JPH08294280A - Current resonance switching power circuit - Google Patents

Abstract

PURPOSE: To promote size, weight and cost reduction in a current resonance switching power circuit and improve its characteristics. CONSTITUTION: This power circuit is provided with a noise removing circuit (common mode chalk coil CMC, across a capacitor CL) for a commercial AC power source AC, and a power factor improving circuit 10 consisting of a small- sized lead inductor LN1 having low inductance serially inserted in an AC line and a parallel resonance capacitor C2A inserted between the AC line and the primary ground. Power factor is improved so that switching output may be superimposed with the AC line through a serial resonant circuit with a serial resonant capacitor C1 and a primary winding N1 to eliminate a filter chalk coil LN which is a formed part of a high-speed recovery diode D2 and an LC low pass filter provided in a rectified output line.

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, by developing a switching element capable of withstanding a relatively large current and voltage of high frequency, most of the power supplies of a switching system are used as a power supply device for rectifying a commercial power supply to obtain a desired DC voltage. It is a device. 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. 9 has been previously proposed by the present applicant. This power supply circuit is a self-excited current resonance type converter using a half bridge.

In the switching power supply circuit shown in this figure, a common mode choke coil CMC and an across capacitor C _L are provided as a noise filter for removing common mode noise from the commercial AC power supply AC. In addition, the inrush current limiting resistor R is provided on the positive electrode side of the AC line that supplies the commercial AC power supply AC to the bridge rectifier circuit D _1.
i is inserted to suppress the inrush current generated when the power is turned on. The commercial AC power supply AC is full-wave rectified by the bridge rectifier circuit D ₁ , and the rectified output is charged in the smoothing capacitor Ci via the power factor correction circuit 20. The configuration and operation of the power factor correction circuit 20 will be described later.

The switching converter of this power supply circuit is provided with _two switching elements Q ₁ and Q _{2 which} are half-bridge coupled as shown in the figure, and is provided with a smoothing capacitor Ci.
Is connected between the connection point on the positive electrode side and the ground on the primary side through respective collectors and emitters. Between each collector and base of the switching elements Q ₁ and Q ₂ ,
Starting resistors R _S and R _S are inserted respectively, and resistors R _B and R _S are inserted.
_B adjusts the base current (drive current) of the switching elements Q ₁ and Q ₂ . In addition, the switching element Q
Damper diodes D _D and D _D are inserted between the base and emitter of ₁ and Q ₂ , respectively. The resonance capacitors C _B and C _B are the drive transformer P described below.
Together with the RT drive windings N _B and N _B , a series resonance circuit for self-excited oscillation is formed.

Drive transformer PRT (Power Regulati
ng Transformer) variably controls the switching frequency 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. control winding N _C is the orthogonal saturable reactor is wound in a direction orthogonal to the windings. _One end of the drive winding N _B on the switching element Q ₁ side of the drive transformer PRT has a resonance capacitor C _B.
To the resistor R _B , and the other end is connected to the emitter of the switching element Q ₁ . Further, one end of the drive winding N _B on the switching element Q ₂ side is grounded to the ground and the other end is connected to the resonance capacitor C _B, and has a polarity opposite to that of the drive winding N _B on the switching element Q ₁ side. The voltage of is output.

Isolation transformer PIT (Power Isolation Tr)
The ansformer transmits 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 the insulating transformer PIT is connected to the emitter of the switching element Q ₁ and the switching element Q via the resonance current detection winding N _D.
The switching output is obtained by connecting to the contact of the collector of ₂ . The other end of the primary winding N ₁ is connected to a contact point of a fast recovery diode D ₂ and a filter choke coil L _N in a power factor correction circuit 20 described later via a series resonance capacitor C ₁ .
The switching output is fed back to the full-wave rectification line. The inductance component of the insulation transformer PIT including the series resonance capacitor C ₁ and the primary winding N ₁ forms a resonance circuit for making the switching power supply circuit a current resonance type. In the case of this switching power supply circuit, the primary winding N is provided on the secondary side of the isolation transformer PIT.
_The induced voltage induced in the secondary winding N ₂ by ₁ is converted into a DC voltage by the bridge rectifier circuit D ₃ and the smoothing capacitor C ₃ to be the output voltage E ₀ .

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

In the switching operation of the switching power supply having the above 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 Q ₁ is turned on _first , the switching element Q ₂ is controlled to be turned off. Then, as the output of the switching element Q ₁ , a resonance current flows through the resonance current detection winding N _D to the primary winding N ₁ and the series resonance capacitor C ₁ , but in the vicinity where the resonance current becomes 0, the switching element Q ₂ Is turned on and the switching element Q ₁ is turned off. And
A resonance current in the opposite direction flows through the switching element Q ₂ . After that, the self-excited switching operation in which the switching elements Q ₁ and Q ₂ are alternately turned on is started. As described above, the switching elements Q ₁ and Q ₂ are alternately opened and closed by using the terminal voltage of the smoothing capacitor Ci as the operating power supply, thereby supplying the drive current close to the resonance current waveform to the primary winding N ₁ of the insulation transformer. , Secondary winding N
_Get the alternating output to ₂ .

Further, when the DC output voltage E _O on the secondary side decreases, the control circuit 1 controls the current flowing through the control winding N _C so that the switching frequency becomes low (close to the resonance frequency). Is controlled to increase the drive current flowing through the primary winding N ₁ to achieve a constant voltage (referred to as a switching frequency control method).

The power factor is improved by the power factor improving circuit 20. The structure of this power factor improving circuit 20, filter capacitor C _N in between the positive output and the negative electrode of the bridge rectifier D ₁ (primary side ground) as shown in the figure is inserted, also, the positive output of the bridge rectifier D ₁ A filter choke coil L _N is connected to one end of the. A normal mode LC low-pass filter is formed by the filter choke coil L _N and the filter capacitor C _N, and high frequency noise of the switching frequency is prevented from flowing into the commercial AC power supply AC. The anode of the fast recovery diode D ₂ is connected to the other end of the filter choke coil L _N , and the cathode thereof is connected to the positive electrode of the smoothing capacitor Ci. That is, the filter choke coil L _N and the fast recovery type diode D ₂ are inserted in series with the full-wave rectification line. This fast recovery type diode D ₂ is provided corresponding to the high frequency current of the switching cycle flowing in the full wave rectification line.

Further, a parallel resonance capacitor C ₂ is connected in parallel to the fast recovery diode D ₂ to form a parallel connection circuit. This parallel resonant capacitor C ₂
Compared to the capacitance of the series resonant capacitor C ₁ ,
It is set so that C ₂ > C ₁ and is connected to the inductance of the filter choke coil L _N to form a resonance circuit. The resonance frequency of this resonance circuit is set to be lower than the minimum switching frequency set for the switching elements Q ₁ and Q ₂ .

The power factor improving operation is as follows.
According to this connection form, the primary winding of the isolation transformer PIT
N₁ And capacitor C₁ Series flowing in series resonant circuit due to
Resonance current I₀ Is a parallel resonant capacitor C₂ Flow through
To be done. In this case, the switch from the series resonant circuit
The holding voltage is the filter choke coil L _N Inductor
The rectified voltage flowing through the
As a result, the switching voltage is superimposed on the full-wave rectified voltage.
In this condition, the smoothing capacitor Ci is charged and
The smoothing capacitor Ci of the smoothing capacitor Ci
The terminal voltage will be lowered in the switching cycle.
Then, the voltage level of the bridge
The charging current flows while the terminal voltage of the sensor Ci is decreasing.
The average AC input current is the AC voltage waveform.
The power factor will be improved by approaching.
The common mode choke coil CMC and ACROSCO
Indexer C_L A noise filter consisting of
Coil L_N And filter capacitor C_N Consisting of
Due to the operation of the low-pass filter in
The high frequency component of the switching cycle flows into the AC power supply AC.
There will be no.

For example, specifically, the AC input voltage V _AC = 1
In order to improve the power factor to about 0.80 under the condition of 00V (50Hz) and load power P _O = 120W, the filter capacitor C _N = 1 μF / 200V and the filter choke coil L _N = 220 μH are selected. To be done.

FIG. 10 shows the filter choke coil L _N actually used in the circuit of FIG.
The filter choke coil L _N is constructed by winding a single wire directly around a drum type ferrite core D as shown in this figure without a bobbin, for example, as described above.
To obtain an inductance of 0 μH, 0.4 mmφ
It is made to wind the polyurethane copper wire.

[0017]

In view 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. It is preferable that the cost reduction and the cost reduction are achieved, and the characteristics such as power efficiency are also improved. For example, in the case of the switching power supply circuit shown in FIG. 9, the filter choke coil L _{N of the} open magnetic circuit forming the normal mode LC low pass filter in the power factor correction circuit 20 and the filter capacitor of relatively large capacity (1 μF) ) Is a medium size, which increases the size of the board and increases the cost. Further, since the high frequency current of the switching cycle is constantly flowing through the open magnetic circuit type filter choke coil L _N (see FIG. 10), if the high frequency leakage magnetic flux is coupled to the common mode choke coil CMC, the commercial alternating current is increased. High frequency leaks to the power source and the power disturbance level deteriorates. For this reason,
On the mounting board, it is necessary to mount the filter choke coil L _N and the common mode choke coil CMC at a distance from each other, which is also a factor that hinders reduction of the board size.

Further, the fast recovery type diode D ₂ provided in the rectified output line causes a power loss corresponding to the amount of forward voltage drop, and further, the switching output supplied to the primary winding N ₁ of the insulating transformer PIT is supplied. Since the power factor is improved by feeding back, the ripple component of the DC output voltage increases more than before the power factor improvement.

[0019]

In view of the above-mentioned problems, the present invention provides a current resonance type switching power supply circuit with a noise removing circuit for removing a noise component flowing into a commercial power supply line. , A parallel resonant capacitor that is inserted between the AC line that supplies commercial power to the rectifier circuit and the primary side ground, a low-inductance inductor that is inserted in series with the AC line, and a switching output that is superimposed on the AC line. And a switching output superimposing unit.

[0020]

According to the above construction, in the current resonance type switching power supply circuit, the noise eliminating circuit is provided in the AC line, and the parallel resonance capacitor inserted between the AC line and the primary side ground and the AC line are connected in series. Is equipped with a low-inductance inductor, the switching output is superimposed on the rectified output line to improve the power factor.In this case, a high-speed recovery type diode inserted in the rectified output line and It is possible to omit the filter capacitor that formed the LC low pass filter together with the filter choke coil. Further, since the open magnetic circuit type choke coil is changed to a low-inductance lead inductor, the coupling degree of the high frequency leakage magnetic flux to the common mode choke coil is significantly reduced.

[0021]

FIG. 1 shows an embodiment of a switching power supply circuit according to the present invention. In this case, since it is a self-exciting current resonance type converter by half bridge coupling, it is the same as FIG. The parts are denoted by the same reference numerals and the description of the switching operation and the constant voltage control is omitted. The power factor correction circuit 10 in the switching power supply circuit of this embodiment is formed by two parts of a lead inductor L _N1 and a parallel resonance capacitor C _2A as shown in the figure. The lead inductor L _N1 is inserted in series with the AC line which is the input line to the bridge rectifier circuit D _{1. In} this case, as shown in the figure, the positive side of the AC line, that is, the rush. It is provided in series between the current limiting resistor Ri and the positive side input terminal of the bridge rectifier circuit D ₁ . As the parallel resonance capacitor C _2A , for example, a film capacitor is used, and the bridge rectifier circuit D
It is inserted between the input terminal _of the positive electrode side and the primary side ground.
The primary winding N of the insulation transformer in this embodiment is
_The series resonance circuit composed of ₁ and the capacitor C ₁ is connected to the input terminal on the positive side of the bridge rectification circuit D ₁ , and therefore, in the path through which the rectification current flows via the capacitive coupling of the series resonance capacitor C _1. On the other hand, the switching output is fed back. It is assumed here that the bridge rectifier circuit D ₁ is formed of a normal low speed recovery type diode.

By the way, the lead inductor L of this embodiment
_N1 corresponds to the filter choke coil L _N in the power factor correction circuit 20 shown in FIG. 9 having a low inductance, and for example, the filter choke coil L _N is 200 μm.
While it is set to H, the lead inductor L _N1 of the present embodiment has a low inductance value of 15 μH. As its structure, for example, as shown in the perspective view of FIG. 8, it is formed by inserting a lead wire Rd bent into a small cylindrical core Cr made of ferrite beads according to a required inductance. Is
The size is the filter choke coil L shown in FIG.
Smaller than _N.

FIG. 2 is a waveform diagram showing the operation of each part of the switching power supply circuit configured as described above by the commercial power supply cycle. For example, when the AC input voltage V _AC is supplied as shown in FIG. 2A, the series resonance current I _O flowing through the series resonance circuit has a high-frequency waveform with the switching cycle shown in FIG. 2E. And is fed back to the rectified current path side. AC line voltage (positive input terminal and between the primary side earth potential of the bridge rectifier D ₁₎ at this time has a waveform shown in FIG. 2 (b). In this waveform, the τ period (the absolute value of the AC input voltage is equal to the voltage Ei across the smoothing capacitor Ci).
High frequency voltage component is superposed as shown in the figure in the beginning and the end of the τ period, except for the period which is considered to be higher than the period), and each low speed recovery type diode element forming the bridge rectifier circuit D ₁ has this high frequency. A switching operation of conducting / non-conducting is performed corresponding to the voltage component. Then, as shown in FIG. 2C, the AC line current I ₁ flowing through the lead inductor L _N1 to the positive input terminal of the bridge rectifier circuit D _{1 in} the AC line is a period other than the τ period and the beginning of the τ period. A high-frequency current due to the switching cycle flows in the end period and the other end period, and the switching operation of the diode of the bridge rectifier circuit D ₁ is stopped to be in the conductive state in the other period, and the waveform flows into the smoothing capacitor Ci side.

According to such a current waveform, a high frequency component of the switching cycle is superimposed on the AC line, and this high frequency component flows through the across capacitor C _L and is suppressed by the common mode choke coil CMC. Therefore, the AC input current I flowing through the AC power supply AC
_AC (Fig. 2 (g)) does not include high frequency components. That is, provided in order to suppress the noise filter according to a common mode choke coil CMC and across capacitors C _L to be mounted to a normal switching power supply circuit in the circuit of FIG. 9, the high frequency components of the switching period that is fed back to the primarily rectified line LC Although the power supply interference is suppressed by both the low-pass filters, it is actually excessive as a noise countermeasure, and the AC line is connected to the AC line only by the noise filter by the common mode choke coil CMC and the across capacitor C _L as in this embodiment. It is possible to suppress even the high frequency component of the switching cycle that flows in, and it is possible to sufficiently cope with power supply interference.

Further, the inductance in the capacitance and the lead inductor L _N1 parallel resonant capacitor C _2A is a period beginning and end of τ period, since the parallel resonance of a relatively small level occurs, it flows through the lead inductor L _N1 The AC line current I ₁ (a waveform having a substantially protruding shape is obtained at the beginning and the end of the τ period in FIG. _2C, and the high frequency current I ₂ flowing through the series resonance capacitor C _2A is shown in FIG.
The waveform is as shown in (d). The charging / discharging current I ₃ due to the high frequency flowing in the smoothing capacitor Ci is shown in FIG.
As shown in (f), a waveform having a substantially convex shape on the plus side is obtained in the τ period. Corresponding to this, as shown in FIG. 2 (g), the _AC input current I _AC has a waveform such that the current flows in a substantially convex shape during the τ period, whereby the average of the AC input current is the AC input voltage waveform. As a result, the conduction angle is actually increased to such an extent that the power factor is improved. Since such an operation waveform is obtained, the AC input current is not
Since the level of the 15th harmonic wave current becomes high, for example, in practice, the power supply harmonic current regulation value classes A, B, C
A switching power supply circuit that clears the regulation value of
This is suitable and suitable for power supply circuits such as lighting equipment.

For example, specifically, in the switching power supply circuit of this embodiment shown in FIG. 1, an AC input voltage V _AC = 10
Under the conditions of 0 V (50 Hz) and load power P _O = 120 W, in order to improve the power factor to about 0.80, the series resonance capacitor C ₁ = 0.018 μF is set, and the power factor correction circuit 10 is connected in parallel. Resonant capacitor C _2A = 0.1μF
/ 200V, and the lead inductor L _N1 is selected so that L _N1 = 15 μH as described above.

Here, comparing the power factor correction circuit 10 of this embodiment with the power factor correction circuit 20 shown in FIG. 9 as a preceding example, the power factor correction circuit 20 shown in FIG. Whereas the power factor correction circuit 10 of this embodiment is composed of parts, it is composed of two parts from which the fast recovery diode D ₂ and the filter capacitor C _N are removed. In this case, since the fast recovery diode D ₂ is omitted, the power loss corresponding to the forward voltage drop is eliminated, and the power conversion efficiency of the power supply circuit is improved accordingly. Further, in the power factor correction circuit 20 of FIG. 9, the filter choke coil L _N has the structure as described with reference to FIG. 10 in order to obtain the inductance of 220 μH. L _N is a small lead inductor L _N1 as shown in FIG. 8, which replaces a smaller, lighter and cheaper one. Further, the lead inductor L _N1 of the present embodiment is an open magnetic circuit type but has a low inductance (15 μH) as described above. Therefore, the lead inductor L _N1 and the common mode choke coil CMC are used.
Even if they are laid out relatively adjacent to each other, the problem of coupling of high frequency leakage magnetic flux is solved, the degree of freedom of the mounting position on the substrate is increased, and the size of the substrate can be reduced accordingly.
As described above, the switching power supply circuit of the present embodiment is greatly promoted in size reduction, weight reduction, and cost reduction as compared with the switching power supply circuit shown in FIG. 9, and is also improved in characteristics such as power conversion efficiency. Becomes

By the way, in the switching power supply circuit of the present embodiment shown in FIG. 1 described above, the bridge rectifier circuit D ₁ is formed by four diodes of the normal low speed recovery type. This is because the high-frequency current level that is supposed to flow in the bridge rectifier circuit D ₁ is low, and therefore it is not necessary to deal with the high-speed recovery type diode in particular, and the cost can be reduced accordingly, and the AC input in this case is also possible. The power characteristics are almost the same as those of the circuit of FIG. Further, in this embodiment, the bridge rectifier circuit D ₁ can be formed by the fast recovery type diodes DF _{1 to} DF ₄ as shown in () of FIG. The power loss is reduced and the AC input power characteristic is 1
It will be improved by about W.

Next, the circuit diagram of FIG. 3 shows the structure of a switching power supply circuit according to another embodiment of the present invention. The same parts as those in FIG. Compared with the power factor correction circuit 10 shown in the embodiment of FIG. 1, the power factor correction circuit 10A of this embodiment has a lead inductor L _N1 on the AC line on the negative input side of the bridge rectifier circuit D _1. Has been inserted against. With such a connection form of the present embodiment as well, the power factor is improved by the same action as in the previous embodiment, and the lead inductor L _N1 may also have the same structure as described in FIG. Therefore, similarly to the previous embodiment, it is possible to reduce the size and weight of the power supply circuit, reduce the cost, and improve the power conversion efficiency. Further, by forming the bridge rectifier circuit D ₁ with the fast recovery type diodes DF _{1 to} DF ₄ , it is possible to further reduce the power loss.

In this case, a drive transformer CDT (Converter Dr) that causes the switching elements Q ₁ and Q ₂ to self-oscillate.
ive Transformer) has no control winding N _C ,
Therefore, the switching frequency is fixed. And insulation transformer PRT (Power Regulating Transform)
er) is an orthogonal type in which the control winding N _C is provided orthogonal to the primary and secondary windings N ₁ and N ₂ , and the control circuit 1 controls the control winding N _C based on the DC output voltage E _{O. A} so-called series resonance frequency control method is adopted in which the control current I _C flowing through _C is varied to control the leakage flux of the insulating transformer PRT and the resonance current flowing through the series resonance circuit is changed to perform constant voltage control.

Next, the circuit diagram of FIG. 4 shows the configuration of a switching power supply circuit of still another embodiment. The same parts as those of FIGS. 1 and 2 are designated by the same reference numerals and the description thereof will be omitted. The current resonant converter in the embodiment of FIG was used in the switching element Q _11, Q ₁₂ and MOS-FET for example, it is separately excited by the half-bridge connection. In this case, the control circuit 1 controls the oscillation drive circuit 2 based on the DC output voltage E _O , and changes the switching drive voltage supplied from the oscillation drive circuit 2 to the gates of the switching elements Q ₁₁ and Q ₁₂ ( For example, the constant voltage control is performed by performing the pulse width variable control of the drive voltage. In addition, D _CL and D _CL connected between the drain and the source of each switching element Q ₁₁ and Q _{12 in} the direction shown in the figure are the paths of the current fed back when the switching elements Q ₁₁ and Q ₁₂ are off. It is a damper diode to be formed. Further, the starting circuit 3 is provided to detect the voltage or current obtained in the rectifying and smoothing line at the time of starting the power source to start the oscillation drive circuit 2, and the starting circuit 3 is provided to the insulating transformer PIT. Tertiary winding N ₃ and rectifier diode D
_The low voltage DC voltage supplied by ₄ is supplied. Since the field effect type switching element used in this embodiment 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 as shown in this figure.

The configuration of the power factor correction circuit 10 in this embodiment is similar to that shown in FIG.
As described above, the power factor is improved. Therefore, for example, even in the configuration of the separately-excited switching converter as shown in this figure, compared with the case where the power factor is improved by the power factor improving circuit 20 as shown in FIG.
The size / weight of the power supply circuit can be reduced, the cost can be reduced, and the power conversion efficiency can be improved. Also, when the four diodes forming the bridge rectifier circuit D ₁ are each fast recovery type diodes (DF _{1 to} DF ₄ ), the AC input voltage, the power conversion efficiency characteristics, etc. are determined in the same manner as in the previous embodiment. Improvement is achieved.

FIG. 5 is a circuit diagram showing the structure of a switching power supply circuit as still another embodiment. In this case, a self-exciting switching converter with a half bridge connection is used, and a switching frequency control is used as a constant voltage control method. Since this is a system, the same parts as those in FIG.

In this case, the configuration of the power factor correction circuit 10 is similar to the configuration described above with reference to FIG. 1, but in this embodiment, the primary winding N ₁ of the insulation transformer PIT and the series resonance capacitor C _{1 are used.} The series resonant circuit that is formed has a primary winding N ₁
Side end is grounded to primary side ground. In this power supply circuit, a series resonance / coupling capacitor C _1A and a choke coil CH are connected in series.

In the case of this embodiment, the capacitance of the series resonance / coupling capacitor C _1A and the self-inductance Ls of the choke coil CH cause a second series resonance circuit (in this case, the primary winding N ₁ and the series resonance capacitor). The series resonance circuit composed of C _{1 is used} as the first series resonance circuit
This is different from the series resonance circuit of
As for the resonance frequency f _{O (A)} of the series resonance circuit, if the resonance frequency of the first series resonance circuit is f _O , then the self-inductance Ls is such that the relationship of f _{O (A)} <f _O is obtained.
And the capacitance of the series resonance / coupling capacitor C _1A is selected.

In this second series resonance circuit, the end on the side of the series resonance / coupling capacitor C _1A is a bridge rectification circuit D ₁
Is the connection between the positive output, the ends of the choke coil CH side of the emitter switching elements Q _1, Q ₂ - is connected to the connection point of the collector.

That is, in each of the embodiments shown in FIGS. 1, 3 and 4, the first series resonant circuit (primary winding N ₁ , series resonant capacitor C ₁ ) is the positive electrode of the bridge rectifier circuit D ₁ . While the switching output is fed back to the AC line by being connected to the input terminal, in the present embodiment, the choke coil CH is connected from the emitter-collector connection point of the switching elements Q ₁ and Q ₂ . The supplied switching output is fed back to the AC line through the capacitive coupling of the series resonance / coupling capacitor C _1A , and the power factor improving circuit 10 acts to improve the power factor.

As a characteristic of this case, in comparison with the feedback method of the switching output shown in each of the previous embodiments, in the present embodiment, the second series resonance circuit is provided so that the first series resonance circuit side is superposed. Since the ripple voltage component in the commercial power supply cycle is reduced, the ripple component appearing in the secondary side DC output voltage E _O can be reduced. In addition, the lower limit of the regulation range can be expanded to the same level as before power factor improvement. It should be noted that in this embodiment as well, FIG.
As described above, if the bridge rectifier circuit D ₁ is formed of a high-speed recovery type diode, the AC input power characteristic can be improved.

FIG. 6 is a circuit diagram showing the configuration of a switching power supply circuit according to still another embodiment. As shown in the figure, a self-excited switching converter with a half bridge connection is used, and a switching frequency control is used as a constant voltage control method. Since this is a system, the same parts as those in FIG.

The power factor correction circuit 10B in this embodiment is different from the structure of the power factor correction circuit 10 shown in the embodiments of FIGS. 1, 4 and 5 in that it is composed of a film capacitor and has a DC output. A ripple suppression capacitor C _N1 for suppressing the ripple component of the voltage E _O is inserted in parallel with the AC line. That is, in this case, it is inserted between the positive / negative input terminals of the bridge rectifier circuit D ₁ . In this case, for example, in order to improve the power factor to about 0.8, the ripple suppression capacitor C _N1 = 0.1 μF and the parallel resonance capacitor C _2A = 0.047 μF are selected.

FIG. 7 is a waveform diagram showing the operation of each part of the switching power supply circuit configured as described above in a commercial power supply cycle. For example, when the AC input voltage V _AC is supplied as shown in FIG. 7A, the AC line current I ₁₁ flowing from the lead inductor L _N1 to the positive input terminal of the bridge rectifier circuit D _{1 in} the AC line is a ripple. Due to the addition of the suppression capacitor C _N1 , the AC line current I ₁ (see FIG. 2C) in the case of the circuit of FIG. 1 is slightly different, and as shown in FIG. There is no conduction during the period, current flows in the switching period as shown in the figure at the beginning and end of the τ period, and the bridge rectifier circuit D is provided at periods other than the beginning and end of the τ period.
The switching operation of the diode _{No. 1} is stopped and the diode becomes conductive, so that a waveform flows into the smoothing capacitor Ci side.
The AC line voltage at this time (bridge rectifier circuit D
₁ the positive input terminal and between the primary-side ground potential), Figure 7
As shown in (e), the waveform has a high-frequency voltage component superimposed in a period other than the τ period. Further, the current I ₁₂ flowing through the series resonance capacitor C _2A has a waveform as shown in FIG. 7D, and the high frequency current flowing with the waveform as shown in the figure during the period other than the τ period and the beginning and end of the τ period. Next to
On the other hand, the high frequency current I ₁₄ flowing in parallel to the AC line via the ripple suppression capacitor C _N1 has a waveform that is substantially H-shaped during the τ period as shown in FIG. 7C. Further, as shown in FIG. 7 (f), the charging / discharging current I ₁₃ due to the high frequency flowing in the smoothing capacitor Ci has a waveform which is substantially convex on the plus side in the τ period.

At this time, as shown in FIG. 7 (g), the AC input current I _AC has a waveform such that the current flows in a substantially convex shape in the period τ, and the conduction angle is expanded as an average waveform to increase the force. The rate will be improved. Also in this case, as compared with the power factor correction circuit 20 shown in FIG. 9 as the prior art, the power factor correction circuit 10B of the present embodiment is formed of three parts in which the fast recovery type diode D ₂ is omitted. Therefore, the power conversion efficiency is improved accordingly.

The DC output voltage E_O Ripple voltage
Component ΔE_O Is shown in the waveform by the straight line in Fig. 7 (h).
However, for example, the ripple suppression condensate
SA C _N1You can see by comparing with the waveform when there is no
As shown, the ripple voltage is greatly suppressed, and
Is suppressed to about 1/3 as a voltage level
For example, the level is almost the same as the circuit before power factor improvement.
It

In this embodiment as well, the bridge rectifier circuit D ₁ is replaced by a fast recovery type diode (DF _{1 to} DF).
When it is formed by ₄ ), the AC input voltage, power conversion efficiency, etc. can be improved as in the previous embodiments.

Further, the power factor improving method of the present invention described so far in each of the above embodiments is the self-excited oscillation type / other-excited oscillation type as the current resonance type switching power supply circuit, the switching frequency control method (the drive transformer is Orthogonal P
RT (Power Regulating Transformer) / series resonance frequency control method (isolation transformer is orthogonal type PRT), switching element half bridge coupling type / full bridge coupling type, etc. It is needless to say that the present invention can be applied to the power supply circuit described above and is not limited to the combination pattern shown as the embodiment in each of the above drawings.

[0046]

As described above, according to the present invention, in various types of current resonance type switching power supply circuits, a circuit for removing noise (common mode choke coil, across capacitor) is provided for a commercial AC power supply. With a small, low-inductance lead inductor inserted in series with the AC line and a parallel resonant capacitor inserted between the AC line and the primary side ground, the switching output is superimposed on the AC line via the series resonant circuit. It is possible to improve the power factor. As a result, the high-speed recovery type diode inserted in series in the rectified output line and the filter capacitor, which was a component of the LC low-pass filter in the rectified output stage, are omitted, and the number of components is reduced, and the inductor is also downsized. Therefore, it is possible to further reduce the cost, reduce the size and weight, and improve the characteristics such as the power conversion efficiency. Further, at this time, since the inductor has a low inductance, the problem of coupling the high frequency leakage magnetic flux with the common mode choke coil is solved, and the degree of freedom in layout on the substrate is improved, which is advantageous for further miniaturization. .

Further, in the above power factor improving configuration, the switching output is fed back to the AC line via the series resonance circuit including the choke coil and the series resonance / coupling capacitor, or between the two poles of the AC line. By inserting the ripple suppression capacitor, it is possible to suppress the ripple component of the DC output voltage.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing the operation of the switching power supply circuit in the example.

FIG. 3 is a circuit diagram showing a switching power supply circuit as another embodiment.

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

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

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

7 is a waveform chart showing the operation of the switching power supply circuit in the embodiment of FIG.

FIG. 8 is a perspective view showing the structure of the lead inductor in the example.

FIG. 9 is a circuit diagram showing a switching power supply circuit as a prior art.

FIG. 10 is a perspective view showing the structure of a filter choke coil.

[Explanation of symbols]

1 Control circuit 2 Oscillation drive circuit 3 Start-up circuit 10, 10A, 10B Power factor correction circuit L _N1 Lead inductor C _N1 Ripple suppression capacitor D ₁ Bridge rectifier circuit DF _{1 to} DF ₄ Fast recovery type diode CH Choke coil PIT (PRT) insulation Transformer CDT (PRT) Drive transformer Q ₁ , Q ₂ , Q ₁₁ , Q ₁₂ Switching element Ci Smoothing capacitor C ₁ Series resonance capacitor C _1A Series resonance / coupling capacitor N ₁ Primary winding

Claims (10)

[Claims] 1. A noise removing means for removing a noise component flowing into a commercial power supply line, a rectifying means for rectifying a commercial power supply, a smoothing means for smoothing an output of the rectifying means, and a voltage output from the smoothing means. A switching means for connecting and disconnecting, a series resonance circuit formed by a primary winding of an insulation transformer and a series resonance capacitor, to which the switching output of the switching means is supplied, and an AC line for supplying commercial AC power to the rectification means. And a parallel resonance capacitor inserted between the primary side ground and a low-inductance inductor that is inserted in series in the AC line, and a switching output superimposing unit that superimposes the switching output on the AC line. A current resonance type switching power supply circuit characterized in that it is provided with. 2. The current according to claim 1, wherein the switching output superimposing means is configured such that a primary winding of the series resonance circuit is connected to the AC line through a series resonance capacitor. Resonant switching power supply circuit. 3. The switching output superimposing means forms a choke coil connected to the output of the switching means, and another series resonance circuit together with the choke coil, and suppresses the switching output supplied to the choke coil. The current resonance type switching power supply circuit according to claim 1, further comprising: a coupling capacitor provided so as to be supplied to the AC line by capacitive coupling. 4. A ripple suppression capacitor inserted to suppress a ripple component of a DC output voltage between both poles of the AC line, wherein the ripple suppression capacitor is inserted. The current resonance type switching power supply circuit described in. 5. The current resonance type switching power supply circuit according to claim 1, wherein the rectifying means is formed by a low speed recovery type rectifying element. 6. The current resonance type switching power supply circuit according to claim 1, wherein the rectifying means is formed by a high-speed recovery type rectifying element. 7. The current resonance type switching power supply circuit according to claim 1, wherein the inductor is formed by inserting a lead wire into a bead type core. . 8. The constant voltage control is performed by changing 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 any one of claims 1 to 7. 9. The constant voltage control is performed by changing the magnetic flux of the insulation transformer based on a DC output voltage obtained on the secondary side of the insulation transformer. A current resonance type switching power supply circuit according to claim 7. 10. The switching means is a separately excited current resonance type converter, and constant voltage control is performed by changing a switching drive signal based on a DC output voltage obtained on the secondary side of the insulation transformer. It is comprised in Claim 1 thru / or Claim 7 characterized by the above-mentioned.
The current resonance type switching power supply circuit according to any one of 1.