JPH10108467A - Power factor improving converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize reduction in size and weight and also realize low manufacturing cost. SOLUTION: A series-connected circuit, consisting of a control coil NC of an orthogonal-type drive transformer PRT, a Zener diode ZD2 and a resistor R are provided in parallel to a smoothing capacitor Ci, and a control current IC is made to flow into the control coil NC via the resistor R1 , the Zener diode ZD2 from a rectifying smoothing voltage Ei. Thereby, the power factor is controlled to be almost constant by varying the switching frequency with the control current IC varied depending on change of an AC input voltage. Moreover, the power consumption by the control current IC can be controlled, when an AC input voltage which assures that the high power factor is rather low by the insertion of the Zener diode ZD2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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, since such an active filter has many factors such as an increase in circuit scale and a high cost due to an increase in the number of components and an increase in size for high EMI countermeasures, it is necessary to reduce the size and cost of the power supply circuit. It is disadvantageous from a viewpoint. 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, since the switching operation of the converter circuit is a current resonance type, low noise is realized and the circuit scale is small as compared with an active filter. Thus, the cost can be reduced accordingly. In addition, power loss is greatly reduced, and power conversion efficiency is improved.

FIG. 5 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 configured 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 drive transformer PRT described below form a series resonance circuit for driving the switching element by self-excited oscillation. Capacitors C _C1 and C _C2 are connected in parallel between the collectors and emitters of the switching elements Q ₁ and Q ₂ , respectively.
A gradient is applied to the rising / falling feedback of the switching voltage of the switching elements Q ₁ and Q ₂ which form a square wave, so as to suppress switching noise.

[0010] Drive transformer PRT (Power Regulati
ng Transformer) drives the switching elements Q ₁ and Q ₂ and variably controls the switching frequency. The drive transformer PRT includes drive windings N _B1 and N _B2 and a winding N _D provided to wind up the drive winding N _B1.
In contrast, a saturable reactor of the orthogonal type provided with a control winding N _C wound so that the winding directions are orthogonal to each other. Drive winding N _B1 has one end resistance R _B1 -
It 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 - resonant capacitor C
Is connected to the base of the switching element Q ₂ via the _B2, it is adapted to reverse polarity voltage is outputted to the drive winding N _B1.

[0011] converter transformer CVT-11 is constructed by winding a primary winding N ₁ and the tertiary winding N _3. In addition,
In this case, the primary winding N ₁ functions as an inductor for superimposing a switching voltage to the rectifier path as described below. One end of the primary winding N ₁ of the converter transformer CVT-11, the switching element through the winding N _D Q
₁ the emitter and the collector of the connection point of the switching element Q ₂ is connected to the (switching output point), the other end a connection point between the filter choke coil L _N and the high-speed recovery type diode D ₂ via the series resonance capacitor C ₁ Connected to According to the above connection configuration, the converter transformer C
Primary winding N ₁ and the series resonant capacitor C ₁ of the VT-11 is to be connected in series, by the primary winding N ₁ of the inductance component and the series resonant capacitor C ₁ capacitance current the switching converter A series resonance circuit for forming a 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.

Further, the transistor Q ₁₀ is connected to the control winding N _C
For supplying the control current I _C to In this case, the base of the transistor Q ₁₀ is rectified and smoothed voltage E
i line and is connected to the voltage dividing point of the voltage dividing resistors R _11, R ₁₂ which is inserted in series with between the primary side ground, a DC current corresponding to the level of the rectification smoothed voltage Ei is supplied. Also,
The tertiary winding N ₃ of the converter transformer CVT-11,
The resulting switching output to the primary winding N _1, but an alternating voltage is excited, the rectifier diode D ₃ which is connected to said tertiary winding N _3, a smoothing capacitor C ₃ half-wave rectifier circuit and a resistor R ₃ and Zener diode Z
Low DC voltage of a predetermined level is generated by the constant voltage circuit consisting of D _1. This DC voltage is applied to the transistor Q ₁₀
Transistor Q through the control winding N _C as the operating power supply
Supplied to ₁₀ collectors. The emitter of the transistor Q ₁₀ is grounded to the primary side ground via a resistor R _13.

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 resonance current detection winding N _D → primary winding N ₁ →
Flows resonance current in series resonant capacitor C _1, in the vicinity of the resonant current becomes zero switching element Q ₂ 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. Hereinafter, switching elements Q ₁ , Q ₂
Are turned on alternately to start a self-excited switching operation. As described above, the switching elements Q ₁ and Q ₂ alternately open and close by using the terminal voltage of the smoothing capacitor Ci as the operating power supply, so that the converter transformer CVT-
Supplying a drive current is close to the resonant current waveform to the primary winding N ₁ of 11. Note that the variable control of the switching frequency by the drive transformer PRT 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.
Is supplied to the primary winding N ₁ of the T-11. Then, an alternating voltage of the switching period generated by the switching output supplied to the primary winding N ₁ in converter transformer CVT-11, via a capacitive coupling of the series resonance capacitor C _1, a filter choke coil L _N It is applied to the connection point of the high speed recovery type diode D _2. The above filter choke coil L _N and high-speed recovery type diode D ₂
, Since it is inserted to the positive output line of the bridge rectifier circuit D _1, the switching voltage applied through the series resonant circuit, that the switching voltage is superimposed on the rectified output voltage across the rectifier path Become. 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 power factor improving converter section 20
In, the smoothing capacitor Ci is charged in a state where the switching output is superimposed on the rectified output voltage,
By the superposition of the switching voltage, the voltage across the smoothing capacitor Ci is reduced in the switching 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.

Further, in a power factor correction converter configured to feed back a switching output of a current resonance type converter to a rectification path, such as a power factor correction converter circuit as shown in FIG. In this case, the power factor characteristic decreases as the input AC input voltage increases. Therefore, by changing the switching frequency of the current resonance type converter using the drive transformer PRT, the power factor can be controlled to be substantially constant with respect to the input AC input voltage level.

[0017] For example, when the AC input voltage V _AC input to a commercial AC power source of the power supply circuit shown in FIG changes as rose, since also increases rectified smoothed voltage Ei corresponding to, rectification base current supplied to the base of the transistor Q ₁₀ via a voltage dividing resistor R ₁₁ from smoothed voltage Ei is increased. Thus the transistor Q _10, since it operates so as to increase the collector current level, the control winding N _C which is connected to the collector, so that the collector current flows as the control current I _C. That is, the control is performed such that the level of the control current I _C flowing through the control winding N _C increases as the AC input voltage level increases. In the drive transformer PRT, as the level of the control current I _C increases as described above, the drive winding N
_Reduce the inductance of _B1 and _NB2 . This allows
The drive winding N _B1 and the resonance capacitor C _B1 , and the drive winding N _B2
Lowers the resonant frequency of the two sets of self-oscillation driving circuit formed by the resonance capacitor C _B2 and the switching element Q
_11, will be controlled so as to increase the switching frequency of the Q _12. In this case, the switching frequency changes with respect to the resonance frequency of the series resonance circuit, and this changes the amount of feedback of the switching output supplied to the series resonance circuit. In this case, the power factor is increased. Will be controlled.

FIG. 6 is a waveform diagram showing the operation of the main part of the power supply circuit shown in FIG. 5 according to the cycle of the commercial power supply. Here, a power factor PF = 0.9 is obtained at the maximum load. The operation waveform under the condition is shown. For example, FIG.
When AC input voltage V _AC of AC100V, as shown in (a) is input, the collector current I _CP of the switching element Q ₂ is, by an envelope shown in FIG. 6 (b), was intermittently at the switching period Obtained as high frequency current. As can be seen from the figure, the collector current _ICP has a waveform such that its amplitude increases in a period τ where the absolute value of the AC input voltage level is higher than the rectified smoothed voltage level. The AC input current I _AC is as shown in FIG.
As shown in (1), a waveform that flows in a sine wave form in the period τ is obtained, and in practice, the conduction angle is increased to such an extent that a power factor of 0.9 is obtained.

FIG. 7 shows a power factor characteristic with respect to a change in the AC input voltage as a characteristic of the power supply circuit shown in FIG. As can be seen from the figure, in the power supply circuit shown in FIG. 5, both the case where the maximum load power P _O = 150 W shown by the solid line and the case where the minimum load power P _O = 10 W shown by the broken line are, The power factor is controlled so as to be maintained at about 0.9 regardless of an increase in the input voltage.

[0020]

From the viewpoint of miniaturization of the size of the equipment on which the power supply circuit is mounted, cost, and the like, the number of parts is reduced as much as possible in the power supply circuit and the power factor correction converter circuit. It is preferable to reduce the size, weight, and cost. For example, if the power source circuit shown in FIG. 5, by providing an amplifier circuit comprising transistors including transistors Q ₁₀ in the power factor improvement converter 20, so that the power factor with respect to the change of the AC input voltage is substantially constant In order to form this amplifier circuit, in addition to the resistors R ₁₁ , R ₁₂ and R ₁₃ connected to the transistor Q ₁₀ , a tertiary winding N ₃ forming a constant voltage circuit is formed. , A rectifier diode D ₃ , a resistor R ₃ , a smoothing capacitor C _3, and a zener diode ZD ₁ . Further, the tertiary winding N ₃ is wound around the converter transformer CVT-11, but which also, the converter with the miniaturization of the transformer CVT-11 becomes difficult, affecting the correspondingly cost and manufacturing steps complicated Will lead to giving.

[0021]

In view of the above-mentioned problems, the present invention performs a switching operation by self-excited oscillation using a rectified smoothed voltage output from a smoothing circuit as an operating power supply, and connects the switching output in series. A self-excited current resonance type converter that is supplied to a series resonance circuit formed by a resonance capacitor and an inductance of a series resonance winding, and a switching output that is fed back from the series resonance circuit to a rectified current path. A power factor improving device includes a power factor improving device configured to improve a power factor, and a power factor controlling device that performs control such that a power factor is substantially constant by changing a switching frequency with respect to an AC input voltage level. The power factor control means is provided in parallel with a smoothing capacitor forming the smoothing circuit. The control winding is arranged such that the winding direction is orthogonal to a series connection circuit comprising at least a resistor and a control winding and a drive winding forming a self-excited oscillation circuit of the self-excited current resonance type converter. And an orthogonal transformer wound and formed. The series connection circuit is formed by inserting a zener diode element in series.

According to the above configuration, the power factor control means for maintaining the power factor constant with respect to the AC input voltage fluctuation in the power factor improving converter circuit is provided for the drive winding for causing the switching element to self-oscillate. It can be formed only by the control winding wound around the orthogonal transformer such that the winding directions are orthogonal to each other, and a resistor connected in series to the control winding. Also, by inserting a zener diode in series with the series connection circuit of the control winding and the resistor, when the AC input voltage is lower than a predetermined level, no current flows through the control winding and the power factor is reduced. The function of the control means can be turned off.

[0023]

FIG. 1 is a circuit diagram showing the configuration of a switching power supply circuit provided with a power factor improving converter according to a first embodiment of the present invention. In the power factor improving converter section 10 shown in FIG. ₁ , the switching is performed via the circuit configuration of the current resonance type converter including the switching elements Q ₁ and Q ₂ and the capacitance coupling of the series resonance capacitor C _1. Since the circuit configuration for improving the power factor for feeding back the output is the same as that in FIG. 5, the components of each circuit are denoted by the same reference numerals and description thereof is omitted. Also, in the other components, the same reference numerals are given to the same portions as those in FIG. 5, and the description will be omitted.

The power factor improving converter 10 shown in FIG.
In the power factor improving converter circuit according to the present embodiment, the control winding N of the orthogonal drive transformer PRT is used.
_C is connected to the positive terminal of the smoothing capacitor Ci one end through a resistor R _1, the other end is connected directly to the primary side ground. According to this, the resistance R ₁ and the control winding N _C
Is provided in parallel with the smoothing capacitor Ci. That is, in the present embodiment, as a power factor control circuit for stabilizing the power factor, for example, an amplifier circuit (N ₃ , D ₃ , R ₃₎ including the switching element Q ₁₀ and its peripheral components as shown in FIG. _3, C _3, Z
Includes a constant voltage circuit consisting of D ₁₎ is not provided,
Alternatively, it can be seen as the series connection circuit of the resistor R ₁ and the control winding N _C is provided.

With the above circuit configuration, when the power factor improving converter section 10 of the present embodiment is compared with the power factor improving converter section 20 shown in FIG. The converter 10 greatly reduces the number of components forming the power factor control circuit. Accordingly, in the present embodiment, the tertiary winding N ₃
Is also omitted, the converter transformer CVT-1
In for making becomes better only wound a primary winding N _1, is realized simplified correspondingly converter transformer CVT-1 of the manufacturing process, it is also possible to reduce the size of that size.

[0026] In the power factor control circuit shown in this figure, by passing through the resistor R ₁ from the rectified smoothed voltage Ei, control winding N
_A control current I _C to be passed to _C is generated. Then, for example, it is assumed that the _AC input voltage VAC input to the commercial AC power supply of the power supply circuit shown in FIG. As a result, the level of the control current I _C flowing through the control winding N _C increases in accordance with the rise of the rectified smoothed voltage Ei. Thereafter, the switching elements Q ₁ and Q ₁ are operated by the same operation as described in FIG. As a result of controlling to increase the switching frequency of No. ₂ , it becomes possible to control to increase the power factor with respect to the increase of the _AC input voltage VAC.

FIG. 2 shows the relationship between the AC input voltage and the power factor in the power supply circuit having the configuration shown in FIG. In this case, the load power is a parameter. In this figure, the solid line indicates the maximum load power (P _O = 1)
50 W), the power factor PF shows a tendency to slightly decrease with an increase in the _AC input voltage VAC. Characteristics can be obtained. When the minimum load power (P _O = 10 W) indicated by the broken line is used, although the value of the power factor PF is slightly lower than that at the time of the maximum load power, the same applies to the increase in the _AC input voltage VAC. The tendency of the power factor PF change is obtained. In the present embodiment, an amplifier circuit is not provided as a power factor control circuit, and the control current I _C flows from the rectified smoothed voltage Ei to the control winding N _C by only the resistor R _1. , because the sensitivity of the control current I _C relative to the change of the ac input voltage V _AC is lower than the power factor improvement converter 20 shown in FIG. 5, as FIG. 2, with the rise of the ac input voltage V _AC The characteristic is such that the power factor PF gradually decreases. In contrast, FIG.
In the operation of the power factor PF improvement converter section 20 shown in FIG.
The power factor P with respect to the change of the ac input voltage V _AC as shown in
Control is performed so that F is substantially constant at 0.9.

However, in this embodiment, if the power factor characteristic as shown in FIG. 2 is obtained, for example, when the AC input voltage is 100 V AC, the power factor becomes 0.9 at both the maximum / minimum load power. Since almost similar characteristics are obtained, there is no problem in practical use, and when considering the merits of reducing the number of parts and simplifying the manufacturing process as described above,
It can be said that this is a power factor improving converter circuit which is more advantageous than the power factor improving converter section 20 of the configuration of FIG. 5 in that it has practicality while realizing low cost.

Further, as the parts selection regarding the power factor control circuit in the power factor improvement converter 11, for example, setting a 220Ω copper wire 60μφ as a control winding N _C of the drive transformer PRT as a DC resistance and 1000T wound the resistor R ₁ in terms of the can be selected 47kohm. This case, the variable range of the control current to be supplied to the control winding N _C as 0～6MA, AC input voltage AC100V
In the condition when the load power is 10W, the rectified smoothed voltage Ei becomes about 140 V, the control power required for the power factor control at this time (i.e., a power generated by the control current I _C flows) is 0.42W Becomes On the other hand, for example, the power factor control circuit (amplifier circuit) shown in FIG.
Control power. Therefore, the power factor control circuit of the present embodiment, for example, the number of turns control winding N _C 40
Increased to 00T, the resistor R ₁ in order to 200KΩ Tosureba control current I _C is constantly reduced, it is possible to obtain the same control power characteristics and the power factor control circuit of FIG.

FIG. 3 is a circuit diagram showing an example of a switching power supply circuit including a power factor improving converter circuit (power factor improving converter section) according to a second embodiment of the present invention. The same parts as those in FIG.

By the way, as a configuration of the power factor improving circuit, the switching output obtained by the applicant of the present invention in the series resonance circuit of the current resonance type converter is fed back to the rectification current path via a magnetic coupling such as a transformer or a choke coil. Although various configurations have been proposed, the power factor improving converter 11 of the present embodiment employs a configuration employing this magnetic coupling method as a power factor improving circuit. The configuration of the rate improvement circuit will be described.

[0032] In the power factor improvement converter 11 shown in this figure, the converter transformer CVT-2 are provided, the converter transformer CVT-2 of the series resonant circuit in the primary winding N ₁ and superimposing winding N ₂ are wound so that magnetic coupling can be obtained. Above winding N
₂ is inserted in series between the positive terminal of the high speed recovery type diode D ₂ cathode and a smoothing capacitor Ci with respect to the rectifier current path. For construction of the power factor correction circuit as described above, the switching output of the current resonant converter obtained at the primary winding N ₁ of the series resonant circuit, the converter transformer CVT-2 of the magnetic coupling of the through superimposing winding N _It is transmitted to 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, for example, the conduction angle of the AC input current is expanded by the same operation as that described with reference to FIG. 5, and the power factor is improved.

In the present 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 action explained in FIGS. 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. A normal mode low-pass filter is formed together with the filter choke coil _LN .

Next, as the power factor control circuit in the power factor improvement converter 11, the configuration of the power factor control circuit in the power factor improvement converter 10 shown in FIG. 1, the Zener diode ZD ₂ is added I have. Zener diode ZD ₂ In this case, an anode connected to one end of the control winding N _C, are provided so as cathode is connected to one end of resistor R _1. In other words, the power factor control circuit in the present embodiment, resistor R ₁ - Zener diode ZD ₂ - series circuit of control winding N _C is thus provided in parallel with the smoothing capacitor Ci. Further, in this power factor control circuit, for example, a rectified smoothed voltage Ei having a level corresponding to the AC input voltage AC 103 V or less.
As is obtained if and is Zener diode ZD ₂ keeps the non-conducting state, when the rectification smoothed voltage Ei of a level corresponding to or higher AC input voltage AC103V is obtained, which becomes conductive state The required related parts are selected. As a result, the control current I _C does not flow through the control winding N _C at the AC input voltage AC 103 V or less,
AC input voltage AC 103 V or less (that is, AC input voltage A
Under the condition of C100V system), no control power is generated.

FIG. 4 shows a relationship between a power factor and a change in AC input voltage as a power factor characteristic of the power supply circuit having the configuration shown in FIG. 3, and in this case, load power is used as a parameter. As a characteristic shown in this figure, the Zener diode ZD ₂
Are conducted, the characteristics of FIG. 2 previously shown as the power factor characteristics of the power supply circuit of FIG. 1 are the same at the time of maximum load power (solid line) and at the time of minimum load power (dashed line). Sufficient practical characteristics have been obtained. On the other hand, when the AC input voltage is lower than AC 103 V, the power factor control becomes invalid, and the power factor decreases as the AC input voltage increases. Is low (at AC 100 V system), a high power factor can be obtained without particularly stabilizing control of the power factor. Therefore, there is no particular problem in this respect.

In each of the embodiments described so far, the power factor improving converter circuit can be added to an existing switching power supply circuit in order to improve the power factor. The improved converter circuit can naturally be used as a single switching power supply circuit itself. For example, if a switching power supply circuit is specifically configured based on the configuration of the power factor correction converter unit 10 illustrated in FIG. 1, although not illustrated, for example, instead of a converter transformer, an insulated converter transformer PIT (Power Isolation Transformer) to provided a primary winding N ₁ is the primary winding, the leakage inductance by winding a separately arranged to loosely-coupled secondary winding for obtaining an alternating voltage on the secondary side Configure. Then, a rectifying and smoothing circuit may be provided on the secondary side so that a secondary DC voltage is obtained by rectifying the alternating voltage obtained on the secondary winding of the insulating converter transformer PIT.

The switching power supply unit 1 shown in each of the above embodiments may be a flyback converter or a forward converter based on a PWM method, or may be an RC converter.
It is needless to say that various types of switching converters such as C (ringing choke converter) may be used. However, a switching converter in which the current waveform or the voltage waveform of the switching operation is a rectangular wave is used. It is suitable for application when connected. In addition, the applicant has previously proposed various switching power supply circuits for improving the power factor by feeding back the switching output of the current resonance type converter to the rectification current path, other than the circuit configuration shown in each of the above embodiments. However, these configurations of the present invention can be applied as the configuration of the power factor improving converter circuit of the present invention.

[0038]

As described above, the present invention provides an orthogonal drive transformer as a power factor control circuit for controlling a power factor in a power factor improvement converter circuit so that the power factor becomes substantially constant with respect to a change in AC input voltage. Since the series connection circuit of the control winding and the resistor is provided in parallel with the smoothing capacitor, the number of components is reduced accordingly, and the circuit is reduced in size / weight and cost. Can be. Also, by inserting and connecting a zener diode to the series connection circuit, when the AC input voltage is equal to or lower than a predetermined level, the control current is not supplied to the control winding, so that the AC input voltage is reduced. Under the condition of a predetermined level or less, power for power factor control is not consumed, so that power consumption can be reduced.

[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 a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating power factor characteristics of the switching power supply circuit according to the first embodiment.

FIG. 3 is a circuit diagram illustrating a configuration of a switching power supply circuit including a power factor correction converter circuit according to a second embodiment.

FIG. 4 is an explanatory diagram illustrating power factor characteristics of a switching power supply circuit according to a second embodiment.

FIG. 5 is a circuit diagram showing a configuration of a switching power supply circuit including a power factor correction converter circuit as a prior art.

6 is a waveform chart showing the operation of the switching power supply circuit shown in FIG. 5 in a commercial power supply cycle.

FIG. 7 is an explanatory diagram illustrating power factor characteristics of the switching power supply circuit illustrated in FIG. 5;

[Explanation of symbols]

1 switching power supply section, 2 control circuits, 10, 11,
Power factor improving converter circuit, D ₁ bridge rectifier circuit,
Ci smoothing capacitor, CVT-1, CVT-2 converter transformer, PRT drive transformer, Q
_1, Q ₂ switching elements, Z _D2 zener diode, C ₁ series 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 (4)

[Claims] 1. A switching operation is performed by self-excited oscillation using a rectified and smoothed voltage output from a smoothing circuit as an operation power supply, and the switching output is supplied to a series resonance circuit formed by a series resonance capacitor and an inductance of a series resonance winding. Self-excited current resonance type converter, power factor improvement means configured to improve a power factor based on a switching output fed back from the series resonance circuit to a rectified current path, and an AC input voltage. Power level control means for controlling the power factor to be substantially constant by varying the switching frequency with respect to the level, wherein the power factor control means is in parallel with a smoothing capacitor forming the smoothing circuit. And a series connection circuit comprising at least a resistor and a control winding; and a self-excited oscillation of the self-excited current resonance type converter. A power transformer comprising: a drive transformer forming a path; and an orthogonal transformer formed by winding the control winding so that the winding direction is orthogonal to the drive winding. Improved converter circuit. 2. The power factor improving converter circuit according to claim 1, wherein a Zener diode element is inserted in series with the series connection circuit. 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 a switching output to the fast recovery type rectifying element and feeding back through the capacitive coupling by the action of the series resonance capacitor. The power factor improving converter circuit according to claim 1, wherein 4. 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 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.