JP2002136136A - Switching power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with magnetic shielding with a copper plate with respect to an insulating converter transformer or a high-voltage generating transformer. SOLUTION: In a switching power circuit with a complex-resonant converter circuit, converter operation is set, so as to be synchronized with a horizontal synchronizing signal used in a cathode-ray tube display, thereby eliminating generation of power beats caused by interference of leakage flux of the converter transformer or the high-voltage generating transformer with the horizontal synchronizing signal. The use of a shielding member for shielding the leakage flux in each of the transformers can be eliminated.

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. 7 is a circuit diagram showing an example of a switching power supply circuit for a television receiver as a prior art, which can be formed 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. 7, 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 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 is connected to the positive electrode (rectified smoothing voltage) of the smoothing capacitor Ci via the detection winding ND. Ei). Therefore, the switching output of the switching element Q1 is supplied to the primary winding N1,
An alternating voltage having a period 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, the primary winding N4 of the high-voltage generating transformer HVT is connected in parallel with the secondary winding N2. In this case, the isolated converter transformer PIT operates as a composite resonance type switching converter, so that the resonance pulse voltage V2 is applied across the secondary side parallel resonance capacitor C2.
Occurs. Then, the high-voltage generating transformer HVT transmits the resonance voltage V2 applied to the primary winding N4 to the secondary side.
The high-voltage generating transformer HVT boosts a resonance voltage generated in the primary winding N4 to generate a high voltage corresponding to, for example, an anode voltage level of a CRT. Therefore, on the secondary side of the high-voltage generating transformer HVT, five sets of boost windings NVH1,
NHV2, NHV3, NHV4 and 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. Furthermore, high voltage rectifier diode DHV
One cathode is connected to the positive terminal of the smoothing capacitor COHV, and the other cathodes of the remaining high-voltage rectifier diodes DHV2 to DHV5 are connected to the winding ends of the step-up windings NVH1 to NVH4, respectively.

That is, on the secondary side of the high voltage generating transformer HVT, [boost winding NHV1, high voltage rectifying diode DHV1]
[Step-up winding NHV2, high-voltage rectifier diode DHV2], [Step-up winding NHV3, high-voltage rectifier diode DHV3], [Step-up winding N
HV4, high voltage rectifier diode DHV4], [boost winding NHV5,
Thus, a so-called multisingle-type half-wave rectifier circuit in which five sets of half-wave rectifier circuits called high-voltage rectifier diodes DHV5] are connected in series is formed.

Therefore, on the secondary side of the high-voltage generating transformer HVT, five sets of half-wave rectifier circuits are provided by the step-up windings NVH1 to NHH.
The operation of rectifying the current induced in V5 and charging the smoothing capacitor COHV is performed.
At both ends of the OHV, a DC high voltage EHV having a level corresponding to about five times the induced voltage induced in each of the boost windings NHV1 to NHV5 is obtained. And this smoothing capacitor COH
The DC high voltage EHV obtained at both ends of V is used, for example, as an anode voltage of a CRT.

In this case, the high-voltage generating transformer HVT
The primary winding N4 is 30 to 50T (turn), and the boost winding N
HV1 to NHV5 are each set to about 530T, and set to about 2650T by winding five layers of interlayer films. The coupling coefficient is about 0.9. For example, as DC high voltage EHV 31.
In order to obtain 5 KV, the primary winding N1 = 90T and the secondary winding N2 =
75T, resonance capacitor Cr = 2700 pF, secondary-side parallel resonance capacitor C2 = 0.017 μF, primary winding N4 of high-voltage generating transformer HVT = 50T, step-up winding NVH1〜
NHV5 = 520T is 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 E
A control signal for constant voltage generation is generated using the HV. 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 = 126
For a variation of W to 0 W, the switching frequency fs is
It is controlled in the range of 80 KHz to 95 KHz. here,
In changing 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. 8 and 9 are waveform diagrams showing the operation of the main part of the power supply circuit shown in FIG. FIG. 8 shows an AC input voltage VAC = 100 V and a maximum high-voltage load power PHV = 126.
FIG. 9 shows an operation waveform when W (= 31.5 KV × 4 mA), and FIG. 9 shows an AC input voltage VAC = 100 V and a maximum high-voltage load power P
This is an operation waveform when HV = 0 W (= 31.5 KV × 0 mA).

[0019]

The power supply circuit shown in FIG. 7 has the following problems. As shown in FIG. 10A, 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. 11 is a sectional view of the high-voltage generating transformer HVT. The high-voltage generating transformer HVT has two U-shaped cores CR11 and CR12 made of, for example, a ferrite material.
The square core CR30 is formed by combining the respective magnetic legs so as to face each other. And U-shaped core CR
A gap G is provided at a portion where the end of the U-shaped core 11 faces the end of the U-shaped core CR12. For example, each gap G is 0.35 mm. Then, as shown, by attaching the low-voltage winding bobbin LB and the high-voltage winding bobbin HB to one magnetic leg of the square core CR30,
The primary winding N4 and the boost winding NHV are separately wound around these low-voltage winding bobbin LB and high-voltage winding bobbin HB. 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 by inserting and winding up the interlayer film F. become.
In the case of this high-voltage generating transformer HVT, 8
Leakage magnetic flux having a frequency of about 0 KHz to 95 KHz is generated.

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 the horizontal deflection circuit operating in synchronization with the horizontal synchronization signal, a deflection yoke is arranged at the neck of a cathode ray tube (CRT), and a high voltage of 30 KV to be supplied to an anode electrode of the CRT is provided on a printed circuit board. Transformer (flyback transformer)
Many reactors and inductors are mounted, such as a horizontal linearity correction coil, a dynamic focus transformer, and the like. When the leakage magnetic flux of the above-described insulating converter transformer PIT and the high-voltage generating transformer HVT is coupled to these components of the horizontal deflection circuit, 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. Resulting in.

As a countermeasure for this, as shown by a broken line in FIG. 10A, 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. 10B 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 by a broken line in FIG. 11, a magnetic shield plate MS made of a copper plate is soldered to a required portion of the high-voltage generating transformer HVT to suppress leakage magnetic flux.

However, the shielding process of the insulating converter transformer PIT and the high-voltage generating transformer HVT requires the material cost of the copper plate,
Due to the necessity of the soldering process, each transformer (PIT, HV
There is a problem that the manufacturing process of T) is complicated and the cost is 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 high-voltage generating transformer HVT, a copper plate must be wound on an insulating plate, or the copper plate must be mounted separately from the transformer. These things are also insulated converter transformer PI
This complicates the manufacturing process of the T and high voltage generating transformer HVT and increases the cost.

[0025]

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

Therefore, according to the present invention, there is provided a switching means formed by including a main switching element for switching and outputting a DC input voltage, and a primary side parallel resonance circuit which makes the operation of the switching means a voltage resonance type. A primary side parallel resonant capacitor provided in such a manner
An insulation converter transformer for loosely coupling the primary side and the secondary side to obtain a required coupling coefficient, and transmitting the output of the main switching means obtained on the primary side to the secondary side; A secondary-side parallel resonance circuit formed by connecting a secondary-side parallel resonance capacitor in parallel to a secondary-side winding wound on a transformer, and a secondary-side winding wound on the insulating converter transformer In parallel with the winding part between one end and the intermediate tap, a series connection circuit including a clamp capacitor and a secondary-side auxiliary switching element is provided, so that the secondary winding wound on the insulating converter transformer is provided. A cathode-side circuit formed as a circuit including a secondary-side active clamp means for clamping a generated voltage and a primary-side drive winding wound on the insulating converter transformer; Primary switching drive means for generating a fixed switching frequency close to the frequency of the horizontal synchronization signal used in the display device to cause the main switching element to perform a switching operation, and a secondary drive winding wound around the insulating converter transformer. Secondary-side switching drive means formed as a circuit including a secondary-side auxiliary switching element for applying a switching drive signal to the secondary-side auxiliary switching element to cause the secondary-side auxiliary switching element to perform a switching operation; and Applying a signal synchronized with the horizontal synchronization signal to synchronize the operation of the primary parallel resonance circuit and the secondary parallel resonance circuit with a horizontal synchronization frequency; Primary winding connected in parallel with the secondary winding A high-voltage generating transformer that transmits a resonance voltage obtained on the secondary winding of the transformer to the secondary side from the primary side to obtain a high-voltage obtained by boosting the resonance voltage from the secondary side; DC high voltage generating means configured to obtain a DC high voltage by performing a half-wave rectification operation on a high voltage obtained on the secondary side of the high voltage generating transformer, and a DC control signal based on the DC high voltage A switching power supply circuit including a constant-voltage generator for applying a voltage to the secondary-side auxiliary switching element to control the conduction angle of the secondary-side auxiliary switching element to make the DC high voltage constant.

Further, the present invention provides a switching device, a primary-side parallel resonance capacitor, an insulating converter transformer, a secondary-side parallel resonance circuit, a secondary-side active clamp means, a high-voltage generating transformer, and a DC high-voltage generating means, similar to the above configuration. Further, based on a signal synchronized with the horizontal synchronization signal used in the cathode ray tube display device, primary-side switching for generating a switching frequency synchronized with the frequency of the horizontal synchronization signal and causing the main switching element to perform a switching operation. Driving means, formed as a circuit including a secondary-side drive winding wound on the insulating converter transformer,
A secondary-side switching drive means for applying a switching drive signal to the secondary-side auxiliary switching element to cause the secondary-side auxiliary switching element to perform a switching operation; and a DC control signal based on the DC high voltage A switching power supply circuit comprising: a constant-voltage generator that applies a voltage to the side auxiliary switching element to control the conduction angle of the secondary-side auxiliary switching element to make the DC high voltage a constant voltage.

Further, similarly to the above configuration, the switching device includes a switching unit, a primary side parallel resonance capacitor, an insulating converter transformer, a secondary side parallel resonance circuit, a secondary side active clamp unit, a high voltage generation transformer, and a DC high voltage generation unit. ,
Further, a primary switching drive means for generating a fixed switching frequency close to the frequency of the horizontal synchronizing signal used in the cathode ray tube display device to cause the main switching element to perform a switching operation, and a secondary drive wound around the insulating converter transformer. Secondary-side switching drive means formed as a circuit including a winding, and applying a switching drive signal to the secondary-side auxiliary switching element to cause the secondary-side auxiliary switching element to perform a switching operation; and Synchronizing means for synchronizing the operation of the primary parallel resonance circuit and the secondary parallel resonance circuit to a horizontal synchronization frequency by applying a signal synchronized with the horizontal synchronization signal to the auxiliary switching element; and And a DC control signal based on Executing the conduction angle control of the side auxiliary switching element so as to have a constant voltage means for making the DC high voltage a constant voltage, and a predetermined on / off timing synchronized with the on / off timing of the main switching element. A primary-side auxiliary switching element that performs switching in the following manner; and a primary-side active clamp means provided to clamp a primary-side parallel resonance voltage generated at both ends of the primary-side parallel resonance capacitor. Is configured.

According to each of the above structures, the primary side is provided with a primary side parallel resonance circuit for forming a voltage resonance type converter, and the secondary side is provided with a secondary winding and a secondary side parallel resonance capacitor. The operation of the so-called composite resonance type switching converter provided with the formed secondary side parallel resonance circuit can be synchronized with the horizontal synchronization frequency. Power beats due to frequency interference do not occur.

[0030]

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

On the primary side of this power supply circuit, a self-excited configuration is shown as a voltage resonance type converter circuit which 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.

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.

Further, between the base of the switching element Q1 and the primary side ground, a drive winding NB having a winding number of 1T (turn) on the primary side of the insulating converter transformer PIT.
And a series resonance circuit for self-excited oscillation driving, which is composed of a series circuit of an inductor LB, a resonance capacitor CB, 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.

The switching element Q1 is connected to the clamp diode DD1 inserted between the base of the switching element Q1 and the negative electrode (primary ground) of the smoothing capacitor Ci.
The path of the clamp current flowing when the switch 1 is off is formed. The collector of the switching element Q1 is connected to one end of the primary winding N1 of the insulating converter transformer PIT, and the emitter is grounded.

A parallel resonance capacitor Cr is connected in parallel between the collector and the emitter of the switching element Q1. In this case as well, the primary parallel resonance circuit of the voltage resonance type converter is formed by the capacitance of the parallel resonance capacitor Cr itself and the leakage inductance L1 on the primary winding N1 side of the insulating converter transformer PIT.

The insulated converter transformer PIT transmits the switching output of the switching element Q1 to the secondary side. The insulated converter transformer PIT, as described with reference to FIG.
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. Gap G is E-type core CR
1 and CR2 can be formed by making the center magnetic leg shorter than the two outer magnetic legs. In addition, as the coupling coefficient k, for example, a loosely coupled state of k ≒ 0.8 is obtained, so that a saturated state is hardly obtained. However, in the case of this example, the short ring SR made of a copper plate as described with reference to FIG. 10 is not provided.

One end of the primary winding N1 of the insulating converter transformer PIT is connected to the collector of the switching element Q1, and the other end is connected to the positive electrode (rectified smoothing voltage Ei) of the smoothing capacitor Ci. 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 parallel resonance capacitor C2 is connected in parallel to the secondary winding N2,
A parallel resonance circuit is formed by the leakage inductance L2 of the secondary winding N2 and the capacitance of the secondary side parallel resonance capacitor C2. With this parallel resonance circuit, the alternating voltage induced in the secondary winding N2 becomes a resonance voltage, so that a voltage resonance operation is obtained on the secondary side. That is, this power supply circuit also includes a "parallel resonance circuit for providing a voltage resonance operation on the primary side and a parallel resonance circuit for obtaining a voltage resonance operation on the secondary side. It adopts the configuration of "switching converter".

An intermediate tap is provided for the secondary winding N2. The winding portion from the winding start end of the secondary winding N2 to the intermediate tap is referred to as a winding N3. Further, for the secondary side of the power supply circuit formed as described above, the winding N
And a half-wave rectifier circuit including a secondary-side rectifier diode DO1 and a smoothing capacitor CO1 connected to a tap output line from an intermediate tap provided in 3;
A secondary DC output voltage EO1 corresponding to the alternating voltage induced between the tap and the secondary ground in the winding N3 is obtained.

In this power supply circuit, an active clamp circuit is provided on the secondary side. That is, the secondary side active clamp circuit includes an auxiliary switching element Q2 of a MOS-FET, a clamp capacitor C3, and a clamp diode DD2 of a body diode. A drive circuit system for driving the auxiliary switching element Q2 includes a drive winding Ng1, a capacitor Cg1, and a resistor Rg.
Comprising one.

A clamp diode DD2 is connected in parallel between the drain and source of the auxiliary switching element Q2. The connection form is a clamp diode D
The anode of D2 is connected to the source, and the cathode is connected to the drain. The drain of the auxiliary switching element Q2 is connected to the intermediate tap line of the secondary winding N2 via the clamp capacitor C3. The source of the auxiliary switching element Q2 is connected to the secondary side ground. Therefore, the secondary side active clamp circuit is configured by connecting a clamp capacitor C3 in series to the parallel connection circuit of the auxiliary switching element Q2 and the clamp diode DD2. And the circuit formed in this way is
It is configured to be further connected in parallel to the winding N3.

As shown in the figure, the drive circuit system of the auxiliary switching element Q2 is connected to the gate of the auxiliary switching element Q2 by a capacitor Cg1-a resistor Rg1-
A series connection circuit of the drive winding Ng1 is connected. Also in this case, the series connection circuit forms a self-excited drive circuit for the auxiliary switching element Q2. That is, the signal voltage (drive voltage VGS) from the self-excited drive circuit is applied to the gate of the switching element Q2 by the resistor R10, and the switching operation is performed. The drive winding Ng1 in this case is
It is formed on the winding start end side of the secondary winding N2, and the number of turns in this case is, for example, 1T (turn). As a result, a voltage excited by the alternating voltage obtained in the primary winding N1 is generated in the drive winding Ng1. Also,
In this case, a voltage having a polarity opposite to that of the secondary winding N2 and the drive winding Ng1 is obtained from the relationship in the winding direction. The number of turns of the drive winding Ng1 is 1T.
In that case, the operation is guaranteed, but is not limited to this.

The primary winding N4 of the high-voltage generating transformer HVT is connected in parallel to the secondary winding N2 of the insulating converter transformer PIT. In this case, since the insulating converter transformer PIT operates as a complex resonance type switching converter, the secondary side parallel resonance capacitor C
2 generate a resonance pulse voltage V2 at both ends. Then, the high-voltage generating transformer HVT transmits the resonance voltage V2 applied to the primary winding N4 to the secondary side. The high-voltage generating transformer HVT boosts a resonance voltage generated in the primary winding N4 to generate a high voltage corresponding to, for example, an anode voltage level of a CRT. Therefore, on the secondary side of the high-voltage generating transformer HVT, five sets of boost windings NVH1, NVH2, NVH3, NVH
4, NHV5 is divided and wound by coaxial winding of the interlayer film. Then, high-voltage rectifier diodes DHV1, DHV1 are connected to the winding start ends of the respective boost windings NHV1 to NHV5.
The anode sides of 2, DHV3, DHV4, and DHV5 are connected. 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 high voltage generating transformer HVT, [boost winding NHV1, high voltage rectifying diode DHV1]
[Step-up winding NHV2, high-voltage rectifier diode DHV2], [Step-up winding NHV3, high-voltage rectifier diode DHV3], [Step-up winding N
HV4, high voltage rectifier diode DHV4], [boost winding NHV5,
Thus, a so-called multisingle-type half-wave rectifier circuit in which five sets of half-wave rectifier circuits called high-voltage rectifier diodes DHV5] are connected in series is formed.

Therefore, on the secondary side of the high-voltage generating transformer HVT, five sets of half-wave rectifier circuits are provided by the step-up windings NVH1 to NHH.
The operation of rectifying the current induced in V5 and charging the smoothing capacitor COHV is performed.
At both ends of the OHV, a DC high voltage EHV having a level corresponding to about five times the induced voltage induced in each of the boost windings NHV1 to NHV5 is obtained. And this smoothing capacitor COH
The DC high voltage EHV obtained at both ends of V is used, for example, as an anode voltage of a CRT.

In this case, the high-voltage generating transformer HVT
The primary winding N4 is 30 to 50T (turn), and the boost winding N
HV1 to NHV5 are each set to about 530T, and set to about 2650T by winding five layers of interlayer films. The coupling coefficient is about 0.9.

As described with reference to FIG. 11, the structure of the high-voltage generating transformer HVT is such that a square core CR30 is formed by combining the magnetic legs of two U-shaped cores CR11 and CR12 made of, for example, a ferrite material so as to face each other. I have. Then, the portion where the end of the U-shaped core CR11 and the end of the U-shaped core CR12 face each other is 0.35 mm.
Gap G is provided. Then, by attaching the low-voltage winding bobbin LB and the high-voltage winding bobbin HB to one of the magnetic legs of the square core CR30, the primary side windings are respectively attached to the low-voltage winding bobbin LB and the high-voltage winding bobbin HB. The line N4 and the step-up winding NHV are divided and wound. The low-voltage winding bobbin LB has a primary winding N
4, and a plurality of step-up windings NVH are wound around the high-voltage winding bobbin HB by interlayer winding in which the interlayer film F is inserted and wound. However, in the case of this example, the magnetic shield plate MS made of a copper plate as described with reference to FIG. 11 is not provided.

In this example, the switching operation of the auxiliary switching element Q2 is controlled by the control circuit 1 to P
WM control is performed. That is, the DC high voltage E
HV is divided by a high-voltage resistor R1 and a divided resistor R2 and supplied to the control circuit 1. The control circuit 1 generates a DC control voltage for constant voltage using the divided DC high voltage EHV and applies the DC control voltage to the gate of the auxiliary switching element Q2, so that the conduction angle of the auxiliary switching element Q2 is reduced. Controlled. Thus, the DC high voltage EHV is made constant with respect to the fluctuation of the AC input voltage VAC and the high-voltage load power PHV.

Further, in the case of this embodiment, the horizontal synchronization frequency fh
In order to synchronize, a horizontal oscillation pulse voltage, a horizontal drive pulse voltage, or a voltage Vfh as a horizontal output pulse voltage used in a horizontal synchronization circuit system of a cathode ray tube display device is supplied via a resistor Rh and a capacitor Ch. Is applied to the gate of the auxiliary switching element Q2. This results in external synchronization.

According to such a power supply circuit, the operation of the composite resonance type switching converter can be synchronized with the horizontal synchronization frequency, whereby the leakage flux of the insulating converter transformer PIT and the high voltage generation transformer HVT and the horizontal synchronization frequency can be reduced. The power beat can be prevented from occurring due to the interference. As described above, the switching frequency fs of the primary-side switching element Q1 is set by the series resonance circuit including the drive winding NB, the inductor LB, the resonance capacitor CB, and the base current limiting resistor RB. Here, switching frequency fs <horizontal synchronization frequency f
If it is set to h, the external frequency synchronization trigger signal of the voltage Vfh to the secondary-side auxiliary switching element Q2 is pulled into fs = fh via the drive windings Ng1 and NB to fix the switching frequency fs. . Therefore, the operation of the composite resonant switching converter is synchronized with the frequency of the horizontal synchronizing signal, so that no power beat occurs due to interference between the leakage magnetic flux of the insulating converter transformer PIT and the high-voltage generating transformer HVT and the horizontal synchronizing frequency.

FIG. 2 shows the operation waveforms of the respective parts when the AC input voltage VAC = 100 V and the high-voltage load power PHV = 126 W. FIG. 3 shows the AC input voltage VAC = 100 V and the high-voltage load power PHV =
The operation waveform at 0 W is shown. In this case, the primary winding N1 = 130T, the secondary winding N2 = 150T (including the winding N3 = 75T), the drive winding NB = Ng1 = 1T, and the resonance capacitor Cr = 0.0T.
12 µF, resonance capacitor C2 = 0.043 µF, clamp capacitor C3 = 0.33 µF, primary winding N4 of the high-voltage generating transformer HVT = 50T, step-up windings NHV1 to NHV5
Are 530T, and the switching element Q2 is 80
The MOS-FET has a withstand voltage of 0 V.

In the case shown in FIGS. 2 and 3, the horizontal synchronization frequency fh = 33.75 KHz, and the illustrated period Th =
29.85 μsec. Then, the ON time TON of the MOS-FET (switching element Q2) and the clamp diode DD2 (body diode) is 15 μsec to 23 μm.
The conduction angle is controlled for sec. High voltage load power PHV = 126
At the time of W, the power conversion efficiency of AC / DC is improved from 90.5% of the conventional example of FIG. 7 to 91.6%, and the input power is reduced by 1.6 W due to a decrease in switching loss of the switching elements Q1 and Q2. be able to. From these operation waveforms, it can be seen that the switching operation as the composite resonance type converter has a cycle of the period Th, that is, is synchronized with the horizontal synchronization frequency.

FIGS. 4A and 4B show AC input voltage VAC =
The graph shows changes in the DC high voltage EHV and the resonance voltages V1 and V3 with respect to a change in the high-voltage load power PHV at 100V. From these figures, it can be seen that the DC high voltage EHV is constant at 31.5 KV with respect to the fluctuation of the high voltage load power PHV. FIG. 4C shows a change in the ON period TON with respect to a change in the high-voltage load power PHV, that is, how the conduction angle of the switching element Q2 is controlled. This figure 4
(C) corresponds to the ON period TON in FIGS.

FIG. 5 shows a switching power supply circuit according to a second embodiment of the present invention. FIG. 5 shows the switching element Q
This is an example of a high-voltage regulator in which MOS-FETs 1 and 2 are used, and an example in which a separately excited oscillation circuit using an IC is provided for the switching element Q1. The same parts as those in FIG. 1 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 which includes a single switching element Q1 and performs a switching operation by a so-called single-end system. Is provided. The voltage resonance type converter here adopts a separately-excited type, and a MOS-FET
, The drain of the switching element Q1 is connected to the positive electrode of the smoothing capacitor Ci via the primary winding N1 of the insulating converter transformer PIT, 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. The capacitance of the parallel resonance capacitor Cr and the primary winding N1 of the insulation converter transformer PIT
The primary side parallel resonance circuit is formed by the leakage inductance obtained as described above. And the switching element Q
The resonance operation by the parallel resonance circuit is obtained according to the switching operation of No. 1, so that the switching operation of the switching element Q1 is a voltage resonance type.

The drain of the switching element Q1
Between the sources, a clamp diode DD1 formed 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 Q1 is switching-driven by a switching drive unit 10 including, for example, one integrated circuit (IC) integrally provided with an oscillation circuit 2 and a drive circuit 3. The switching drive unit 10 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 switching driving unit 10 is started by applying the power voltage via the starting resistor Rs. It has been like that.

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.

The secondary side of the insulated converter transformer PIT and the primary side and secondary side of the high voltage generating transformer HVT are substantially the same as those shown in FIG.
The voltage Vfh for external synchronization is not applied to the auxiliary switching element Q2.

Also in the case of such a switching power supply circuit, the operation of the composite resonance type switching converter is synchronized with the frequency of the horizontal synchronizing signal. Therefore, the leakage flux of the insulating converter transformer PIT and the high voltage generating transformer HVT and the horizontal synchronizing frequency A power beat does not occur due to interference of the power supply. Therefore, it is not necessary to provide a magnetic shield in the insulating converter transformer PIT or the high-voltage generating transformer HVT.

FIG. 6 shows a switching power supply circuit according to a third embodiment of the present invention. This is for each switching element Q
In this example, an 800 V withstand voltage IGBT (insulated gate bipolar transistor) is used as Q1, Q2, and Q3, and an active clamp circuit is also provided on the primary side. This is an example of the configuration of a high voltage regulator that is common to the AC 100 V system and the 200 V system. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

In this case, the switching elements Q1 and Q3 of the IGBT are arranged on the primary side. The switching element Q1 constitutes a switching converter that inputs and outputs a rectified smoothed voltage Ei (DC input voltage). The collector of the switching element Q1 is connected to the isolation converter transformer P
It is connected to the positive electrode of the smoothing capacitor Ci through the IT primary winding N1, and the emitter is connected to the primary side ground.

Further, the collector of the switching element Q1
A parallel resonance capacitor Cr is connected in parallel between the emitters. The capacitance of the parallel resonance capacitor Cr and the primary winding N of the insulating converter transformer PIT
The primary side parallel resonance circuit is formed by the leakage inductance obtained in (1). 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. The clamp diode DD1 is connected in parallel between the collector and the emitter of the switching element Q1, thereby forming a path for a clamp current flowing during a period in which the switching element is turned off.

The switching element Q 1 includes, for example, an integrated circuit (I
Switching driving is performed by the switching driving unit 10 according to C). The switching drive unit 10
It 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, it is started 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 the case of this example, for example, in a television receiver or the like on which the switching power supply circuit is mounted, the horizontal synchronization frequency fh = 33.
Assuming that the frequency is 75 KHz, the switching frequency fs =
An oscillation signal is generated at about 33.5 KHz.

On the primary side, a primary side active clamp circuit for clamping a parallel resonance voltage obtained at both ends of the parallel resonance capacitor Cr is provided. In this case, the primary-side active clamp circuit includes an auxiliary switching element Q3 using an IGBT and a clamp capacitor C.
4, constituted by a clamp diode DD3. Also,
The drive circuit system for driving the auxiliary switching element Q3 includes a drive winding Ng2, a capacitor Cg2, and a resistor Rg.
1, R2.

A clamp diode DD3 is connected in parallel between the collector and the emitter of the auxiliary switching element Q3. Here, the anode of the clamp diode DD3 is connected to the emitter, and the cathode is connected to the collector. The collector of the auxiliary switching element Q3 is connected via a clamp capacitor C4 to a connection point between the line of the rectified smoothed voltage Ei and the end of the primary winding N1. Also, the auxiliary switching element Q
The emitter No. 3 is connected to the winding start end of the primary winding N1. That is, the primary-side active clamp circuit is configured by connecting a clamp capacitor C4 in series to a parallel connection circuit of the auxiliary switching element Q3 and the clamp diode DD3. The circuit thus formed is connected in parallel with the primary winding N1 of the insulating converter transformer PIT.

As shown in the figure, the drive circuit system of the auxiliary switching element Q3 is connected to the gate of the auxiliary switching element Q3 by a resistor Rg2-a capacitor Cg2-
The series connection circuit of the drive winding Ng2 is connected. This series connection circuit forms a self-excited oscillation drive circuit for the auxiliary switching element Q2. Here, the drive winding Ng2
Has a number of turns of, for example, 1T (turn). In this case, a voltage having a polarity opposite to that of the primary winding N1 and the drive winding Ng2 is obtained from the relationship in the winding direction. In addition,
In practice, if the number of turns of the drive winding Ng2 is 1T, the operation is guaranteed, but the present invention is not limited to this. The resistor R1 is connected to the insulation converter transformer P
It is inserted between the connection point of the primary winding N1 of the IT and the drive winding Ng2.

The auxiliary switching element Q3 is turned on / off in synchronization with the main switching element Q1. That is, the auxiliary switching element Q3 is turned off during the on period of the main switching element Q1, and the auxiliary switching element Q3 is turned on during the off period of the main switching element Q1. As a result of the operation of the primary side active clamp circuit, the voltage appearing at both ends of the resonance capacitor Cr is clamped.

The secondary side of the insulating converter transformer PIT,
The configuration of the primary side and the secondary side of the high-voltage generating transformer HVT is substantially the same as that of FIG. However, the auxiliary switching element Q2 is an example in which an IGBT is used. That is, as the secondary side active clamp circuit, I
An auxiliary switching element Q2 of a GBT (insulated gate bipolar transistor), a clamp capacitor C3, and a clamp diode DD2 of a body diode are provided. Also,
A drive circuit system for driving the auxiliary switching element Q2 includes a drive winding Ng1, a capacitor Cg1, and a resistor Rg.
g1.

A clamp diode DD2 is connected in parallel between the collector and the emitter of the auxiliary switching element Q2. As the connection form, the anode of the clamp diode DD2 is connected to the emitter, and the cathode is connected to the collector. The collector of the auxiliary switching element Q2 is connected to the end of the secondary winding N2 via a clamp capacitor C3. Further, the emitter of the auxiliary switching element Q2 is connected to the secondary side ground. Therefore, the secondary side active clamp circuit is configured by connecting a clamp capacitor C3 in series to the parallel connection circuit of the auxiliary switching element Q2 and the clamp diode DD2. The circuit thus formed is further connected in parallel to a secondary parallel resonance circuit including the winding N3 and the parallel resonance capacitor C2.

As shown in the figure, the driving circuit system of the auxiliary switching element Q2 is connected to the gate of the auxiliary switching element Q2 by a capacitor Cg1-a resistor Rg1-
A series connection circuit of the drive winding Ng1 is connected. Also in this case, the series connection circuit forms a self-excited drive circuit for the auxiliary switching element Q2. That is, the signal voltage (drive voltage VGS) from the self-excited drive circuit is applied to the gate of the switching element Q2 by the resistor R10, and the switching operation is performed.

In the case of this power supply circuit, the voltage Vfh synchronizing with the horizontal synchronizing frequency is applied to the auxiliary switching element Q2, as in FIG.
As described above, the switching frequency fs of the switching element Q1 on the primary side is set such that the switching frequency fs <the horizontal synchronization frequency fh, so that the external synchronization trigger signal of the voltage Vfh for the auxiliary switching element Q2 on the secondary side allows Through the operation of the drive windings Ng1 and Ng2 and the operation of the primary side active clamp circuit, fs is pulled to fs = fh, and the switching frequency fs is fixed. Therefore, the operation of the composite resonant switching converter is synchronized with the frequency of the horizontal synchronizing signal, so that no power beat occurs due to interference between the leakage magnetic flux of the insulating converter transformer PIT and the high-voltage generating transformer HVT and the horizontal synchronizing frequency. Therefore, the insulation converter transformer P
It is not necessary to provide a magnetic shield in the IT and the high voltage generating transformer HVT.

Although the embodiments of the present invention have been described above, the switching power supply circuit of the present invention is not limited to the above-described circuit configurations, and it is needless to say that various modifications are possible.

[0076]

As described above, the present invention relates to a switching power supply circuit using a complex resonance type converter circuit.
Since 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 and the high voltage generation transformer interfere with the horizontal synchronization signal to generate a power beat. Disappears. Therefore, there is no need to provide a short ring or a shield plate made of a copper plate for shielding the leakage magnetic flux in the converter transformer or the high-voltage generating transformer. As a result, there is an effect that the manufacturing cost of each transformer can be reduced, manufacturing can be simplified, and efficiency can be improved. Further, not providing a short ring or a shield plate also has an advantage that the temperature rise of each transformer is reduced.

The switching frequency of the complex resonance type converter circuit is about 80 KHz to 95 KHz.
Since the frequency is set to about 1.5 KHz to 47.25 KHz, the size of the converter transformer is increased due to the lowering of the switching frequency, but the switching loss of the switching element is reduced and the power conversion efficiency is improved. There is also.

Further, a secondary parallel resonance capacitor is connected in parallel to a winding portion between one end of the secondary winding wound around the insulating converter transformer and the intermediate tap to form a secondary parallel resonance circuit. In addition, by configuring a secondary-side active clamp means including a clamp capacitor and a secondary-side auxiliary switching element in parallel with a winding portion between one end of the secondary-side winding and the intermediate tap, MOS- as an auxiliary switching element of the secondary side active clamp means
FETs and IGBTs have lower withstand voltage, for example, withstand voltage of 1500 V
Can be set to a withstand voltage of 800 V. Therefore, the switching loss of the MOS-FET or the IGBT can be reduced.

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

FIG. 3 is a waveform chart showing an operation of a main part in the power supply circuit of the embodiment.

FIG. 4 is an explanatory diagram showing a relationship among load power, DC high voltage, resonance voltage, and conduction angle control according to the embodiment.

FIG. 5 is a circuit diagram illustrating a configuration of a switching power supply circuit according to a second embodiment.

FIG. 6 is a circuit diagram illustrating a configuration of a switching power supply circuit according to a third embodiment.

FIG. 7 is a circuit diagram showing a configuration example of a switching power supply circuit as a prior art.

FIG. 8 is a waveform chart showing an operation of a main part of the power supply circuit shown in the 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 cross-sectional view and a perspective view showing a configuration of an insulating converter transformer.

FIG. 11 is a cross-sectional view illustrating a configuration of a high-voltage generating transformer.

[Explanation of symbols]

1 control circuit, 2 oscillation circuit, 3 drive circuit, 10
Switching driver, Q1 (main) switching element, Q2, Q3 auxiliary switching element, PIT isolation converter transformer, HVT high voltage generation transformer, N1
Primary winding, N2 secondary winding, N4 primary winding, NHV
Boost winding, Cr primary side parallel resonance capacitor, C2 secondary side parallel resonance capacitor, DO1 secondary side rectifier diode, DHV high voltage rectifier diode, COHV smoothing capacitor

Claims (3)

[Claims] 1. A switching power supply circuit for a cathode ray tube display device, comprising: a switching means formed with a main switching element for switching and outputting a DC input voltage; And a primary side parallel resonance capacitor provided so as to form a side parallel resonance circuit, and a primary side and a secondary side are loosely coupled so that a required coupling coefficient is obtained, and the primary side An insulating converter transformer for transmitting the output of the main switching means to the secondary side, and a secondary winding formed by connecting a secondary parallel resonance capacitor in parallel to the secondary winding wound on the insulating converter transformer. A secondary parallel resonance circuit and a winding portion between one end of the secondary winding wound around the above-mentioned insulated converter transformer and the intermediate tap. By providing a series connection circuit of a clamp capacitor and a secondary side auxiliary switching element in parallel with the secondary side active clamping means for clamping a voltage generated in a secondary side winding wound on the insulating converter transformer. A switching operation is performed on the main switching element by generating a fixed switching frequency close to the frequency of a horizontal synchronizing signal used in the cathode ray tube display device, which is formed as a circuit including a primary side drive winding wound on the insulating converter transformer. And a secondary drive winding wound around the insulating converter transformer, and applying a switching drive signal to the secondary auxiliary switching element to perform the secondary drive. Secondary switch that causes the auxiliary switching element to perform switching operation By applying a signal synchronized with the horizontal synchronization signal to the switching drive means and the secondary auxiliary switching element, the operations of the primary parallel resonance circuit and the secondary parallel resonance circuit are synchronized with the horizontal synchronization frequency. A primary winding connected in parallel with a secondary winding wound on the insulating converter transformer, and a resonance voltage obtained on the secondary winding of the insulating converter transformer, from the primary side. A high-voltage generating transformer configured to obtain a high voltage obtained by boosting the resonance voltage from the secondary side by transmitting the voltage to the secondary side, and a half-wave rectifying operation on the high voltage obtained on the secondary side of the high-voltage generating transformer. Performing a DC high voltage generating means configured to obtain a DC high voltage; and applying a DC control signal based on the DC high voltage to the secondary-side auxiliary switching element. A switching power supply circuit comprising: a constant-voltage generating means for performing a conduction angle control of the secondary auxiliary switching element to convert the DC high voltage to a constant voltage. 2. A switching power supply circuit for a cathode ray tube display device, comprising: a switching means formed with a main switching element for switching and outputting a DC input voltage; And a primary side parallel resonance capacitor provided so as to form a side parallel resonance circuit, and a primary side and a secondary side are loosely coupled so that a required coupling coefficient is obtained, and the primary side An insulating converter transformer for transmitting the output of the main switching means to the secondary side, and a secondary winding formed by connecting a secondary parallel resonance capacitor in parallel to the secondary winding wound on the insulating converter transformer. A secondary parallel resonance circuit and a winding portion between one end of the secondary winding wound around the above-mentioned insulated converter transformer and the intermediate tap. And a secondary-side active clamping means for clamping a voltage generated in the secondary winding by providing a series connection circuit of a clamp capacitor and a secondary-side auxiliary switching element in parallel with each other, and used in the cathode ray tube display device. Primary side switching drive means for generating a switching frequency in synchronization with the frequency of the horizontal synchronization signal based on a signal synchronized with the horizontal synchronization signal to cause the main switching element to perform a switching operation; Secondary-side switching drive means formed as a circuit including a secondary-side drive winding and applying a switching drive signal to the secondary-side auxiliary switching element to cause the secondary-side auxiliary switching element to perform a switching operation; Connected in parallel with the secondary winding wound on the insulated converter transformer By transmitting a resonance voltage obtained on the secondary winding of the insulating converter transformer from the primary side to the secondary side, a high voltage obtained by boosting the resonance voltage from the secondary side is provided. A high-voltage generating transformer adapted to obtain, by performing a half-wave rectification operation on a high-voltage obtained on the secondary side of the high-voltage generating transformer, a DC high voltage generating means configured to obtain a DC high voltage, Applying a DC control signal based on the DC high voltage to the secondary-side auxiliary switching element to perform conduction angle control of the secondary-side auxiliary switching element, thereby making the DC high voltage a constant voltage. Means, and a switching power supply circuit comprising: 3. A switching power supply circuit for a cathode ray tube display device, comprising: a switching means formed with a main switching element for switching and outputting a DC input voltage; And a primary side parallel resonance capacitor provided so as to form a side parallel resonance circuit, and a primary side and a secondary side are loosely coupled so that a required coupling coefficient is obtained, and the primary side An insulating converter transformer for transmitting the output of the main switching means to the secondary side, and a secondary winding formed by connecting a secondary parallel resonance capacitor in parallel to the secondary winding wound on the insulating converter transformer. A secondary parallel resonance circuit and a winding portion between one end of the secondary winding wound around the above-mentioned insulated converter transformer and the intermediate tap. And a secondary-side active clamping means for clamping a voltage generated in the secondary winding by providing a series connection circuit of a clamp capacitor and a secondary-side auxiliary switching element in parallel with each other, and used in the cathode ray tube display device. Primary switching drive means for generating a fixed switching frequency close to the frequency of the horizontal synchronizing signal to cause the main switching element to perform a switching operation, and is formed as a circuit including a secondary drive winding wound around the insulating converter transformer. Secondary switching drive means for applying a switching drive signal to the secondary auxiliary switching element to cause the secondary auxiliary switching element to perform a switching operation; By applying a signal synchronized with the synchronization signal, the primary side A synchronizing means for synchronizing the operation of the resonance circuit and the secondary parallel resonance circuit with a horizontal synchronization frequency; and a primary winding connected in parallel with a secondary winding wound on the insulating converter transformer. A high-voltage generating transformer configured to transmit a resonance voltage obtained on a secondary winding of a converter transformer from a primary side to a secondary side to obtain a high-voltage obtained by boosting the resonance voltage from the secondary side; DC high voltage generating means configured to obtain a DC high voltage by performing a half-wave rectification operation on a high voltage obtained on the secondary side of the high voltage generating transformer, and a DC control signal based on the DC high voltage. A constant-voltage generating means for applying a voltage to the secondary-side auxiliary switching element to control a conduction angle of the secondary-side auxiliary switching element to convert the DC high voltage to a constant voltage; A primary-side auxiliary resonance element that performs switching at a predetermined on / off timing synchronized with the on / off timing of the switching element, so that a primary-side parallel resonance voltage generated at both ends of the primary-side parallel resonance capacitor is provided. And a primary side active clamp means provided to clamp the switching power supply circuit.