JPH0880045A - Switching power circuit - Google Patents

Abstract

PURPOSE: To improve the power factor of a voltage doubler rectifier type switching power circuit. CONSTITUTION: A rectifier circuit consisting of rectifier diodes D1 , D2 and a smoothing capacitor C1 is supplied with a commercial AC power supply through an inductance LN and a capacitor CN, and switching elements Q1 , Q1 connected to two half bridges bonded with the voltage doubler rectifier power supply are interrupted, thus constituting the current resonance type switching power supply, in which a DC output E0 is obtained from the secondary side of an insulating transformer PRT. A switching current supplies the rectifier circuit side with switching voltage through a magnetic coupling transformer MCT, and the rectifier diodes D1 , D2 are interrupted, thus improving a power factor.

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 switching power supply circuit with improved power factor and voltage fluctuation rate of the power supply.

[0002]

2. Description of the Related Art In recent years, most of the power supply devices of a switching system have been developed as a power supply device for rectifying a commercial power supply to obtain a desired DC voltage by developing a relatively large current having a high frequency and a switching element capable of withstanding the current. 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.

Generally, when a commercial power source is rectified,
In particular, in the case of voltage doubler rectification, 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 source is impaired. Further, a measure (EMI) for suppressing harmonics generated by the distorted current waveform
Is needed. To improve the power factor of the power supply,
For example, it is simplest to use a rectifier circuit of the choke input type and preferable in terms of countermeasures against electromagnetic noise (EMI), but this type requires an inductor exhibiting a large impedance as a choke coil, which reduces the size of electronic devices. This impedes the increase in cost and increases the cost.

For example, FIG. 8 (a) shows a voltage doubler for rectifying a commercial power source AC through a common filter CMC with two rectifying diodes D ₁ and D ₂ and alternately charging smoothing capacitors C _i and C _i. Switching element Q that constitutes a rectifier circuit and is half-bridge connected from the voltage doubler rectifier circuit
Supply voltage to ₁ and Q ₂ . Switching element Q ₁ , Q
Midpoint of ₂ is supplied to the primary winding N ₁ of the insulating transformer PIT via the resonance capacitor C _1, the resonance current and the isolation transformer by the resonant capacitor C ₁ is induced in the secondary winding N _2, the induced The output is rectified by the bridge diode D ₁ . Then, the rectified DC output E ₀ is supplied to the control winding NC of the orthogonal drive transformer PRT via the control circuit, and the magnetic characteristics of the transformer are varied to generate a signal output from the drive coil N _B. The output frequency is adjusted by changing the switching frequency at which the switching elements are alternately turned on / off.

This type of switching power supply uses a choke coil PCC inserted in a voltage doubler rectifier circuit.
As shown by I _AC in FIG. 8B, the inrush current of the capacitor C is flattened and comes close to the waveform of the voltage V _AC , which has the effect of improving the power factor. However, in order to reduce the ripple voltage ΔE _i Since the impedance value needs to have a value corresponding to the frequency of the commercial power supply, it is inevitably large and heavy, and the leaking magnetic field causes screen shaking in the case of a television receiver. was there.

Therefore, a method has also been developed in which an active filter is inserted on the rectifier circuit side to improve the power factor. FIG. 9 shows a voltage doubler rectifier circuit portion using a partial smoothing circuit as one of the active filter systems. In this figure, Q ₃ and Q ₃ are transistors for supplying a voltage to the smoothing capacitors C _i and C _i for doubled voltage at a switching cycle, respectively, and both have choke coil L ₁ with a secondary winding. It constitutes a self-excited oscillator. That is, the oscillation is started with the potential of the capacitor C ₂ connected in series with the smoothing capacitor C _i being charged to some extent, and the switching voltage accompanying this oscillation is applied to the diode D.
Charge the smoothing capacitor via ₃ . Therefore, since this partial smoothing circuit switches the charging current of the capacitor in most of each cycle of the alternating current to flow the charging current,
The conduction angle of the rectifier diodes D ₁ and D ₂ can be widened to improve the power factor.

[0007]

The partial smoothing circuit, together with the subsequent switching power supply, has problems in terms of noise countermeasures due to switching and a decrease in efficiency. The ripple voltage ΔE _i 'of the smoothing capacitor C _i is also shown in FIG. As you can see, there is the problem of becoming expensive. Further, in the case of the voltage doubler rectifier circuit, two partial smoothing circuits are required, which causes an increase in cost. Therefore, in the case of the voltage doubler rectifier circuit, as shown in FIG. 10, four smoothing capacitors C and six diodes D ₄ to
In some cases, the use of a Schottney voltage divider circuit using D ₉ is applied to lighting-related equipment. However, as shown in the operation waveform diagram of FIG. 7B, the power factor of this voltage circuit is improved to about 0.85, but the ripple voltage ΔE _i "> 100V and the combination with the switching power supply is achieved. Has a problem in terms of regulation.

[0008]

A voltage doubler rectifying means for rectifying a commercial power source, a smoothing means composed of a smoothing capacitor for smoothing the output of the voltage doubler rectifying means, and a voltage or current output from the smoothing means is intermittently connected. And a switching element for supplying to the primary side of the isolation transformer to obtain a predetermined alternating voltage from the secondary side of the isolation transformer. As a recovery semiconductor element, the switching voltage of the switching power supply is inserted into the charging circuit of the voltage doubler rectifier circuit. In addition, the current resonance type switching power supply for varying the switching frequency to make the output voltage constant is provided, and the switching power supply is connected to the charging circuit side by the magnetic coupling transformer to which the current flowing in the primary winding of the transformer is supplied. Allow them to return.

[0009]

In a region where the AC power source is 100V system, the power factor of the voltage doubler rectifying and smoothing circuit can be easily improved, and the size and size can be reduced. Further, since the power supply fluctuation rate is improved, it is not necessary to increase the withstand voltage of the smoothing capacitor and the switching transistor, and the cost can be reduced.

[0010]

FIG. 1 is a switching power supply circuit showing an embodiment of the present invention, where AC is an AC power supply, L _N and C _N are low-pass filters for blocking signals of a switching frequency, and D.
₁ and D ₂ are diodes for voltage doubler rectification, and C _i is a smoothing capacitor. Q ₁ and Q ₂ are switching elements forming a half-bridge type switching circuit, the output of which is a magnetic coupling ferrite transformer MCT (hereinafter referred to as MCT).
The primary winding L ₃₎ of that, and is supplied to the primary winding N ₁ of the insulating transformer PRT of orthogonal through the resonance capacitor C _1. Then, the secondary winding N ₂ of the orthogonal isolation transformer
The induced voltage induced in the DC voltage is converted into a DC voltage via the rectifying element D ₁ and becomes the output voltage E ₀ .

The MCT has a self-inductance L _i (2
The next winding N _i ) and the coil L ₃ are connected by a ferrite core.
For example, they are tightly coupled with a winding ratio of 1: 1 so that the switching voltage corresponding to the resonance current flowing through the insulating transformer PRT is superimposed on the self-inductance L _i . Therefore, the rectified full-wave rectified voltage has the switching voltage superimposed on the winding N _i of the self-inductance L _i , and is charged in the two smoothing capacitors C _i and C _i for doubled voltage. The rectifying elements D ₁ and D ₂ are intermittently supplied with this switching voltage and supply a discontinuous charging current I ₁ to the smoothing capacitor C _i .

The CDT is a drive transformer which alternately turns on / off the switching elements Q ₁ and Q ₂ and constitutes a self-excited oscillation circuit, and its drive coil N _B ,
The voltage output from N _B is supplied to the base electrodes of the switching elements Q ₁ and Q ₂ via capacitors C _B and C _B and resistors R _B and R _B. D ₁ and D ₁ are damper diodes.

Since the switching power supply circuit of the present invention is constructed as described above, if the primary winding L _{3 of the} MCT is removed and both ends thereof are short-circuited, a current resonance type current rectifying circuit consisting of a voltage doubler rectifying circuit is used. It will operate as a switching power supply circuit. That is, in this case, the two smoothing capacitors C _i and C _i are alternately charged with positive and negative AC voltages through the diodes D ₁ and D ₂ and the self-inductance L _i , and the terminal voltage is the peak current of the AC voltage. It will be almost double. Then, by using the terminal voltage as an operating power source, the switching elements Q ₁ and Q ₂ alternately open and close to supply a drive current close to the resonance current waveform to the primary side winding N ₁ of the insulating transformer, and the secondary side. An alternating output is obtained at the winding N ₂ . When the DC output voltage E ₀ on the secondary side drops, a control current is supplied to the control winding NC of the insulating transformer by the control circuit, and the secondary output voltage E ₀ becomes constant due to a change in the magnetic saturation characteristic of the transformer. Is controlled.

Since the charging current rushes into the two smoothing capacitors C _i and C _i 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, since the smoothing self-inductance L _i is magnetically coupled by the coil L ₃ and the MCT which are coupled in series with the capacitor C ₁ through which the resonance current flows, the smoothing choke is performed. self-inductance L _i in the switching voltage corresponding to the switching current comprising a coil (e.g., 1
00 KHz) and this signal pulls down the terminal voltages of the two smoothing capacitors C _{i in} the switching period depending on the positive or negative polarity of the AC voltage.

Then, the charging current starts to flow even during the period in which the terminal voltage of the capacitor C _i is lower than the rectified voltage V _AC of the rectifying element, and the MCT is set so that this period extends over almost the entire cycle period of the alternating current. By setting the winding ratio of, the power factor shows a value close to 1. That is, as shown in (a) of FIG. 2, the charging voltage I ₁ flows intermittently due to the switching voltage being superimposed on the rectified voltage V _AC , and the average current I _AC is the rectified voltage V _AC . It becomes similar to the waveform. In addition, V ₁ is a diode D ₁ , D ₂
, V ₂ is the voltage supplied to the switching power supply by C _i of the smoothing capacitor, and V ₃ is 1 of MCT.
A switching voltage induced in the secondary winding, the frequency of which is the switching frequency (for example, 130 KHz).

FIG. 2 (b) shows a waveform diagram of a signal flowing through each part in a switching cycle. That is, I _Q1
Is a current flowing through the switching element Q ₁ , I ₀ is a resonance current, and V ₃ is a switching voltage induced in the winding N ₃ . In the switching power supply circuit of the present invention, 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 MCT by this drive current also becomes small. Therefore, when the load is light, the level of the charging current I _AC becomes small, and when the load is heavy, the charging current becomes large. Therefore, the phenomenon that the terminal voltage of the smoothing capacitor C _i rises abnormally at a light load is eliminated, and the regulation is improved. It can be performed.

Further, as will be described in an embodiment described later, the switching elements Q ₁ and Q ₂ are connected to the damper diode D.
_d1, It is preferable to form a D _d2, a period in which the charging current does not flow by the switching voltage to the smoothing capacitor C as shown in t4 to t2 in FIG. 2, occurs (pause period), the capacitor C ₁ in this period Can be reversely charged to the smoothing capacitor C _i side. This idle period is the third winding N
₃ and the inductance L _i are arbitrarily set, and for example, the power factor is set to 0.75 by increasing the idle period during which no current flows.
When it is set to about 0.9, the power supply efficiency can be increased. That is, when the rest period in which the charging current does not flow is formed, the current can be supplied from the resonance capacitor C ₁ to the smoothing capacitor C _i via the diode D _d1 during this rest period, and the efficiency is improved and the regulation is improved. Will be improved.

FIG. 3 is a circuit diagram when the present invention is applied to a self-excited current resonance type switching power supply circuit. In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. PRT represents a quadrature drive transformer for self-excitation, which has a drive coil N _{D on} the primary side and 2 on the secondary side.
Two drive coils L _B and L _B are provided. The drive coil N _D is supplied with the resonance current flowing through the resonance capacitor C ₁ , and the voltage induced by this resonance current is supplied from the drive coil N _B to the capacitor C _B and the switching elements Q ₁ and Q via the resistor. Supplied on base of ₂ .

Further, the drive transformer PRT is provided with a control winding NC, and this control winding has a secondary winding N.
A current corresponding to the DC voltage E ₀ output from ₂ is supplied from the control circuit, and a relatively high voltage output from the winding N ₄ on the secondary side of the insulating transformer PIT is supplied to the self-inductance L _i via the MCT. It is fed back to the charging circuit side so as to supply the switching voltage to. In this embodiment, the switching frequency is controlled by the output voltage E ₀ of the secondary winding N ₂ . Then, as described above, the constant voltage control is performed by changing the switching frequency so that the output voltage E ₀ becomes constant.

Also in this embodiment, the voltage induced in the secondary winding N ₄ of the insulating transformer PIT is magnetically coupled to the self-inductance L _i inserted in the charging circuit via the MCT. This coupling widens the conduction angle of the charging current. Therefore, as described above, the rectifier diodes D ₁ and D _{2 of the} voltage doubler rectifier circuit are interrupted by the switching voltage to improve the power factor when operating the switching power supply. Further, the voltage of the resonance capacitor C ₁ is fed back to the smoothing capacitor C _i via the damper diode D _d1 , and the ripple and the power supply efficiency are improved.

FIG. 4 shows a tertiary winding N ₃ in which the switching voltage in FIG. 3 is provided in the insulating transformer PIT.
This switching voltage is directly output to the charging path of the rectifier circuit, and CH is a choke coil, and other symbols have the same configuration as in FIG.

FIG. 5 shows a case where the switching power supply of the present invention is composed of a _single transistor (MOSFET) Q ₁ . The rectifier circuit is a voltage doubler rectifier system as in the above embodiment, but the switching power source is a flyback power source circuit, and the MCT winding N ₃ is connected in series to the primary winding N ₁ of the insulating transformer CVT. It is provided and is magnetically coupled to the inductor L _i that serves as a choke coil. The switching pulse of the transistor Q _{1 is} of the separately excited type supplied from the control circuit, and the control circuit controls the pulse width by the output voltage E ₀ of the secondary winding.
The output voltage is made constant by WM control.

In FIG. 6, a resonance capacitor C ₂ and a damper diode D ₃ are provided in the winding N ₃ forming the MCT in FIG. 5, and the switching voltage fed back to the self-inductance L _i side is an AC half cycle. So that the voltage is continuous. That is, the inductance L _i of the winding N ₃ and the capacitance of the capacitor C ₂ are selected so as to substantially resonate with the switching frequency. Since the energy of the inductor L ₃ resonates with the capacitor C ₂ via the diode D ₃ when the voltage of the winding N ₃ becomes zero, a half cycle of an alternating current is supplied to the charging path of the rectified current. Is controlled so that a continuous charging current is supplied via the inductor L ₃ . It should be noted that this embodiment is based on the forward word switching power supply system in which the voltage of the secondary winding N ₂ is supplied to the load when the voltage is supplied to the primary winding N ₁ .

FIG. 7 shows a modification of the above-mentioned FIG.
A quaternary winding N ₄ is provided on the secondary side of the insulating transformer CVT, and the switching voltage is fed back from this quaternary winding to the rectifier circuit side via the MCT. The rectifying diodes D ₁ and D ₂ are forcibly interrupted in the switching cycle by the switching voltage fed back by the MCT, as in each of the above-described embodiments, to widen the flow angle of the charging current.

Since the voltage applied to the rectifying diodes D ₁ and D ₂ used in each embodiment is a combination of the switching voltage and the rectifying voltage, the rectifying diode is also intermittent in this switching cycle. Will be done. Therefore, it is preferable that the diode forming the rectifier circuit is a high-speed recovery diode having a certain amount of current capacity. It is also possible to connect small capacity diodes in parallel.

[0026]

As described above, in the switching power supply circuit of the present invention, in various switching power supply systems using the voltage doubler rectifier circuit, the MCT is provided in the path of the drive current input to the primary side isolation transformer. , This MCT
Since the voltage of the switching cycle is superimposed on the smoothing inductance coupled to, the charging period of the current charged in the smoothing capacitor becomes longer,
Power factor can be improved.

Further, when the switching power supply circuit is of a resonance type, by setting the coupling coil of the MCT so as to have a predetermined inductance, it is possible to provide a pause period for charging, and to improve efficiency. In addition to being settable, the damper current of the resonance current is caused to flow into the smoothing capacitor during this idle period, so that fluctuations in voltage can be suppressed and efficiency can be increased. Further, since the one-converter system is used, switching noise and harmonics can be easily prevented from being emitted to the outside by providing a normal mode low-pass filter (L _N , C _N ) on the AC input side.

Since the MCT provided for switching the rectifier circuit can be easily made by winding a high-frequency choke coil which has been conventionally used, a harmonic distortion countermeasure can be realized at low cost. The effect is that you can do it. Further, when the current resonance type switching power supply is used, the leakage inductance on the primary side increases due to the MCT, so that the capacitance of the resonance capacitor can be reduced and the control range can be expanded.

[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 diagram showing voltage and current waveforms of respective parts of FIG.

FIG. 3 is a circuit diagram of a current resonance type switching power supply.

FIG. 4 is a circuit diagram showing a modified example of a current resonance type switching power supply.

FIG. 5 is a circuit diagram showing a flyback type switching power supply.

FIG. 6 is a power supply circuit diagram for single-stone switching in which a switching voltage is in a continuous mode.

FIG. 7 is a one-stone switching power supply circuit diagram in which a switching frequency is supplied from a secondary winding.

FIG. 8 is a current resonance type switching power supply circuit diagram in which a choke coil is inserted in a voltage doubler rectifier circuit.

FIG. 9 is a circuit diagram showing a power source section in which a partial smoothing circuit is added to a voltage doubler rectifier circuit.

FIG. 10 shows an embodiment in which the voltage doubler rectifier circuit is composed of a Schottney voltage divider circuit.

[Explanation of symbols]

L _N , C _N Low pass filter for harmonic suppression D ₁ , D ₂ Double voltage rectifier diode Q ₁ , Q ₂ Switching element MCT Magnetic coupling transformer C _i Smoothing capacitor C ₁ Resonant capacitor PIT Isolation transformer PRT Orthogonal drive transformer

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[Procedure amendment]

[Submission date] October 24, 1994

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Claims (5)

[Claims] 1. A voltage doubler rectifying means for rectifying a commercial power supply,
The insulating transformer is provided with a smoothing unit including a smoothing capacitor that smoothes the output of the voltage doubler rectifying unit, and a switching element that intermittently supplies the voltage or current output from the smoothing unit to the primary side of the insulating transformer. In a switching power supply circuit capable of obtaining a predetermined alternating voltage from the secondary side, the rectifying element of the double voltage rectifying circuit is a high-speed recovery semiconductor element, and the switching voltage of the switching power supply is a charging circuit of the double voltage rectifying circuit. A switching power supply circuit characterized by being inserted into a power supply. 2. The switching power supply circuit according to claim 1, wherein the switching element is half-bridge connected to an insulating transformer. 3. The switching power supply circuit according to claim 1, wherein the switching power supply is a current resonance type circuit. 4. The switching voltage is supplied by a magnetic coupling transformer magnetically coupled to a coil to which a current flowing through the primary winding of the isolation transformer is supplied. The switching power supply circuit according to claim 1, 2, or 3. 5. The switching power supply circuit according to claim 4, wherein the switching frequency is variably controlled by a DC output voltage.