JP3326655B2 - Current resonant switching power supply - Google Patents

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 having improved power factor and voltage fluctuation rate of a power supply.

[0002]

2. Description of the Related Art In recent years, as a power supply device for obtaining a desired DC voltage by rectifying a commercial power supply by developing a switching element capable of withstanding a relatively large voltage and current of a high frequency, a switching type power supply device is mostly used. 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 reduce the size of a transformer and other devices.

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 efficiency of use of the power supply is impaired. Further, there is a need for a measure for suppressing harmonics generated due to the distorted current waveform.

In order to improve the power factor of a power supply, it is known to use a rectifier circuit of a choke input type as shown in FIG. This power supply circuit is a commercial power supply AC
Rectifier circuit D via common filter CMC
1 and the rectified output is charged to a smoothing capacitor Ci via a choke coil L. Q
Reference numerals 1 and Q2 denote switching transistors connected in series, and a current flows from an intermediate point to the primary winding N1 of the output isolation transformer PIT via the primary winding ND of the drive transformer PRT and the resonance capacitor C1. To do.
Then, the output of the secondary winding N2 of the insulating transformer is rectified by the rectifier diode D0 to obtain a DC output E0.

The drive transformer PRT is an orthogonal transformer having a control winding NC, and its secondary windings NB, 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. That is, when the DC output E0 becomes low, the switching frequency becomes higher than the resonance capacitor C1
(Upper side control) so that the output voltage becomes constant. Note that RB and CB denote impedances for setting the level of the drive signal, and D2 and D3 denote damper diodes.

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

[0007]

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

[0008]

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

According to the first aspect of the present invention, there is provided a communication system from a commercial power supply.
A first rectifier circuit for rectifying the current voltage;
A smoothing capacitor for smoothing the force, at least a primary winding,
Insulation transformer with secondary winding and primary of insulation transformer
Connected in series with the winding and in series with the primary winding
Resonant capacitors and smoothing capacitors that make up a resonant circuit
The current supplied to the series resonance circuit from
Sufficiently higher than the frequency and the resonance frequency of the series resonant circuit
Intermittently at a switching frequency near
A switching element that allows resonance current to flow through the primary winding of
Secondary winding of the isolation transformer connected to the secondary winding of the transformer
A second rectifier circuit for rectifying the alternating voltage from the line;
The output voltage of the rectifier circuit of the
And the switching frequency close to the resonance frequency of the series resonant circuit.
Stabilizes the output voltage by controlling
And a control circuit.
Coupling coefficient is low for secondary winding and secondary winding
A tertiary winding is provided, and the tertiary winding is a smoothing capacitor
Connected in series to the charging path of
The switching voltage is superimposed on the output voltage of the first rectifier circuit
The current in the first rectifier circuit
The feature is that the distribution angle of
You.

According to a second aspect of the present invention, the power supply from
A first rectifier circuit for rectifying the current voltage, and an output of the rectifier circuit.
Smoothing capacitor, at least primary winding and secondary
Insulation transformer having windings and primary winding of insulation transformer
Connected in series with the primary winding and a series resonant circuit
And a smoothing capacitor in series
Make the current supplied to the resonance circuit higher than the frequency of the commercial power supply.
A switch high enough and near the resonant frequency of the series resonant circuit
Intermittently at the switching frequency to the primary winding of the isolation transformer.
A switching element that allows a resonant current to flow, and an insulation transformer
Alternating from the secondary winding of the isolation transformer connected to the secondary winding
A second rectifier circuit for rectifying the voltage and an output of the second rectifier circuit;
Detects input voltage and switches when output voltage drops
The frequency is controlled so that it approaches the resonance frequency of the series resonance circuit.
Control circuit to stabilize the output voltage by controlling
And a second insulating transformer having a primary winding and a secondary winding.
A lance is provided, and a secondary winding of the second insulating transformer is provided.
The line is connected in series to the charging path of the smoothing capacitor,
Switching voltage induced in the secondary winding of the insulated transformer
Voltage is superimposed on the output voltage of the first rectifier circuit.
As a result, the flow angle of the current in the first rectifier circuit is reduced.
It is characterized by being made to spread.

[0011]

A current resonance type switching power supply according to 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 flows intermittently in almost all cycles of the AC signal. Can improve the power factor.

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

[0013]

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 which blocks a signal of a switching frequency. The filter D1 is a bridge type rectifier. Q1 and Q2 are switching elements forming a half-bridge type switching circuit, the output of which is provided through an isolation transformer PI via a resonance capacitor C1.
T is supplied to the primary winding N1. Then, the induced voltage induced in the secondary winding N2 of the insulating transformer PIT is converted to a DC voltage via the rectifying element D0, and is set as the output voltage E0.

A tertiary winding N3 is connected to the insulating transformer PIT.
Are 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 superimposed with the switching voltage via the leakage inductance coil Li described later, and charges 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 output voltage E0 is a constant voltage. It is planning to make it.

Since the switching power supply circuit of the present invention is configured as described above, the switching voltage between the switching elements Q1 and Q2 is alternately opened and closed by using the terminal voltage of the smoothing capacitor Ci as the operating power supply, thereby reducing the voltage of the isolated transformer.
A drive current close to the resonance current waveform is supplied to the secondary coil N1, and an alternating output is obtained to the secondary coil N2. When the DC output voltage on the secondary side drops, the control circuit controls the switching frequency to lower (closer to the resonance frequency) and controls the drive current flowing through the primary coil to increase. .

In the conventional power supply circuit, the smoothing capacitor Ci
Since the charging current is supplied only 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 through which the resonance current flows is supplied to the output side of the choke coil CH for smoothing. This signal is V1 of FIG.
Is superimposed on the rectified voltage as shown in FIG.

Therefore, as shown in FIG.
The flow angle of the current I1 flowing from 1 changes from t1 to t2, and the 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 shown in c, the harmonic distortion is reduced, and the power factor is improved. The current I flowing out of the rectifier circuit
1 is cut off at a switching cycle and flows discontinuously, so that it is required that the rectifying element of the bridge rectifier circuit D1 also use, for example, a high-speed recovery type diode.

The rest period t2~t4 current I ₁ is set by induced voltage of the tertiary winding N3, reverse charging the charge of the resonance capacitor during this period is moved to the smoothing capacitor Ci side is performed. If this pause period is appropriately set, the power factor is set to about 0.75 to 0.90, and if this is extended, the power factor decreases. At the same time, the power supply 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 particularly in the case of a current resonance type switching power supply circuit.

As shown in FIG. 3A, the insulating transformer PIT having the primary winding, the secondary winding, and the tertiary winding mounted thereon has a tertiary winding N3 with respect to the primary winding N1. Are preferably located at magnetically separated positions. 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.
1 and the tertiary winding N3. Then
The magnetic coupling coefficient K between the two windings can be set to, for example, about 0.75 to 0.85. Accordingly, in the equivalent circuit of the transformer using both windings, as shown in FIG. 2B, a leakage inductance component Lg is added to the ideal transformer T, and the leakage inductance component Lg is added to the smoothing choke coil of the smoothing capacitor Ci. Work as L.

The tertiary winding N3 may be separated from the coil in the depth direction of the coil. The value of the leakage inductance generated by the separation is an impedance and an impedance that respond to the cycle of the switching frequency. I just need to be. FIG. 3C shows the overall shape of the insulating transformer PIT. A magnetic gap g is provided on the middle leg of the core Cr. The tertiary winding N3 is disposed on both legs so that the above-described leakage inductance can be obtained.

FIG. 4A shows another embodiment of the present invention, and the same parts as those in FIG. 1 are denoted 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 a switching voltage is provided. That is,
A second winding N2 'is provided on the secondary side of the insulating transformer, and its output is supplied to a tertiary winding N3. The self-inductance coil N magnetically coupled to the tertiary winding N3
i. The switching voltage generated in the self-inductance coil Ni is equal to the smoothing capacitor C.
The switching voltage is supplied to one 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.
Can be improved.

FIG. 4B shows the magnetic coupling transformer MC.
T and the core of the insulating transformer PIT are integrated to reduce the occupied area of the power supply device, and a pair of Es having a central gap g are formed.
1 winding a shaped core Cr _(1), 2 winding and a second 2
MCT for the insulation transformer around the next winding N2 '
Is provided, and an E-shaped core Cr ₍₂₎ is provided.
_A tertiary winding N3 and a self-inductance coil Ni are applied to ₍₂₎ . The center 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 configured to be shared with a part of the insulating transformer PIT. It should be noted that a modification can be made 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, a rectifier circuit for rectifying an AC power supply forms a voltage doubler rectifier circuit by rectifier diodes D1 and D2. Further, the magnetic coupling transformer MCT and the insulating transformer are integrated as shown in FIG. 5B, and are constituted by an orthogonal transformer whose magnetic characteristics are variable by the control winding Nc. The tertiary winding N3 and the primary winding N1 constituting the MCT are connected in series, and are formed so that the resonant switching current intermittently supplied by the switching transistors Q1 and Q2 is directly supplied.

In this embodiment, the insulation transformer is constituted by an orthogonal transformer PRT, and a DC voltage E0 output from a secondary winding is supplied to a control winding NC thereof through a control circuit. By controlling the magnetic characteristics of the orthogonal type insulation transformer PRT, the resonance frequency of the circuit is varied to stabilize the output voltage.

Also in this embodiment, the switching voltage is superimposed on the charging path of the voltage doubler rectifier circuit by the switching voltage output to the self-inductance coil Ni, and the power factor is improved by increasing the conduction angle of the charging current. Will be Similarly to the switching power supply of FIG. 4, the core Cr ₍₁₎ of the insulating transformer and the core Cr ₍₂₎ of
As shown in FIG. 2B, it is preferable that the area occupied by the switching transformer be reduced and the volume occupied by the core be reduced. By making the magnetic coupling coefficient K of the MCT coarse, the leakage is reduced as shown in FIG.
A di-inductance can be created to provide a choke coil function.

In this embodiment, the reduction of the power factor, which is a particular problem in the conventional switching power supply, can be improved by employing the voltage doubler rectifier circuit. In the case of the conventional choke coil type switching power supply, In this case, it is necessary to switch the choke coil in response to the change in the input voltage, and the switching is complicated.
There is a characteristic that it can be adapted to a 00V system commercial power supply and a 200V system commercial power supply by a simple switching circuit.

[0028]

As described above, in the current resonance type switching power supply of the present invention, a predetermined leakage inductance is created by making the tertiary winding loosely coupled to the insulating transformer. Since the output switching voltage charges the smoothing capacitor via the leakage inductance, the leakage inductance acts as a choke coil, increasing the conduction angle of the current charged in the smoothing capacitor and reducing 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 pause period for charging in the switching cycle. With this setting, the voltage variation rate can be reduced, and the power supply efficiency can be designed to increase. Further, since a 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, the core of the magnetic coupling transformer for returning the switching voltage to the rectifying and charging circuit side is shared with a part of the core of the insulating transformer, so that the power supply unit can be miniaturized without increasing the number of parts. There is an advantage that can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a basic outline of a switching power supply circuit according to 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 insulating 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.

[Explanation of symbols]

 LN, CN Low-pass filter for harmonic suppression D1 Bridge type rectifier circuit Q1, Q2 Switching element MCT Magnetic coupling transformer Ci Smoothing capacitor C1 Resonant capacitor PIT Isolation transformer PRT Quadrature drive transformer

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/06 H02M 3/28 H02M 7/04 H02M 7/10

Claims (2)

(57) [Claims] A first power supply for rectifying an AC voltage from a commercial power supply;
Rectifier circuit, a smoothing capacitor for smoothing the output of the rectifier circuit, and an insulating transformer having at least a primary winding and a secondary winding
And connected in series to the primary winding of the insulating transformer
A resonance capacitor forming a series resonance circuit with the primary winding;
And capacitors, are supplied to the series resonant circuit from said smoothing capacitor
The current is sufficiently higher than the frequency of the
Switching frequency near the resonance frequency of the series resonant circuit
The number of resonance currents in the primary winding of the isolation transformer
A switching element for flowing current, and an insulating transformer connected to a secondary winding of the insulating transformer.
A second rectifier circuit that rectifies the alternating voltage from the secondary winding of the
Circuit, and an output voltage of the second rectifier circuit.
When the pressure decreases, the switching frequency changes to the series resonance.
By controlling it to be close to the resonance frequency of the circuit,
A control circuit for stabilizing the output voltage, wherein the insulating transformer further includes the primary winding and the secondary winding.
A tertiary winding with a low coupling coefficient to the
And the tertiary winding is charged with the smoothing capacitor.
Is connected in series with the electric circuit, and the switch induced in the tertiary winding.
The switching voltage is superimposed on the output voltage of the first rectifier circuit.
In the first rectifier circuit.
Current characterized by widening the angle of current flow
Resonant switching power supply. 2. A first rectifier for rectifying an AC voltage from a commercial power supply.
Rectifier circuit, a smoothing capacitor for smoothing the output of the rectifier circuit, and an insulating transformer having at least a primary winding and a secondary winding
And connected in series to the primary winding of the insulating transformer
A resonance capacitor forming a series resonance circuit with the primary winding;
And capacitors, are supplied to the series resonant circuit from said smoothing capacitor
The current is sufficiently higher than the frequency of the
Switching frequency near the resonance frequency of the series resonant circuit
The number of resonance currents in the primary winding of the isolation transformer
A switching element to flow, by detecting the output voltage of the second rectifier circuit, the output current
When the pressure decreases, the switching frequency changes to the series resonance.
By controlling it to be close to the resonance frequency of the circuit,
A control circuit for stabilizing the output voltage, and a second insulating transformer having a primary winding and a secondary winding.
Is provided, and a secondary winding of the second insulating transformer is provided.
Is connected in series to the charging path of the smoothing capacitor,
A switch induced in a secondary winding of the second insulating transformer
A switching voltage is superimposed on an output voltage of the first rectifier circuit.
This allows the current in the first rectifier circuit to be
Current resonance type characterized by widening the flow angle
Switching power supply.