JP2918436B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply, and more particularly to a switching power supply using a commercial AC power supply as an input source.

[0002]

2. Description of the Related Art In recent years, switching power supplies have been frequently used as power supplies for various electronic devices due to their high efficiency conversion characteristics. However, most of them employ a capacitor input method as an input circuit, and thus have a poor power factor. And harmonic components included in the input current have been regarded as a problem. As a method of improving a power factor and reducing a harmonic component included in an input current, there is a technique of providing an active circuit for shaping an input current in an input circuit of a switching power supply device.

FIG. 6 shows a conventional example using this active filter. In FIG. 6, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 40 is an active filter, a choke coil 41, a switching means 4
The active filter 40 supplies the input DC voltage of the switching converter 50 to the input capacitor 7.

[0004] The input AC voltage is full-wave rectified by the full-wave rectifier circuit 3, and this rectified voltage is applied to the choke coil 41 when the switching means 42 is on, and is switched from the full-wave rectifier circuit 3 through the choke coil 41. 42
A current flows through the path, and the choke coil 41 is excited.
When the switching means 42 is off, the choke coil 41
Is excited by the diode 43 from the full-wave rectifier circuit 3.
To the input capacitor 7 via the Control circuit 44
Monitors the voltage of the input capacitor 7, that is, the input DC voltage of the switching converter 50, and also detects the rectified voltage and the current flowing through the choke coil. The waveform is set, and the on / off period of the switching means 42 is adjusted so that the peak value of the current flowing through the choke coil 41 follows this reference waveform. Since the input AC current is obtained by smoothing the current flowing through the choke coil 41 by the input filter 2, the input AC current has a sinusoidal waveform proportional to the input AC voltage by the above operation.

[0005]

In such a conventional configuration, since the switching converter has a two-stage configuration, there is a problem that the circuit scale becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply capable of simplifying a circuit scale, shaping an input AC current into a sine wave shape, and improving a power factor and reducing harmonic components.

[0007]

SUMMARY OF THE INVENTION A switching power supply according to the present invention includes a rectifier circuit for receiving an AC voltage from an input AC power supply and outputting a rectified voltage, an input capacitor, and at least first and second primary windings. And a transformer having a secondary winding, a series circuit of the first primary winding and switching means connected to both ends of the input capacitor, and an output DC voltage supplied to a load to the secondary winding. Connected to the secondary side rectifying and smoothing circuit, and to the positive and negative output terminals of the rectifying circuit, a series circuit composed of the second primary winding, a choke coil, and the input capacitor is connected, and the A control circuit is provided for connecting the first diode in the direction of charging the input capacitor and for adjusting the on / off ratio of the switching means so as to control the output DC voltage. And it features.

[0008]

According to this structure, the choke current supplied from the rectifier circuit to the input capacitor via the choke coil by the on operation of the switching means is a triangular wave current having a peak value proportional to the rectified voltage. The input AC current smoothed via the above has a sinusoidal waveform in proportion to the input AC voltage, so that the power factor can be improved and harmonic components can be reduced. Further, the number of parts is smaller than that in the case where a conventional active filter is used.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2 show a first embodiment.

In FIG. 1, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil,
5 is a first diode, 6 is a switching means, and 7 is an input capacitor. Reference numeral 8 denotes a transformer having a first primary winding 81, a second primary winding 82, and a secondary winding 83. The numbers of turns of the first primary winding 81 and the second primary winding 82 are assumed to be equal. 9 is a secondary-side rectifying / smoothing circuit, 10 is a control circuit, and 11 is a load.

First, the switching means 6, the input capacitor 7, the first primary winding 81 of the transformer 8, the secondary winding 8
3. The secondary-side rectifying / smoothing circuit 9 and the control circuit 10 are configured as a normal switching converter using the voltage of the input capacitor 7 as an input DC voltage, and convert the input DC voltage into a high-frequency AC voltage by turning on and off the switching means 6. Then, the high-frequency AC voltage induced in the secondary winding 83 is rectified and smoothed by the secondary-side rectifying and smoothing circuit 9 and supplied to the load 11 as an output DC voltage. The control circuit 10 has a function of detecting the output DC voltage and adjusting the ON / OFF period of the switching means 6 so as to be stabilized.

Next, an operation in which the input AC current is shaped into a sine wave by this configuration will be described. The full-wave rectifier circuit 3 receives an input AC voltage from the input AC power supply 1 via the input filter 2, and outputs a rectified voltage Ei ((a) in FIG. 2).
When the switching means 6 is ON, the voltage of the input capacitor 7 is applied to the first primary winding 81 of the transformer 8 and the voltage of the input capacitor 7 is induced to the second primary winding 82. Therefore, the sum of the rectified voltage and the voltage of the input capacitor 7 is applied to the first diode 5,
Further, a potential difference between the sum voltage and the voltage of the input capacitor 7, that is, a rectified voltage is applied to the choke coil 4. The choke coil 4 to which the rectified voltage is applied is excited, and the choke current IL that linearly increases is
The current flows from the full-wave rectifier circuit 3 through the second primary winding 82 to charge the input capacitor 7, and the excitation energy is stored in the choke coil 4. When the switching means 6 is turned off, the voltage of each winding of the transformer 8 is inverted, and the voltage is inverted because the choke coil 4 also emits excitation energy. At this time, the flyback voltage induced in the second primary winding 82 is a rectified voltage. If it is larger, the first diode 5 conducts, and the choke current IL that degausses the choke coil 4 flows while decreasing linearly to charge the input capacitor 7 via the first diode 5. Second primary winding 8
When the flyback voltage induced in 2 is less than the rectified voltage,
The choke current IL that decreases linearly flows from the full-wave rectifier circuit 3 through the second primary winding 82 to charge the input capacitor 7, and demagnetizes the choke coil 4. FIG. 2B shows the choke current IL. If the capacitance of the input capacitor 7 is sufficiently large and the voltage can be regarded as a substantially stable DC voltage in a steady state, the ON / OFF period of the switching means 6 for stabilizing the output DC voltage becomes substantially constant. Choke current I in the cycle
The peak value of L is substantially proportional to the rectified voltage Ei. As described above, the input AC current Ii is obtained by smoothing the current approximate to the choke current IL by the input filter 2, although the input AC current Ii slightly depends on the conduction condition of the first diode 5.
A sinusoidal waveform as shown in FIG.

As described above, the second primary winding 82 is provided in the transformer 8 of the switching converter, and the full-wave rectifier circuit 3 is provided.
Primary winding 82 and choke coil 4
And a series circuit comprising an input capacitor 7 and connecting the first diode 5 in a direction for charging the input capacitor 7 via the choke coil 4. Since the choke current IL having a peak value substantially proportional to the rectified voltage Ei flows through the full-wave rectifier circuit 3, the input DC current Ii smoothed by the input filter 2 has a sinusoidal waveform, and the power factor is improved. And the harmonic components can be reduced.

In this embodiment, the choke coil 4 has been described on the premise of discontinuous operation. However, if the input AC current waveform is not sinusoidal, the choke coil 4 has a higher power than the capacitor input system even in continuous operation. The characteristics of the rate and low harmonic components can be obtained.

FIG. 3 shows a second embodiment. 3, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil, 5 is a first diode,
6 is a switching means, 7 is an input capacitor. 8
Is a transformer, a first primary winding 81, a second primary winding 8
2. It has a secondary winding 83. The first primary winding 81 and the second
Of the primary winding 82 are equal. 9 is a secondary-side rectifying / smoothing circuit, 10 is a control circuit, and 11 is a load. The above is the same as the configuration in FIG. 1 in that the second diode 12 is connected in series with the choke coil 4 in the direction in which the input capacitor 7 is charged.

With respect to the switching power supply device thus configured, the same components as those shown in FIG. 1 operate in the same manner, and therefore description thereof will be omitted.
The operation and role of No. 2 will be described.

When the choke coil 4 is in a discontinuous operation without the second diode 12, the choke coil 4 has its inductance and parasitic capacitance before the switching means 6 is turned on after the choke current has finished flowing. Causes a resonance phenomenon. Since one end of the choke coil 4 is connected to the input capacitor 7, the resonance voltage having the amplitude based on the potential of the input capacitor 7 is applied to the second primary winding 82.
The flyback voltage superimposed on the
Since the voltage is applied to the full-wave rectifier circuit 3, a high-voltage rectifier circuit 3 is required to have a high withstand voltage. Also leads. However, by inserting the second diode 12 as shown in FIG. 3, the resonance phenomenon of the choke coil 4 is cut off by the second diode 12 to the full-wave rectifier circuit 3 and is completed by the choke coil 4. . That is, it serves to prevent the resonance phenomenon of the choke coil 4 from being transmitted to the full-wave rectifier circuit 3.

As described above, the second direction in which the input capacitor 7 is charged in series with the choke coil 4 of the first embodiment.
By connecting the diode 12, the resonance phenomenon that occurs after the choke coil 4 has finished flowing the current prevents the resonance phenomenon from being transmitted to the full-wave rectifier circuit 3, and protects the full-wave rectifier circuit 3. Noise increase due to the resonance phenomenon can be suppressed.

FIG. 4 shows a third embodiment. In FIG. 4, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil, 5 is a first diode,
6 is a switching means, 7 is an input capacitor. 8
Is a transformer, a first primary winding 81, a second primary winding 8
2. It has a secondary winding 83. The first primary winding 81 and the second
Of the primary winding 82 are equal. 9 is a secondary-side rectifying / smoothing circuit, 10 is a control circuit, and 11 is a load. The above is the same as the configuration in FIG. The difference from the configuration in FIG. 1 is that the third diode 13 is connected from the full-wave rectifier circuit 3 to the input capacitor 7.

The operation of the switching power supply having the above-described configuration, which is similar to the configuration shown in FIG.
The operation and role of No. 3 will be described.

In the first embodiment having the circuit configuration shown in FIG. 1, in the case of a switching converter of the type in which the ON period of the switching means 6 does not fluctuate so much with a load fluctuation,
When the load becomes heavy, the input power supplied through the choke coil 4 becomes insufficient due to the on / off of the switching means 6, and the choke coil 4 and the second primary winding 82 of the transformer 8 are superimposed with direct current. Such DC superposition makes the design of the choke coil 4 and the transformer 8 difficult, and in the worst case, causes magnetic saturation, which may cause a great deal of stress on each component. However, the insertion of the third diode 13 allows the third diode 13 to be supplied from the full-wave rectifier circuit 3 to the input capacitor 7 separately from the current flowing through the choke coil 4 when the switching means 6 is turned on and off under heavy load. A loop is provided for flowing an input current through the circuit, thereby preventing DC superposition on the choke coil 4 and the transformer 8 and clamping the output voltage of the full-wave rectifier circuit 3 to the voltage of the input capacitor 7.

As described above, by connecting the third diode 13 from the full-wave rectifier circuit 3 to the input capacitor 7 in the first embodiment, the DC superposition of the choke coil 4 and the transformer 8 and the magnetic saturation due to the DC superposition can be reduced. In addition, the output voltage of the full-wave rectifier circuit 3 can be clamped to the voltage of the input capacitor 7 to reduce the withstand voltage.

FIG. 5 shows a fourth embodiment. In FIG. 5, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil, 5 is a first diode,
6 is a switching means, 7 is an input capacitor. 8
Is a transformer, a first primary winding 81, a second primary winding 8
2. It has a secondary winding 83. The first primary winding 81 and the second
Of the primary winding 82 are equal. 10 is a control circuit, and 11 is a load. The above is the same as the configuration in FIG. Reference numeral 12 denotes a second diode having the same configuration as that of FIG. Reference numeral 13 denotes a third diode having the same configuration as that of FIG. 14 and 15 are diodes, 16
Denotes a secondary choke coil, and 17 denotes an output capacitor. The diodes 14 and 15, the secondary choke coil 16 and the output capacitor 17 constitute a choke input type rectifying / smoothing circuit 90.

The operation of the thus configured switching power supply will be described below. The switching means 6, the input capacitor 7, the first primary winding 81, the secondary winding 83 of the transformer, the choke input type rectifying / smoothing circuit 90, and the control circuit 10 are feedforward converters that use the voltage of the input capacitor 7 as an input DC voltage. The input DC voltage is converted into a high-frequency AC voltage by the on / off operation of the switching means 6 and applied to the first primary winding 81 of the transformer, and the high-frequency AC voltage induced in the secondary winding 83 is choked input type. It is rectified and smoothed by the rectifying and smoothing circuit 90 and supplied to the load 11 as an output DC voltage. The control circuit 10 has a function of detecting the output DC voltage and adjusting the ON / OFF period of the switching means 6 so as to be stabilized. The first embodiment has described that the choke coil 4, the first diode 5, and the second primary winding 82 make the input AC current a sine wave, and perform the functions of improving the power factor and reducing harmonic components. It is on the street. The role of the second diode is as described in the second embodiment, and the role of the third diode is as described in the third embodiment.

Usually, such a feedforward converter has a reset winding for demagnetizing the magnetic flux of the transformer 8 when the switching means 6 is off.
Is provided. Hereinafter, it will be described that the second primary winding 82 also functions as a reset winding in the present embodiment.

In FIG. 5, when the switching means 6 is turned off, each winding voltage of the transformer 8 is inverted to generate a flyback voltage. On the other hand, the voltage of the choke coil 4 is also inverted to release the excitation energy, and the degaussing current flows to the input capacitor 7 via the first diode 5 and the second diode 12. The flyback voltage generated in the second primary winding 82 is clamped by the first diode 5 and the third diode 13 to the voltage of the input capacitor 7, and the excitation energy stored in the transformer 8 is regenerated to the input capacitor 7. Is done. That is, the second primary winding 82 also has a function of a reset winding for degaussing the transformer 8.

As described above, in the first embodiment, the secondary side rectifying / smoothing circuit is a choke input type rectifying / smoothing circuit, and the second diode 12 is connected in series with the choke coil 4 to charge the input capacitor 7. Connected to the input capacitor 7 from the full-wave rectifier circuit 3 to the third diode 13
, The function of the reset winding can be shared by the second primary winding 82.

In the first to fourth embodiments, the second
The number of turns of the primary winding 82 is the same as that of the first primary winding 81. However, it is needless to say that the number of turns may be different, though this affects the setting of the on / off ratio of the switching means 6 and the conduction period of the input AC current. .

[0029]

As described above, according to the present invention, a rectifier circuit for receiving an AC voltage from an input AC power supply and outputting a rectified voltage, an input capacitor, at least first and second primary windings and a secondary A transformer having a winding, and a series circuit of the first primary winding and switching means connected to both ends of the input capacitor, and a secondary winding for supplying an output DC voltage to a load is connected to the secondary winding. Side rectifying / smoothing circuit, a positive / negative output terminal of the rectifying circuit is connected to a series circuit including the second primary winding, a choke coil, and the input capacitor, and the input capacitor is connected via the choke coil. A first diode is connected in a charging direction, and a control circuit for adjusting an on / off ratio of the switching means so as to control the output DC voltage is provided.
An excellent switching power supply device capable of shaping an input AC current into a sine wave shape and improving a power factor and reducing harmonic components with a smaller number of components than in the case where a conventional active filter is provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of a switching power supply device of the present invention.

FIG. 2 is an input waveform diagram of the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment of the switching power supply device of the present invention.

FIG. 4 is a configuration diagram of a third embodiment of the switching power supply device of the present invention.

FIG. 5 is a configuration diagram of a fourth embodiment of the switching power supply device of the present invention.

FIG. 6 is a configuration diagram of a conventional switching power supply device.

[Description of Signs] 1 Input AC power supply 2 Input filter 3 Full-wave rectifier circuit [Rectifier circuit] 4 Choke coil 5 First diode 6 Switching means 7 Input capacitor 8 Transformer 81 First primary winding 82 Second primary winding Line 83 Secondary winding 9 Secondary side rectifying and smoothing circuit 10 Control circuit 11 Load 12 Second diode 13 Third diode 90 Choke input type rectifying and smoothing circuit [Secondary side rectifying and smoothing circuit]

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshinori Kobayashi 10-13 Minamicho, Hanno City, Saitama Prefecture Inside Shindengen Industry Co., Ltd. (72) Inventor Yutaka Sekine 10-13 Minamimachi, Hanno City, Saitama Prefecture Shindengen (56) References JP-A-4-181407 (JP, A) JP-A-4-29566 (JP, A) JP-A-6-217537 (JP, A) JP-A-7-15967 ( JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02M 7/00-7/40 H02M 3/00-3/44

Claims (4)

(57) [Claims] A rectifier circuit for receiving an AC voltage from an input AC power supply and outputting a rectified voltage; an input capacitor; a transformer having at least first and second primary and secondary windings; A series circuit of the first primary winding and the switching means is connected to both ends of the capacitor, and a secondary rectifying and smoothing circuit for supplying an output DC voltage to a load is connected to the secondary winding, A series circuit consisting of the second primary winding, a choke coil, and the input capacitor is connected to the positive and negative output terminals of the rectifier circuit, and a first diode is charged in a direction in which the input capacitor is charged via the choke coil. A switching power supply device which is connected and provided with a control circuit for adjusting an on / off ratio of the switching means so as to control the output DC voltage. 2. A first diode is connected in a direction for charging an input capacitor in series with a choke coil.
A switching power supply as described. 3. The switching power supply according to claim 1, wherein a third diode is connected so that a current flows from the rectifier circuit to the input capacitor. 4. A second diode is connected in series with a choke coil in a direction of charging the input capacitor, and a third diode is connected so that current flows from the rectifier circuit to the input capacitor. 2. The switching power supply according to claim 1, wherein the rectifying and smoothing circuit is a choke input type.