of its lifespan.

The present invention was devised in view of these points, and its purpose is to facilitate the adjustment of the output capacity of the generated high voltage, and to realize the adjustment circuit with a simple configuration and at low cost. able to
The purpose of the present invention is to provide a high voltage generation circuit for CRT.

(Means for solving the problem) The present invention to solve the above problem has a flyback transformer in which a deflection coil and a resonant capacitor whose one end is grounded are connected in parallel to the primary winding, A DC voltage is applied to one end of the primary winding of the flyback transformer, and a switching circuit turns on and off the current flowing through the primary winding of the flyback transformer, so that the secondary winding is used in a non-resonant mode. A flyback pulse is obtained in a boosted form at the high potential side terminal of the winding, and the flyback pulse is rectified to obtain a high voltage direct current.
The high voltage generating circuit for CRT is characterized in that a trimmer capacitor for voltage adjustment is connected between the high potential side terminal of the winding of the flyback transformer and ground.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an electrical configuration diagram showing an embodiment of the present invention. Components that are the same as those in FIG. 2 are designated by the same numbers. The difference from FIG. 2 is that a trimmer capacitor Ct' is connected between the high voltage side terminal of the boost coil (hoist winding) _L4 in the flyback transformer and ground. The other constituent parts are essentially the same as in FIG. 2. The operation of the circuit configured as described above will be explained below.

Let C _O be the capacitance of the trimmer capacitor Ct′ connected to the high potential side terminal of the boost coil, that is, the winding L ₄ .
The turns ratio of coils L ₁ , L ₂ and L ₃ , L ₄ is n (n>1)
Then, the trimmer capacitor Ct' is equivalently added in parallel to the original resonant capacitor Ct as a capacitance value of n ² _CO . Therefore, even if the trimmer capacitor Ct' has a small capacitance of several pF to several tens of pF, when it is added to Ct, it acts as an equivalent capacitance of several tens of nF, so it is at most several pF to several tens of nF. This means that the output voltage V _O can be adjusted with a small capacitance of 10 pF. According to the present invention, unlike conventional circuits, there is no need to combine multiple capacitors to adjust the output voltage.
Since it is only necessary to trim the trimmer capacitor, the number of adjustment steps is greatly reduced. In this case, since the trimmer capacitor Ct' is connected to the high potential side of the booster coil for high voltage generation, the withstand voltage of the capacitor Ct' is required to be about 2 to 3 KV.

Next, a description will be given of how to configure such a trimmer capacitor Ct'.

FIG. 3 is a configuration diagram showing an example of the mounting state of the circuit of the present invention. In the figure, 1 is the mounting board, 2 is the board of the Kotsukucroft circuit D _A , 3 is the insulating case that covers the Kotsukucroft circuit D _A, etc., and 4 is the output V _O of the high voltage generation circuit taken out from the case 3.
This is an anode cap that applies voltage to the anode of a CRT. The Kotsukucroft circuit board 2 is mounted floating from the mounting board 1 via a spacer. 5 is ZNR, 6 is a smoothing capacitor, 7 is a winding coil _L4 is a high potential side tap. Conductor foils are respectively attached to the inner and outer surfaces of the insulating case 3, and 8 is an outer conductor foil and 9 is an inner conductor foil.

A lead wire comes out from the tap 7 and is soldered to the inner conductor foil 9, and the outer conductor foil 8 is grounded to the mounting board 1. Then, the outer conductor foil 8, the inner conductor foil 9, and the insulating case 3 sandwiched between these
and constitute the above-mentioned trimmer capacitor Ct'. The facing area of the outer foil 8 and the inner foil 9 is S,
When the distance between them is d and the dielectric constant of the insulating case 3 is ε, the capacitance C _O of Ct' is expressed by the following equation.

C _O =εS/d (F) As is clear from the above equation, if the area S where the two layers face each other is changed, the capacitance C _O changes.

Therefore, the area S can be varied by forming the outer conductor foil 8 with a removable conductor layer, such as copper foil or aluminum foil coated with adhesive, and peeling or pasting it as necessary. It can be used as a trimmer capacitor. In the illustrated embodiment, the trimmer capacitor Ct' is implemented using the insulating case 3, which is convenient because it does not take up much space for mounting. In addition, the trimmer capacitor
Ct' does not necessarily have to have such a configuration, and may have any configuration as long as it can adjust the capacitance.

In the above-described embodiment, a non-insulated winding tap type flyback transformer is used, but the present invention is not limited to this, and an insulated primary and secondary winding type flyback transformer may also be used.

(Effects of the invention) As explained in detail above, according to the invention,
By connecting a trimmer capacitor between the high-potential side terminal of the flyback transformer's winding and ground, it is possible to realize a CRT high-voltage generating circuit with a simple configuration that allows the output voltage to be adjusted extremely easily. can.

[Brief explanation of the drawing]

FIG. 1 is an electrical configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a conventional circuit, and FIG. 3 is a diagram showing a state in which the present invention is implemented. 1... Mounting board, 2... Circuit board, 3... Insulating case, 4... Anode cap, 5... ZNR,
6... Smoothing capacitor, 7... Tap, 8... Outer conductor foil, 9... Inner conductor box, OS... Oscillator,
T ₁ ... Drive transformer, T ₂ ... Flyback transformer, L ₁ to _{L 4} ... Coil, L ₅ ... Chiyork coil, L ₆ , L ₆ ' ... Horizontal deflection coil, L ₇ ... Linearity correction coil , L ₈ ... amplitude adjustment coil, DY ... deflection yoke, D ₁ , D ₂ ... diode, D _A ... Kotsukucroft circuit, C ₁ to _{C 3} , Ct ... capacitor,
Ct′...trimmer capacitor, ZNR...varistor.

Claims (1)

[Scope of utility model registration request] It has a flyback transformer in which a deflection coil and a resonant capacitor whose one end is grounded are connected in parallel to the primary winding, and a DC voltage is applied to one end of the primary winding of the flyback transformer. The current flowing through the primary winding is turned on and off by a switching circuit, and a flyback pulse is obtained in a boosted form at the high potential side terminal of the winding winding used in the non-resonant mode, which is the secondary winding. In a high voltage generation circuit for a CRT configured to rectify the flyback pulse to obtain high voltage direct current, a trimmer capacitor for voltage adjustment is grounded between the high potential side terminal of the winding of the flyback transformer and the ground. A high voltage generation circuit for CRT characterized by the following.