JPH10112976A - Power factor improving converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To curtail the number of parts and to reduce the cost by providing a self-excited voltage-resonance type converter circuit composed by providing a switching element, as a switching converter. SOLUTION: In a power factor improving converter section 10, a self-excited voltage-resonance type converter by a high-withstand-voltage switching semiconductor element Q10 is provided. The base of the switching element Q10 is connected to the positive polarity side of a smoothing capacitor C1 through an activating resistor Rs , and the base current in activating is obtained from a rectified and smoothed voltage Ei . Besides, a resonance circuit for self oscillation comprising a resonance capacitor CB and a driving winding NB, and a base current limiting resistor RB are connected in series between the base of the switching element Q10 and the ground. In a resonance circuit, a switching output is fed back to a rectified current route through an electrostatic capacity coupling of its resonance capacitor Cr .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a power factor improving converter circuit configured as a switching power supply circuit capable of improving a power factor.

[0002]

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

In general, when a commercial power supply is rectified, the current flowing through the smoothing circuit has a distorted waveform, which causes a problem that the power factor indicating the efficiency of use of the power supply is impaired. Further, there is a need for a measure for suppressing harmonics generated due to the distorted current waveform.

Therefore, as a power factor improving means for improving a power factor in a switching power supply circuit, there is known a method of providing a PWM control type boost converter in a rectifying circuit system and providing a so-called active filter for bringing the power factor close to one. ing. However, such an active filter has many factors that lead to an increase in circuit scale and a high cost due to an increase in the number and size of components for high EMI measures. It is disadvantageous from the viewpoint of realization. It is also known that power loss in an active filter is relatively large.

[0005] Therefore, the applicant has previously switched the rectified output using a self-excited current resonance type converter,
There have been proposed various power factor improving converter circuits configured to increase the conduction angle of the AC input current to thereby improve the power factor. In a power factor improving converter circuit using such a current resonance type converter, the switching operation of the converter circuit is of a resonance type, thereby realizing lower noise and a smaller circuit size compared to an active filter. Accordingly, it is possible to reduce the cost. In addition, power loss is greatly reduced, and power conversion efficiency is improved.

FIG. 7 is a circuit diagram showing an example of a power supply circuit having a power factor improving converter circuit as a switching power supply circuit which can be constructed based on the invention previously filed by the present applicant. In the power supply circuit shown in this figure, a common mode choke coil CMC and an across capacitor _CL are provided as a noise filter for removing common mode noise from the commercial AC power supply AC. AC voltage AC is full-wave rectified by a bridge rectifier D _1. In this case, the rectified output line of the bridge rectifier circuit D _1, a smoothing capacitor Ci is smooth circuit
A power factor improving converter section 20 is provided for the space therebetween, and improves the power factor as described later.

The switching power supply 1 performs a switching operation by inputting a rectified and smoothed voltage Ei obtained between both ends of a smoothing capacitor Ci, and performs DC output voltages E ₁ and E from a secondary side.
_In this case, for example, a switching converter for performing constant voltage control by a PWM method is provided.

In the power factor improving converter section 20 shown in FIG. ₁ , first, a line (rectified output line) between the positive output terminal of the bridge rectifier circuit D1 and the positive terminal of the smoothing capacitor Ci is applied to the filter choke coil L. _N - high speed recovery type diode D ₂ are connected in series. Here, the high speed recovery type diode D ₂ is inserted by the direction in which the anode is a bridge rectifier circuit D ₁ side.
In this case, the connection point of the positive output terminal and said filter choke coil L _N of the bridge rectifier circuit D _1, a filter capacitor C _N is inserted between the positive terminal of the smoothing capacitor Ci, normal mode with filter choke coil L _N Is formed. Further, resonant capacitor C ₂ is connected in parallel for high speed recovery type diode D _2. The resonance capacitor C
The operation of ₂ will be described later.

The power factor improving converter section 20 includes a self-excited current resonance type converter using the rectified smoothed voltage Ei as an operating power supply. As the current resonance type converter, switching elements Q ₁ and Q 2 of two bipolar transistors half-bridge-coupled as shown in the figure are used.
_2, and performs a switching operation using the rectified smoothed voltage Ei as an operation power supply. In this case, the switching element Q ₁
The collector is connected to the positive terminal of the smoothing capacitor Ci, the emitter is connected to the collector of the switching element Q _2. The emitter of the switching element Q ₂ is grounded to the primary side ground. The starting resistors R _S1 and R _S1 are connected between the collectors and the bases of the switching elements Q ₁ and Q ₂ , respectively.
_S2 is inserted, and the base current (drive current) of the switching elements Q ₁ and Q ₂ is adjusted by the resistors R _B1 and R _B2 .
Further, the bases of the switching elements Q _1, Q ₂ - each clamp diode between the emitter D _B1, D _B2 is inserted. Low-speed diodes are used for the clamp diodes _DB1 and _DB2 . The resonance capacitors C _B1 and C _B2 together with the drive windings N _B1 and N _{B2 of} the converter transformer CVT described below form a series resonance circuit for driving the switching element by self-oscillation. Also,
Capacitors C _C1 and C _C2 are connected in parallel between the collectors and the emitters of the switching elements Q ₁ and Q ₂ , respectively, to provide a rising / falling feedback of the switching voltage of the switching elements Q ₁ and Q ₂ forming a square wave. A gradient is given to suppress switching noise.

[0010] Converter transformer CVT (Converter Dr
ive Transformer) is provided to drive the switching elements Q ₁ and Q ₂ . This converter transformer CV
Drive windings N _B1 and N _B2 and a primary winding N ₁ forming a series resonance circuit described later are wound around T. Incidentally, the primary winding N ₁ of this case functions as an inductor for superimposing a switching voltage to the rectifier path as described later. Drive winding N _B1 has one end resistance R _B1 - is connected to the base of switching element Q ₁ via a resonant capacitor C _B1, and the other end is connected to the emitter of the switching element Q _1. One end of the drive winding N _B2 is is grounded to the earth, the other end resistor R _B2 - and is connected to the base of the switching element Q ₂ through the resonant capacitor C _B2, the drive winding N _B1 is A voltage of the opposite polarity is output. One end of the primary winding N ₁ of the converter transformer CVT is connected the collector of the connection point of the switching elements to Q ₁ emitter and the switching element Q ₂ and the (switching output point) and the other end series resonant capacitor C ₁ It is connected to the connection point between the filter choke coil L _N and the high-speed recovery type diode D ₂ through.

According to the above connection configuration, the primary winding N _{1 of} the converter transformer CVT and the series resonance capacitor C ₁ are connected in series, but the inductance component of the primary winding N ₁ and the series resonance capacitor C ₁ are connected. With the capacitance, a series resonance circuit for making this switching converter a current resonance type is formed. A switching output obtained by the switching operation of the switching elements Q ₁ and Q ₂ is supplied to the series resonance circuit, and this switching output is connected to a connection point between the filter choke coil _LN and the high-speed recovery type diode D ₂ . To be applied.

The power factor improving converter section 20 is constructed as described above. The switching operation of the current resonance type converter is as follows. First, when a commercial AC power source is turned on, for example, starting resistors R _S1, although the base to the base current of the switching element Q _1, Q ₂ through R _S2 will be supplied, for example, the switching element Q ₁ is ahead if turned on, the switching element Q ₂ is being controlled to be turned off. And the switching element Q ₁
Output of the primary winding N ₁ → series resonance capacitor C ₁
The resonance current flows through the switching element Q ₂ in the vicinity of the resonance current becomes 0 is turned on, the switching element Q ₁ is controlled so as to be turned off. The reverse resonant current flows from the preceding through the switching element Q _2. Thereafter, a self-excited switching operation in which the switching elements Q ₁ and Q ₂ are turned on alternately is started. As described above, the switching elements Q ₁ and Q ₂ alternately open and close with the terminal voltage of the smoothing capacitor Ci as the operating power supply, thereby supplying a drive current close to the resonance current waveform to the primary winding N ₁ of the converter transformer CVT. I do. Note that the variable control of the switching frequency by the converter transformer CVT will be described later.

The power factor improving operation in the power factor improving converter section 20 is as follows. As described above, when the switching operation of the current resonance type converter is performed, the switching output is output from the converter transformer CV.
It is supplied to the primary winding N ₁ of T. Then, converter alternating voltage of the switching period generated by the switching output supplied to the primary winding N ₁ in transformer CVT, via a capacitive coupling of the series resonance capacitor C _1, the filter choke coil L _N and Fast Recovery It is applied to the connection point of type diode D _2. The filter choke coil L _N and the high-speed recovery type diode D _2, since that is inserted to the positive output line of the bridge rectifier circuit D _1, the switching voltage applied through the series resonant circuit, the rectifier via the rectifying path The switching voltage is superimposed on the output voltage. Then, the superposed portion of the switching voltage, a fast-recovery diode D ₂ in the rectified current is inserted in the rectification path that operates intermittently at the switching period is obtained.
By this operation, the smoothing capacitor Ci is charged in a state where the switching output is superimposed on the rectified output voltage in the power factor correction converter section 20, and the voltage across the smoothing capacitor Ci is switched by the superimposed amount of the switching voltage. It is made to decrease in a cycle. Therefore, the charging current flows to the smoothing capacitor Ci even during the period when the rectified output voltage level is lower than the voltage across the smoothing capacitor (rectified smoothed voltage Ei). As a result, the average waveform of the AC input current is made closer to the waveform of the AC input voltage, and the conduction angle of the AC input current is increased, thereby improving the power factor.

Further, resonant capacitor C ₂ connected in parallel to the high speed recovery type diode D _2, for example a filter choke coil L _N and filter capacitor C
Form a parallel resonance circuit with _N. The resonance impedance of the parallel resonance circuit is changed in response to a load change. When the load of the power supply circuit is reduced, the switching voltage fed back to the rectification path is suppressed. As a result, an increase in the terminal voltage of the smoothing capacitor Ci at a light load is suppressed.

FIG. 8 is a circuit diagram showing another example of a power supply circuit having a power factor improving converter circuit as a switching power supply circuit which can be configured based on the invention previously filed by the present applicant. It is. The same parts as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. In the power factor improving converter section 21 shown in this figure, first, the filter capacitor C _N is inserted between the connection point of the filter choke coil L _N and the high-speed recovery type diode D ₂ and the positive terminal of the smoothing capacitor Ci. However, even in such a connection form, a normal mode low-pass filter is formed together with the filter choke coil _LN .

In the power factor improving converter section 21, a choke coil CH is inserted in series in a rectified current path. In this case, it is inserted between the positive terminal of the high speed recovery type diode D ₂ cathode and a smoothing capacitor Ci. Further, resonant capacitor C ₂ is connected in parallel to the choke coil CH. Furthermore, the primary winding N ₁ is connected to the connection point between the cathode and the choke coil CH of the high speed recovery type diode D ₂ via the series resonance capacitor C _1.

In such a circuit configuration, the switching output obtained in the series resonance circuit is applied so as to be superimposed on the rectified voltage obtained in the self-inductance of the choke coil CH via the magnetic coupling effect of the choke coil CH. You. This makes it the switching voltage is superimposed on the rectified voltage, the superimposed portion of the switching voltage, so that the operation intermittently a rectified current in the switching period by fast-recovery diode D ₂ is obtained. Thereafter, the conduction angle of the AC input current is expanded by the same operation as that described with reference to FIG. 7, and the power factor is improved.

[0018]

By the way, from the viewpoint of miniaturization and cost reduction of the equipment on which the power supply circuit having the above-mentioned configuration is mounted, for example, a power factor improving converter provided in the power supply circuit is also required. It is preferable to reduce the size / weight and cost by reducing the number of parts as much as possible. Further, it is preferable that the reliability as a product is also improved.

For example, in the power factor improving converter units 20 and 21 shown in FIGS. 7 and 8, as a switching converter, a self-excited current resonance type converter in which two switching elements Q ₁ and Q ₂ are half-bridge-coupled. However, in this case, it is necessary to select the switching elements Q ₁ and Q ₂ that have the same characteristics of the storage time t _stg and the current amplification factor h _FE , and these characteristics vary from one another. And each switching element Q
_1, the power loss in the Q ₂ becomes unequal, there is a case where much ensure reliability as a product becomes difficult. Also, as shown in FIGS. 7 and 8, the switching element Q
_1, to configure a drive circuit for driving the Q ₂ are starting resistor (R _S1, R _S2), the resonant circuit (C _B1 -N for self-excited oscillation
_B1, C _B2 -N _B2), a base current limiting resistor (R _B1,
R _B2 ), relatively many peripheral components such as clamp diodes (D _B1 , D _B2 ) and capacitors (C _C1 , C _C2 ) are required. Further, in the power factor improving converter units 20 and 21 having the configurations shown in FIGS. 7 and 8, the switching output is fed back from the rectified current path to the smoothing capacitor Ci so as to regenerate the power. frequency current due to switching frequency flowing through the C ₂ and the choke coil CH is known to flow the entire period of the switching cycle. Therefore, it is necessary to select a low loss products for resonant capacitor C ₂ and the choke coil CH.

[0020]

In view of the above-mentioned problems, the present invention has a single switching element,
A self-excited voltage resonance type switching operation is performed using the rectified smoothed voltage output from the smoothing circuit as an operation power supply, and the switching output is supplied to a resonance circuit formed by a resonance capacitor and an inductance of a resonance winding. A power factor improving converter circuit comprising a self-excited voltage resonance type converter and power factor improving means adapted to improve a power factor based on a switching output fed back to the rectified current path from the resonant circuit. It was decided to.

Further, power factor control means for controlling the power factor to be substantially constant with respect to the level change of the AC input voltage is provided, and the power factor control means is provided in a smoothing capacitor forming a smoothing circuit. A series connection circuit comprising at least a resistor and a control winding provided in parallel to the control winding and a driving winding forming a self-excited oscillation circuit of the self-excited voltage resonance type converter are controlled so that their winding directions are orthogonal to each other. An orthogonal transformer formed by winding a winding is provided.

According to the above configuration, a power factor improving converter circuit can be formed by a self-excited voltage resonance type converter using one switching element and a power factor improving means of a switching output feedback type. Further, if the power factor control means having the above configuration is provided, the power factor can be maintained substantially constant with respect to a change in the AC input voltage, though the configuration is simple.

[0023]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply circuit provided with a power factor improving converter circuit according to an embodiment of the present invention. The same parts as those in FIGS. 7 and 8 are denoted by the same reference numerals, and description thereof will be omitted. In the power factor improvement converter 10 shown in this drawing, a self-excited voltage resonance converter by the switching element Q ₁₀ of high withstand voltage of one stone (e.g. 900V breakdown voltage article is selected) is provided. The base of the switching element Q ₁₀ is connected to the positive electrode side of the smoothing capacitor Ci via a starting resistor R _S, base current during startup is to be obtained from the rectification smoothed voltage Ei. Further, between the base and the ground of the switching element Q ₁₀ resonant circuit of a self-mutabilis that a base current limiting resistor R _B and the resonance capacitor C _B consisting drive winding N _B are connected in series. In this case, drive winding N _B is the converter transformer CVT (Conv
erte Drive Transformer) to obtain the required inductance to set the switching frequency. Also, the clamp diode D _B which is inserted between the primary side ground base and the smoothing capacitor Ci of the switching elements Q _10, the switching element Q ₁₀
To form a path for the damper current flowing when the switch is off. The collector of the switching element Q ₁₀ is connected to one end of the primary winding N ₁ of the converter transformer CVT,
The emitter is grounded to the primary ground.

In this case, the converter transformer CVT
The primary winding N ₁₀ of the parallel resonant capacitor Cr, form a resonance circuit as a voltage resonant converter.
Although the detailed description is omitted here, the switching element Q
During ₁₀ off, by the action of the resonant circuit, the collector-emitter voltage V _CP of the switching element Q ₁₀ is actually become a sinusoidal pulse waveform, so-called "switching is performed when the switching voltage is 0 Zero
Volt Switching, a voltage-resonant type of operation that can be obtained. In this case, the primary winding N ₁₀ is
One end connected to the collector of the switching element Q _10, the other end is connected to the positive terminal of the smoothing capacitor Ci. Also, the resonant capacitor Cr is essentially the collector of the switching element Q ₁₀ - emitter (primary side ground)
But in which it is provided in parallel between, in this case, that are connected so as to insert between the anode side of the collector and the high-speed recovery type diode D ₂ of the switching element Q _10, the resonance capacitor one end of the Cr, the primary winding N ₁₀ - through a series connection of the smoothing capacitor Ci, so that is grounded to the primary side ground. In the present embodiment, the resonance circuit is configured as described above so that the switching output is fed back to the rectified current path via the capacitive coupling of the resonance capacitor Cr. is there.

The power factor improving converter section 10 of the present embodiment
The power factor improving circuit section of the filter choke coil L
_N , a filter capacitor C _N , a fast recovery diode D ₂ , and a resonance capacitor C ₂ ,
Since the connection configuration of these component elements is the same as the connection configuration of the power factor improvement circuit section in the power factor improvement converter circuit 20 shown in FIG. 7, the description of the connection configuration is omitted here. In this case, one end of the resonant capacitor Cr as described above is connected to the anode of the high speed recovery type diode D _2. Thus, switching output of the switching element Q ₁₀ is thus fed back to the rectified current path through the capacitive coupling of the resonant capacitor Cr, the same effect as later explained in FIG. 7, a high speed by intermittent operation of the rectified current in the switching cycle by recovery type diode D ₂ is prompted, it would result in the AC input current I _AC conduction angle is enlarged power factor improvement is achieved.

[0026] As the above-described structure, the power factor improvement converter 10 of the present embodiment, the switching converter is a voltage resonance type self-excited by the switching element Q ₁₀ of the stone, for example, FIGS. 7 and Compared with the self-excited current resonance type switching converter provided in the power factor correction converter units 20 and 21 of FIG. 8, the current resonance type converter has at least two switching elements connected in a half bridge and a self-excited oscillation drive circuit thereof. whereas it is necessary, will be only needs the switching element Q ₁₀ of the stone its self-oscillation driving circuit in this embodiment, it is possible to correspondingly simplified circuit configuration. Also,
In the present embodiment, the number of switching elements forming the voltage resonance type converter is one, so that two switching elements are formed as in the case of the current resonance type converter formed by half-bridge coupling of two switching elements. It is not necessary to consider the balance between the accumulation time t _stg and the characteristics of the current amplification factor h _FE .

FIG. 2 is a waveform diagram showing the operation of the main part of the power supply circuit of the power factor correction converter section shown in FIG. 1 in a switching cycle. In the case of the present embodiment, the switching frequency of the switching element Q10 is, for example, ₁₀₀ KHz.
And so that, the time constant of the series resonant circuit of a self-mutabilis consisting resonance capacitor C _B and the drive winding N _B or the like is selected. For example, the collector of the switching element Q ₁₀ - the ground potential between V _CP, as shown in FIG. 2 (a), sinusoidal appearing only in the period t1~t2 of period t1~t3 the switching element Q ₁₀ is turned off The wave-like pulse waveform indicates that a voltage resonance type operation is obtained. The collector current I _CP of the switching element Q ₁₀ is a state flowing in the positive direction is obtained during the period t3~t4 the switching element is turned on by the waveform shown in FIG. 2 (b). The waveform shown in the period t2~t3 the same FIG. 2 (b), the clamp diode D _B based switching elements Q ₁₀ - corresponding to the damper current flowing through the emitter.

In such a voltage resonance type converter, the charge / discharge current Ir of the resonance capacitor Cr flowing through the high-speed recovery type diode D ₂ or the resonance capacitor C ₂ is switched as shown in FIG. Element Q ₁₀
Only during the periods t1 to t2 in which the is turned off, a high-frequency current flows with a waveform as shown in FIG. That is, in the operation of the voltage resonance type converter, the series resonance current does not flow over the entire switching period as in the current resonance type converters shown in FIGS. It can be considered that it flows only during the period. Thus in this embodiment, for example, it is possible to select a general-purpose product rather than the resonant capacitor C ₂ with a low loss products.

FIG. 3 is a waveform diagram showing the operation of each part of the switching power supply circuit having the configuration shown in FIG. For example, if the ac input voltage V _AC is supplied as shown in FIG. 3 (a), the current I ₁ flowing through the high speed recovery type diode D ₂ in the full-wave rectified line, Figure 3
As shown in (c), in the period τ where the absolute value of the _AC input voltage VAC is higher than the voltage Ei across the smoothing capacitor Ci, the switching of the high-speed recovery type diode D ₂ by the action of the feedback switching output is performed. By performing the operation, a waveform in which the high frequency component of the switching cycle is superimposed is obtained. Further, as shown in FIG. 3D, the voltage V ₂ corresponding to the voltage across the resonance capacitor C ₂ has a high frequency component of the switching cycle superimposed on a voltage having a level corresponding to the full-wave rectified voltage V _1. The resulting waveform is obtained. As shown in FIG. 3B, the AC input current I _AC has a waveform in which the current flows in the period τ, but the conduction angle is actually widened to such an extent that the power factor can be improved. Will be. Incidentally, it is in this embodiment to set the appropriate power factor by variably setting the degree of expansion of the τ time by changing the ratio of the capacitance value of the resonant capacitor Cr and resonant capacitor C ₂ It is possible.

Next, a circuit diagram of FIG. 4 shows a configuration of a switching power supply circuit as another embodiment of the present invention, and the same parts as those in FIGS. Omitted. In the power factor improvement converter 11 shown in this figure, in addition to the primary winding N ₁₀ and the drive winding N _B is the converter transformer CVT, it constituted the superimposing winding N ₂ is wound. At this time, in the converter transformer CVT, at least the primary winding N ₁₀ and the superimposing winding N ₂ is wound so that the magnetic coupling is obtained. The superimposing winding N ₂ is rectified current path is inserted in series with, in this case, is inserted between the positive terminal of the cathode and the smoothing capacitor Ci fast-recovery diode D _2.

The case where the power factor correction circuit as described above, the switching output of the current resonant converter obtained at the primary winding N ₁₀ of the series resonant circuit, superimposing winding via the magnetic coupling of the converter transformer CVT It is transmitted to the line N _2. Since the superimposing winding N ₂ is being inserted in the rectification current path, so that the switching voltage is superimposed on the rectified output voltage across the rectifier path. Then, the superposed portion of the switching voltage, a fast-recovery diode D ₂ in the rectified current is inserted in the rectification path that operates intermittently at the switching period is obtained. By this operation, thereafter, the conduction angle of the AC input current is expanded by the same operation as described with reference to FIG. 8, for example, and the power factor is improved.

In this embodiment, the resonance capacitor C ₂ is provided in parallel with the superposition winding N ₂ , but in such a connection form, the resonance capacitor C _{2 is provided.} to form a parallel resonant circuit together with the primarily superimposing winding N ₂ inductance, thus to suppress an increase in the terminal voltage of the smoothing capacitor Ci at light loads by the same operation as described above with reference to FIG. Further, in the present embodiment, one end of the filter capacitor C _N is connected to the connection point between the filter choke coil L _N and the high-speed recovery type diode D _2. Forming a normal mode low-pass filter together with the filter choke coil _LN is the same as that described with reference to FIG.

FIG. 5 shows a power factor improving converter circuit (power factor improving converter section) as still another embodiment of the present invention.
FIG. 9 is a circuit diagram showing a configuration example of a switching power supply circuit configured to include the same components as those in FIGS. 1, 4, 7, and 8 described above. The description of the resonance-type switching operation and the power factor improvement operation is omitted.

When the switching output is fed back to the rectification path as in the power factor improving converter circuit described above, if the switching frequency is fixed, the input AC input is It has been found that the power factor characteristic decreases as the voltage increases.
Therefore, by varying the switching frequency of the voltage resonance type converter, the power factor can be controlled so as to be substantially constant with respect to the input AC input voltage level.

In the power factor improving converter section 12 shown in this figure, a drive transformer PRT capable of variably controlling a switching frequency is provided. Drive transformer PRT, to the drive winding N _B for driving the switching elements Q _10, the control winding N _C as winding method are orthogonal is wound, as a saturable reactor orthogonal It is configured. And only the primary winding N ₁₀ is wound on the converter transformer CVT contrast. One end of the control winding N _C is connected to the positive terminal of the smoothing capacitor Ci via a resistor R _1, the other end is grounded to the primary side ground. That is, the resistance R ₁ - is provided in parallel to the series connection circuit of control winding N _C smoothing capacitor Ci. Thus, control of the level of the control winding N _C which is variable according to the level of the rectification smoothed voltage Ei current I _C
Will flow.

For example, if the AC input voltage input to the commercial AC power supply of the power supply circuit shown in this figure changes as if it increased, the rectified smoothed voltage Ei also increases. Control is performed so that the level of the control current I _C flowing from Ei to the control winding N _C via the resistor R ₁ is also increased. In the drive transformer PRT, by the level of the control current I _C as described above increases, to reduce the inductance of the drive windings N _B. Thus, lowering the resonant frequency of the self-oscillation driving circuit formed by the resonance capacitor C _B and the driving winding N _B, will be controlled so as to increase the switching frequency of the switching element Q _10. In this case, the resonance circuit (N ₁ , C
The switching frequency changes with respect to the resonance frequency of r), whereby the feedback amount of the switching output supplied to the resonance circuit changes, and in this case, the power factor is controlled to be increased. Will be. This makes it possible to keep the power factor substantially constant with respect to AC input voltage, load fluctuation, and the like.

In the AC 100 V system, a zener diode is inserted in series between the resistor R ₁ and the control winding N _C in consideration of that a sufficient power factor can be obtained without performing power factor stabilization control. Thus, it is conceivable that the Zener diode is configured not to conduct at the rectified smoothed voltage level corresponding to the AC 100 V system. With this, AC100V
In the system, the power factor control circuit does not operate, and the power loss can be reduced accordingly. In addition, as described above, as the power factor control circuit for maintaining the power factor substantially constant, an amplifier circuit formed with an amplifying element such as a transistor is provided, and this amplifier circuit responds to a level change of the rectified smoothed voltage Ei. A configuration is conceivable in which a control current I _C is obtained, and a power factor control circuit having such an amplifier circuit has a higher control ability to stabilize the power factor, but a resistor R ₁ as shown in FIG. - even power factor control circuit according to the series connection circuit of the control winding N _C, in particular with practically sufficient power factor characteristics are obtained under the condition at the time of the alternating input voltage AC100V system, reduce the number of components and manufacturing processes In terms of simplification and the like, it is possible to configure a much more advantageous power factor improving converter circuit (power factor improving converter section).

FIG. 6 is a circuit diagram showing a configuration example of a switching power supply circuit including a power factor improving converter circuit as still another embodiment of the present invention. The switching power supply circuit shown in the figure has a current resonance type switching power supply unit 1A employing a current resonance type converter as a switching power supply unit with respect to the subsequent stage of the power factor correction converter unit 13.
Is provided. The same components as those in FIGS. 1, 4, and 5 are denoted by the same reference numerals as the configuration of the voltage resonance type converter and the power factor improving circuit in the power factor improving converter 13, and description thereof will be omitted. Further, since the current resonance type switching power supply unit 1A employs a self-excited converter in which bipolar switching elements are half-bridge coupled, the same components as those of the current resonance type converter shown in FIGS. 7 and 8 are the same. The description of the switching operation and the like is omitted with the reference numerals.

Here, the configuration of the current resonance type switching power supply section 1A will be described first. In this case, in the current resonance type switching power supply unit 1A, the switching element Q
_1, Q ₂ drive transformer PRT to switching drive the is configured to variably control the switching frequency for the constant voltage control to be described later. The drive transformer PRT is wound with drive windings N _B1 and N _B2 and a resonance current detection winding N _D, and a control winding N _C is also used so that the winding directions are orthogonal to these windings. Has been played. Therefore, in the present embodiment, the drive transformer PRT is configured as an orthogonal type saturable reactor. The current resonance type switching power supply unit 1
A series resonance circuit for making A a current resonance type includes a series connection of a primary winding N ₁ and a series resonance capacitor C _1. One end of the primary winding N ₁ is connected to a series resonance capacitor C 1.
₁ - are connected to the switching output point through a series connection of a resonance current detection winding N _D. The other end of the primary winding N ₁ is grounded to the primary side ground. In the case where the current resonance type converter is a switching power supply unit, the primary winding N ₁ is wound on the primary side of the insulating transformer PIT as in FIG.

Further, the connection point of the switching elements Q corresponding drive winding ₂ N _B2 and base current limiting resistor R _B2, resonant capacitor C _B - base of the switching element Q ₁₀ via the base current limiting resistor R _B Is connected. Thus, in this embodiment, the drive drive winding N _B2 of transformer PRT is, a switching element Q ₂ of current resonance type switching power supply unit 1A side, the power factor improvement improvement converter 1
It is configured to be also used as a drive winding for driving the switching element Q ₁₀ of 3. Therefore, the switching element Q ₂ is in this embodiment the switching element Q ₁₀
Are synchronously driven for switching.

The insulating transformer PIT is provided for transmitting the switching outputs of the switching elements Q ₁ and Q _{2 to} the secondary side. This is the primary side of the insulating transformer PIT, as described above, the primary winding N ₁ to form a series resonant circuit at a current resonance type switching power source unit 1A is wound. In the case of this switching power supply circuit, the isolation transformer P
The secondary winding N ₁₂ of the center tap provided in the IT of the secondary side, the rectifier diode D _3A, D _3B, and full-wave rectifier circuit is provided by the smoothing capacitor C _O, from the primary winding N ₁ has a excited alternating voltage in the secondary winding N ₁₂ is outputted as an output voltage E ₀ is converted into a DC voltage. The control circuit 2 compares the DC output voltage E _O on the secondary side with the reference voltage, and outputs a DC current (control current I _C ) having a variable level according to the error, to the drive transformer PRT.
An error amplifier is supplied to the control winding N _C of.

[0042] As such the constant voltage control in configured current resonance type switching power supply unit 1A, for example, when the DC output voltage E _O of the secondary side is lowered to the control winding N _C by the control circuit 2 variably so that the control current flowing decreases, the switching frequency decreases (it becomes closer to the resonance frequency) as controls and controls so that the drive current is increased to flow to the primary winding N _1, a constant voltage (Switching frequency control method).

According to the switching frequency control method as described above, the level of the DC output voltage E _O on the secondary side increases due to a change in conditions such as an increase in the AC input voltage and a reduction in the load. In the case where the influence appears, the control circuit 2 increases the level of the control current I _C flowing through the control winding N _C according to the level change to increase the switching frequency of the switching elements Q ₁ and Q _2. Although will be controlled to, in this embodiment, substantially the same to the switching element Q ₁₀ of the power factor improvement converter 13 such change in switching frequency is driven in synchronism with the switching element Q ₂ Will be obtained. Thus, also in the power factor improvement converter 13 of the present embodiment, in the same manner as the power factor improvement converter 12 of FIG. 5, so as to keep the switching frequency of the switching element Q ₁₀ substantially constant variable to the power factor Can be controlled.

By the way, the power factor improving converter units (10, 11, 12, 13) shown in FIGS. 1 and 4 to 6 as the respective embodiments described so far have been used to improve the power factor. However, the converter circuit of the present invention can be used as a single switching power supply circuit itself. Omitted specific illustration or the like, for example, instead of the converter transformer CVT for driving the switching element Q _10, an insulating converter transformer PIT (Power Isolation Transformer),
A primary winding N ₁ is the primary winding, constituting the leakage inductance by winding a separately arranged to loosely-coupled secondary winding for obtaining an alternating voltage on the secondary side. And
A rectifying and smoothing circuit may be provided on the secondary side so that a secondary side DC voltage is obtained by rectifying the alternating voltage obtained on the secondary side winding of the insulating converter transformer PIT.

The applicant has previously proposed various switching power supply circuits for improving the power factor by feeding back the switching output of the voltage resonance type converter to the rectified current path, other than the circuit configuration shown in each of the above embodiments. However, these configurations of the present invention can also be applied as the configuration of the power factor correction converter circuit of the present invention.

[0046]

As described above, the present invention relates to a power factor improving converter circuit for improving a power factor of a power supply circuit by feeding back a switching output of a switching converter to a rectifying current path and superimposing the switching output. Although a self-excited voltage resonance type converter circuit including one switching element is provided, for example, a self-excited voltage resonance type converter circuit configured by half-bridge coupling of two switching elements as a switching converter is provided. The number of parts is greatly reduced as compared with the case where the excitation type current resonance type converter is provided. Further, it is not necessary to consider the balance between the characteristics such as the storage time t _stg and the current amplification factor h _{FE of} the two switching elements. Further, in the operation of the voltage resonance type converter, since the resonance current flowing through the resonance capacitor of the power factor correction circuit is about 1/3 of the switching cycle, it is not necessary to select a low loss product for the resonance capacitor. And a general-purpose product can be selected. As described above, according to the present invention, the number of components can be reduced, and various conditions regarding component selection are relaxed. Therefore, it is possible to provide a power factor improving converter circuit which is smaller and lighter and whose cost reduction is promoted. Become.

By providing a power factor control circuit for varying the switching frequency with respect to the power factor improving converter circuit, it is possible to keep the power factor substantially constant with respect to a change in the AC input voltage. The power factor control circuit
If a configuration is adopted in which a control current is supplied from the rectified and smoothed voltage to the control winding via a resistor after providing an orthogonal transformer in which the drive winding and the control winding are wound, the number of components can be reduced. This does not hinder miniaturization / weight reduction and cost reduction of the circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an operation of a main part of the switching power supply circuit of the present embodiment by a switching cycle.

FIG. 3 is a waveform diagram showing an operation of a main part of the switching power supply circuit according to the present embodiment with a commercial power supply cycle.

FIG. 4 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit as another embodiment.

FIG. 5 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit as still another embodiment.

FIG. 6 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit as still another embodiment.

FIG. 7 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit as a prior art.

FIG. 8 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit as a prior art.

[Explanation of symbols]

1 switching power supply section, 2 control circuits, 10, 11,
12,13 power factor improving converter circuit, D ₁ bridge rectifier circuit, Ci smoothing capacitor, CVT converter transformer ,, PRT drive transformer, Q ₁₀ switching elements, Cr resonant capacitor, N ₁ primary winding, N ₂ superimposing winding, L _N filter choke coil, C _N filter capacitor, D ₂ high speed recovery type diode, C ₂ resonance capacitor

Claims (5)

[Claims] A self-excited voltage resonance type switching operation is performed using a rectified and smoothed voltage output from a smoothing circuit as an operation power supply, and the switching output is used as an inductance of a resonance capacitor and a resonance winding. A self-excited voltage resonance type converter supplied to a resonance circuit formed by: a power factor improved based on a switching output fed back to a rectified current path from the resonance circuit. A power factor improving converter circuit comprising: an improving unit; The power factor improving means includes a normal mode low-pass filter including a filter choke coil and a filter capacitor provided for an output of the rectifier circuit, and a high-speed recovery inserted in series in a rectifier current path of the rectifier circuit. Type rectifying element, and switching output feedback means for applying a switching output to the fast recovery type rectifying element and feeding back the switching output through the capacitive coupling by the action of the resonance capacitor. 2. The power factor improving converter circuit according to claim 1, wherein: 3. A normal mode low-pass filter comprising a filter choke coil and a filter capacitor provided for an output of a rectifier circuit, and a high-speed recovery device inserted in series in a rectifier current path of the rectifier circuit. Type rectifying element, and switching output feedback means for applying switching output to the fast recovery type rectifying element via magnetic coupling and performing feedback. The power factor improving converter circuit according to claim 1. 4. The power factor improving converter according to claim 1, further comprising power factor control means for controlling the power factor to be substantially constant with respect to a level change of the AC input voltage. circuit. 5. The power factor control means is provided in parallel with a smoothing capacitor forming the smoothing circuit, and includes a series connection circuit comprising at least a resistor and a control winding, and a self-excited voltage resonance type converter. And an orthogonal transformer formed by winding the control winding so that the winding direction is orthogonal to the drive winding forming the excitation oscillation circuit. The power factor improving converter circuit according to claim 4.