JP2002186256A - Switching power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need of a copper plate magnetic shield for a flyback transformer. SOLUTION: In the switching power supply circuit comprising a voltage resonance converter circuit, converter operation is synchronized with a horizontal synchronizing signal being used in a cathode ray tube display in order to prevent generation of a power supply beat through interference of leakage flux of a flyback transformer and the synchronizing signal. Consequently, the transformer does not require any member for shielding the leakage flux and power conversion efficiency is enhanced by suppressing the ringing component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode ray tube (CRT) such as a television receiver or a video monitor.
And a switching power supply circuit suitable for a display device using the same.

[0002]

2. Description of the Related Art For example, as a switching power supply for a television receiver, the applicant of the present invention uses a composite resonance type converter combining a voltage resonance type converter having a single-pole configuration on the primary side and a half wave rectification type voltage resonance circuit on the secondary side. Had proposed. In this case, in order to control the DC output voltage at a constant voltage with respect to the fluctuation of the AC input voltage and the load power, a complex control method for simultaneously controlling the switching frequency and the conduction angle of the primary-side switching element has been adopted.

FIG. 8 is a circuit diagram showing an example of a prior art switching power supply circuit for a television receiver which can be constructed based on the invention proposed by the present applicant. In the power supply circuit shown in this figure, first, as a rectifying and smoothing circuit for receiving a commercial AC power supply (AC input voltage VAC) to obtain a DC input voltage, a full-wave rectifying circuit including a bridge rectifying circuit Di and a smoothing capacitor Ci. And generates a rectified smoothed voltage Ei corresponding to a level that is one time the AC input voltage VAC.

As a switching converter which receives the rectified smoothed voltage Ei (DC input voltage) and is intermittent, the following is known.
A voltage resonance type converter including a stone switching element Q1 and performing a so-called single-ended switching operation is provided. In the case of FIG. 8, a self-excited configuration is adopted as a voltage resonance type converter circuit that performs single-ended operation by one switching element Q1. In this case, a high withstand voltage bipolar transistor (BJT; junction transistor) is employed as the switching element Q1.

Between the base of the switching element Q1 and the ground on the primary side, a series resonance circuit for driving a self-excited oscillation composed of a series connection circuit of a drive winding NB, a resonance capacitor CB and a base current limiting resistor RB is connected. Further, a clamp diode DD inserted between the base of the switching element Q1 and the negative electrode (primary ground) of the smoothing capacitor Ci provides
A path for a clamp current flowing when the switching element Q1 is turned off is formed. The starting resistance RS
Is inserted in order to obtain the base current at the time of starting from the rectifying and smoothing line.

A parallel resonance capacitor Cr is connected in parallel between the collector and the emitter of the switching element Q1. And the parallel resonance capacitor Cr
Own capacitance and isolation converter transformer PI
The primary parallel resonance circuit of the voltage resonance type converter is formed by the leakage inductance L1 on the primary winding N1 side of T.

The orthogonal control transformer PRT shown in FIG.
Is a saturable reactor on which a resonance current detection winding ND, a drive winding NB, and a control winding NC are wound. This orthogonal control transformer PRT drives the switching element Q1 and is provided for constant voltage control. As shown, the orthogonal control transformer PRT is wound with a resonance current detection winding ND and a drive winding NB, and a control winding NC in a direction orthogonal to these two windings. Is wound.

In the orthogonal control transformer PRT, the switching output obtained in the resonance current detection winding ND is induced in the drive winding NB via a transformer coupling. As a result, a series resonance circuit (NB,
A drive current is output from CB) to the base of the switching element Q1 via the base current limiting resistor RB. As a result, the switching element Q1 performs a switching operation at a switching frequency determined by the resonance frequency of the series resonance circuit. The switching output obtained at the collector is transmitted to the primary winding N1 of the isolated converter transformer PIT.

[0009] The insulating converter transformer PIT transmits the switching output of the switching element Q1 to the secondary side. In this insulating converter transformer PIT, a primary winding N1 and a secondary winding N2 are divided and wound around an EE type core,
By forming a gap G for the center magnetic leg, a loose coupling state with a required coupling coefficient can be obtained.
A saturated state is hardly obtained.

The winding start end of the primary winding N1 of the insulating converter transformer PIT is connected to the collector of the switching element Q1, and the winding end end is connected to the positive electrode (rectified smoothing voltage) of the smoothing capacitor Ci via the detection winding ND. Ei). Accordingly, by supplying the switching output of the switching element Q1 to the primary winding N1, an alternating voltage having a cycle corresponding to the switching frequency is generated.

On the secondary side of the insulating converter transformer PIT, an alternating voltage induced by the primary winding N1 is generated in the secondary winding N2. In this case, the secondary side parallel resonance capacitor C2 is connected in parallel to the secondary winding N2, so that the leakage inductance L2 of the secondary side winding N2 and the capacitance of the secondary side parallel resonance capacitor C2 are determined. A parallel resonance circuit is formed. With this parallel resonance circuit,
The alternating voltage induced in the secondary winding N2 becomes a resonance voltage.
That is, a voltage resonance operation is obtained on the secondary side.

That is, in this power supply circuit, the primary side is provided with a parallel resonance circuit for performing a voltage resonance type switching operation, and the secondary side is provided with a parallel resonance circuit for obtaining a voltage resonance operation. Thus, the switching converter configured to operate with the resonance circuits provided on the primary side and the secondary side has a configuration as the above-mentioned “composite resonance type switching converter” described in this specification.

On the secondary side of the power supply circuit formed as described above, a flyback transformer FBT and a high voltage generating circuit 40A comprising a rectifying and smoothing circuit for obtaining a high DC voltage are provided. First, the primary winding N4 of the flyback transformer FBT is connected in parallel with the secondary winding N2. In this case, when the insulating converter transformer PIT operates as a complex resonance type switching converter, a resonance pulse voltage V2 is generated at both ends of the secondary parallel resonance capacitor C2. Then, the flyback transformer FBT transmits the resonance voltage V2 applied to the primary winding N4 to the secondary side. The flyback transformer FBT and its rectifying and smoothing circuit on the secondary side boost the resonance voltage generated in the primary winding N4 to generate a high voltage corresponding to, for example, the anode voltage level of the CRT. Therefore, on the secondary side of the flyback transformer FBT, five sets of boost windings N
HV1, NHV2, NHV3, NHV4, NHV5 are divided and wound by coaxial winding of an interlayer film. The anodes of the high-voltage rectifier diodes DHV1, DHV2, DHV3, DHV4, and DHV5 are connected to the winding start ends of the boost windings NHV1 to NHV5. Further, the cathode of the high-voltage rectifier diode DHV1 is connected to the positive terminal of the smoothing capacitor COHV, and the respective cathodes of the remaining high-voltage rectifier diodes DHV2 to DHV5 are connected to the winding ends of the step-up windings NVH1 to NHV4, respectively.

That is, on the secondary side of the flyback transformer FBT, [a boost winding NHV1, a high-voltage rectifier diode DHV
1], [boost winding NHV2, high voltage rectifier diode DHV2],
[Step-up winding NHV3, high-voltage rectifier diode DHV3], [Step-up winding NHV4, high-voltage rectifier diode DHV4], [Step-up winding N
HV5, high-voltage rectifier diode DHV5], that is, a so-called multisingle-type half-wave rectifier circuit in which five sets of half-wave rectifier circuits are connected in series.

Therefore, on the secondary side of the flyback transformer FBT, five sets of half-wave rectifier circuits
~ NHV5 rectifies the current induced and smoothes capacitor CO
An operation of charging the HV is performed, and a high DC voltage E of a level corresponding to about five times the induced voltage induced in each of the boost windings NVH1 to NHV5 is provided across the smoothing capacitor COHV.
HV will be obtained. Then, the DC high voltage EHV obtained between both ends of the smoothing capacitor COHV is
It is used as the anode voltage of T.

In this case, the flyback transformer F
The primary winding N4 of the BT is about 30 to 50T (turns), the boost windings NHV1 to NHV5 are each about 530T, and about 5650T by winding five layers of interlayer films. The coupling coefficient is about 0.9. For example, DC high voltage EHV is 3
In order to obtain 1.5 KV, the primary winding N1 of the isolated converter transformer PIT = 90T, the secondary winding N
2 = 75T, resonance capacitor Cr = 2700 pF, secondary-side parallel resonance capacitor C2 = 0.017 μF, primary winding N4 = 50T of the flyback transformer FBT, and boost windings NHV1 to NHV5 = 520T are selected.

The DC high voltage EHV is divided by a high voltage resistor R1 and a divided resistor R2 and supplied to the control circuit 1. In the control circuit 1, the divided DC high voltage EHV
Is used to generate a control signal for constant voltage. That is, in the control circuit 1, the level of the control current (DC current) flowing through the control winding NC is changed according to the change in the voltage level of the DC high voltage EHV. Thereby, the inductance LB of the drive winding NB is varied, and the resonance frequency of the series resonance circuit in the self-excited oscillation drive circuit, that is, the switching frequency of the switching element Q1 is variably controlled. This makes the DC high voltage EHV a constant voltage. AC input voltage VAC = 90V-120V, high voltage load power PHV = 126W
For a variation of ~ 0 W, the switching frequency fs is 8
It is controlled in the range of 0 KHz to 95 KHz. Here, in varying the switching frequency, the period TOFF during which the switching element Q1 is turned off is kept constant, and the period TON during which the switching element Q1 is turned on is variably controlled. In this specification, such complex control is referred to as a “complex control method”.

FIGS. 9 and 10 are waveform diagrams showing the operation of the main part of the power supply circuit shown in FIG. FIG. 9 shows an AC input voltage VAC = 100 V and a maximum high-voltage load power PHV = 12.
It is an operation waveform at the time of 6W (= 31.5KV × 4mA),
FIG. 10 shows operation waveforms when the AC input voltage VAC = 100 V and the maximum high-voltage load power PHV = 0 W (= 31.5 KV × 0 mA).

[0019]

The power supply circuit shown in FIG. 8 has the following problems. As shown in FIG. 11A, the insulating converter transformer PIT includes, for example, E-shaped cores CR1 and CR made of a ferrite material.
An EE-type core in which the magnetic legs 2 are opposed to each other is provided. A primary winding N1 and a secondary winding N2 are provided to the center magnetic leg of the EE-type core by using a divided bobbin B. Are wound separately. A gap G is formed for the center magnetic leg as shown in the figure. As a result, loose coupling with a required coupling coefficient can be obtained. The coupling coefficient is, for example, about 0.8. As a result, a leakage magnetic flux of about 20% is generated near the insulating converter transformer PIT. The frequency of the leakage magnetic flux ranges from 80 KHz to 95 KHz by controlling the switching frequency fs.

FIG. 12 shows a flyback transformer FBT.
A flyback transformer FBT includes two U-shaped cores CR11,
A rectangular core CR30 is formed by combining the magnetic legs of CR12 so as to face each other. A gap G is provided at a portion where the end of the U-shaped core CR11 and the end of the U-shaped core CR12 face each other. For example, each gap G is 0.35 mm. Then, as shown in the drawing, with respect to one magnetic leg of the square core CR30,
By attaching the low-voltage winding bobbin LB and the high-voltage winding bobbin HB, the primary winding N4 and the boost winding NH are respectively attached to the low-voltage winding bobbin LB and the high-voltage winding bobbin HB.
V is divided and wound. In this case, the primary winding N4 is wound around the low-voltage winding bobbin LB, and a plurality of boost windings NHV are wound around the high-voltage winding bobbin HB.
Is inserted and wound up by interlayer winding. Also in the case of the flyback transformer FBT, a leakage magnetic flux having a frequency of about 80 KHz to 95 KHz is generated in the vicinity thereof.

On the other hand, the frequency fh of the horizontal synchronizing signal of the television receiver is fh = 15.75K in the NTSC system.
Hz, fh = 33.75KHz in the high-vision system,
In the double speed system of the NTSC system, fh = 31.5 KHz, 3
The double-speed system differs depending on various television broadcasting systems such as fh = 47.25 KHz. With respect to a horizontal deflection circuit operating in synchronization with the horizontal synchronization signal, a deflection yoke is provided at a neck portion of a cathode ray tube (CRT), and a horizontal linearity correction coil, a dynamic focus transformer and the like are provided on a printed circuit board. Many reactors and inductors are mounted. When the leakage magnetic flux of the above-mentioned insulating converter transformer PIT and flyback transformer FBT is coupled to the components of these horizontal deflection circuits,
A power beat of oblique stripes is generated on the surface of the CRT due to interference between the horizontal synchronization frequency fh and the switching frequency fs.

As a countermeasure against this, as shown by a broken line in FIG. 11A, a short ring SR in which a copper plate is wound one turn and soldered is arranged around the gap G of the insulating converter transformer PIT. FIG. 11B is a schematic diagram showing a state where the short ring SR is wound. A required portion H of the short ring SR is soldered. By magnetically shielding the leakage magnetic flux by the short ring SR, generation of a power beat is suppressed. Further, as schematically shown in FIG. 12 by a broken line in the flyback transformer FBT,
Magnetic shield plate M made of copper plate after soldering required parts
S is provided to suppress the leakage magnetic flux.

However, due to the cost of material of the copper plate and the necessity of the mounting / soldering process, each transformer (PIT, PIT,
There is a problem that the manufacturing process of FBT) is complicated and costs are increased.

In the isolated converter transformer PIT,
In order to prevent the ferrite core and the copper plate from squeaking in the audible frequency band due to vibration, it was necessary to fix the copper plate by performing varnish impregnation after assembling the transformer.
In the flyback transformer FBT, it is necessary to wind a copper plate on an insulating plate or mount the copper plate away from the transformer. These also complicate the manufacturing steps and increase the cost of the insulating converter transformer PIT and the flyback transformer FBT.

[0025]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention eliminates the need to shield a magnetic flux leakage from an insulating converter transformer PIT or a flyback transformer FBT in a switching power supply circuit for a cathode ray tube display. It is intended to be.

Therefore, the present invention provides a rectifying / smoothing means for obtaining a DC input voltage as a rectified / smoothed voltage obtained by rectifying / smoothing an AC input voltage, and a switching device formed by including a switching element for switching and outputting the DC input voltage. Means, a primary-side parallel resonance capacitor provided so as to form a primary-side resonance circuit that makes the operation of the switching means a voltage resonance type, and a signal synchronized with a horizontal synchronization signal used in the cathode ray tube display device. Switching driving means for causing the switching element to perform a switching operation in synchronization with a horizontal synchronization signal; and a primary winding and a secondary high-voltage winding which are tightly coupled to each other. A flyback converter that transmits the output to the secondary high-voltage winding and obtains a high-voltage alternating voltage boosted from the secondary. DC high voltage generating means configured to obtain a DC high voltage by performing a half-wave rectification operation on a high-voltage alternating voltage obtained on the secondary side of the flyback transformer, and the flyback transformer. A controlled winding connected in series with the primary winding and provided so as to function as an inductance component of the primary resonance circuit, and a control winding in which the winding is orthogonal to the controlled winding And a control current, which is varied according to the level of the DC high voltage, is supplied to the control winding to change the inductance of the controlled winding. A constant-voltage control unit configured to perform constant-voltage control on the voltage to constitute a switching power supply circuit.

According to the above configuration, on the primary side, the operation of the switching converter provided with the primary side resonance circuit for forming the voltage resonance type converter can be synchronized with the horizontal synchronization frequency. Also, power beat due to interference between the leakage magnetic flux of the high voltage generating transformer and the horizontal synchronization frequency is prevented. Further, the DC high voltage is stabilized by controlling the inductance of the controlled winding of the orthogonal control transformer.

Further, in the switching power supply circuit according to the present invention, in the above configuration, the DC high-voltage generating means inserts a rectifier diode in series for each of the divided secondary high-voltage windings, so that the high-voltage alternating voltage is Rectifier circuit, and a smoothing capacitor for smoothing the rectified output of the multi-stage rectifier circuit, thereby generating and outputting a DC high voltage of a required level and rectifying the multi-stage rectifier circuit. The ringing suppression circuit is connected to the current path. Alternatively, a ringing suppression circuit is connected in series with the primary winding of the flyback transformer. With such a configuration, the switching power supply circuit has an operation of suppressing a ringing current flowing on the secondary side or the primary side.

In the switching power supply circuit according to the present invention, the control winding of the orthogonal control transformer has a structure in which a plurality of wires are bundled and wound. Thus, the time constant of the control winding can be reduced while maintaining the magnetomotive force, and the high-speed transient response is improved.

[0030]

FIG. 1 shows a configuration of a switching power supply circuit according to a first embodiment of the present invention.
The circuit shown in FIG. 1 includes a voltage resonance type converter that performs a switching operation in a so-called single-end system by a self-excited system. A high withstand voltage bipolar transistor (BJT: junction transistor) is employed as one switching element Q1 provided in this voltage resonance type converter.

A rectifying / smoothing circuit including a bridge rectifying circuit Di and a smoothing capacitor Ci is connected to the commercial AC power supply AC, and generates a rectified / smoothed voltage Ei corresponding to a level almost equal to the AC input voltage VAC. It is supplied as a DC input voltage to a subsequent voltage resonance type converter.

The base of the switching element Q1 is connected to a smoothing capacitor Ci (rectified smoothing voltage E) via a starting resistor RS.
It is connected to the positive electrode side of i) so that the base current at the time of startup is obtained from the rectification smoothing line.

Between the base of the switching element Q1 and the ground on the primary side, a drive winding NB having a winding number of 1T (turn) on the primary side of the flyback transformer FBT.
And a series resonance circuit for self-excited oscillation driving, which is composed of a series circuit of a resonance capacitor CB, an inductor LB and a base current limiting resistor RB. Switching frequency f for turning on / off switching element Q1 by this self-excited oscillation circuit
s is generated. For example, assuming that the horizontal synchronizing frequency fh = 33.75 KHz in a television receiver or the like on which the switching power supply circuit is mounted, the switching frequency fs by the series resonance circuit is set to about 33.5 KHz.

Further, in the case of this example, the horizontal synchronization frequency fh
The horizontal oscillation pulse voltage, the horizontal drive pulse voltage, or the voltage Vfh as the horizontal output pulse voltage used in the horizontal synchronization circuit system of the cathode ray tube display device is synchronized via the resistor Rh and the capacitor Ch in order to synchronize with the display. Is applied to the base of the switching element Q1. As a result, the switching operation of the switching element Q1 is externally synchronized.

Further, the clamp diode DD inserted between the base of the switching element Q1 and the negative electrode (primary side ground) of the smoothing capacitor Ci provides the switching element Q1.
Of the switching element Q1 is connected to one end of the primary winding N4 of the flyback transformer FBT, and the emitter is grounded.

The collector of the switching element Q1
A parallel resonance capacitor Cr is connected in parallel between the emitters. The parallel resonance capacitor Cr includes its own capacitance, the primary winding N4 of the flyback transformer FBT, and the orthogonal control transformer PRT (Power
A parallel resonance circuit of the voltage resonance type converter is formed by the combined inductance (L4 + LR) obtained by connecting the controlled winding NR of the Regulating Transformer in series.
When the switching element Q1 is turned off, the voltage V1 across the resonance capacitor Cr is actually a sinusoidal pulse waveform by the action of the parallel resonance circuit, so that a voltage resonance type operation can be obtained.

The orthogonal control transformer PRT is a saturable reactor in which the controlled winding NR and the control winding NC are wound. In the orthogonal control transformer PRT, the inductance LR of the controlled winding NR is varied by a control current supplied to the control winding NC by the control circuit 1. Thereby, the DC high voltage EHV described later is stabilized.

The control winding NC of the orthogonal control transformer PRT is formed by winding 400 to 200 T (turns) using, for example, 3 to 6 bundles of litz wires of 60 μmφ. FIG. 2 shows the structure of the orthogonal control transformer PRT. FIG.
2A is an external perspective view for explaining the overall structure, and FIG. 2B is a cross-sectional perspective view for explaining a winding direction of a wound winding. The orthogonal control transformer PRT is formed by a three-dimensional core 20 in which two double U-shaped cores 21 and 22 (ferrite cores) are combined.
One double U-shaped core 21 has four magnetic legs 2.
1a, 21b, 21c, 21d, and the other double U-shaped core 22 also has four magnetic legs 22a, 22b, 2
2c and 22d. Then, the two magnetic legs 21a to 21d, 2 of these two double U-shaped cores 21, 22 are formed.
The three-dimensional core 20 is formed by joining the ends of 2a to 22d. A gap G is provided at each joint of the double U-shaped cores 21 and 22.

In this case, for example, a double U-shaped core 21
A control winding NC is wound around the two magnetic legs 21b and 21c, and a controlled winding NR is wound around the magnetic legs 22c and 22d of the double U-shaped core 22. That is, the controlled winding NR
, A control winding NC is wound as a saturable reactor wound in a direction orthogonal to the control winding NC.

As shown in the figure, the control winding NC is wound about 400 T in a state where three bundles of litz wires NC1, NC2 and NC3 each having a diameter of, for example, 60 μm are bundled. 4 bundles, 5 bundles
A bundle of six litz wires may be bundled and wound. For example, 6
In the case of a bundle, it is wound about 200T. By bundling a plurality of bundles of litz wires and reducing the number of turns, the DC resistance and inductance of the control winding NC can be reduced as compared with the case of using a single bundle of litz wires. The time constant can be reduced while maintaining the same. this is,
The variable control of the inductance LR of the controlled winding NR by the control current flowing through the control winding NC improves the high-speed transient response.

In the circuit shown in FIG.
The switching output obtained at 1 is transmitted to the primary winding N4 of the flyback transformer FBT forming the high voltage generation circuit 40. As shown, the flyback transformer FBT has a primary winding N4 wound on the primary side.
Also, as the secondary side high-voltage winding, five sets of boost windings NVH1, NH
V2, NHV3, NHV4, and NHV5 are wound. These boost windings NHV1 to NHV5 are actually divided and wound around the core in an independent state. These boost windings NHV
1 to NHV5 are wound so as to have the opposite polarity to the primary winding N4, so that a flyback operation can be obtained.

These boost windings NVH1, NVH2, NVH3, NH
As shown in the figure, V4 and NHV5 are connected in series with each of the high-voltage rectifier diodes DHV1, DHV2, DHV3, DHV4, and DHV5 to form a total of five sets of half-wave rectifier circuits. A half-wave rectifier circuit is further connected in multiple stages in series. Then, a smoothing capacitor C is applied to a multi-stage rectifier circuit composed of these five sets of half-wave rectifier circuits.
OHVs are connected in parallel.

However, in the present embodiment, as shown, a high-voltage rectifier diode DHV is provided between the winding start end of the boost winding NVH5 and the secondary side ground, as shown in the figure.
An additional high voltage rectifier diode DHV6 is connected in series with the same conduction direction as 1 to DHV5. That is, the additional high-voltage rectifier diode DHV6 is provided at the lowermost stage of the multi-stage rectifier circuit in the rectification current path of the secondary-side rectifier / smoothing circuit. This additional high voltage rectifier diode DHV6
Functions as the ringing suppression circuit 41A.

The operation of the secondary-side rectifying / smoothing circuit is as follows. The primary winding N4 of the flyback transformer FBT and the boost windings NHV1 to NHV5 are tightly coupled, and a positive sine wave pulse voltage generated in the primary winding N4 when the switching element Q1 of the primary side voltage resonance converter is off. Is boosted by the boost windings NHV1 to NHV5. Then, on the secondary side of the flyback transformer FBT, the five sets of half-wave rectifier circuits convert the voltages induced in the boost windings NHV1 to NHV5 into:
An operation of rectifying by the high voltage rectifier diodes DHV1 to DHV5 (and the additional high voltage rectifier diode DHV6) and charging the smoothing capacitor COHV is performed. by this,
At both ends of the smoothing capacitor COHV, each boost winding NHV1 to NHV
A DC voltage at a level corresponding to five times the voltage induced in HV5 is obtained. Then, the DC voltage obtained at both ends of the smoothing capacitor COHV is output as a DC high voltage EHV. The DC high voltage EHV is used, for example, as an anode voltage of a CRT.

Further, a series connection circuit of voltage dividing resistors R1-R2 is provided in parallel with the smoothing capacitor COHV from which the DC high voltage EHV is obtained. The voltage dividing resistor R1−
The voltage dividing point of R2 is connected to the control circuit 1. That is, in the present embodiment, a voltage level obtained by dividing the DC high voltage EHV by the voltage dividing resistors R1 and R2 is input to the control circuit 1 as the detection voltage. Further, a resistor R3 is inserted between the smoothing capacitor COHV and the secondary-side ground, and a voltage at one end of the resistor R3 is supplied to the control circuit 1 as a detection voltage.

The control circuit 1 is configured as an error voltage amplifier, and varies the level of the control current (DC current) flowing through the control winding NC according to the change in the DC high voltage EHV, thereby changing the inductance of the controlled winding NR. LR is variably controlled. This stabilizes the DC high voltage EHV.

FIGS. 3 and 4 show an example of the structure of the flyback transformer FBT provided in the circuit shown in FIG. The illustration of the drive winding NB shown in FIG. 1 is omitted. First, in the flyback transformer FBT shown in FIG. 3, the U-U-shaped core CR is formed by combining the magnetic legs of two U-shaped cores CR1 and CR2 made of, for example, a ferrite material so as to face each other.
Then, the magnetic leg end of the U-shaped core CR1 and the U-shaped core C
The gaps G1 and G
2 are provided. Then, as shown in the figure, the low-voltage winding bobbin LB on which the primary winding N4 is wound
-Attach so as to penetrate one magnetic leg of the U-shaped core CR. Then, the high-voltage winding bobbin HB on which the boost windings NHV (1 to 5) are wound is attached to the outside of the low-voltage winding bobbin LB so as to pass therethrough. As a result, a structure in which the primary winding N4 and the boost winding NHV (1 to 5) are divided and wound is obtained.

Here, as the boost winding NHV wound around the high-voltage winding bobbin HB, for example, a plurality of boost windings NHV (1 to
It is necessary to wind each of 5) in an insulated state. For this reason, the winding method of the step-up windings NHV depends on each step-up winding NVH (1 to
5) is a so-called interlayer winding in which an interlayer film F is interposed for each winding layer obtained by winding a predetermined number of times.
Then, the primary winding N4 and the step-up winding NVH are filled with a filler such as a polymer epoxy resin, thereby ensuring their insulation. Then, after winding the step-up winding NVH (1 to 5) as described above,
In terms of the circuit, the high-voltage rectifier diodes DHV (1 to DHV (1 to
6) Connect and attach.

In order to obtain an insulated state for each of the step-up windings NVH (1 to 5), in addition to the structure shown in FIG. 3, as shown in FIG. (Slit winding) can also be adopted. In FIG. 4, the same parts as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. When the step-up winding NHV is wound by the division winding, as shown in the figure, the high-voltage winding bobbin H
A partition plate DV is formed integrally with the inside of B1. As a result, a plurality of slits S, which are winding regions, are formed between adjacent partition plates DV. The step-up windings NHV are wound around the respective slits S so as to obtain insulation between the step-up windings NHV.

Depending on the structure of the flyback transformer FBT shown in FIG. 3 or FIG. 4, the primary winding N4 and the secondary side boosting winding NHV (1-5) are wound around the same magnetic leg. So that a tightly coupled state is obtained as a mutually coupled state. For example, in practice, close coupling with a coupling coefficient k of about 0.98 is obtained. Further, in the case of this example, the magnetic shield plate MS made of a copper plate as described with reference to FIG. 12 is not provided.

The stabilization of the DC high voltage EHV is performed as follows. As described above, the control circuit 1 includes the DC high voltage E
A control current of a level corresponding to the fluctuation of the DC high voltage EHV is applied to the control winding NC of the orthogonal transformer PRT so that HV is constant, and the inductance LR of the controlled winding NR is controlled.
It operates to change. The parallel resonance circuit on the primary side is
Although it can be seen that it is formed by the combined inductance (L4 + LR) of the primary winding N4 and the controlled winding NR and the capacitance of the parallel resonance capacitor Cr,
When the inductance LR of the controlled winding NR changes due to the operation of the control circuit 1, the resonance condition of the primary side parallel resonance circuit changes to control the pulse width of the resonance voltage obtained at both ends of the switching element Q1 and the parallel resonance capacitor Cr. Is obtained. Here, the pulse width of the resonance voltage is the off period of the switching element Q1, in other words, controlling the pulse width of the resonance voltage is equivalent to the switching element Q1.
It is nothing more than controlling the DC output voltage of the secondary side by controlling the ON period of 1. That is, in the present embodiment, the operation is performed so as to stabilize the secondary-side output voltage by controlling the ON period of the switching element Q1.

In the switching power supply circuit of this embodiment, the primary winding N4 = 60T, each boost winding NHV = 530T, the inductance L1 = 1.5mH, the parallel resonance capacitor Cr
= 1000 pF, AC input voltage VAC = 10
0 V ± 10%, DC high voltage EHV = 31.5 KV, DC high current IHV = 4 mA to 0 mA, and the variable range of the inductance LR of the controlled winding NR is 50 μH to 150 μ.
H makes it possible to make the DC high voltage EHV constant.

Further, according to the power supply circuit shown in FIG. 1, the operation of the voltage resonance type switching converter can be synchronized with the horizontal synchronization frequency, whereby the leakage flux of the flyback transformer FBT and the horizontal synchronization frequency can be adjusted. The power beat can be prevented from occurring due to the interference. As described above, the primary-side switching element Q1
The switching frequency fs is set by a series resonance circuit including a drive winding NB, a resonance capacitor CB, an inductor LB, and a base current limiting resistor RB. Here, if the switching frequency fs is set to be smaller than the horizontal synchronization frequency fh, the switching frequency fs is fixed by being pulled to fs = fh by the external synchronization trigger signal of the voltage Vfh synchronized with the horizontal synchronization frequency. For example, fs = 3
The fixed frequency is 3.75 KHz. For this reason, the operation of the voltage resonance type switching converter is synchronized with the frequency of the horizontal synchronizing signal, so that no power beat occurs due to the interference between the leakage magnetic flux of the flyback transformer FBT and the horizontal synchronizing frequency. Of course, in the case of this example, since the insulating converter transformer PIT is not used, the problem regarding the leakage magnetic flux of the insulating converter transformer PIT mentioned in the prior art of FIG. 8 does not occur.

FIG. 5 shows the operation waveforms of the respective parts when the AC input voltage VAC = 100 V, the DC high voltage EHV = 31.5 KV, and the DC high current IHV = 4 mA. FIG. 6 shows the AC input voltage VAC = 1.
The operation waveforms at 00 V and high DC current IHV = 0 W are shown. In this case, the horizontal synchronization frequency fh = 33.75 KHz
Since the switching frequency fs is synchronized with this, the switching cycle is 9 μm as shown in FIGS.
sec + 20.6 μsec = 11.1 μsec + 18.
5 μsec = 29.6 μsec. That is, the switching cycle is fixed and synchronized with the horizontal synchronization frequency. By controlling the inductance LR, the on / off period of the switching element Q1 is variably controlled within a fixed cycle. Therefore, as can be seen by comparing FIGS. 5 and 6, when the AC input voltage is low and the high-voltage load is heavy, the inductance LR of the controlled winding NR is reduced,
The pulse width of the voltage resonance pulse voltage V1 generated on the primary side is reduced, and the peak value is increased. On the other hand, when the AC input voltage is high and the high-voltage load is light, the inductance LR of the controlled winding NR increases, the pulse width of the voltage resonance pulse voltage V1 increases, and the peak value decreases. By such an operation, the DC high voltage EHV is made constant.

As described above, in the present embodiment, in the secondary rectifying and smoothing circuit of the flyback transformer FBT, an additional high-voltage rectifying diode is provided as a ringing suppressing circuit 41A for the rectifying current path of the multi-stage rectifying circuit. DHV6 is provided. That is, the boost windings NHV1 to NHV
The high-frequency ringing (oscillation) current component is generated due to the distributed capacitance of 5 and the leakage inductance of the primary winding N4 and the boost windings NHV1 to NHV5.
The ringing component is reduced by HV6. As a result, a significant reduction in power loss is achieved, thereby improving power conversion efficiency. In the case of this example, the power conversion efficiency of AC / DC is improved from 85.7% of the circuit example of FIG. 8 to 87.5%, and the input power can be reduced. The input power can be reduced by 3.0 W at the maximum high-voltage load, and can be reduced by 3.0 W at the high-voltage no-load.

FIG. 7 shows a switching power supply circuit according to a second embodiment of the present invention. FIG. 7 shows the switching element Q1
Is a MOS-FET, and a separately excited oscillation circuit by an IC is provided for the switching element Q1. FIG.
The same parts as those described above are denoted by the same reference numerals, and description thereof will be omitted.

Also in this case, as a switching converter which inputs and outputs a rectified and smoothed voltage Ei (DC input voltage), a voltage resonance type converter having a single switching element Q1 and performing a so-called single-end switching operation. Is provided. The voltage resonance type converter here adopts a separately-excited type, and a MOS-FET
Is connected to the positive electrode of the smoothing capacitor Ci via the primary winding N4 and the controlled winding NR of the flyback transformer FBT, and the source is connected to the primary side ground.

The drain of the switching element Q1
A parallel resonance capacitor Cr is connected in parallel between the sources. A primary side parallel resonance circuit is formed by the capacitance of the parallel resonance capacitor Cr and the leakage inductance (L4 + LR) obtained in the primary winding N4 and the controlled winding NR. The resonance operation of the parallel resonance circuit is obtained in accordance with the switching operation of the switching element Q1, so that the switching operation of the switching element Q1 is a voltage resonance type.

Further, the drain of the switching element Q1
Between the sources, a clamp diode DD constituted by a so-called body diode provided in the MOS-FET
Are connected in parallel to form a path for a clamp current flowing during a period when the switching element is turned off.

The switching element Q 1 is switching-driven by a switching driver 10 comprising, for example, one integrated circuit (IC) integrally provided with an oscillation circuit 2 and a drive circuit 3. In addition, this switching drive unit 1
Numeral 0 is connected to the line of the rectified and smoothed voltage Ei via the starting resistor Rs. For example, at the time of starting the power, the power is applied by applying the power supply voltage via the starting resistor Rs.

The oscillation circuit 2 in the switching drive section 10 performs an oscillation operation to generate and output an oscillation signal. Then, the drive circuit 3 converts this oscillation signal into a drive voltage and outputs it to the gate of the switching element Q1. Thus, the switching element Q1 performs a switching operation based on the oscillation signal generated by the oscillation circuit 2. Therefore, the switching frequency of the switching element Q1 and the duty of the ON / OFF period within one switching cycle are determined depending on the oscillation signal generated by the oscillation circuit 2. In particular, in the case of this example, a voltage Vfh as a horizontal oscillation pulse voltage, a horizontal drive pulse voltage, or a horizontal output pulse voltage used in the horizontal synchronization circuit system of the cathode ray tube display device.
Is supplied to the oscillation circuit 2 via the resistor Rh and the small-capacity capacitor Ch, and external synchronization is achieved. That is, the oscillation circuit 2
Generates an oscillation signal synchronized with the horizontal synchronization frequency, whereby the switching operation of the switching element Q1 is synchronized with the horizontal synchronization frequency.

Further, in the case of the present embodiment, a ringing suppressing circuit 41B is inserted in series from the primary winding N4 via the controlled winding NR. As shown in the figure, the ringing suppression circuit 41B includes an inductor L10,
It has a capacitor C10 and a resistor R10. Inductor L
10 is inserted in series from the end of the primary winding N4 to the positive terminal of the smoothing capacitor Ci.
A capacitor C10 is connected to the inductor L10.
A series connection of resistors R10 is connected in parallel; That is, a so-called LCR parallel resonance circuit is formed, and this LCR parallel resonance circuit is configured to be connected in series to the primary winding N4.
Note that the ringing suppression circuit 41A shown in FIG. 1 is not provided.

In such a switching power supply circuit as well, the operation of the voltage resonance type switching converter is synchronized with the frequency of the horizontal synchronizing signal. Therefore, the power supply beat caused by the interference between the leakage magnetic flux of the flyback transformer FBT and the horizontal synchronizing frequency. Does not occur. Therefore, it is not necessary to provide a magnetic shield in the flyback transformer FBT. Further, the ringing component is reduced by the ringing suppression circuit 41B, and the AC / DC power conversion efficiency can be improved.

Although the embodiments of the present invention have been described above, it is needless to say that the switching power supply circuit of the present invention is not limited to the above-described circuit configurations, and various modifications can be considered. For example, flyback transformer FBT
The rectifier circuit on the secondary side is not limited to the above configuration, and another circuit configuration may be adopted as long as a level required as the DC high voltage EHV can be obtained. For example, a circuit configuration as one set of a high-voltage winding and a quadruple voltage rectification method may be adopted.

[0065]

As described above, the present invention relates to a switching power supply circuit using a voltage resonance type converter circuit.
Because the converter operation by switching operation is synchronized with the horizontal synchronization signal used in the cathode ray tube display device, the leakage flux of the converter transformer or flyback transformer interferes with the horizontal synchronization signal to generate a power beat. Disappears. Therefore, for example, it is not necessary to provide a flyback transformer with a shield plate made of a copper plate for shielding leakage magnetic flux. This has the effect of reducing the manufacturing cost of the transformer, simplifying the manufacturing, and increasing the efficiency. Further, not providing the shield plate has an advantage that the temperature rise of the transformer is reduced.

Further, the provision of the ringing suppressing means for suppressing the high-frequency ringing component of the flyback transformer has the effect of improving the power conversion efficiency and reducing the input power.

The control winding of the orthogonal control transformer is formed by bundling and winding a plurality of litz wires to reduce the time constant while maintaining the magnetomotive force. As a result, the high-speed transient response characteristic is improved, and the stabilizing operation appropriately responding to a steep change of the high-voltage load or the like becomes possible. Further, the number of turns in the control winding process at the time of manufacturing the orthogonal control transformer becomes 1/3 (in the case of 3 litz wire bundles) to 1/6 (in the case of 6 litz wire bundles) or the like. There is also an advantage that the time is greatly reduced and productivity can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply circuit according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an orthogonal control transformer according to the embodiment.

FIG. 3 is an explanatory diagram of a structure example of a flyback transformer according to the embodiment;

FIG. 4 is an explanatory diagram of a structural example of a flyback transformer according to the embodiment;

FIG. 5 is a waveform chart showing an operation of a main part in the power supply circuit of the embodiment.

FIG. 6 is a waveform chart showing an operation of a main part in the power supply circuit of the embodiment.

FIG. 7 is a circuit diagram illustrating a configuration of a switching power supply circuit according to a second embodiment.

FIG. 8 is a circuit diagram showing a configuration example of a switching power supply circuit as a prior art.

FIG. 9 is a waveform chart showing an operation of a main part of the power supply circuit shown in the prior art.

FIG. 10 is a waveform chart showing an operation of a main part of the power supply circuit shown in the prior art.

FIG. 11 is an explanatory diagram of a magnetic shield of the insulating converter transformer.

FIG. 12 is an explanatory diagram of a magnetic shield of a flyback transformer.

[Explanation of symbols]

1 control circuit, 2 oscillation circuit, 3 drive circuit, 10
Switching drive section, 40 high voltage generation circuit, 41A,
41B Ringing suppression circuit, Q1 switching element, PRT orthogonal control transformer, FBT flyback transformer, N4 primary winding, NHV boost winding, Cr primary side parallel resonance capacitor, DHV high voltage rectifier diode,
COHV smoothing capacitor

Claims (4)

[Claims] 1. A switching power supply circuit for a cathode ray tube display, comprising: a rectifying / smoothing means for obtaining a DC input voltage as a rectified and smoothed voltage obtained by rectifying and smoothing an AC input voltage; and a switching element for switching and outputting the DC input voltage. A primary-side parallel resonance capacitor provided so as to form a primary-side resonance circuit that makes the operation of the switching means a voltage resonance type, and a horizontal synchronization used in the cathode ray tube display device. A switching drive unit for causing the switching element to perform a switching operation in synchronization with a horizontal synchronization signal using a signal synchronized with the signal; a primary winding and a secondary high voltage winding being tightly coupled; The output of the switching means obtained as described above is transmitted to the secondary high voltage winding, and the high voltage alternating voltage boosted from the secondary side is transmitted. A DC high voltage generator configured to obtain a DC high voltage by performing a half-wave rectification operation on a flyback transformer configured to obtain a high voltage and a high voltage alternating voltage obtained on a secondary side of the flyback transformer. Means, a controlled winding connected in series with the primary winding of the flyback transformer and provided so as to function as an inductance component of the primary resonance circuit; An orthogonal control transformer is provided around which the control winding is wound so as to be orthogonal to the control winding, and a control current that is varied according to the level of the DC high voltage is supplied to the control winding. A switching power supply circuit comprising: constant voltage control means for performing constant voltage control on the high DC voltage by changing inductance. 2. The multi-stage rectifier circuit for rectifying the high-voltage alternating voltage by inserting a rectifier diode in series for each of the divided secondary high-voltage windings. By providing a smoothing capacitor for smoothing the rectified output of the rectifier circuit, a DC high voltage of a required level is generated and output, and a ringing suppression circuit is connected to the rectifier current path of the multi-stage rectifier circuit. The switching power supply circuit according to claim 1, wherein 3. The switching power supply circuit according to claim 1, wherein a ringing suppression circuit is connected in series with the primary winding of the flyback transformer. 4. The switching power supply circuit according to claim 1, wherein the control winding of the orthogonal control transformer is formed by bundling a plurality of litz wires.