JPH02211061A - Switching regulator - Google Patents

Abstract

PURPOSE:To improve the power factor of an apparatus by providing an input side smoothing capacitor of small capacity, first and second output circuits for smoothing, rectifying and outputting power induced in the secondary winding of a converter transformer, an output terminal with which the output of said first and second output circuits are connected in parallel, and a feedback circuit. CONSTITUTION:In an apparatus, a capacitor 7 of comparatively small capacity corresponding to the switching frequency of a transistor Q being a switching element is used as the smoothing capacitor of an input side smoothing circuit and secondary windings L1, L2 of a converter transformer 8 are provided to constitute first and second output circuits respectively separated from each other. Then, the outputs of said circuits are joined together and outputted to an output terminal 5 and the second secondary winding L2 is connected according to a flyback connection for outputting power while the switching element 7 is OFF. When said apparatus is constituted in such manner, the terminal voltage of said input side smoothing capacitor 7 lowers so that the period of time for power to be supplied form an AC power supply 1 becomes longer and that for current to cease to flow decreases and the value of current flowing at every moment becomes smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching regulator, and particularly to a switching regulator that has a good power factor with respect to an AC power source.

[Conventional technology]

Recently, switching regulators are often used as DC constant voltage power supplies because they are small, lightweight, and have good power efficiency.

FIG. 7 is a circuit diagram showing an example of a conventional switching regulator.

AC power from an AC power supply 1 is full-wave rectified by a rectifier 2 made of a diode bridge, and smoothed by an electrolytic capacitor 3, which is a large-capacity input-side smoothing capacitor.

The DC power charged in the electrolytic capacitor 3 is supplied to a series path between the primary winding Lp of the conversion transformer 4 and the transistor Q, which is a switching element.

High switching frequency (typically 50KHz to 200KHz)
It is turned on and off by a transistor Q driven at a frequency (KHz).

Therefore, AC power is induced in the secondary winding LS of the conversion transformer 4, and after being rectified by the diode D1, it is smoothed by a choke input type smoothing circuit consisting of a choke CH and a large-capacity capacitor C1, and is then smoothed at the output terminal 5. DC power of an output voltage VQ is supplied to the load 6 via.

The diode D2 is for supplying the energy stored in the choke CH as a magnetic force when the transistor Q is on to the capacitor CI when the transistor Q is off.

The feedback circuit includes a control circuit 11, a driver 12, a pulse transformer 13, and an auxiliary power source 14. The auxiliary power source 14 converts AC power from the AC power source 1 into DC power and supplies the DC power to the control circuit 11 and driver 12.

The control circuit 11 receives the output voltage v□ of the output terminal 5, compares it with a preset reference output voltage Vs, and outputs the difference signal to the driver 12.

The driver 12 drives the transistor Q by applying a pulse-width-modulated drive signal with a predetermined switching frequency to the emitter-base of the transistor Q via the pulse transformer 13, but the pulse width (on-duty ratio) is determined by the control circuit 11.
According to the difference signal input from the reference output voltage VS, the output voltage v□ is modulated such that it decreases if it is higher than the reference output voltage VS, and increases if it is lower than the reference output voltage VS.

Therefore, the output voltage VO supplied to the load 6 is stabilized to the reference output voltage VS.

[Problem to be solved by the invention]

However, as explained above, the conventional switching regulator uses a capacitor input type that uses a large-capacity electrolytic capacitor 3 in the smoothing circuit on the input side, so the instantaneous value of the AC voltage from the AC power supply 1 No current flows while the terminal voltage is lower than the terminal voltage of the electrolytic capacitor 3, and all the necessary power is supplied only during a short period of time when the voltage is high, so a large current flows compared to the output power capacity.
A lot of reactive power flows and the power factor is poor (low).

Unlike in the case of an inductive load such as a motor, this low power factor is not caused by a phase shift, so it cannot be improved with a phase advance capacitor or the like.

In addition, since large currents flow instantaneously, as the power capacity of switching regulators increases, the capacity of fuses, circuit breakers, wiring, rectifiers, etc. must be increased, which may pose safety problems and affect other equipment. It has become impossible to ignore.

In order to prevent this instantaneous current from becoming excessive, a smoothing capacitor is connected in parallel to the output stage of the rectifier via a current limiting impedance element, as shown in, for example, Japanese Patent Application Laid-Open No. 63-107457.

There is a device that limits the current when charging the smoothing capacitor by connecting a diode in parallel with the current limiting impedance element so that it turns on when the charging voltage of the smoothing capacitor is higher than the output voltage of the rectifier. .

However, when a resistor is used as an impedance element, the loss increases and efficiency is reduced, and when an inductor is used, a large capacity inductor is required, resulting in an expensive and large size.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a switching regulator with improved power factor while taking advantage of the advantages of being small and lightweight and having good power efficiency.

[Means to solve the problem]

In order to achieve the above object, the present invention uses a large capacity electrolytic capacitor corresponding to the commercial frequency (507 to 607) of the input side smoothing circuit to match the switching frequency of the switching element in the switching regulator as described above. In addition to replacing it with a corresponding capacitor of relatively small capacity,
Two secondary windings of the conversion transformer are provided, each having an independent first and second output circuit, and their outputs are combined and output to an output terminal.

The second secondary winding has a flyback connection that outputs power while the switching element is off.

Alternatively, a constant voltage circuit whose output voltage is set slightly lower than the reference output voltage vs is provided on the output side of the second output circuit.

Alternatively, the output side of the second output circuit has a function that turns off when the output voltage of the first output circuit is equal to or higher than the reference output voltage VS, and turns on when it is less than the reference output voltage VS, and the output voltage is set to the reference output voltage VS. A constant voltage circuit is provided which is set approximately equal to vs.

(Function) By configuring this invention as described above, the terminal voltage of the input side smoothing capacitor is significantly reduced, so the time during which power is supplied from the AC power source is extended, and the time during which no current flows is reduced. Along with.

The current value flowing at each instant becomes smaller.

Therefore, it is possible to provide a switching regulator with improved power factor while taking advantage of the advantages of being small, lightweight, and high power efficiency.

〔Example〕

The present invention will be described in detail below based on embodiments, but prior to that, the basic circuit will be described with reference to FIG. 5.

In FIG. 5, the same parts as those in the conventional example shown in FIG. 7 are given the same reference numerals, and their explanation will be omitted.

In this circuit example, a transistor Q, which is a switching element, is used as a smoothing capacitor in the input side smoothing circuit, instead of a large-capacity electrolytic capacitor 3 corresponding to the commercial frequency of the conventional example.
A capacitor 7 of relatively small capacity corresponding to the switching frequency of is provided, and other than that, it is the same as the conventional example.

In the conventional example, commercial frequencies were considered, so even if a full-wave rectifier made of a diode bridge is used as the rectifier 2, the smoothing capacitor 1 corresponding to the frequency of 100 Hz to 1207, for example, in the case of an output capacity of 200 W class, 1
Electrolytic capacitors of 000 μF or more were used.

According to this invention, the smoothing capacitor on the input side is not required in principle, but if no capacitor is placed at all, noise with the switching frequency as the fundamental wave will leak to the AC power supply side. Even if a noise filter is installed, it cannot be prevented.

Therefore, a small-capacity capacitor 7 is provided on this circuit side and in all the embodiments of the present invention to prevent noise leakage.

This capacitor 7 is not intended for frequencies from 100Hz to 120Hz, but for switching frequencies such as 50Hz.
Since the purpose is to suppress noise from KHz to 200 KHz, the frequency ratio handled is 500 times or more.

Therefore, even in the case of the same output capacity of 200 W class, sufficient effects were experimentally obtained with a relatively small capacitor of 10 μF or less.

However, since this capacitor is required to have a high Q even in a high frequency range, it is preferable to use a film capacitor, a ceramic capacitor, etc., rather than an electrolytic capacitor.

Even if such a capacitor is used, the capacitance is 1/100 or less of that of the conventional example, so the size of the input smoothing capacitor is small.

FIG. 6 is a waveform diagram showing voltage or current for comparing and explaining this circuit example and a conventional example, and FIG. 6(a) shows a full-wave rectified waveform outputted by the rectifier 2.

Fig. 6(b) shows the terminal voltage of the electrolytic capacitor 3 of the conventional example (Fig. 7), and Fig. 6(c) similarly shows its charging current.
As is clear from the figure, the charging time is short and the instantaneous current value is large.

FIG. 6(d) shows the current flowing through the rectifier 2 when the electrolytic capacitor 3 is removed from the conventional example, and it can be seen that the high frequency component causing noise is extremely large.

FIG. 6(a) shows the terminal voltage of the capacitor 7 in this circuit example, and FIG. 6(f) shows the current flowing through the rectifier 2.

Since the switching frequency is high, the capacitor 7 starts discharging before being charged to the voltage of the rectified waveform shown by the broken line, and starts charging before being completely discharged to Ov.

Therefore, the terminal voltage of the capacitor 7 is AC 1'! except in the vicinity where the voltage of the rectified waveform becomes O! The waveform approximates the absolute voltage value of 7N1 and shows a lower voltage waveform.

Therefore, the time during which current flows through the rectifier 2 becomes longer, the instantaneous current value becomes smaller, and the time during which no current flows becomes shorter, so that the power factor is improved.

However, although it is short, there is a time when no current flows and power is not supplied to the secondary side of the conversion transformer 4.
During this period, output power is supplied by discharging the smoothing capacitor C1 on the output side, so that the output voltage vo partially drops as shown by the arrow in FIG. 6(g).

The following embodiment prevents this partial voltage drop from occurring.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention,
The same parts as in the conventional example (FIG. 7) and the above-mentioned circuit example (FIG. 5) are given the same reference numerals, and their explanation will be omitted.

The input side circuit, feedback circuit, and output side circuit of the circuit example serve as the input side circuit, feedback circuit, and first output circuit of this first embodiment, respectively.

The conversion transformer 8 is provided with two secondary windings, and the first secondary winding L1 is the secondary winding LS in the circuit example (Fig. 5), and is used as the power supply for the first output circuit. It has become.

The second secondary winding L2 is a power source for the second output circuit, and is connected to the output side smoothing capacitor C1 after being single-wave rectified by the diode D3.

Therefore, the smoothing capacitor C1 is the first. It is shared by a second output circuit, and the second output circuit is of the capacitor input type.

The polarity of the two secondary windings LL+L2 is 1. For example, the first secondary winding L1 is forward connected, and the second secondary winding L2 is flyback connected, so the power is supplied only when transistor Q is turned on. When the transistor Q is off, the energy stored in the conversion transformer 8 as magnetic force is supplied to the first output circuit, and when the transistor Q is off, the energy is supplied to the second output circuit.

1st. The output voltage of the second output circuit is the secondary winding L 1 *
It is affected by the turns ratio of L2, but if we assume that the output side smoothing capacitors have the same number of turns and are independent of each other, then the first output circuit is a choke input type and the second
Since the output circuit of is a capacitor input type, the output voltage of the latter is higher.

Also, the power generated in the winding of the flyback connection is:

Compared to the power generated in a forward-connected winding, it is less affected by the pulse width (duty ratio), and if the switching frequency is constant, almost constant power is generated.

Therefore, output power is normally supplied mainly from the first output circuit, but when a partial voltage drop in the output voltage as shown in FIG. 6(g) occurs, the output power is mainly supplied from the second output circuit. Therefore, one partial voltage drop is suppressed.

This first embodiment is put to practical use when the output side smoothing capacitor 7 has a sufficiently large capacity and some voltage drop is acceptable, and since the circuit is relatively simple, the cost is low.

FIG. 2 is a circuit diagram showing a second embodiment of the invention,
The same parts as in the first embodiment (FIG. 1) are given the same reference numerals.

The difference between this second embodiment and the first embodiment is that the second output circuit is not directly connected to the output circuit of cylinder 1, but an independent capacitor-input type smoothing circuit consisting of smoothing capacitor C2 is provided, and the output voltage is connected to the first output circuit via a constant voltage circuit 20 set slightly lower than the reference output voltage vS.

The constant voltage circuit 20 is mainly composed of an IC 21 for a series regulator such as NEC's μPC317H, and is composed of a voltage divider consisting of resistors R1t and R2, and an auxiliary circuit consisting of a capacitor CR and a diode D4, and its output voltage is adjusted to a predetermined voltage by the voltage division ratio of the voltage divider.

Its operation as a constant voltage circuit is already well known, so a description thereof will be omitted.

Since the output voltage of the constant voltage circuit 20 is slightly lower than the reference output voltage vs, power is normally output from the first output circuit and not from the second output circuit, so the smoothing capacitor C2 is It is charged.

When a partial voltage drop occurs and the output voltage VO is about to drop below the output voltage of the constant voltage circuit 20, power begins to be supplied from the second output circuit, and the output voltage VO becomes equal to the output voltage of the constant voltage circuit 20. Retained.

The capacitance and charging voltage of the smoothing capacitor C2 may be sufficient as long as the output voltage of the constant voltage circuit 20 is maintained until power starts to be supplied from the first output circuit again.

Therefore, in this second embodiment, the output voltage vO of this switching regulator is mostly the reference output voltage VS
The voltage drop only occurs for a short period of time when the voltage drop occurs, and the voltage change at the time of switching is extremely smooth because the capacitor C1 on the output side has a large capacity, so it is not practical. It can be regarded as a constant voltage.

FIG. 3 is a circuit diagram showing the output circuit portion in the third embodiment of the present invention, and the other circuits on the power input side, feedback circuit, etc. are the same as in the second embodiment.

As is clear from FIG. 1, in this third embodiment, the constant voltage circuit 24 is mainly a step-down chopper, which is composed of a chopper IC 25 with a built-in control circuit, such as Sanken Electric's 5TR7005.

It is composed of a voltage divider consisting of a resistor Rt t R2 and an auxiliary circuit consisting of a smoothing choke CHZ.

The output voltage is adjusted to a predetermined voltage by the voltage division ratio of the voltage divider.

Its operation as a constant voltage circuit is already well known, so a description thereof will be omitted.

The output voltage of this constant voltage circuit 24 is also set slightly lower than the reference output voltage VS, similar to the constant voltage circuit 20 in the second embodiment, so the effect as a switching regulator is the same as in the second embodiment. be.

However, in a constant voltage circuit using a step-down chopper, a constant voltage is maintained by turning on and off the current, so a choke CH2 is provided on the output side of the IC25, and a choke input type smoothing circuit is configured together with the output side smoothing capacitor C1. ,
A voltage divider consisting of a series circuit of resistors R1+RZ and taking out a signal that controls the output voltage of the constant voltage circuit 24 is connected to
It is placed on the output side of H2.

Instead, compared to the series type IC 21 in the constant voltage circuit 20 of the second embodiment, there is no power loss due to voltage drop, and the overall power efficiency is improved.

FIG. 4 is a circuit diagram showing a fourth embodiment of the invention,
The same parts as in the second and third embodiments are given the same reference numerals.

This fourth embodiment is the second embodiment. The difference from the third embodiment is that the second embodiment
A constant voltage circuit 28 provided in the output circuit of the first output circuit is configured around an IC 29 for a series type regulator having an on/off function, and is turned on/off according to the output voltage of the first output circuit.
It is to be turned off.

The constant voltage circuit 28 is centered around the IC 29, and includes resistors Rt,
It is constituted by a voltage divider made up of R2, and an auxiliary circuit made up of a variable resistor VR and a constant voltage diode RD.

IC29 has an output voltage determined by the model number, such as Sanken Electric's 5TR9000 series IC, and a variable resistor V inserted between the 2nd terminal and ground.
The output voltage can be finely adjusted by the resistance value of R.
The output voltage is adjusted to be approximately equal to the reference output voltage vs.

Further, when the No. 3 terminal of the IC 29 is at a potential of 10, the output is off, and when it is at L°, that is, Ov, it has an on/off function of outputting the power of the adjusted output voltage as a constant voltage element.

The first output circuit has a choke input type smoothing circuit consisting of a dedicated smoothing capacitor C3 and a choke CH, and is connected to the output smoothing capacitor C1 via a backflow prevention diode D5.

The voltage divider consisting of resistors R1t and R2 generates a constant voltage when the output voltage of the first output circuit drops slightly below the reference output voltage Vs (more specifically, the voltage obtained by adding the voltage drop of approximately 0.6V of the diode D5). IC via diode RD
The voltage division ratio is set so that the voltage applied to the No. 3 terminal of No. 29 becomes Ov.

Most of the power output from the output terminal 5 of the switching regulator to the load 6 is supplied from the first output circuit, but a partial voltage drop occurs in the output circuit and the terminal voltage of the smoothing capacitor C3 increases. When the voltage drops slightly, IC29 turns on.

The power stored in the capacitor C2 of the second output circuit while the first output circuit is outputting is supplied to the load 6 at a constant voltage while the IC 29 is on.

During this time, the capacitor C3 of the first output circuit is neither discharged nor charged, so that it maintains a potential slightly below the normal terminal voltage, and as soon as the partial voltage drop is restored, the first output circuit is powered up. Started supplying IC29 3
Return the potential applied to the terminal to 10 and turn it off.

The second output circuit therefore stops supplying power and returns to the charging cycle of capacitor C2.

In this fourth embodiment, since the output voltage of the IC 29 is adjusted to be approximately equal to the reference output voltage vS, the output voltage is maintained at the reference output voltage vS even during a period when a partial voltage drop occurs, and 2. During the same period as in the third embodiment,
The output voltage will not drop even slightly.

Furthermore, the terminal voltage of capacitor C3 drops slightly after a partial voltage drop occurs in the first output circuit until IC29 is turned on, but the capacitance of output side smoothing capacitor C1 is equal to the capacitor C3's capacitance. Since the diode D5 prevents current from flowing backward, the voltage drop across the capacitor C1 is negligibly small.

Even if the output voltage of IC29 is slightly higher than the reference output voltage V5, due to the backflow prevention effect of diode D5, the voltage applied to the voltage divider made of resistors R1*R2 will rise, and IC29 will repeatedly turn off and on. This oscillation phenomenon does not occur.

The present invention has been described above with respect to the first to fourth embodiments. However, the input side smoothing capacitor is replaced with a large capacity electrolytic capacitor 3 corresponding to the conventional commercial frequency, and a relatively small capacitor corresponding to the switching frequency of the switching element is used. The power factor is improved by using the capacitor 7, and on the other hand, the partial voltage drop that occurs due to this is prevented by providing the second output circuit in parallel.

Furthermore, by replacing a large-capacity electrolytic capacitor with a small-capacity capacitor, the switching regulator, which is originally small and lightweight, can be made even smaller and lighter.

Furthermore, for the same reason, the excessive inrush current that occurs at the moment the power switch is turned on, which could not be avoided with conventional power supplies that employ capacitor input type smoothing circuits, can be eliminated.
Because I was able to do it.

There is also the advantage that there is no instantaneous drop in AC power supply voltage due to this rush current, and that turning on the power switch does not adversely affect other equipment.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a switching regulator with improved power factor while taking advantage of the advantages of being small and lightweight and having good power efficiency.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing the first and second embodiments of the present invention, respectively. FIG. 3 is a circuit diagram showing only the essential parts of the third embodiment of the invention. FIG. 4 is a circuit diagram showing a fourth embodiment. FIG. 5 is a circuit diagram for explaining the circuit that is the basis of this invention, and FIG. 6 is a waveform diagram of each part thereof. FIG. 7 is a circuit diagram showing an example of a conventional switching regulator. 1... AC power supply 2... Rectifier 5.
...Output terminal 6...Load 7...Capacitor 8...Replacement transformer 11...
・Control circuit 12...Driver 13...
・Pulse transformer 14...Auxiliary power supply 20.2
4.28... Constant voltage circuit 21.25.29... IC Lp... Primary winding Ll, Lz... Secondary winding Q... Transistor (switching element) 6th prison procedure correction (Responsive Patent Office Commissioner Yoshi 1) Takeshi Moon 1, Indication of the case Patent application No. 1-27924 2, Name of the invention Switching regulator 3, Relationship with the person making the amendment Patent applicant Nakamagome, Ota-ku, Tokyo 1-3-6 (674) Rico Co., Ltd.-4, Agent 1-20-56, Higashiikebukuro, Toshima-ku, Tokyo 170 (Telephone 986-2380) Contents of amendment (1) Page 11 of the specification "Circuit side" in the 8th line is r circuit example.
I am corrected. (2) "Capacitor 7" on page 12, line 17 of the same book is corrected as "capacitor 7A." (3) "Approximate" on page 13, line 6 of the same book is corrected as "similar." (4) In the same letter, page 140, line 13, "r single-wave rectification" is corrected to "r half-wave rectification." (5) In the first line of page 18 of the same book, ``Because it is smooth'' is corrected to ``It is smooth.'' (6) "Replacement transformer" in the first line of page 25 of the same book is corrected to "conversion transformer J." (7) "Figures 3 and 4" of the drawings are corrected as shown in the attached corrected drawing. that's all

Claims (1)

[Scope of Claims] 1. A rectifier connected to an AC power supply, a series circuit of the primary winding of a conversion transformer and a switching element connected between the DC output terminals of the rectifier, and a switching element connected in parallel to the series circuit. a first smoothing capacitor connected to the input side and having a relatively small capacity that corresponds to the switching frequency of the switching element; and a first smoothing capacitor that smooths and rectifies the power induced in the first secondary winding of the conversion transformer and outputs the smoothing capacitor. an output circuit, a second output circuit that inputs the power induced in the second secondary winding of the conversion transformer when the switching element is off, smoothes and rectifies it, and outputs the same; an output terminal in which the outputs of two output circuits are connected in parallel; and a feedback circuit that maintains the output voltage at a reference output voltage by changing the duty ratio of the switching element according to the output voltage of the output terminal. A switching regulator comprising: 2. A rectifier connected to an AC power supply, a series circuit of the primary winding of a conversion transformer and a switching element connected between the DC output terminals of the rectifier, and the switching element connected in parallel to the series circuit. an input-side smoothing capacitor with a relatively small capacity that corresponds to the switching frequency of the element; a first output circuit that smooths and rectifies the power induced in the first secondary winding of the conversion transformer and outputs the same; A second output circuit smoothes and rectifies the power induced in the second secondary winding of the transformer and outputs the same; a constant voltage circuit set slightly low; an output terminal in which the output of the first output circuit and the output of the constant voltage circuit are connected in parallel; and the switching according to the output voltage of the output terminal. A switching regulator comprising: a feedback circuit that maintains the output voltage of the output terminal at the reference output voltage by changing the duty ratio of the element. 3. A rectifier connected to an AC power source, a series circuit of the primary winding of a conversion transformer and a switching element connected between the DC output terminals of the rectifier, and the switching element connected in parallel to the series circuit. an input-side smoothing capacitor with a relatively small capacity that corresponds to the switching frequency of the element; a first output circuit that smooths and rectifies the power induced in the first secondary winding of the conversion transformer and outputs the same; a second output circuit that smoothes and rectifies the power induced in the second secondary winding of the transformer and outputs the same; and an output voltage of the first output circuit that is connected to the output side of the second output circuit. a constant voltage circuit having a function of being turned off when the output voltage is above a reference output voltage and turned on when it is less than the reference output voltage, and whose output voltage is set to be approximately equal to the reference output voltage; and an output of the first output circuit. The output voltage of the output terminal is set to the reference output voltage by changing the duty ratio of the switching element according to the output voltage of the output terminal and the output terminal of the output terminal connected in parallel with the output of the constant voltage circuit. A switching regulator characterized in that it is comprised of a feedback circuit that maintains