JPH08126323A - Switching power source circuit - Google Patents

Abstract

PURPOSE: To reduce the size and weight of a switching power source circuit and easily control the production of the circuit and, at the same time, to reduce the manufacturing cost of the circuit. CONSTITUTION: A switching power source circuit provided with a self-excitation voltage-resonant converter is constituted in such a way that a magnetically- coupled transformer MCT is added to the circuit so as to improve the power factor of the circuit and a drive winding NB is wound around the transformer MCT so as to obtain required inductance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit using a resonant converter for which power factor is improved.

[0002]

2. Description of the Related Art In recent years, with the development of switching elements capable of withstanding relatively large currents and voltages of high frequency, most of the power supply circuits for rectifying a commercial power supply to obtain a desired DC voltage are switching type power supplies. It is a circuit. The switching power supply circuit is used as a power supply for various electronic devices as a high-power DC-DC converter, as well as reducing the size of transformers and other devices by increasing the switching frequency.

By the way, in general, when a commercial power supply is rectified, the current flowing through the smoothing circuit has a distorted waveform, which causes a problem that the power factor indicating the utilization efficiency of the power supply is impaired. In addition, there is a need for measures to suppress harmonics generated by the distorted current waveform. In order to improve the power factor of the power supply, it is the easiest to use a rectifier circuit of the choke input type, for example, and it is preferable in terms of measures against electromagnetic noise (EMI).

As a switching power supply circuit with improved power factor, the applicant has previously magnetically coupled the choke coil with a voltage corresponding to the switching output from the primary side or the secondary side of the insulating transformer. A switching power supply circuit has been proposed in which a transformer is provided, and thereby a voltage of a switching cycle is superimposed on the rectified output of a bridge rectifier circuit to improve the power factor (Japanese Patent Application No. 6-192737).

FIG. 10 is a circuit diagram showing an example of a switching power supply circuit including a magnetic coupling transformer according to the above invention. In this case, a half bridge type self-excited current resonance type using transistors for the switching elements Q ₁ and Q ₂ is used.

In this figure, AC indicates a commercial AC power source. For this AC power supply AC, an LC low-pass filter composed of an impedance element of a filter choke coil L _N and a filter capacitor C _N is provided, which prevents high frequency noise of the switching frequency from flowing into the AC line. It is supposed to do. D ₁ is a bridge rectification circuit composed of four diodes, and performs full-wave rectification on the input AC power supply AC. A so-called fast recovery type (shown as D _FR ) is used for the two rectifying diodes indicated by broken lines, which is provided corresponding to a high-frequency current of a switching cycle flowing in a full-wave rectifying output line described later. It is supposed to be. A secondary winding Ni of a magnetic coupling transformer, which will be described later, is provided for the positive side rectified output line of the bridge rectifier circuit D ₁ . Therefore, the full-wave rectified output of this circuit is charged in the smoothing capacitor Ci via the secondary winding Ni of the magnetic coupling transformer.

The switching elements Q ₁ , Q _{2 of} this circuit
Is connected between the connection point on the positive electrode side of the smoothing capacitor Ci and the ground via respective collectors and emitters. Further, a resistor R _S1, R _S2 is the starting resistor, also the bases of the switching elements Q _1, Q ₂ - D _D1 inserted between the emitter, D _D2 each represent a clamp diode, the switching element Q _1, Q ₂ Forms a path for the damper current that flows when is off. The resistors R _B1 and R _B2 are damping resistors for adjusting the base currents (drive currents) of the switching elements Q ₁ and Q ₂ , respectively. C _B1 and C _B2 are capacitors for resonance, and together with the drive windings N _B1 and N _{B2 of} the drive transformer CDT, which will be described next, form a resonance circuit for self-excited oscillation to set the switching frequency. Note that L _B1 and L _B2 represent the inductances of the drive windings N _B1 and N _B2 .

CDT (Converter Drive Transformer)
Indicates a drive transformer for switching and driving the switching elements Q ₁ and Q ₂ at a predetermined switching frequency. In the case of this figure, the drive windings N _B1 and N _B2 and the resonance current detection winding N _D are wound. There is. _One end of the drive winding N _B1 on the switching element Q ₁ side of the drive transformer CDT is connected to the capacitor C _B1 and the other end is connected to the emitter of the switching element Q ₁ . Further, one end of the drive winding N _B2 on the switching element Q ₂ side is grounded to the ground and the other end is connected to the capacitor C _B2 , so that a voltage having a polarity opposite to that of the drive winding N _{B1 of the} switching element Q ₁ is applied. It is designed to be output. The resonance current detection winding N _D has one end connected to the emitter-collector connection point of the switching transistors Q ₁ and Q ₂ , and the other end connected to the resonance capacitor C 1.
It is connected to the primary winding N _{1 of} the insulation transformer PRT via ₁ .

PRT (Power Regulating Transformer)
Is an insulating transformer for transmitting the switching output of the switching elements Q ₁ and Q _{2 to} the secondary side. In this case, the primary winding N ₁ and the secondary winding N ₂ are controlled to be orthogonal to each other. A winding N _C is provided and is configured to perform constant voltage control as described below. This isolation transformer P
One end of the primary winding N ₁ of RT is connected in series with the resonance current detection winding N _D via the resonance capacitor C ₁ , and the other end is connected to one end of the primary winding N ₃ of the magnetic coupling transformer MCT. ing. A series resonance circuit is formed by the inductance component of the insulating transformer PRT including the resonance capacitor C ₁ and the primary winding N ₁ . On the secondary side,
The induced voltage induced in the secondary winding N ₂ by the switching output flowing in the primary winding N ₁ becomes the bridge rectification circuit D ₂
And is converted into a DC voltage by the smoothing capacitor C ₂ and output as an output voltage E ₀ . The control circuit 4 compares, for example, the DC voltage output E _O on the secondary side with a reference voltage, and uses a DC current corresponding to the error as a control current for the insulation transformer P.
Supply to the control winding N _C of RT.

In this figure, the MCT is a magnetic coupling transformer. This magnetic coupling transformer MCT is inserted into a full-wave rectified output line and has a secondary winding Ni (Li indicates self-inductance) that functions as a choke coil and a winding that corresponds to a tertiary winding of an insulating transformer PRT. The line N ₃ (inductance L ₃ ) is used as a primary winding and is tightly coupled by a ferrite core at a winding ratio of, for example, 1: 1. Here, the primary winding N ₃ of the magnetic coupling transformer MCT has one end connected to the primary winding N _{1 of the} insulating transformer PRT and the other end grounded.

In the switching operation of the switching power supply having the above configuration, when a commercial AC power supply is first turned on, for example, the switching element Q is activated via the starting resistors R _S1 and R _{S2.
Although the} base current is supplied to the bases of ₁ and Q ₂ , if the switching element Q ₁ is turned on _first , the switching element Q ₂ is controlled to be turned off. Then, as the output of the switching element Q ₁ , the resonance current detection winding N _D → resonance capacitor C ₁ → primary winding N
_Although the resonance current flows in ₁ , the switching element Q ₂ is turned on and the switching element Q ₁ is turned on when the resonance current becomes 0.
Is controlled to be turned off. Then, a resonance current in the opposite direction to the above flows through the switching element Q ₂ . After that, the self-excited switching operation in which the switching elements Q ₁ and Q ₂ are alternately turned on is started. As described above, the switching elements Q ₁ and Q ₂ are alternately opened and closed by using the terminal voltage of the smoothing capacitor Ci as the operating power supply, thereby supplying the drive current close to the resonance current waveform to the primary winding N ₁ of the insulation transformer. , An alternating output is obtained at the secondary winding N ₂ .

Further, in the constant voltage control in this case, the control circuit 1 varies the current flowing through the control winding N _C based on the DC output voltage E _O on the secondary side to isolate the insulating transformer PR.
The saturation characteristic of T is controlled. As a result, a so-called series resonance frequency control method is adopted in which the series resonance frequency of the switching converter circuit is controlled with respect to the switching frequency to achieve a constant voltage.

As the power factor improving operation, the magnetic coupling transformer MCT causes the switching voltage corresponding to the resonance current flowing in the insulating transformer PRT to be transferred to the self winding of the secondary winding Ni by the primary winding N ₃ of the magnetic coupling transformer MCT. The inductance Li is excited. Therefore, the rectified full-wave rectified voltage has a switching voltage superimposed on the winding Ni of the self-inductance Li and is charged in the smoothing capacitor Ci, and the terminal of the smoothing capacitor Ci is charged by the superimposed amount of the switching voltage. The voltage will be reduced in the switching cycle. Then
From the rectified voltage level of the bridge rectifier circuit, the capacitor Ci
The charging current starts to flow even during the period when the terminal voltage of is reduced, and the power factor is set to 1 by setting the number of turns of the magnetic coupling transformer MCT so that this period extends during the half cycle of the alternating current. Will show a value close to. That is, the average value of the AC input current is made to approach the AC voltage waveform, and the power factor is improved.

In the power supply circuit using the magnetic coupling transformer, the drive current of the insulating transformer PRT becomes small when the load is light, so that the switching signal induced on the secondary side of the magnetic coupling transformer MCT by this drive current is also small. become. Therefore, since the level of the charging current becomes small when the load is light and the charging current becomes large when the load is heavy, the phenomenon that the terminal voltage of the smoothing capacitor Ci abnormally rises is solved especially when the load is light, and the normal MS (magnet switch) is eliminated. It is possible to improve the regulation which was difficult with the method. Therefore, for example, even if the AC input voltage V _AC varies by ± 20%, the rectified and smoothed voltage Vi is
Is suppressed, the switching elements Q ₁ , Q ₂
It is not necessary to improve the withstand voltage of the smoothing capacitor Ci and the like.

Since the current I ₁ flowing out of the rectifier circuit is cut off in the switching cycle and flows discontinuously, for example, use a fast recovery type for any two diodes in the bridge rectifier circuit D _1. Is requested. In this figure, the two diodes on the positive electrode output side indicated by the broken line D _FR are of the fast recovery type.

[0016]

From the viewpoint of the size and cost of electronic devices, the switching power supply circuits mounted in these devices should have as few parts as possible and use small and inexpensive parts. Therefore, it is preferable to reduce the size and weight and reduce the cost, which is also advantageous in terms of production management.

[0017]

Therefore, the present invention is directed to a rectifier circuit for rectifying a commercial power source, a smoothing circuit including a choke coil and a smoothing capacitor for smoothing the output of the rectifier circuit, and a voltage output from the smoothing circuit. A voltage resonance type switching converter comprising a switching element which is intermittently output to the primary winding of an insulation transformer, and a resonance circuit formed by the primary winding of the insulation transformer and a resonance capacitor. , A switching power supply circuit comprising at least the choke coil and a magnetic coupling transformer wound so as to magnetically couple the alternating output supply coil to which the alternating output obtained based on the switching operation of the switching element is supplied. I decided to configure it. At this time, a normal mode low-pass filter is provided on the line of the commercial power source, and a high-speed recovery type diode is used in the rectifier circuit. Further, in the case of the self-excited voltage resonance type switching converter, the drive winding, which is an impedance element for setting the switching frequency, is wound around the magnetic coupling transformer to obtain the required inductance.

Further, a capacitor is connected in parallel with the secondary winding of the insulation transformer so that a resonant circuit is formed by the inductance component of the insulation transformer, and the alternating circuit obtained on the secondary side of the insulation transformer is formed. The rectifier circuit for rectifying the output to obtain the DC output voltage is configured by a full-wave rectifier circuit or a half-wave rectifier circuit. Further, the alternating output supply coil can be connected in series with the secondary winding of the insulation transformer, and the switching converter can be configured by push-pull coupling two switching elements.

The constant voltage control is performed by changing the magnetic flux of the insulating transformer based on the DC output voltage, or by making the control winding orthogonal to the choke coil and the alternating output supply coil in the magnetic coupling transformer. The coil is wound around and the control current flowing through the control winding is changed based on the DC output voltage, so that the inductance of the choke coil and the alternating output supply coil is changed.

[0020]

According to the above construction, the switching power supply circuit is provided with the magnetic coupling transformer for improving the power factor for the voltage resonance type converter. For example, in the case of the current resonance type converter, Is a half bridge consisting of two stones, or a full bridge coupling consisting of four stones, while the voltage resonance type makes it easy to realize a switching operation with one stone. The number of components required will be reduced when compared to a switching power supply circuit with a combined converter. In the case of the self-excited voltage resonance type, if the drive winding for driving the switching element is wound around the magnetic coupling transformer to obtain the required inductance, the drive transformer for switching drive can be omitted. It becomes possible to do.

Further, in the present invention, in addition to the constant voltage control system in which the magnetic flux of the isolation transformer is varied, a control winding is provided in the magnetic coupling transformer so as to be orthogonal to other windings.
Constant voltage control can be performed by changing the inductances of the primary and secondary windings of the magnetic coupling transformer.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit diagram of FIG. 1 shows a switching power supply circuit according to an embodiment of the present invention. This switching power supply circuit will be described with reference to FIG. 10 for a self-excited voltage resonance type switching converter. The magnetic coupling transformer is combined to improve the power factor. The same parts as those in FIG. 10 are designated by the same reference numerals and the description thereof will be omitted.

In this figure, the voltage resonance type switching converter is constituted by one stone provided with a switching element Q ₁ . Then, this switching element Q ₁
The base of is connected to the positive electrode side of the smoothing capacitor Ci via the starting resistor R _{S so} that the base current at the time of starting can be obtained from the rectifying and smoothing line. Further, a resonance circuit for self-excited oscillation including a damping resistor R _B , a resonance capacitor C _B, and a drive winding N _B is connected in series between the base of the switching element Q ₁ and the ground. In this case, the drive winding N _B
Is wound around the magnetic coupling transformer MCT so as to obtain a required inductance for setting the switching frequency. Further, the clamp diode D _D inserted between the base of the switching element Q ₁ and the negative electrode (ground) of the smoothing capacitor Ci forms a path for the damper current flowing when the switching element Q ₁ is off. Also,
The collector of the switching element Q ₁ is an isolation transformer PRT.
Is connected to one end of the primary winding N ₁ and the emitter is grounded.

A resonance capacitor C ₁ is connected in parallel between the collector and the emitter of the switching element Q ₁ , and the voltage resonance converter C ₁ and the primary winding N ₁ of the insulation transformer PRT are connected. Forming a resonance circuit of.

Next, the magnetic coupling transformer MCT of this embodiment.
In, in addition to the primary winding N ₃ and the secondary winding Ni, configured by winding the drive winding N _B as described above. Primary winding N ₃ of the magnetic coupling transformer MCT in this case
Has one end connected to the primary winding N _{1 of the} isolation transformer. The other end is connected to the positive electrode of the smoothing capacitor Ci, so that the high frequency component of the switching cycle flowing through the primary winding N ₃ of the magnetic coupling transformer MCT flows to the ground via the smoothing capacitor Ci. .

Further, the secondary winding N _{2 of} the insulation transformer PRT
A capacitor C ₂ for resonance is provided in parallel with.
This capacitor C ₂ forms a resonance circuit by its capacitance and the inductance component of the insulating transformer PRT to obtain voltage resonance, and the waveform of the output voltage V ₂ excited on the secondary side becomes a sine wave. It is supposed to approach you.

FIG. 2 is a waveform diagram showing the operation of the main part in the commercial power supply cycle (here, 50 Hz) in the switching power supply circuit having the configuration shown in FIG. For example, as shown in FIG. 2A, the AC input voltage V _AC
Is supplied to the magnetic coupling transformer M in the circuit of the present embodiment as well, as described with reference to FIG.
The switching output supplied to the primary winding N ₃ of CT is
Since it is excited by the secondary winding Ni of the magnetic coupling transformer MCT, the current I ₁ flowing from the positive output terminal of the bridge rectifier circuit D _{1 to} the secondary winding Ni of the magnetic coupling transformer MCT.
2 has a waveform in which the high-frequency component due to the switching period is superimposed on the full-wave rectified output current as shown in FIG. The charging / discharging current Ii flowing through the smoothing capacitor Ci at this time also has a waveform in which high-frequency components are superimposed, as shown in FIG. Then, the AC input current flowing in the AC line flows as shown in FIG. 2D, and the conduction angle is enlarged so as to approach 0V of the _AC input voltage V _AC so that a required power factor is actually obtained. Has been done. The power factor is set, for example, by the inductance of the winding N ₃ of the magnetic coupling transformer.

FIG. 3 is a waveform diagram showing the operation of the main part in the switching cycle at the peak of the _AC input voltage V _AC in the switching power supply circuit shown in FIG. In addition, here, the case where the switching frequency is 50 KHz is shown, and in this figure, the periods t _{1 to} t ₄ are shown.
Is the switching cycle. For example, t shown in this figure
_{When the} switching element is turned off at time 1, the primary winding N _{1 of} the isolation transformer PRT and the resonance capacitor C ₁
Due to the action of the resonant circuit consisting of the current I ₀ , the current I ₀ flowing through the primary winding N ₁ has a period t ₁ to t as shown in FIG.
_{At 2} , a current close to the resonance waveform will flow.
Also, following the waveform shown in the period t ₂ ~t ₃ of the same FIG. 3 (b), the switching element Q ₁ from the clamp diode D _D
Corresponding to the damper current flowing in the primary winding N ₁ via the base-emitter of the. Then, the switching element Q
Voltage V ₁ across resonant capacitor C ₁ when ₁ is off
(Collector voltage of switching element Q ₁ ) is shown in FIG.
The waveform becomes sinusoidal as shown in the period t _{1 to} t ₂ of (a), and the voltage resonance type operation is obtained.

The switching element Q ₁ changes to ON at the time t ₃ when the current I ₀ crosses _zero, but during the period t _{3 to} t ₄ which is the ON period of the switching element Q ₁ , the voltage across the resonance capacitor C ₁ is increased. V ₁ is shown in FIG.
As shown in FIG. 3, 0V continues, and the current I ₀ has a waveform as shown in FIG. 3B due to the inductance action of the primary winding N ₁ . Further, since the secondary side AC voltage V ₂ in the switching cycle is provided with the capacitor C ₂ , the bridge rectifier circuit D ₂ , and the smoothing capacitor C ₃ ,
A waveform as shown in FIG. 3C is obtained.

As described above, the switching power supply circuit according to the present embodiment is configured to improve the power factor by providing the magnetic coupling transformer MCT for the voltage resonance type switching converter with one stone. For example, in the switching power supply circuit shown in FIG. 10, the current resonance converter is a self-excited type, and the switching elements Q ₁ and Q ₂ are half-bridge coupled to each other. Two driving circuit systems (starting resistance R _S , damping resistance R _B ,
Capacitor C _B , drive winding N _B, etc.) are required. In the case of dealing with a heavy load, although not shown, a full bridge type composed of four switching transistors may be used. In this case, four switching elements and four drive circuits are required. Will be done. On the other hand, in the switching power supply circuit shown in FIG. 1 of the present embodiment, since it is a self-excited voltage resonance type converter, it is possible to realize the switching operation by at least one switching transistor. Therefore, only one drive circuit system is required. Further, in the switching power supply circuit of the present embodiment, the drive winding N _B is wound around the magnetic coupling transformer MCT to obtain a required inductance, and together with the capacitor C _B , a resonance circuit having a switching period by self-excited oscillation is formed. I am trying to do it. Therefore, the drive transformer CDT as shown in FIG. 10 can be omitted.

As described above, in the switching power supply circuit of the present embodiment shown in FIG. 1, in comparison with the switching power supply circuit of FIG.
Since the DT is deleted, the number of parts forming the switching power supply circuit is significantly reduced, and the size of the mounting substrate can be significantly reduced accordingly. In addition, raw material costs and processing costs are reduced, production management becomes advantageous, and cost reduction and manufacturing efficiency can be improved.

Next, the circuit diagram of FIG. 4 shows the configuration of a switching power supply circuit as another embodiment of the present invention. The same parts as those in FIG. In the switching power supply circuit of this figure, the capacitor C ₂ provided in parallel with the secondary winding N ₂ of the insulation transformer PRT in the circuit diagram of FIG. 1 is omitted, and the diode D ₃ and smoothing circuit are omitted. The DC output voltage E _O is obtained by the half-wave rectifying / smoothing circuit using the capacitor C ₃ for use. The circuit configured as shown in this embodiment can be used in the case of handling a light load such as a load power of about 100 W or less, and when compared with the circuit of FIG.
The number of parts of the circuit system on the secondary side will be further reduced.

FIG. 5 shows the configuration of a switching power supply circuit according to still another embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the switching power supply circuit of this figure, the primary winding N ₃ of the magnetic coupling transformer MCT is connected in series with the secondary winding N ₂ of the insulating transformer PRT. The end of the secondary winding N ₂ of the insulation transformer PRT is connected to the input terminal Tb of the bridge rectifier circuit D _2.
The end of the primary winding N ₃ of the magnetic coupling transformer MCT is connected to the input terminal Ta of the bridge rectifier circuit D ₂ . Further, one end of the primary winding N ₁ of the insulation transformer PRT is connected to the connection point of the collector of the switching element Q ₁ and the resonance capacitor C ₂ as in the case of FIG. 1, but the other end is connected to the smoothing capacitor Ci. Will be connected to the positive electrode side.

In the case of such a configuration, the isolation transformer
The secondary winding N in the PRT₂ Excited switch
The alternating voltage of the switching cycle is the primary winding of the magnetic coupling transformer MCT.
Line N ₃ Will be supplied to. As a result,
The magnetic coupling transformer MCT is the same as that shown in FIG.
Primary winding N₃ From the secondary winding Ni to the switching cycle
The alternating output is excited and this is one of the isolation transformer PRT.
The power factor will be superimposed on the full-wave rectification line on the secondary side.
It will be improved.

Next, the circuit diagram of FIG. 6 shows the configuration of a switching power supply circuit which is a further embodiment of the present invention and which performs switching by push-pull operation.
The same parts as those in FIG. In this figure, a switching element Q ₂ is further provided in addition to the switching element Q ₁ . The components of the drive circuit system for driving the switching element Q ₁ are represented by a starting resistor R _S1 , a damping resistor R _B1 , a capacitor C _B1 , a drive winding N _B1 , and a clamp diode D _D1 , respectively. similarly for _2, starting resistor R _S2, damping resistor R _B2, the capacitor C _B2, drive winding N _B2, driving circuit system constituted by the elements of the clamp diode D _D2 is formed. In addition, magnetic coupling transformer MC
The two drive windings N _B1 , N provided for T
_B2 is wound so that outputs of opposite polarities are obtained. Further, a resonance capacitor C is provided in parallel between the collector and the emitter of the switching element Q _2.
1B (here, the resonance capacitor on the switching element Q ₁ side is indicated by C _1A ) is provided so that a resonance circuit for voltage resonance is formed together with the primary winding N _{1 of} the insulating transformer. Further, in this case, both ends of the primary winding N ₁ of the insulating transformer are respectively connected to the switching elements Q ₁ and Q ₁ .
_It is connected to the collector of ₂ and is provided with a center tap, and the primary winding N _{3 of the} magnetic coupling transformer MCT is provided between this center tap terminal and the positive electrode of the smoothing capacitor Ci.
Are connected so as to be inserted.

As described above, the switching power supply circuit of this embodiment is a so-called push-pull coupling type self-excited voltage resonance in which switching operation is performed in which _two switching elements Q ₁ and Q ₂ are turned on / off at alternate timings. Type converter is provided, and is used in response to a heavy load such as a load power of about 150 W or more.

In this case, the switching element Q is connected to the primary winding N _{3 of the} magnetic coupling transformer MCT via the center tap of the primary winding N ₁ of the insulating transformer.
_Since the switching outputs of ₁ and Q ₂ are supplied, the power factor is improved by the magnetic coupling transformer MCT as in the switching power supply circuit of FIG. 1, for example.

FIG. 7 is a circuit diagram showing a switching power supply circuit according to still another embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In this case, as shown in the figure, in the magnetic coupling transformer, the control winding N _C is wound so as to be orthogonal to the primary winding N ₃ and the secondary winding Ni thereof. That is, in this embodiment, the magnetic coupling transformer is a PRT (Power Regulating Transformer). The isolation transformer has no control winding P
It is called IT (Power Isolation Transformer). In such a configuration, the magnetic coupling transformer PRT performs the power factor correction and the constant voltage control operation. As the constant voltage control operation, the DC control current flowing from the control circuit 1 to the control winding N _C is changed in accordance with the fluctuation of the DC output voltage E _O , and the primary winding N ₃ and the secondary winding thereof are changed. This is done by controlling the inductance of Ni. The control circuit 1 in this embodiment is the same as the insulating transformer PRT as in the embodiments shown in FIGS. 1 and 4 to 6.
The polarity is reversed from that in the case of controlling the saturation characteristic of the control circuit 1, and the control circuit 1 operates so as to reduce the control current at the time of heavy load and low AC input voltage, for example.

FIG. 8 is a circuit diagram showing a switching power supply circuit according to still another embodiment of the present invention. The same parts as those in FIGS. 1, 5 and 7 are designated by the same reference numerals and the description thereof will be omitted. In the embodiment shown in this figure, the PRT in which the magnetic coupling transformer is provided with the control winding N _C , as in the embodiment shown in FIG.
The magnetic coupling transformer PRT is used to perform power factor correction and constant voltage control. In this case, as shown in FIG.
Similarly to the embodiment shown in FIG. 1, the primary winding N ₃ of the magnetic coupling transformer is connected in series with the secondary winding N ₂ of the isolation transformer, and the switching output excited on the secondary side is the magnetic coupling transformer PRT. It is fed back to the full-wave rectified output line on the primary side via. Further, in this embodiment, as in the embodiment of FIG. 2, on the secondary side of the insulating transformer, the DC output voltage E _O is obtained by the half-wave rectifying / smoothing circuit by the diode D ₃ and the capacitor C _3, and at the time of light load. When dealing with it, we are trying to further reduce the cost.
However, in this case, the secondary winding N ₂ of the isolation transformer PIT
A resonance capacitor C ₂ is connected in parallel with the output voltage of the secondary side so that the alternating output voltage on the secondary side approaches a sine wave.

Here, the magnetic coupling transformer P used in the switching power supply circuit shown in FIG. 7 or FIG.
The structures of the RT and the insulating transformer PIT are shown in FIG.
The magnetic coupling transformer PRT has cores C _R1 and C _R2 of the same shape having four magnetic legs, as shown in FIG.
The magnetic cores form a box-shaped core that is assembled such that the ends of the magnetic legs face each other. Then, as shown in the figure, the primary and secondary windings N ₃ and Ni are wound around the box-shaped core so as to straddle the two magnetic legs, and the control winding N _C is
The windings N ₃ and Ni are wound around two magnetic legs so as to be orthogonal to the winding direction of the windings. Further, the insulating transformer PIT forms an EE type core in which E type cores C _R1 and C _R2 made of a ferrite material are combined, and the primary winding N ₁ and the insulating transformer primary winding N ₁ and It is configured by winding a secondary winding N ₂ .

The power factor improving method of the present invention described so far in each of the above embodiments is designed to improve the power factor by combining the magnetic resonance transformer with the switching converter of the voltage resonance type. As long as it is one, it can be applied to a power supply circuit configured by other various combination patterns, and is not limited to the combination pattern shown as an example in each of the above-mentioned drawings. It is also possible to make changes in other circuit parts, such as making the obtained DC output voltage plural.

[0042]

As described above, according to the present invention, in a self-excited voltage resonance type switching power supply circuit, a magnetic coupling transformer provided for improving the power factor is combined to form a self-excited voltage resonance type switching power supply circuit. Compared with the case where a current resonance type switching converter and a magnetic coupling transformer are combined, it is possible to reduce the number of switching elements and the number of drive transformers and drive circuit system components that drive these switching elements. This has the effect that the reduction in size / weight and cost reduction can be greatly promoted.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply circuit as an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an operation of a main part of the switching power supply circuit of the present embodiment in a commercial power supply cycle.

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

FIG. 4 is a circuit diagram showing a switching power supply circuit as another embodiment.

FIG. 5 is a circuit diagram showing a switching power supply circuit as another embodiment.

FIG. 6 is a circuit diagram showing a switching power supply circuit as another embodiment.

FIG. 7 is a circuit diagram showing a switching power supply circuit as another embodiment.

FIG. 8 is a circuit diagram showing a switching power supply circuit as another embodiment.

FIG. 9 is a perspective view showing the structures of a magnetic coupling transformer and an insulating transformer according to still another embodiment.

FIG. 10 is a circuit diagram showing a switching power supply circuit as a conventional example.

[Explanation of symbols]

1 Control circuit L _N Filter choke coil C _N filter capacitor D ₁ Bridge rectifier circuit D _FR Fast recovery type diode MCT (PRT) Magnetic coupling transformer PRT (PIT) Insulation transformer Q ₁ , Q ₂ Switching element Ci Smoothing capacitor C ₁ , C _1A , C _1B Resonant capacitor C ₂ Resonant capacitor on secondary side N ₁ Primary winding N ₂ Secondary winding R _B , R _B1 , R _B2 Damping resistance C _B , C _B1 , C _B2 Resonant capacitor for self-oscillation N _B , N _B1 , N _B2 drive winding

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H02M 7/217 9472-5H

Claims (10)

[Claims] 1. A rectifying means for rectifying a commercial power source, a smoothing means comprising a choke coil and a smoothing capacitor for smoothing an output of the rectifying means, and a voltage output from the smoothing means is intermittently connected to a primary winding of an insulating transformer. A voltage resonance type switching converter including a switching element configured to output to a line, and a resonance circuit formed by a resonance capacitor provided in parallel with the primary winding of the insulation transformer and the switching element. At least the choke coil and an alternating output supply coil to which an alternating output obtained based on the switching operation of the switching element is supplied, and a magnetic coupling transformer wound so as to be magnetically coupled. A switching power supply circuit characterized in that 2. The switching power supply circuit according to claim 1, wherein a normal mode low-pass filter is provided on the line of the commercial power supply. 3. The switching power supply circuit according to claim 1, wherein a high speed recovery type diode is used in the rectifying means. 4. The switching converter is of a self-excited type, and a drive winding that is an impedance element for setting a switching frequency is wound around the magnetic coupling transformer to obtain a required inductance. Claim 1 or Claim 2 or Claim 3 characterized by
The switching power supply circuit described in. 5. A capacitor is connected in parallel to the secondary winding of the insulating transformer, and a resonance circuit is formed by the inductance component of the insulating transformer. The switching power supply circuit according to any one of claims 1 to 4. 6. The rectifier circuit for rectifying the alternating output obtained on the secondary side of the insulation transformer to obtain a DC output voltage is a full-wave rectifier circuit or a half-wave rectifier circuit. The switching power supply circuit according to any one of claims 1 to 5. 7. The switching power supply circuit according to claim 1, wherein the alternating output supply coil is connected in series with the secondary winding of the insulation transformer. 8. The switching power supply circuit according to claim 1, wherein the switching converter is configured by push-pull coupling two switching elements. 9. The switching power supply according to claim 1, wherein a constant voltage control is performed by varying a magnetic flux of the insulation transformer based on the DC output voltage. circuit. 10. The magnetic coupling transformer is configured by winding a control winding so as to be orthogonal to the choke coil and the alternating output supply coil, and the control winding is connected to the control winding based on the DC output voltage. 9. The constant voltage control is performed by varying the inductance of the choke coil and the alternating output supply coil to change the control current to be flown to perform constant voltage control. Switching power supply circuit.