JPH08149814A - Current resonance type switching power supply circuit - Google Patents

Abstract

PURPOSE: To reduce the number of parts and to miniaturize a switching power supply circuit by supplying the switching current of a switching converter part while superposing the current to the line between a rectification circuit and a smoothing circuit and at the same time providing a parallel resonance circuit for a switching current which is superposed on the rectification current of a double-voltage rectification circuit. CONSTITUTION: A filter capacitor is directly connected to a commercial power supply and one terminal of a filter choke coil LN is connected to the middle point of diodes D1 and D2 for constituting a double-voltage rectification circuit. Also, the filter choke coil LN operates as a load for the switching current of a switching power supply which is in half-bridge connection. Then, switching output is superposed on the diodes D1 and D2 for performing double-voltage rectification. A capacitor C2 for resonance is connected in parallel to the diodes D1 and D2 for double-voltage rectification and switching output is partially bypassed by the capacitor C2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current resonance type switching power supply circuit for improving power factor.

[0002]

2. Description of the Related Art In recent years, most of switching power supply devices 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 relatively large current and voltage 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, 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.

Therefore, as one of the switching power supply circuits with improved power factor, a switching power supply circuit as shown in the circuit diagram of FIG. 7 has been previously proposed by the applicant of the present invention. It is a self-excited current resonance type converter.

In this figure, AC indicates a commercial AC power source. Further, D ₁ is a bridge rectification circuit composed of four diodes, and performs full-wave rectification on the input AC power supply AC. A filter choke coil L _N , a fast recovery diode D ₂ , and a choke coil CH are provided in series with the line between the positive output terminal of the bridge rectifier circuit D _{1 and} the positive electrode of the smoothing capacitor Ci as shown in the figure. . Further, the filter capacitor C _N is composed of the filter choke coil L _N and the fast recovery type diode D ₂
The filter capacitor C _N and the filter choke coil L _N form a normal mode LC low-pass filter.

This LC low pass filter is designed to prevent high frequency noise of the switching frequency from flowing into the AC line. Further, the high-speed recovery type diode D ₂ corresponds to a high-frequency current having a switching period described later flowing through the full-wave rectified output line.

C ₂ is a parallel resonance capacitor,
As shown in the figure, it is connected in parallel with the choke coil CH to form a parallel resonance circuit together with the choke coil CH. The resonance frequency of the parallel resonance circuit is set to be substantially the same as the resonance frequency of the switching power supply. The operation will be described later.

Q ₁ and Q ₂ are switching elements forming a half-bridge type switching circuit. As shown in the figure, a collector and an emitter are respectively connected between a connection point on the positive electrode side of the smoothing capacitor Ci and the ground. It is connected. Each collector of the switching elements Q ₁ and Q ₂
The resistors R _S and R _S inserted between the bases are start-up resistors, and D _D and D _D inserted between the bases and emitters of the switching elements Q ₁ and Q ₂ are damper diodes. The resistors R _B and R _B are resistors for adjusting the base current (drive current) of the switching elements Q ₁ and Q ₂ , respectively. C _B and C _B are capacitors for resonance, which form a series resonance circuit for self-excited oscillation together with drive windings N _B and N _{B of} the drive transformer PIT described next.

PRT represents a drive transformer for variably controlling the switching frequencies of the switching elements Q ₁ and Q ₂ , and in the case of this figure, the drive windings N _B and N _B and the resonance current detection winding N _D are wound. Further, a control winding N _C is wound in a direction orthogonal to each of these windings to form an orthogonal saturable reactor. This drive transformer PR
One end of the drive winding N _B on the switching element side of T has a resistor R
_B , the other end is connected to the emitter of the switching element. Further, one end of the drive winding N _B on the side of the switching element Q ₂ is grounded to the ground, and the other end is connected to the resistor R _B to output a voltage having a polarity opposite to that of the drive winding N _B. It is done like this. The current detection winding N _D is connected to the contacts of the emitter of the switching element and the collector of the switching element Q ₂ , and is connected to one end of the primary winding N ₁ of the insulating transformer PIT via a series resonance capacitor C ₁ . Connected.

PIT is an insulating transformer for transmitting the switching outputs of the switching elements Q ₁ and Q _{2 to} the secondary side. One end of the primary winding N ₁ of this insulating transformer PIT is connected via a series resonance capacitor C _1. It is connected in series with the current detection winding N _D, and the other end is connected to the connection point between the fast recovery diode D ₂ and the choke coil CH. Then, by the inductance component of the insulating transformer PIT including the series resonance capacitor C ₁ and the primary winding N ₁ ,
A resonance circuit is formed to make the switching power supply circuit a current resonance type. In the case of this switching power supply circuit,
On the secondary side of the insulation transformer PIT, the primary winding N ₁
The induced voltage induced in the secondary winding N ₂ is converted into a DC voltage by the bridge rectifier circuit D ₃ and the smoothing capacitor C ₃ C ₃ to be the output voltage E ₀ .

The control circuit 1 compares the DC voltage output E ₀ on the secondary side with a reference voltage, and supplies a DC current corresponding to the error as a control current I _{C to} the control winding N _C of the drive transformer PRT. Error amplifier.

In the switching operation of the switching power supply having the above-mentioned structure, when the commercial AC power supply is first turned on, the switching element Q is turned on, for example, via the starting resistors R _S and R _{S.
Although the} base current is supplied to the bases of ₁ and Q ₂ , if the switching element is turned on first, the switching element Q ₂ is controlled to be turned off. Then, as the output of the switching element, a resonance current flows through the current detection winding N _D → capacitor C ₁ → primary winding N ₁ , but in the vicinity where the resonance current becomes 0, the switching element Q ₂ turns on and the switching element Is controlled to be turned off. Then, a resonance current in the opposite direction to the above flows through the switching elements Q ₁ and 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. In this way, the switching element Q is operated with the terminal voltage of the smoothing capacitor Ci as the operating power supply.
_By alternately opening and closing ₁ , and Q ₂ , a drive current close to the resonance current waveform is supplied to the primary winding N ₁ of the insulating transformer, and an alternating output is obtained at the secondary winding N ₂ .

When the DC output voltage (E ₀ ) on the secondary side decreases, the control circuit 2 controls the current flowing through the control winding N _C so that the switching frequency becomes low (close to the resonance frequency. Controlled by the primary winding N ₁
The drive voltage is controlled so that the drive current is increased to achieve a constant voltage.

The power factor improving operation is as follows. In this circuit, the primary winding N ₁ of the isolation transformer PIT
The switching output corresponding to the resonance current flowing in the direct choke coil CH is directly superimposed on the rectified voltage of the commercial AC power source flowing in the self-inductance Li of the winding Ni of the choke coil CH. As a result, the smoothing capacitor Ci is charged in a state where the switching voltage is superimposed on the full-wave rectified voltage, and the terminal voltage of the smoothing capacitor Ci is reduced in the switching cycle by the superimposed amount of the switching voltage. Then, the charging current starts flowing while the terminal voltage of the capacitor Ci is lower than the rectified voltage level of the bridge rectifier circuit, and the average AC input current approaches the AC voltage waveform to improve the power factor. .

In the power supply circuit for improving the power factor by such a method, the drive current of the insulating transformer PIT becomes small when the load is light, so that the switching current flowing in the full-wave rectified output line is also made small by this drive current. 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 it is difficult for the normal MS method. The regulation can be improved. Therefore, for example, the fluctuation of the rectified and smoothed voltage Vi is suppressed even if the fluctuation of the _AC input voltage V _AC ± 20%, and it is not necessary to consider the improvement of the breakdown voltage of the switching element or the smoothing capacitor.

Further, since the current resonance type switching power supply is controlled so that the switching frequency becomes high when the load is light, the self-inductance L of the choke coil is increased.
The resonance capacitor C ₂ connected to i suppresses the switching voltage fed back to the rectifying and smoothing line when the load of the switching power supply becomes light. As a result,
This suppresses an abnormal rise in the terminal voltage Ei of the smoothing capacitor Ci when the load is light.

That is, in the power supply circuit configured as shown in FIG. 7, the switching frequency is controlled to increase as the power supply load decreases, but at this time, the switching voltage returned to the charging circuit side is suppressed by the capacitor C ₂ . Prevents the terminal voltage from rising. Further, when the power supply load increases, the switching frequency decreases, and the switching frequency approaches the resonance frequency of the resonance circuit of the self-inductance coil Ni and the capacitor C ₂ to increase the switching voltage fed back. Therefore, in this power supply circuit, the voltage fluctuation rate at which the terminal voltage of the smoothing capacitor fluctuates due to the power supply load is reduced, which makes it easy to make the DC output E ₀ a constant voltage.

The filter choke coil L _N and the choke coil CH actually used in the circuit of FIG. 7 are shown in FIGS. 8 (a) and 8 (b), respectively. As shown in (a), the filter choke coil L _N has a polyurethane copper wire wound directly around a drum-shaped ferrite core D. Further, as shown in FIG. 8B, the choke coil CH forms an EE type core in which the E type ferrite core C _R is combined as shown in the figure, and at this time, a gap G is provided in the middle leg as shown in the figure. Therefore, the leakage magnetic flux is prevented from leaking to the outside of the choke coil. And winding N
As i, for example, a polyurethane copper wire having a diameter of 60 μ is wound around a winding bobbin (not shown) so that the inductance Li is not saturated at the maximum load. Specifically, in the choke coil CH, when the load power of the DC output voltage E ₀ is 120 W, for example, EE-16 is used for the core, the litz wire is 60 μ / 80 bundle, and Li = 15 μH. If the load power is 230 W, the core is EE-25, the litz wire is 60 μ / 130 bundle, and Li = 1.
It is set to 00 μH.

By the way, the load of the switching power supply is 15
When it becomes 0 W or more, the higher the smoothing voltage to be switched, the lower the switching current can be made relatively, and the current capacity of each device constituting the power supply circuit can be reduced to reduce the size and weight, and at the same time. It becomes easy to support a wide power supply. In FIG. 9, the switching power supply described above is operated by a voltage doubler rectifier circuit, and the same parts are designated by the same reference numerals. In this figure, the diode bridge circuit that performs full-wave rectification is omitted, and the double voltage rectification of the commercial power source is performed by the _two diodes D ₁ and D ₂ and the smoothing capacitors Ci ₁ and Ci ₂ .

[0020]

From the viewpoint of the size and cost of equipment, the switching power supply circuit can be made small and lightweight by reducing the number of parts as much as possible and using small and inexpensive parts. Also, it is preferable to achieve low cost, and it is also preferable to improve characteristics such as power conversion efficiency.

[0021]

SUMMARY OF THE INVENTION Therefore, according to the present invention, a voltage doubler rectifier circuit for rectifying a commercial power source and a smoothed rectified output thereof are provided in order to make the switching power source useful when operating the switching power source by the voltage doubler method. In a smoothing circuit and a current resonance type switching converter section that interrupts the voltage output from the smoothing circuit, the switching current of the switching converter section is superimposed on the line between the rectifying circuit and the smoothing circuit. In addition to being supplied, a parallel resonant circuit is formed for the switching current superimposed on the rectified current of the voltage doubler rectifier circuit.

In the parallel resonance circuit, a parallel resonance capacitor is connected to a rectifying diode, and the resonance frequency of the resonance capacitor and the choke coil that blocks switching noise is set to the minimum frequency of the switching frequency or lower. is there.

The switching power supply is of a self-excited type, and is configured to perform constant voltage control by changing the switching frequency of the switching converter unit based on the DC output voltage obtained on the secondary side of the insulating transformer. Alternatively, a constant voltage control is performed by changing the magnetic characteristic of the insulating transformer based on the DC output voltage obtained on the secondary side of the insulating transformer.

Further, when the MOSFET is used as the switching power source in the separately excited type, the duty of the switching pulse is varied according to the smoothed voltage, and the DC output voltage obtained at the secondary side of the insulation transformer is used. The switching frequency is changed to control the constant voltage.

[0025]

According to the above configuration, in various types of current resonance type switching power supply circuits, switching noise is prevented from leaking to the input side by the filter capacitor for blocking switching noise and the filter choke coil inserted in the power supply rectification line. In addition to preventing this, a resonance circuit is formed by this impedance element and a resonance capacitor connected in parallel with the voltage doubler rectifier diode, so that the switching output of the current resonance circuit on the primary side is superimposed on the rectification output line. Therefore, the number of choke coils required for the rectifier circuit side of the commercial power supply can be reduced to one.

[0026]

FIG. 1 shows an embodiment of a current resonance type switching power supply circuit of the present invention. The same parts as those in FIG. 9 are designated by the same reference numerals and their description is omitted. In the circuit of this embodiment, the filter capacitor C _N is directly connected to the commercial power source, and one end of the filter choke coil L _N is connected to the intermediate point of the diodes D ₁ and D ₂ which form the voltage doubler rectifier circuit. There is. Further, the filter choke coil L _N acts as a load against the switching current of the switching power supply connected in the half bridge, so that the switching output is superposed on the rectifying diodes D ₁ and D ₂ for performing the voltage doubler rectification as described above. Is configured. A resonance capacitor C ₂ is connected in parallel to each of the diodes D ₁ and D ₂ for voltage doubler rectification, and a part of the switching output is bypassed by the capacitors C ₂ and C ₂ .

In this embodiment, parallel capacitors C ₂ , C
The capacitance of ₂ and the resonance frequency (C _N > C ₂ ) of the filter choke coil L _N and the filter capacitor C _N C _N are below the minimum frequency of the switching power supply, and are almost below the resonance frequency of the current resonance circuit of the switching power supply circuit. Is set so that C ₁ <C ₂ with respect to the series resonance capacitor C ₁ of the switching power supply circuit.

FIG. 2 shows current waveforms of the respective parts of the switching power supply. The switching power supply performs a switching operation to rectify the diodes D ₁ and D _2.
Will also be intermittent in the switching cycle. Diodes D ₁ and D ₂ are generated by the positive and negative voltages of the commercial power supply V _AC.
Will alternately charge the smoothing capacitors Ci ₁ and Ci ₂ , but this charging current will be charged by superimposing a switching output of high frequency (100 KHz) as shown by I ₃ and I _4. The conduction angle of the current becomes wide as shown by τ, and the average current becomes close to the voltage waveform V _AC of the commercial power supply as shown by I _AC . for that reason,
The power factor of this double voltage type switching power supply is improved. In addition, the smoothing capacitors Ci ₁ and Ci ₂
The current flowing through the switch has a switching output superimposed on it, as indicated by I ₇ and I ₈ .

Since one of the rectifying diodes is on during the conduction angle τ of the rectifying diode, the operating waveform becomes almost the same as that of the half-bridge type switching power supply operating at the double voltage rectified voltage, and the filter capacitor C Almost no switching current flows through _N and the resonance capacitor C ₂ during this period. In addition, the rectifying diode D
_{In the} rest period in which ₁ and D ₂ are off, a switching current flows through the capacitors C ₂ and C ₂ , and this current is I ₅ ,
It is indicated by I ₆ . Further, in this idle period, the filter choke coil L _N and the filter capacitor C
_A small amount of switching current flows into _N , but this current is not output as noise to the outside.

The present embodiment prevents the switching output fed back from leaking to the commercial power source side by moving the filter choke coil L _N to the terminal side of the smoothing capacitor as compared with the embodiment shown in FIG. It also serves as a low-pass filter. Therefore, the power supply efficiency is improved as compared with that of FIG. Further, since the switching frequency is controlled to increase when the load of the switching power supply becomes lighter, the switching output fed back at this time works so as to bypass the rectifying diodes D ₁ and D ₂ and, as a result, smooths when there is no load. It is possible to suppress an increase in the voltage of the capacitor and improve the power supply fluctuation rate. The power factor becomes higher when the capacitance of the parallel resonance capacitor C ₂ is reduced, but in this case, the inductance value of the filter choke coil must be increased.

FIG. 3 shows the characteristics of the rectified and smoothed voltage Ei with respect to the AC input voltage.
= 0) and the characteristics under heavy load (Po = 230 W) are shown. The black circles ● and the black triangles ▲ are the embodiments of the present invention including the parallel capacitor C ₂ , and the white circles ○ and the white triangles Δ are the characteristics when the capacitor C ₂ is not provided. As is clear from this characteristic, it is understood that the difference between the smooth rectified voltage Ei under heavy load and under no load is reduced by providing the parallel resonant capacitor C ₂ .

FIG. 4 is a diagram showing power source efficiency,
The mark is attached as in FIG. In the case of the present embodiment, it can be seen that the power supply efficiency is improved compared with the case of FIG. 9 in both cases of no load and heavy load. That is, in the present example, the power consumption was 7.5 W in the conventional case when there was no load, but it was reduced to 3.5 W, and the power conversion efficiency was improved from 88.5% to 89.5%. There is. These effects are achieved by eliminating the choke coil to improve power supply efficiency.

FIG. 5 shows another embodiment of the present invention. In this switching power supply, an insulation transformer is constituted by a quadrature type transformer (PRT), and a control circuit is provided in a control winding N _C of the insulation transformer PRT. By applying a control current corresponding to the DC output E ₀ from 1, the resonance frequency of the resonance circuit of the switching power supply is changed. In the case of this embodiment, the switching frequency is the converter transformer CDT (Converter Drive Tran).
sformer) will keep it constant. Further, the parallel capacitor C ₂ is one capacitor C ₂ '(C ₂ ' = 2
It is connected in parallel to the diode D ₂ as C ₂ ). The other parts of this circuit are designated by the same reference numerals as in FIG.

FIG. 6 shows still another embodiment of the present invention, which is a current resonance type switching power supply using a MOSFET as a switching element. Since the electrolytic effect type switching element is driven by voltage and self-excited oscillation becomes difficult, it is preferable to provide the oscillation drive circuit 2 and the starting circuit 3. In this embodiment, the control circuit 1 controls the pulse widths of the switching elements Q ₁ and Q ₂ , and the rectified voltage Ei controls the switching frequency to control the constant voltage of the DC output voltage. The other circuit elements are the same, but the switching element Q
Damper diodes D _D1 and D _D2 are required that conduct in the opposite direction with respect to ₁ and Q ₂ (MOSFET).

[0035]

As described above, in the current resonance type switching power supply circuit of the present invention, the filter choke coil which directly connects the filter capacitor to the commercial power supply input and constitutes the low pass filter in cooperation with this filter capacitor is provided. Since the switching output is superimposed on the rectified current by installing it on the voltage doubler rectifier circuit side, it is necessary to improve the power factor for the voltage doubler rectification type switching power supply with a simple configuration. You can

Further, by loading the resonant capacitor on the rectifying diode, it becomes possible to improve the regulation at the same time with respect to the load fluctuation of the power supply. Further, as a result of being able to reduce the choke coil, there is an effect that cost reduction and further size and weight reduction are realized. Since this choke coil had to be increased in size in accordance with the amount of load power, it is particularly effective for a switching power supply circuit that handles heavy loads.

In the choke coil, power loss occurs due to factors such as the generation of eddy currents. By reducing this, the power conversion efficiency is improved, for example, under heavy load, and the reactive power is remarkably increased during no-load standby. It will be reduced and the power consumption will be greatly saved. Therefore, it also has an effect of suppressing heat generation.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing the operation of the current resonance type switching power supply circuit of the embodiment.

FIG. 3 is a diagram showing a rectified smoothed voltage characteristic with respect to an AC input voltage in the example.

FIG. 4 is a diagram showing an AC input power characteristic with respect to an AC input voltage in an example.

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

FIG. 6 is a circuit diagram showing a current resonance type switching power supply circuit as still another embodiment.

FIG. 7 is a circuit diagram showing a current resonance type switching power supply circuit as a conventional example.

FIG. 8 is a perspective view showing a structure of a filter choke coil and a choke coil.

[Explanation of symbols]

1 Control Circuit 2 Oscillation Drive Circuit 3 Start Circuit L _N Filter Choke Coil C _N Filter Capacitor C ₂ Resonance Capacitor D ₁ Bridge Rectifier Circuit D ₂ Fast Recovery Type Diode CH Choke Coil PIT Insulation Transformer PRT Control Transformer CDT Drive Transformer Q ₁ , Q ₂ Switching element Ci Smoothing capacitor C ₁ , C _1A , C _1B Series resonance capacitor N ₁ Primary winding

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H02M 7/48 Y 9181-5H 7/5387 A 9181-5H

Claims (5)

[Claims] 1. A voltage doubler rectifying means for rectifying a voltage of a commercial power supply, a smoothing means for smoothing an output of the voltage doubler rectifying means, and a half bridge-connected switching means for connecting and disconnecting a voltage output from the smoothing means. And a switching power supply circuit adapted to obtain a DC output from an insulating transformer that supplies a switching current intermittently supplied by the switching means to a primary winding of the insulating transformer and a secondary side of the insulating transformer. In the above, in the input side of the voltage doubler rectification means to which the commercial power is supplied, a filter capacitor for blocking switching noise and a filter choke coil connected in series with the rectifier circuit are provided, and switching interrupted by the switching means is provided. A diode whose current constitutes the voltage doubler rectifying means through the primary winding. A current resonance type switching power supply circuit, characterized in that it is configured to be applied to the current resonance type switching power supply circuit. 2. A parallel resonance capacitor is connected in parallel to the diode for voltage doubler rectification, and the resonance frequency of the filter choke coil and the parallel resonance capacitor is lower than the minimum switching frequency. The current resonance type switching power supply circuit according to claim 1, wherein: 3. A constant voltage control is performed by varying the switching frequency of the switching means based on a DC output voltage obtained on the secondary side of the insulation transformer. The current resonance type switching power supply circuit according to claim 1 or 2. 4. The constant voltage control is performed by changing the magnetic characteristic of the insulating transformer and changing the resonance frequency of the switching power supply based on the DC output voltage obtained on the secondary side of the insulating transformer. The current resonance type switching power supply circuit according to claim 1, wherein the current resonance type switching power supply circuit is provided. 5. The switching means is a separately excited current resonance type converter, and constant voltage control is performed by varying a switching drive signal based on a DC output voltage obtained on the secondary side of the insulation transformer. 3. The current resonance type switching power supply circuit according to claim 1, wherein the current resonance type switching power supply circuit is configured as follows.