JPH08103077A - Current resonance switching power supply - Google Patents

Abstract

PURPOSE: To improve regulation by providing a loosely coupled tertiary winding for an insulation transformer and supplying a charging current for a smoothing capacitor through the tertiary winding. CONSTITUTION: A tertiary winding N3 is formed for an insulation transformer PIT, and switching signals induced to the tertiary winding N3 are inserted in a charging circuit of a smoothing capacitor Ci. That is, the switching voltage induced to the insulation transformer PIT is supplied to a charging line of the smoothing capacitor Ci. Therefore, the switching voltage is superimposed through a leakage inductance coil Li to the full-wave rectified voltage and is charged to the smoothing capacitor Ci. Using the terminal voltage of a smoothing capacitor Ci as operating power supply, a drive current similar to a resonance waveform is supplied to the primary coil N1 of the insulation transformer PIT by repeating the opening and closing alternately by the switching elements Q1 and Q2 and an alternating output is obtained at the secondary coil N2 .

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, and more particularly to a current resonance type switching power supply circuit with improved power factor and voltage fluctuation rate.

[0002]

2. Description of the Related Art In recent years, most of power supply devices of a switching type have been developed as a power supply device for rectifying a commercial power supply to obtain a desired DC voltage by developing a switching element capable of withstanding a relatively large voltage and current of high frequency. It has become. The switching power supply is used as a power supply for various electronic devices as a high-power DC-DC converter, while increasing the switching frequency to downsize transformers and other devices.

By the way, generally, when a commercial power supply is rectified, the current flowing through the smoothing circuit has a distorted waveform, so that there arises a problem that the power factor indicating the utilization efficiency of the power supply is deteriorated. 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 source, it is known to use a choke input type rectifier circuit as shown in FIG. 6, for example. This power circuit is commercial power AC
Through the common filter CMC to the bridge rectifier circuit D
1 and the rectified output is charged to the smoothing capacitor Ci via the choke coil L. Q
Reference numerals 1 and Q2 denote switching transistors connected in series, and a current is caused to flow from an intermediate point to the primary winding N1 of the isolation transformer PIT for output through the primary winding ND of the drive transformer PRT and the resonance capacitor C1. To do so.
Then, the output of the secondary winding N2 of the insulation transformer is rectified by the rectifier diode D0 to obtain the DC output E0.

The drive transformer PRT is an orthogonal type transformer having a control winding NC, and its secondary windings NB and N.
A drive signal for turning on / off the switching transistor is formed from B. The output voltage E0 is supplied to the control winding NC of the drive transformer PRT via a control circuit, and the switching frequency is controlled by changing the magnetic characteristics of the drive transformer PRT with this voltage. In other words, when the DC output E0 becomes low, the switching frequency becomes the resonance capacitor C1 and the insulation transformer PIT
Is controlled so as to approach the resonance frequency formed by the leakage inductance of (1) (upper side control) so that the output voltage becomes constant. RB and CB are impedances that set the level of the drive signal, and D2 and D3 are damper diodes.

[0006] Such a switching power supply is the simplest circuit for removing the harmonic distortion by suppressing the distortion waveform of the charging current by the choke coil L, and is also preferable as a measure (EMI) for suppressing electromagnetic noise. However, this method requires an inductor exhibiting a large impedance corresponding to a commercial power supply frequency as a choke coil, which hinders downsizing of electronic devices and increases cost.

[0007]

Therefore, a capacitorless system in which the output of the rectifier circuit is directly interrupted to operate the switching power supply, an active filter which interrupts the output of the rectifier circuit at high frequency to improve the distortion current waveform, or A partial rectification smoothing circuit is used. In the capacitorless system, the smoothing capacitor for the power supply that drives the switching power supply is omitted (a capacitor with a small value is attached), and the power factor improvement effect is high, but the ripple voltage twice the frequency of the commercial power supply is generated. It cannot be used as a large-capacity power supply device because it is superimposed on the output of the secondary side and the regulation becomes poor, and it is difficult to withstand instantaneous interruption of the input voltage. Further, the partial smoothing circuit switches the charging current of the capacitor to widen the conduction angle of the rectifying element, but this causes the ripple voltage of the smoothing capacitor to become high, which causes a problem that the regulation of the subsequent switching power supply deteriorates. .

[0008]

The present invention has been made to solve the above problems, and the first invention comprises a rectifying means for rectifying a commercial power source and a smoothing capacitor for smoothing the output of the rectifying means. And a switching element that intermittently supplies the voltage output from the smoothing means to the primary side of the insulating transformer via a resonant capacitor, and resonates resonance current flowing in the primary side of the insulating transformer. In a current resonance type switching power supply circuit in which a frequency is controlled so that a predetermined alternating voltage is obtained from a secondary winding of an isolation transformer, a normal mode LC filter is provided in a line for supplying the commercial power and The transformer is provided with a tertiary winding having a coarse coupling coefficient so that the charging current of the smoothing capacitor can be supplied through the tertiary winding. It is.

A second aspect of the invention is provided with a self-inductance coil for charging the smoothing capacitor, which is magnetically coupled to a tertiary winding to which the secondary side output of the insulation transformer is supplied. The magnetic coupling transformer is configured. Further, the magnetic coupling transformer and the isolation transformer are configured such that a part of the core constituting the magnetic circuit is shared.

Furthermore, a third aspect of the invention is to provide a voltage doubler rectifying means in a rectifying circuit for rectifying a commercial power source, a smoothing means comprising a smoothing capacitor for smoothing the output of the rectifying means, and a voltage output from the smoothing means. Isolation transformer 1
A switching element supplied to the secondary side through a resonance capacitor is provided, and the magnetic characteristics of the insulation transformer are controlled according to the DC output voltage so that a predetermined alternating voltage can be obtained from the secondary winding of the insulation transformer. In the current resonance type switching power supply circuit described above, a normal mode LC filter is provided on the line for supplying the commercial power supply, and the insulation transformer is constituted by an orthogonal core.
A magnetic coupling transformer that magnetically couples a self-inductance coil with a third winding connected in series with the next winding is provided, and the self-inductance coil is inserted into the charging circuit of the smoothing capacitor.

[0011]

The current resonance type switching power supply of the present invention is provided with a tertiary winding in which a switching voltage is induced by a resonance current or a self-inductance coil magnetically coupled to the tertiary winding. By inserting the switching voltage generated in the tertiary winding or the self-inductance coil into the charging path of the smoothing capacitor, the charging current is intermittently flowed in almost all cycles of the AC signal. You can improve the power factor with.

In particular, in the embodiment of the present invention, the switching power supply circuit is of the current resonance type, and its regulation is improved as compared with the PWM type switching power supply in which the output voltage is controlled by varying the switching frequency. By changing the coupling coefficient of the coil supplied with voltage, the choke coil can be omitted. Further, since the impedance of this choke coil rises when the load is light, its function is sufficiently exerted, which helps suppress the ripple voltage and reduces the fluctuation of the power supply fluctuation rate and the power factor.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a current resonance type switching power supply circuit according to an embodiment of the present invention. As shown in FIG. 6, AC is an AC power supply and LN and CN are low-pass for blocking signals of a switching frequency. A filter, D1, is a bridge type rectifying element. Q1 and Q2 are switching elements forming a half-bridge type switching circuit, and the output thereof is an insulating transformer PI via a resonance capacitor C1.
It is supplied to the T primary winding N1. Then, the induced voltage induced in the secondary winding N2 of the insulating transformer PIT is converted into a DC voltage via the rectifying element D0 and becomes the output voltage E0.

The insulation transformer PIT has a tertiary winding N3.
Is formed, and the switching signal induced in the tertiary winding is inserted into the charging circuit of the smoothing capacitor Ci. That is, the switching voltage induced in the insulating transformer PIT is supplied to the charging path of the smoothing capacitor Ci. Therefore, the rectified full-wave rectified voltage is superposed with the switching voltage via the leakage inductance coil Li described later, and is charged in the smoothing capacitor Ci. The switching elements Q1 and Q2 are configured such that the switching frequency changes in accordance with the output voltage supplied to the control winding NC of the orthogonal drive transformer PRT as described above, and the constant voltage of the output voltage E0. I am trying to make it.

Since the switching power supply circuit of the present invention is constructed as described above, the switching elements Q1 and Q2 are alternately opened and closed by using the terminal voltage of the smoothing capacitor Ci as the operating power supply, and thereby the isolation transformer 1
A drive current close to the resonance current waveform is supplied to the secondary coil N1 to obtain an alternating output to the secondary coil N2. When the DC output voltage on the secondary side drops, it is controlled by the control circuit so that the switching frequency becomes low (close to the resonance frequency), and the drive current flowing through the primary coil increases. .

In the conventional power supply circuit, the smoothing capacitor Ci
Since the charging current is supplied only to the terminal when the terminal voltage is lower than the rectified voltage, the conduction angle of the rectifying element is small and the power factor is about 0.6. However, in the case of the switching power supply circuit of the present invention, the switching voltage (for example, 100 KHz) output from the tertiary winding N3 of the insulating transformer PIT in which the resonance current flows is supplied to the output side of the smoothing choke coil CH. And this signal is V1 in FIG.
Is superimposed on the rectified voltage as shown in.

Therefore, as shown in FIG. 2, the rectifier circuit D
The flow angle of the current I1 flowing out of 1 changes from t1 to t2, and a charging current having an average value close to a sine wave flows. As a result, the AC current supplied from the commercial AC power supply is Ia in FIG.
As seen in c, harmonic distortion is reduced and the power factor is improved. The current I flowing out of the rectifier circuit
Since 1 is cut off in the switching cycle and flows discontinuously, it is required that the rectifying element of the bridge rectifying circuit D1 also use, for example, a fast recovery type diode.

The quiescent period t2 to t4 of the current I ₁ is set by the induced voltage in the tertiary winding N3, and during this period, reverse charging is performed in which the charge of the resonance capacitor moves to the smoothing capacitor Ci side. It should be noted that the power factor is set to about 0.75 to 0.90 when the rest period is appropriately set, and the power factor is reduced when the rest period is lengthened, but if the power factor is maintained at about 0.8, the EMI regulation is performed. At the same time, the power efficiency can be improved.

Further, since the ripple voltage of the smoothing capacitor Ci can be suppressed by the reverse charging, the regulation of the output voltage can be easily improved especially in the case of the current resonance type switching power supply circuit.

As shown in FIG. 3A, the insulation transformer PIT in which the primary winding, the secondary winding, and the tertiary winding are mounted has a tertiary winding N3 with respect to the primary winding N1. Are preferably magnetically separated. That is, as shown in the sectional view, a coil bobbin B is provided for the core Cr of the transformer, and the primary winding N is provided at both ends of the bobbin B.
It is arranged so that the first and third windings N3 are located. Then
The magnetic coupling coefficient K between the both windings can be set to, for example, 0.75 to 0.85. Therefore, as shown in FIG. 2B, a leakage inductance component Lg is added to the ideal transformer T in the equivalent circuit of the transformer having both windings, and the leakage inductance component Lg is a smoothing choke coil of the smoothing capacitor Ci. Work as L.

The tertiary winding N3 may be separated from each other in the winding depth direction of the coil, and the value of the leakage inductance generated by the separation is an impedance enough to respond to the cycle of the switching frequency. It should be. FIG. 3C shows the overall shape of the insulating transformer PIT, in which a magnetic gapup g is provided on the middle leg of the core Cr. The tertiary winding N3 is arranged on both legs so that the above-mentioned leakage inductance can be obtained.

FIG. 4A shows another embodiment of the present invention, in which the same parts as in FIG. 1 are designated by the same reference numerals. However, in the case of this embodiment, a magnetic coupling transformer (MCT) using a magnetic core having a winding portion for feeding back the switching voltage is provided. That is,
A second winding N2 ′ is provided on the secondary side of the isolation transformer, and its output is supplied to the tertiary winding N3. Then, the self-inductance coil N magnetically coupled to the tertiary winding N3.
i. The switching voltage generated in the self-inductance coil Ni is the smoothing capacitor C.
The switching voltage is supplied to the first charging path. Therefore, in this case as well, the voltage of the switching cycle is superimposed on the rectified voltage, and the charging current flows in almost the entire cycle of the AC voltage, so that the power factor is 1
Can be improved to be closer to.

FIG. 4B shows the magnetic coupling transformer MC.
It is configured to reduce the occupied area of the power supply device by integrating the core of T with the insulating transformer PIT, and a pair of Es having a central gap g formed therein.
The primary winding, the secondary winding, and the second two on the V-shaped core Cr ₍₁₎
MCT for the insulation transformer which wound the next winding N2 '
E-shaped core Cr ₍₂₎ that constitutes the
_A secondary winding N3 and a self-inductance coil Ni are applied to ₍₂₎ . The central magnetic leg of the core Cr ₍₂₎ is coupled to the core Cr via a magnetic gap gm,
A part of the magnetic circuit of T is shared with a part of the isolation transformer PIT. It should be noted that it is also possible to modify so that the current interrupted by the switching transistors Q1 and Q2 is directly supplied to the tertiary winding of the magnetic coupling transformer.

FIG. 5 shows still another embodiment of the present invention. In this embodiment, the rectifying circuit for rectifying the AC power source is configured by the rectifying diodes D1 and D2 to form a voltage doubler rectifying circuit. Further, the magnetic coupling transformer MCT and the isolation transformer are integrated as shown in FIG. 5B, and are constituted by orthogonal transformers whose magnetic characteristics are variable by the control winding Nc. The tertiary winding N3 and the primary winding N1 that form the MCT are connected in series so that the resonant switching current interrupted by the switching transistors Q1 and Q2 is directly supplied.

In the case of this embodiment, the insulating transformer is composed of a quadrature type transformer PRT, and the DC voltage E0 output from the secondary winding is supplied to the control winding NC thereof via the control circuit. The resonance frequency of the circuit is varied and the output voltage is stabilized by controlling the magnetic characteristics of the orthogonal isolation transformer PRT.

Also in the case of this embodiment, the switching voltage output to the self-inductance coil Ni superimposes the switching voltage on the charging path of the voltage doubler rectifier circuit, and the conduction angle of the charging current is widened to improve the power factor. Be seen. In addition, as in the switching power supply of FIG. 4, the core Cr ₍₁₎ of the insulation transformer and the core Cr _{(2) of the} MCT are shown in FIG.
It is preferable that they are integrated as shown in (b) to reduce the occupied area of the switching transformer and the occupied volume of the core. By making the magnetic coupling coefficient K of the MCT coarse, the leakage rate is increased as shown in FIG.
The function of choke coil can be provided by creating a di-inductance.

This embodiment can improve the reduction of the power factor which is a particular problem in the conventional switching power supply by adopting the voltage doubler rectifier circuit, and in the case of the conventional choke coil type switching power supply. Requires switching the choke coil in response to changes in the input voltage, and the switching is complicated, but in the case of the present embodiment, it is 1
It has a feature that it can be adapted to a commercial power source of 00V and a commercial power source of 200V by a simple switching circuit.

[0028]

As described above, the current resonance type switching power supply of the present invention creates a predetermined leakage inductance by coarsely coupling the tertiary winding to the insulation transformer, and this tertiary winding is created. The output switching voltage charges the smoothing capacitor via the leakage inductance, so the leakage inductance acts as a choke coil, widening the conduction angle of the current charged in the smoothing capacitor and increasing the power factor. Can be improved.

Further, since the switching power supply is of the current resonance type, by setting the inductance of the tertiary winding to a predetermined value, it is possible to set an excessive idle period for charging by the switching cycle, With this setting, the voltage fluctuation rate can be pressed and the power supply efficiency can be improved. Further, since the one-converter system is used, switching noise can be easily prevented from being emitted to the outside by providing a normal mode low-pass filter on the AC input side.

Furthermore, by making the core of the magnetic coupling transformer for returning the switching voltage to the rectification charging circuit side shared with a part of the core of the insulation transformer, the power supply unit can be downsized without increasing the number of parts. There is an advantage that can be done.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic outline of a switching power supply circuit of the present invention.

FIG. 2 is a waveform diagram showing current and voltage waveforms of respective parts in FIG.

FIG. 3 is an explanatory diagram of an insulation transformer PIT of the present invention.

FIG. 4 is a current resonance type switching power supply circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram when the present invention is applied to a voltage doubler rectifier circuit.

FIG. 6 is a circuit diagram of a conventional choke input type current resonance type switching power supply circuit.

[Explanation of symbols]

 LN, CN Harmonic suppression low pass filter D1 Bridge type rectifier circuit Q1, Q2 Switching element MCT Magnetic coupling transformer Ci Smoothing capacitor C1 Resonance capacitor PIT Isolation transformer PRT Quadrature drive transformer

Claims (4)

[Claims] 1. A rectifying means for rectifying a commercial power source, a smoothing means composed of a smoothing capacitor for smoothing an output of the rectifying means, and a voltage output from the smoothing means is intermittently resonated on the primary side of an insulating transformer. A current that is provided with a switching element that is supplied via a capacitor and that controls the resonance frequency of the resonance current that flows in the primary side of the insulation transformer so that a predetermined alternating voltage can be obtained from the secondary winding of the insulation transformer. In the resonance type switching power supply circuit, a normal mode LC is connected to the line for supplying the commercial power.
A current resonance characterized in that a filter is provided and a tertiary winding having a coarse coupling coefficient is provided in the insulating transformer, and the output of the tertiary winding is inserted into the charging circuit of the smoothing capacitor. Type switching power supply. 2. A rectifying means for rectifying a commercial power source, a smoothing means including a smoothing capacitor for smoothing an output of the rectifying means, and a voltage output from the smoothing means is intermittently resonated on the primary side of an insulating transformer. A current that is provided with a switching element that is supplied via a capacitor and that controls the resonance frequency of the resonance current that flows in the primary side of the insulation transformer so that a predetermined alternating voltage can be obtained from the secondary winding of the insulation transformer. In the resonance type switching power supply circuit, a normal mode LC is connected to the line for supplying the commercial power.
A magnetic coupling transformer that magnetically couples a self-inductance coil with a tertiary winding to which the secondary output of the insulating transformer is supplied is provided, and the self-inductance of the magnetic coupling transformer is equal to that of the smoothing capacitor. A current resonance type switching power supply characterized by being inserted in a charging circuit. 3. A rectifying means for rectifying a voltage of a commercial power source, a smoothing means comprising a smoothing capacitor for smoothing an output of the rectifying means, and a voltage output from the smoothing means is intermittently connected to the insulating transformer 1. A switching element supplied to the secondary side via a resonance capacitor is provided, and the magnetic characteristics of the insulation transformer are controlled according to the DC output voltage so that a predetermined alternating voltage can be obtained from the secondary winding of the insulation transformer. In the current resonance type switching power supply circuit, the normal mode LC is connected to the line for supplying the commercial power supply.
A filter is provided, and the insulation transformer is composed of an orthogonal type core and is connected in series with its primary winding.
A current resonance type switching power supply characterized in that a magnetic coupling transformer for magnetically coupling the secondary winding and the self-inductance coil is provided, and the self-inductance coil is inserted in the charging circuit of the smoothing capacitor. 4. The current resonance type switching according to claim 2, wherein a part of the core of the magnetic coupling transformer is configured to share the magnetic path of the core of the insulating transformer. Power supply.