JPH06268883A - High voltage generating circuit and fly-back transformer - Google Patents

Abstract

PURPOSE:To prevent the occurrence of the abnormal state caused by open circuit of a resonance capacitor or the like due to a failure of work, a broken pattern on a board, or the like. CONSTITUTION:A horizontal drive pulse is supplied to the gate of a MOS field- effect transistor FET 41 as a high voltage output transistor TR. The source of the FET 41 is grounded, and the drain is connected to a power terminal 44 through a low voltage coil 42a of a flyback transformer 42 and a filter 43. One end of a high voltage coil 42b of the transformer 42 is connected to a high voltage rectifier circuit 45, and the other end is connected to one end of the low voltage coil 42a. The resonance capacitor is not connected to the primary side of the transformer 42, and only the inductance of the low voltage coil 42a and the internal stray capacitance constitute a resonance circuit. A boosted resonance pulse voltage is obtained in the high voltage coil 42b, and a high voltage HV is obtained by the rectifier circuit 45. It is unnecessary to mount the resonance capacitor on the circuit board, and the abnormal state caused by the open circuit of the resonance capacitor or the like due to a failure of work cannot occur.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage generating circuit and a flyback transformer suitable for use in a small television receiver or television monitor using a cathode ray tube.

[0002]

2. Description of the Related Art FIG. 6 shows a flat cathode ray tube (flat CR
T) 1 is shown. In the figure, 1a is a neck portion provided with an electron gun (not shown), 1b is a funnel portion, 1
Reference numeral c is a screen panel, 1d is a front panel, and 1e is a fluorescent screen formed on the screen panel 1c. The screen panel 1c, the front panel 1d, etc. are made of transparent glass. The fluorescent screen 1e is inclined at a relatively small angle with respect to the central axis of the electron gun.
The image displayed on the screen is observed from the front panel 1d side which is substantially perpendicular to the central axis of the electron gun.

In such a flat cathode ray tube 1, keystone distortion (inverse trapezoidal distortion) occurs due to its structure. That is,
The horizontal deflection scanning is performed from the upper part to the lower part of the phosphor screen 1e. However, since the deflection angle θ1 of the upper part and the deflection angle θ2 of the lower part are different, when the horizontal deflection scanning is performed with a constant deflection power (current), it approaches the lower part. As the scanning amplitude decreases, keystone distortion occurs.

In order to correct this keystone distortion, it is necessary to dynamically increase the horizontal deflection current Ipp as the fluorescent screen 1e is scanned from the upper part to the lower part. Here, the power supply voltage eo of the horizontal deflection circuit and the horizontal deflection current Ipp
Has a relationship of eo = Ly (Ipp / Ts) = K.Ipp, where Ly is the inductance of the horizontal deflection coil (H.DY) and Ts is the horizontal scanning period. Here, K = (Ly / Ts). That is, it is understood that the power supply voltage eo needs to be dynamically changed in order to dynamically increase the horizontal deflection current Ipp. In order to realize this, a so-called power supply modulation method in which a power supply voltage is modulated by a sawtooth wave signal having a vertical cycle is generally widely used.

By the way, as the high voltage generation circuit and the horizontal deflection circuit of the cathode ray tube, there are a well-known conventional separate type in which the high voltage generation circuit and the horizontal deflection circuit are separated, and a conventional type in which these circuits are not separated.
The conventional type is suitable when the image distortion such as pincushion distortion or keystone distortion is small, but when the image distortion is large, the correction has a very large effect on the high voltage generation circuit and is not suitable. As described above, in the flat cathode ray tube, the correction amount of keystone distortion is very large,
Separate type is used.

FIG. 7 shows a separate type high voltage generating circuit. Reference numeral 11 is a high-voltage output transistor, and a drive pulse is supplied to the base of the transistor 11 from a high-voltage drive circuit (not shown). The emitter of the transistor 11 is grounded, and the damper diode 12 and the resonance capacitor 13 are connected in parallel between the collector and the ground.

The collector of the transistor 11 is connected to a power supply terminal 15 to which a DC voltage + Vcc is supplied via a low voltage coil (primary winding) 14a of a flyback transformer (high voltage generating transformer) 14. One end of the high-voltage coil (secondary winding) 14b of the transformer 14 is connected to a high-voltage rectifier circuit 16 having a multiple voltage. The high-voltage rectifier circuit 16 rectifies the boosted pulse voltage obtained at one end of the high-voltage coil 14b, and the high-voltage HV is led to the terminal 17. The other end of the high voltage coil 14b of the transformer 14 is connected to the low voltage coil 1
It is connected to one end of 4a.

FIG. 8 shows the waveform of each part in the example of FIG. In the figure, A is supplied to the base of the transistor 11.
Horizontal drive pulse, collector current ic in FIG.
p, the same C is the damper current id, and the same D is the low voltage coil 14a.
A current iL1 flowing through the same, and FIG. 6E shows a collector voltage Vcp. Note that tr is a blanking period and ts is a scanning period.

Here, the low voltage coil 14a of the transformer 14
The maximum value ipcpm of the collector current icp is given by the following equation, where L1 is the inductance of.

Vcc = L1di / dt = L1icpm / (ts / 2) ∴icpm = (ts / 2)  (Vcc / L1) (1) Flow to low voltage coil 14a during retrace period tr The current iL is given by the following equation.

IL = icpmcos ωot (2) where ωo is the resonance angular frequency between the low voltage coil 14 a of the transformer 14 and the resonance capacitor 13, and the low voltage coil 1
When the inductance of 4a is L1 and the capacitance of the resonance capacitor 13 is C1, the following equation holds. fo is the resonance frequency, and its 1/2 cycle is in the blanking period tr. ωo = 2πfo = 1 / √ (L1C1) (3) fo is the resonance frequency, and its 1/2 cycle is the blanking period. tr
And the following equation holds.

Tr = 1 / (2fo) (4) Further, from the equation (2), the following equation is obtained.

L1 · diL / dt = −ωoL1 · icpm sin ωot (5) Therefore, the maximum value Vcpm of the collector voltage Vcp is obtained by the following equation.

Vcpm = ωoL1 · icpm + Vcc = ωoL1 · (ts / 2) · (Vcc / L1) + Vcc = Vcc (1 + πfoots) ≈Vcc {1+ (π / 2) · (ts / tr)} (6) In the high voltage generation circuit of the example of FIG. 7, the high voltage HV is obtained from the pulse voltage obtained by boosting the resonance pulse voltage obtained from the relationship of the equation (6) by the turns ratio of the transformer 14.

From equation (6), it can be seen that the collector voltage Vcpm increases as the blanking period tr decreases. Then, it is the inductance L1 of the low-voltage coil 14a of the transformer 14 and the capacitance C1 of the resonance capacitor 13 that determine the blanking period tr, as is clear from the equations (3) and (4). Therefore, in order to keep the high voltage HV constant, it is necessary to consider variations in both the inductance L1 and the capacitance C1.

In general, the resonance capacitor 13 is mounted on a circuit board as an external component. Therefore, when the resonance capacitor 13 is opened due to a mistake in work or a pattern break on the board, the collector voltage Vcpm becomes very high, and the circuit and the transformer 14 main body. There is a problem that the cathode ray tube is radiated with X-rays due to the high voltage HV supplied to the cathode ray tube being abnormally high due to the destruction of the cathode ray tube to cause smoke and ignition.

In order to prevent such an abnormal operation, conventionally, an abnormal high voltage is detected to operate a protection circuit, or a four-leg capacitor is used as the resonance capacitor 13. A four-leg capacitor has two terminal pins connected to each terminal, and by connecting each of these two terminal pins to the circuit board, the frequency of occurrence of an open state due to disconnection of the capacitor can be reduced. .

However, since a small cathode ray tube such as a flat cathode ray tube is a compact and low-cost product, an expensive protection circuit and a four-leg capacitor cannot be used. For example, the high voltage HV must be lowered before driving. It corresponds with.

[0019]

However, when the cathode ray tube is driven by lowering the high voltage, the acceleration of the electron beam is lowered and the focusing is deteriorated, so that the resolution is lowered and a high quality image is obtained. There is a problem that you cannot do it.

FIG. 9 shows the structure of the conventional flyback transformer 14. In the figure, 14c is a low pressure bobbin, and the low voltage coil 14a described above is wound around this low pressure bobbin 14c. 14d is a high voltage bobbin, and the high voltage coil 14b described above is wound around the high voltage bobbin 14d. 14e is a core.

In this transformer 14, the low-voltage coil 14a and the high-voltage coil 14b are wound around separate bobbins 14c and 14d which are concentrically arranged in order to reduce the influence of wet magnetic flux such as high-voltage fluctuation and prevention of raster ringing. The configuration is such that the low-voltage coil 14a and the high-voltage coil 14b are tightly coupled and the distributed capacitance is reduced.

It is an object of the present invention to prevent the occurrence of an abnormal state due to the opening of a resonant capacitor due to a work error or a pattern breakage of a substrate.

[0023]

A high voltage generating circuit according to a first aspect of the present invention includes a flyback transformer, and a resonance circuit is configured only by the inductance and internal distributed capacitance of a low voltage coil of the flyback transformer. The resonant pulse voltage boosted by the high voltage coil is obtained.

In the flyback transformer according to the second aspect of the present invention, the low voltage coil and the high voltage coil are divided and wound into an integral split slit structure bobbin, and the low voltage coil and the high voltage coil are loosely coupled.

For example, the high voltage coil comprises a first high voltage coil wound adjacent to the low voltage coil and a second high voltage coil wound adjacent to the first high voltage coil. The number of turns of one high-voltage coil is equal to or greater than the number of turns of the second high-voltage coil.

[0026]

In the first aspect of the invention, since the resonance circuit is constituted only by the inductance of the low voltage coil and the internal distributed capacitance,
Since it is not necessary to mount the resonance capacitor on the circuit board, it is possible to prevent the occurrence of an abnormal state due to the opening of the resonance capacitor due to a work error or a pattern break of the board.

In the second aspect of the invention, the low voltage coil and the high voltage coil are divided and wound into an integral type split slit structure bobbin, and the low voltage coil and the high voltage coil are loosely coupled so that the low voltage coil and the high voltage coil are connected. The distributed capacity between
Moreover, this distributed capacity has a small variation, and
It is possible to obtain a suitable flyback transformer by using the invention.

The number of turns of the first high-voltage coil wound adjacent to the low-voltage coil is equal to or greater than the number of turns of the second high-voltage coil wound adjacent to the first high-voltage coil. This makes it possible to reduce the leakage magnetic flux.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In the figure, 20 is a horizontal deflection circuit.
Reference numeral 21 is an N-channel enhancement type MOS field effect transistor as a horizontal output transistor. A horizontal drive pulse is supplied to the gate of the transistor 21. The source of the transistor 21 is grounded, and its drain is connected to the DC voltage + V via the choke coil 22.
It is connected to the power supply terminal 23 to which cc is supplied. The resonance capacitor 24, the horizontal deflection coil 25, and the S-shaped correction capacitor 2 are connected between the drain of the transistor 21 and the ground.
Six series circuits are connected in parallel.

FIG. 2 shows a MOS field effect transistor 21.
The horizontal axis represents the drain-source voltage VDS, and the vertical axis represents the drain current ID. And
Curve a in the figure shows the relationship between the voltage VDS and the current ID when the transistor 21 is on (ON characteristic), and curve b shows the relationship between the voltage VDS and the current ID when the transistor 21 is off (diode characteristic). Is shown.

Next, the operation will be described with reference to the waveform chart of FIG. A of the same drawing shows a horizontal drive pulse, B of the same shows a drain current, C of the same shows a drain voltage, D of the same shows a resonant capacitor current, and E of the same shows a deflection current.

When a horizontal drive pulse as shown in FIG. 3A is supplied to the gate of the transistor 21, a deflection current (sawtooth wave current) flows through the deflection coil 25 as shown in FIG.

That is, when a positive pulse is supplied to the base of the transistor 21, the transistor 21 is turned on and a current that linearly increases with time flows through the deflection coil 25 (t11 to t12).

Next, when a negative pulse is supplied to the gate of the transistor 21, the transistor 21 is turned off, and the current continues to flow in the same direction due to the inductance inertia to charge the resonance capacitor 24. This charging current decreases with time and the voltage of the resonant capacitor 24 increases. The charging current becomes zero, and the voltage (drain voltage) of the resonance capacitor 24 reaches a peak (t12 to t13).

Next, the resonance capacitor 24 is used for the deflection coil 2
5, the voltage gradually decreases, and the reverse current increases in the deflection coil 25. Resonance capacitor 24
Voltage returns to its original value and the reverse current reaches a peak (t13 to t14).

Next, due to the counter electromotive force of the deflection coil 25, the transistor 21 conducts as a diode (see the diode characteristic of the curve b in FIG. 2), and the current continues to flow in the same direction. The magnitude of the current gradually decreases (t14 to t15). Then, when a positive pulse is supplied to the gate of the transistor 21 and the transistor 21 is turned on, the transistor 21 is turned on this time (see the characteristic of the curve a in FIG. 2), and the current continues to flow in the same direction. The magnitude of the current gradually decreases to zero (t15 to t16).

Next, since the transistor 21 is turned on, a current that linearly increases with time again flows through the deflection coil 25. Through the above cycle, a sawtooth current flowing through the deflection coil 25 is formed.

Returning to FIG. 1, reference numeral 40 is a high voltage generating circuit. Reference numeral 41 is an N-channel enhancement type MOS field effect transistor as a high voltage output transistor. A horizontal drive pulse is supplied to the gate of the transistor 41. The source of the transistor 41 is grounded, and the drain thereof is connected to a power supply terminal 44 to which a DC voltage + Vcc is supplied via a low voltage coil (primary winding) 42a of a flyback transformer (high voltage generating transformer) 42 and a low pass filter 43. Connected. One end of the high-voltage coil (secondary winding) 42b of the transformer 42 is connected to a terminal 46 via a high-voltage rectifier circuit 45 with a multiple voltage. Transformer 4
The other end of the second high-voltage coil 42b has a low-voltage coil 42a.
Connected to one end of.

In the above configuration, the MOS field effect transistor 41 is used as the high voltage output transistor, and its operation is basically the same as the operation of the horizontal deflection circuit 20 described above. However, in this high voltage generation circuit 40, a resonance capacitor is not connected, and the resonance circuit is configured only by the inductance of the low voltage coil 42a of the transformer 42 and the internal distributed capacitance.

A resonance pulse voltage is obtained at the drain of the transistor 41 (see FIG. 3C), a boosted pulse voltage is obtained at the high voltage coil 42b of the transformer 42, and a high voltage HV is derived from the high voltage rectifier circuit 45 to the terminal 46. To be done.

In this example, since the resonance circuit is composed only of the inductance of the low voltage coil 42a and the internal distributed capacitance, it is not necessary to mount the resonance capacitor on the circuit board as in the conventional case, and a work error or a pattern break of the board is generated. It is possible to prevent the occurrence of an abnormal state due to the opening of the resonance capacitor due to the above. Therefore, when the high voltage generation circuit of this example is used in a CRT television receiver or the like, it is not necessary to reduce the high voltage, and it is possible to prevent the resolution from being degraded due to focusing deterioration. Further, a protection circuit or the like for detecting and protecting an abnormally high voltage is not necessary.

FIG. 4 shows the internal structure of the flyback transformer 42. In the figure, 42c is a low-voltage high-pressure integral type bobbin having a split slit structure. This bobbin 42
A low voltage coil 42a is wound around the first slit of c,
A first high voltage coil 42b1 forming the high voltage coil 42b is wound around the second slit, and a second high voltage coil 42b2 forming the high voltage coil 42b is wound around the third slit. The end of winding of the high voltage coil 42b is connected to the high voltage rectifier circuit 45. 42d is a core.

The flyback transformer 42 is shielded by covering the outer circumference with a metal shield case 47.
Then, in order to increase the withstand voltage, a silicon insulating resin 48 is filled between the shield case 47 and the flyback transformer 42.

The flyback transformer 42 shown in FIG.
The coils 42a and 42b and the shield case 4 as shown in FIG.
7 and between the low voltage coil 42a and the high voltage coil 42b. As described above, the low voltage coil 42
a and the high-voltage coil 42b are separately wound on the bobbin 42c, the low-voltage coil 42a and the high-voltage coil 42b are thus wound.
The coupling between them becomes sparse, and the low voltage coil 42a and the high voltage coil 4 are
The distributed capacity between 2b becomes large. Therefore, it is possible to form a sufficient distributed capacitance corresponding to the primary side resonance capacitor of the high voltage generation circuit 40. The dielectric constant of the silicon insulating resin 48 is also positively used for this distributed capacitance. Since the low-voltage coil 42a and the high-voltage coil 42b are wound around the low-pressure high-voltage integrated bobbin 42c, it is possible to obtain a distributed capacity with less variation than that wound around another bobbin.

By the way, as described above, the low-voltage coil 42
When a and the high voltage coil 42b are loosely coupled, the leakage magnetic flux increases and the image quality deteriorates due to the occurrence of raster ringing or the like. Therefore, in this example, the number of windings of the first high-voltage coil 42b1 wound around the second slit is set to be equal to or larger than the number of windings of the second high-voltage coil 42b2 wound around the third slit. . Thereby, the leakage magnetic flux can be reduced, the influence of the leakage magnetic flux can be reduced, and the deterioration of image quality can be suppressed.

[0047]

According to the first aspect of the present invention, since the resonance circuit is configured only by the inductance of the low voltage coil and the internal distributed capacitance, it is not necessary to mount the resonance capacitor on the circuit board.
It is possible to prevent the occurrence of an abnormal state due to the opening of the resonance capacitor due to a work mistake or a pattern break of the substrate. As a result, it is not necessary to reduce the high pressure, and it is possible to prevent a decrease in resolution due to focusing deterioration. Further, a protection circuit for detecting and protecting the abnormal high voltage is not necessary.

According to the second aspect of the invention, the low voltage coil and the high voltage coil are divided and wound into an integral type split slit structure bobbin, and the low voltage coil and the high voltage coil are loosely coupled. And the distributed capacity between
Moreover, this distributed capacity has a small variation, and
A flyback transformer suitable for use in the invention can be obtained.

The number of windings of the first high voltage coil wound adjacent to the low voltage coil is equal to or larger than the number of windings of the second high voltage coil wound adjacent to the first high voltage coil. Therefore, the leakage magnetic flux can be reduced. As a result, the influence of the leakage magnetic flux can be reduced, and the deterioration of image quality can be suppressed.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of a high voltage generating circuit according to the present invention.

FIG. 2 is a diagram showing characteristics of a MOS field effect transistor.

FIG. 3 is a diagram showing a waveform of each part of the example of FIG.

FIG. 4 is a cross-sectional view showing the internal structure of a flyback transformer.

FIG. 5 is a diagram for explaining distributed capacitance of a flyback transformer.

FIG. 6 is a plan view and a side view showing a flat cathode ray tube (flat CRT).

FIG. 7 is a connection diagram showing a configuration of a conventional high voltage generation circuit.

8 is a diagram showing a waveform of each part of the example of FIG.

FIG. 9 is a diagram showing an internal structure of a conventional flyback transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flat cathode ray tube 20 Horizontal deflection circuit 21,41 MOS field effect transistor 22 Choke coil 23,44 Power supply terminal 24 Resonant capacitor 25 Horizontal deflection coil 26 S-shaped correction capacitor 40 High voltage generation circuit 42 Flyback transformer 42a Low voltage coil 42b High voltage coil 42b1 1st high voltage coil 42b2 2nd high voltage coil 42c Bobbin 42d Core 43 Low pass filter 45 High voltage rectifier circuit 47 Shield case 48 Silicon insulating resin

Claims (3)

[Claims] 1. A flyback transformer is provided, and a resonance circuit is configured only by an inductance and an internal distributed capacitance of a low-voltage coil of the flyback transformer, and a resonance pulse voltage boosted from the high-voltage coil of the flyback transformer is obtained. Characteristic high voltage generation circuit. 2. A flyback transformer characterized in that the low-voltage coil and the high-voltage coil are divided and wound in an integral split slit structure bobbin, and the low-voltage coil and the high-voltage coil are loosely coupled. 3. The high-voltage coil comprises a first high-voltage coil wound adjacent to the low-voltage coil and a second high-voltage coil wound adjacent to the first high-voltage coil. The flyback transformer according to claim 2, wherein the number of windings of the first high-voltage coil is equal to or greater than the number of windings of the second high-voltage coil.