JP2002034254A - Switching power supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the dimensional reduction, cost reduction, the conversion gain improvement and noise suppression of an apparatus while a high input power factor is maintained. SOLUTION: This switching power supply apparatus has 1st and 2nd transformers 3 and 2 having respective primary windings and secondary windings, two rectifier circuits rectifying an AC input voltage VAC to generate ripple voltages VR, a smoothing circuit 13 smoothing the ripple voltage generated by one rectifier circuit (11 and 12) to generate a DC voltage VDC, and a switching device 4. A series circuit comprising the primary winding 3a of the 1st transformer 3 and the switching device 4 is connected between the positive polarity output terminal and negative polarity output terminal of the other rectifier circuit 21, and the primary winding 2a of the 2nd transformer 2 is connected between the smoothing circuit 13 and the positive polarity output terminal of the other rectifier circuit 21. By turning on/off the switching device 4, voltages induced in the respective secondary windings 2a and 3a of both the transformers 2 and 3 are rectified and synthesized to generate an output voltage V0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for generating an output voltage based on a smoothed DC voltage and a pulsating voltage, and more particularly to a switching power supply capable of converting a voltage at a high power factor. Things.

[0002]

2. Description of the Related Art Generally, in a capacitor-input type switching power supply, input current harmonics are generated when an input current flows in a pulse shape. Therefore, when the power generated by the switching power supply is large or when a plurality of power supplies are used at the same time, this harmful harmonic component has a large effect on the commercial power system. It causes various problems such as heating. For this reason, in recent years, reduction of input current harmonics has been demanded, and various power factor improving switching power supply devices capable of reducing the input current harmonics have been proposed. As a switching power supply of this type, the applicant has already developed a power supply 41 shown in FIG.

The power supply device 41 includes a capacitor input type buck-boost converter circuit 46 and a buck-boost converter circuit 47 for power factor improvement.
6, 47 employs a flyback configuration in which one switching element is commonly used. Specifically, the power supply device 41 includes transformers 42 and 43,
The diodes 11, 12, the capacitor 13, and the diode 44 are provided on the primary circuit side of the circuits 2, 43 as circuits constituting a part of the buck-boost converter circuit 46.
On the primary circuit side, a diode stack 21 as a circuit constituting a part of the buck-boost converter circuit 47,
A noise filter 22 composed of capacitors 23 and 24 and a choke coil 25, a diode 45, and a switch 4 composed of, for example, an FET are provided.
On the other hand, diodes 31, 32 and a capacitor 33 are provided on the secondary circuit side of the transformers 42, 43.

In this power supply device 41, a diode 11,
The DC voltage VDC is generated by rectifying and smoothing the input AC VAC by the capacitor 12 and the capacitor 13, and the diode stack 21 rectifies the input AC VAC to generate a pulsating voltage VR. In this case, the high voltage period of the pulsating voltage VR (the period of the mountain)
, The buck-boost converter circuit 47 outputs the output voltage VO
Generate Specifically, during the ON period of the switch 4,
A current I11 flows through a path composed of the diode stack 21, the noise filter 22, the primary winding 43a of the transformer 43, the diode 45, and the switch 4, whereby energy is stored in the transformer 43. Next, during the OFF period of the switch 4, the diode 32 and the capacitor 33
Generates the output voltage VO by rectifying and smoothing the voltage induced in the secondary winding 43b of the transformer 43.

On the other hand, when the voltage of the pulsating voltage VR gradually decreases, the input power for the buck-boost converter circuit 47 to generate power as the output voltage VO becomes insufficient. Therefore, the step-up / step-down converter circuit 46 gradually contributes to the generation of the output voltage VO, and only the step-up / step-down converter circuit 46 generates the output voltage VO during the period when the pulsating voltage VR is the lowest. In this case, during the ON period of the switch 4, the positive terminal of the capacitor 13 and the transformer 42
A current I12 flows through a path composed of the primary winding 42a, the diode 44, the switch 4, and the negative terminal of the capacitor 13, whereby energy is stored in the transformer 42. Next, during the OFF period of the switch 4, the diode 31 and the capacitor 33 generate an output voltage VO by rectifying and smoothing the voltage induced in the secondary winding 42b of the transformer 42. As a result, the output voltage VO is stably generated over one cycle of the input AC VAC. Also,
In the power supply device 41, since the input current based on the input AC VAC flows over almost the entire cycle of the input AC VAC, a good power factor improving effect can be obtained.
Because of the converter system, the output voltage VO can be generated with high efficiency.

[0006]

However, the power supply device 41 has the following points to be improved. That is, in the power supply device 41, the current I11 (or I12) flows through the diode 45 (or 44) during the ON period of the switch 4, so that the power loss due to the diode 45 (or 44) always occurs. For this reason, the conversion efficiency is reduced accordingly, and it is preferable to improve this. In the off period of the switch 4, a current in the same direction as the current I 11 or the current I 12 is supplied to the parasitic capacitance 5 built in the switch 4.
, The parasitic capacitance 5 is charged. In this case, the energy stored in the parasitic capacitance 5 is prevented from being released by the diodes 44 and 45. Therefore, when the switch 4 is turned on, both ends of the parasitic capacitance 5 are short-circuited by the switch 4, so that the stored energy of the parasitic capacitance 5 is lost. For this reason, the conversion gain may be reduced or noise may be generated. As a result, it is preferable to improve this point. In this case, diode 4
It is also conceivable to directly connect the winding start side terminal of the primary winding 42a and the winding end side terminal of the primary winding 43a without disposing the 4, 45. However, in such a case, when a voltage is induced in one primary winding 42a (or 43a), a short-circuit phenomenon occurs that a current flows into the capacitor 24 (or 13) via the other primary winding 43a (or 42a). Occurs, and in such a case, there is a problem that more power is lost.

Further, in the power supply device 41, the pulsating voltage VR
During the high voltage period, the buck-boost converter circuit 47 generates the output voltage VO, and during the low voltage period (valley period) of the pulsating voltage VR, the buck-boost converter circuit 46 generates the output voltage VO. Therefore, both transformers 42, 43
Need to have respective capacities corresponding to the output power of the device, so that two switching transformers having the same capacity are required. Therefore, the power supply 41
In addition, the cost of parts increases and the size of the apparatus is increased. It is preferable to improve this.

Further, as a technically related power supply device,
A switching power supply disclosed in Japanese Patent Application Laid-Open No. Hei 7-22247 is also conventionally known. In this switching power supply, both ends of the parasitic capacitance built in the switch element (24) are switched by the switch element (24). Because of the short-circuit, there is a problem that the conversion gain is reduced and noise is generated as in the case of the power supply device 41 described above. Also,
This switching power supply device is different from the power supply device 41 in that the transformers 42 and 43 in the power supply device 41 are configured by one transformer (20). However, in this switching power supply device, a diode (1
Since 1) is disposed in the DC voltage supply path, a loss always occurs due to the DC current flowing through the diode (11). For this reason, this switching power supply has a problem that efficiency is poor. Also,
In this switching power supply device, during the low voltage period of the pulsating voltage, a so-called non-current state in which the input current IIN does not flow through any of the full-wave rectifier (3) and the first and second diodes (8) and (9). Continuous period te (see FIG. 2 of the publication)
(D), there is also a problem that the input power factor is low and it is difficult to satisfy the harmonic regulation.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a switching power supply device capable of reducing the size and cost of the device, improving the conversion gain, and reducing noise while maintaining a high input power factor. The purpose is to provide.

[0010]

According to a first aspect of the present invention, there is provided a switching power supply device comprising: a first and a second transformer having a primary winding and a secondary winding; To generate pulsating voltage respectively 2
A rectifying circuit, a smoothing circuit for smoothing a pulsating voltage generated by one of the rectifying circuits to generate a DC voltage, and a switching element; and a series circuit of a primary winding of the first transformer and the switching element. Is connected between the positive output terminal and the negative output terminal of the other rectifier circuit, the primary winding of the second transformer is connected between the smoothing circuit and the positive output terminal of the other rectifier circuit, and the switching element is switched. Thus, an output voltage is generated by rectifying and combining voltages induced in each secondary winding of both transformers.

According to a second aspect of the present invention, there is provided a switching power supply device comprising: a first and a second transformer each having a primary winding and a secondary winding; and a rectifying circuit for rectifying an input AC to generate a pulsating voltage. A smoothing circuit for smoothing a pulsating voltage to generate a DC voltage, a one-way element connected between the rectifying circuit and the smoothing circuit for conducting only a current from the rectifying circuit to the smoothing circuit, and a switching circuit. And a first element.
A series circuit of the primary winding of the transformer and the switching element is connected between the positive output terminal and the negative output terminal of the rectifier circuit, and the primary winding of the second transformer is connected to the smoothing circuit and the positive output terminal of the rectifier circuit. An output voltage is generated by rectifying and combining the voltages induced in the respective secondary windings of the two transformers by switching the switching elements.

According to a third aspect of the present invention, there is provided a switching power supply device including a first and a second transformer having a primary winding and a secondary winding, respectively, and a rectifying circuit for rectifying an input AC to generate a pulsating voltage. A smoothing circuit for smoothing the pulsating voltage supplied from the rectifier circuit through the primary winding of the second transformer to generate a DC voltage, and a switching element. A series circuit with the element is connected between the positive output terminal and the negative output terminal of the rectifier circuit, a primary winding of the second transformer is connected between the smoothing circuit and the positive output terminal of the rectifier circuit, and a switching element is connected. By switching, the output voltage is generated by rectifying and combining the voltages induced in the respective secondary windings of both transformers.

Further, a switching power supply according to a fourth aspect of the present invention is the switching power supply according to any one of the first to third aspects, wherein only the noise filter and a current flowing from the noise filter to the series circuit are conducted. The directional element is connected between the positive output terminal of the rectifier circuit and the series circuit.

According to a fifth aspect of the present invention, there is provided a switching power supply device according to any one of the first to fourth aspects, wherein the switching power supply device is a forward type switching power supply device, wherein the height of each secondary winding in both transformers is high. First and second rectifying diodes each having an anode connected to a potential terminal and a cathode connected to each other; a smoothing choke coil connected between the cathodes of both diodes and a high potential output unit; A smoothing capacitor connected between one end of the choke coil on the high potential output side and the low potential output portion, and an anode connected to the low potential terminal and the low potential output portion of each secondary winding and the cathode thereof. And a commutating diode connected to the cathodes of both diodes.

According to a sixth aspect of the present invention, there is provided a switching power supply apparatus according to any one of the first to fifth aspects, wherein the switching element is capacitively connected in parallel to the switching element. The energy stored in the element is controlled to the ON state after being regenerated to the smoothing circuit side via both primary windings.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a switching power supply according to the present invention will be described below with reference to the accompanying drawings. The same components as those of the power supply device 41 are denoted by the same reference numerals, and redundant description will be omitted, and redundant description of the same operation will be omitted.

As shown in FIG. 1, a power supply 1 is a flyback type switching power supply, and includes a switching transformer 2 (second transformer) and a transformer 3.
(First transformer). In this case, the winding end side terminal of the primary winding 2a in the transformer 2 is connected to the positive terminal of the capacitor 13, and the winding start side terminal of the primary winding 2a is connected to the winding end side terminal of the primary winding 3a in the transformer 3. It is connected to the positive output terminal of the diode stack 21 (the other rectifier circuit, rectifier circuit). On the other hand, the winding start side terminal of the primary winding 3 a of the transformer 3 is connected to the negative output terminal of the diode stack 21 via the switch 4.

The power supply device 1 includes two buck-boost converter circuits 6 and 7 in the same manner as the power supply device 41. The buck-boost converter 6 includes diodes 11 and 12 for rectifying the input AC VAC, a smoothing capacitor 13 for smoothing the rectified voltage to generate a DC voltage VDC, transformers 2 and 3, and a switch 4 as a switching element. The step-up / step-down converter 7 for power factor improvement includes a diode stack 21, a transformer 3, and a switch 4. That is, also in the power supply device 1, the switch 4 is commonly used by both the buck-boost converters 6 and 7. The diodes 11 and 12 constitute one rectifier circuit of the present invention, and the capacitor 13 constitutes a smoothing circuit of the present invention. On the other hand, diodes 31 and 32 for rectification and a capacitor 3 for smoothing are provided on the secondary winding 2b side of the transformer 2 and the secondary winding 3b side of the transformer 3.
3 are provided.

In the power supply device 1, the diodes 11, 1
2 and a capacitor 13 generate a DC voltage VDC by rectifying and smoothing the input AC VAC shown in FIG.
By rectifying the input AC VAC, the diode stack 21 generates a pulsating voltage VR (see FIG. 3B) whose maximum voltage VMAX is substantially equal to the DC voltage VDC. During a high voltage period of the pulsating voltage VR (for example, a period exceeding the voltage VS shown in FIG. 3B), the buck-boost converter 7 mainly generates the output voltage VO.
That is, in the power supply device 1, during the ON period of the switch 4, the DC voltage VDC between the primary winding 2a of the transformer 2 and the primary winding 3a of the transformer 3 is substantially equal to the maximum voltage VMAX of the pulsating voltage VR. And a pulsating voltage VR is applied to both ends of the primary winding 3a of the transformer 3. Therefore, the DC voltage V is applied across the primary winding 2a of the transformer 2.
A voltage difference between DC and pulsating voltage VR is applied. Therefore,
The smaller the voltage difference, the greater the contribution of the buck-boost converter 7 to generate power, and the greater the voltage difference, the greater the contribution of the buck-boost converter 6 to generate power. Therefore, during the high voltage period of the pulsating voltage VR,
When the switch 4 is turned on, the current I1 mainly flows through a path composed of the positive output terminal of the diode stack 21, the primary winding 3a of the transformer 3, the switch 4, and the negative output terminal of the diode stack 21, Thereby, energy is stored in the transformer 3. Next, during the OFF period of the switch 4, the diode 32 and the capacitor 33 generate an output voltage VO by rectifying and smoothing the voltage induced in the secondary winding 3b of the transformer 3.

Next, during a low voltage period in which the voltage of the pulsating voltage VR gradually decreases and the voltage of the pulsating voltage VR becomes lower than the voltage VS, the buck-boost converter 6 mainly generates the output voltage VO. More specifically, in this period, during the ON period of the switch 4, the current I2 flows through the positive terminal of the capacitor 13, the primary winding 2a of the transformer 2, the primary winding 3a of the transformer 3, the switch 4, and the diode stack 2.
1 and a current path composed of the negative terminal of the capacitor 13, whereby energy is stored in the transformers 2 and 3. In this case, the diode stack 21
Function as a one-way element to prevent current from flowing from the primary winding 2a of the transformer 2 to the positive output terminal. Next, during the OFF period of the switch 4, the diodes 31, 32 and the capacitor 33 rectify and smooth the voltages induced in the secondary windings 2b, 3b of the transformers 2, 3, respectively, to generate an output voltage VO.

The voltage value of the voltage VS defining the boundary between the high voltage period and the low voltage period of the pulsating voltage VR is determined by the inductance of the primary winding 2a in the transformer 2 and the inductance of the primary winding 3a in the transformer 3. Are “L2” and “L3”, respectively, and the DC voltage V
When the DC voltage value is “VMAX”, the inductance L
The inductance L is the sum of the inductance 2 and the inductance L3.
It is obtained by multiplying the value obtained by dividing 3 by the voltage value VMAX. Further, the inductance L2 is defined to be larger than the inductance L3 (for example, 5: 3). In this case, as the inductance L2 is made larger than the inductance L3, the voltage value of the voltage VS decreases.
The contribution of the buck-boost converter circuit 6 to the generation of the output voltage VO is reduced. Further, the capacity required for each of the transformers 2 and 3 is about the same as the output power of the device for the transformer 3, and for the transformer 2, the inductance L2 is obtained by adding the inductance L2 and the inductance L3. Is multiplied by the capacity of the transformer 3. Therefore, in the above example (for example, 5: 3), the transformers 2 and 3 as a whole are:
The capacity is 1.37 times (1 + 3/8 times) the output power of the device. For this reason, the transformer 2 can be reduced in size as compared with the conventional power supply device 41 (about twice), so that the size of the device can be reduced, and the cost of parts and the cost of the device can be reduced. Can be achieved.

With the above operation, as shown in FIGS. 2C and 2D, during the period when the pulsating voltage VR is higher than the voltage VS, the current I1 is mainly supplied to the primary winding 3a of the transformer 3. Flows, the output voltage VO is generated, and during the period when the voltage of the pulsating voltage VR is lower than the voltage VS, the current I is mainly supplied to both the primary windings 2a and 3a.
2 flows to generate an output voltage VO. On the other hand, as shown in FIG. 2E, when the pulsating voltage VR is near the maximum voltage VMAX, the input current I1IN flows into the diodes 11 and 12 in a pulsed manner. Therefore, the input current IIN flowing into the power supply device 1 is as shown in FIG.
(E) and the input current I1IN shown in (e) of the figure, the current waveform is as shown in (f) of the figure.
Therefore, the current IIN flows over almost the entire cycle of the input AC VAC, and as a result, the input power factor becomes 0.85-0.
A good power factor improvement effect of about 9 can be obtained. Therefore, the input power factor can be sufficiently improved as compared with the switching power supply disclosed in Japanese Patent Application Laid-Open No. 7-2222447 having a discontinuous period.

On the other hand, when the switch 4 is turned off, a current in the same direction as the current I1 or the current I2 flows into the parasitic capacitance 5, so that the parasitic capacitance 5 is charged. In this case, in the power supply device 1, since no semiconductor element such as a diode for preventing the outflow of current is provided in the path from the switch 4 to the capacitor 13, the parasitic capacitance 5, the primary winding 3 a of the transformer 3, A current in a direction opposite to the current 1 flows through a path including the primary winding 2a of the transformer 2 and the capacitor 13. Thereby, the energy stored in the parasitic capacitance 5 is regenerated, and the charging voltage of the parasitic capacitance 5 decreases. Then, a resonance phenomenon occurs in which charge and discharge are repeated, that is, a current flows thereafter to charge the parasitic capacitance 5 again. Therefore, a switching control circuit (not shown) controls the switch 4 to be turned on when the charging voltage of the parasitic capacitance 5 decreases to 0 volts or near 0 volts. Thereby, a so-called zero volt switch is performed. Note that the resonance frequency f is determined by setting the capacitance value of the parasitic capacitance 5 to “COSS”.
Is represented by the following equation. f = 1 / (2 × π × √ ((L2 + L3) × COSS)) formula

Therefore, part or all of the stored energy of the parasitic capacitance 5 is regenerated to the capacitor 13,
A short circuit when the switch 4 is turned on can be avoided. As a result, since the power loss can be reduced, the conversion gain of the device can be improved, and the short-circuit noise can be reduced. Also, the power supply device 41,
Unlike the switching power supply disclosed in Japanese Patent Application Laid-Open No. Hei 7-22247, diodes are connected between the primary winding 2a of the transformer 2 and the switch 4 and between the primary winding 3a of the transformer 3 and the switch 4. Power loss due to the diode can be avoided,
Conversion efficiency can be improved.

Next, a power supply device 1A according to another embodiment is described.
Will be described with reference to FIG. As shown in the figure, the power supply device 1A differs from the power supply device 1 in that a diode stack (full-wave rectifier) 21 corresponding to the other rectifier circuit of the present invention functions as one rectifier circuit of the present invention. Is adopted. Further, between the positive electrode output terminal of the diode stack 21 and the capacitor 13 corresponding to the smoothing circuit in the present invention,
Diode 14 (unidirectional element) for conducting only current from diode stack 21 to capacitor 13
Is connected. Therefore, according to the power supply device 1A, two rectifier circuits can be configured with one rectifier, and accordingly, the size and cost of the device can be reduced. The diode 14 may be connected between an anode of a diode 26 described later and a positive terminal of the capacitor 13.

Further, unlike the power supply 1, the power supply 1A includes a noise filter 22 and a diode 26 corresponding to a one-way element in the present invention. The noise filter 22 includes a positive output terminal of the diode stack 21 and the primary windings 2a,
It is connected between the connection portions 3a. The noise filter 22 includes, for example, two capacitors 23 and 24 and a choke coil 25. On the other hand, the diode 26 is connected between the connection portion between the noise filter 22 and the primary windings 2a and 3a of the transformers 2 and 3, and only the current flowing from the noise filter 22 to the connection portion between the primary windings 2a and 3a. To prevent the current from flowing back from the primary winding 2a of the transformer 2 and the primary winding 3a of the transformer 3 to the noise filter 22. By adopting this configuration, the noise filter 22 removes switching noise generated at the time of switching by the switch 4, so that the amount of noise leakage to the input unit side to which the input AC VAC is supplied can be reduced. it can. In this power supply device 1A, basically, it operates in the same manner as the power supply device 1. Therefore, in FIG.

Next, a power supply device 1B according to still another embodiment will be described with reference to FIG. As shown in the figure, in the power supply device 1B, similarly to the power supply device 1A, a diode stack 21 corresponding to the other rectifier circuit of the present invention also functions as one rectifier circuit of the present invention. Is employed, and the capacitor 13 as a smoothing circuit is connected to the primary winding 2a in the transformer 2.
And a pulsating voltage VR supplied from the diode stack 21 through the primary winding 2a to generate a DC voltage VDC.

In the power supply device 1B, the input current I1IN
Flows through a path including the positive output terminal of the diode stack 21, the primary winding 2a of the transformer 2, and the capacitor 13, so that the capacitor 13
And is charged. According to this configuration, since the two diodes 11 and 12 functioning as rectifier circuits can be omitted, the size and cost of the device can be reduced accordingly. In addition, since the power supply device 1B basically operates in the same manner as the power supply device 1, the same components as those of the power supply device 1 are denoted by the same reference numerals in FIG.
The description of the operation is omitted.

Further, as shown in FIG. 5, the switching power supply according to the present invention comprises a forward power supply 1C.
It can also be applied to The power supply device 1C includes a diode 31 (second diode) and a diode 32 (first diode) in the secondary circuits on the secondary windings 2b and 3b sides of both transformers 2 and 3.
, A commutation diode (flywheel diode) 34, a smoothing capacitor 33, and a smoothing choke coil 35. In this case, in this secondary circuit, the diode 32 and the choke coil 35 are connected between the winding end side terminal (high potential terminal) of the secondary winding 3b of the transformer 3 and the high potential output section (+ voltage output terminal). Connected and the secondary winding 2 of the transformer 2
The diode 31 and the choke coil 35 are connected between the winding end side terminal (high potential terminal) of b and the high potential output section. Further, a capacitor 33 is connected between the high potential output section and the low potential output section (earth potential terminal). Further, the diode 34 has an anode connected to a winding start terminal (low potential terminal) of each of the secondary windings 2b and 3b of the transformers 2 and 3, and a low potential output section, and a cathode connected to the cathodes of the diodes 31 and 32. It is connected to the.

In the power supply device 1C, basically, as in a normal forward type power supply device, both diodes 31, 32 are induced in each of the secondary windings 2b, 3b during the ON period of the switch 4. The voltage is rectified, and the choke coil 35 and the capacitor 33 generate the output voltage VO by smoothing the rectified DC voltage. Also,
A diode conducts a flywheel current based on the energy stored in the choke coil. According to the power supply device 1C, since one diode 34 functions as a flywheel diode, the secondary circuit of the forward-type switching power supply device can be easily configured.

The switching power supply according to the present invention is not limited to the configuration of the power supply devices 1 to 1C described above, and can be appropriately changed. For example, the power supply devices 1, 1B, and 1C can be provided with the noise filter 22 and the diode 26, of course. Further, the present invention relates to transformers 2 and 3
The number of turns of each of the primary windings 2a and 3a and the secondary windings 2b and 3b is not particularly limited, and can be appropriately changed. Further, the switch 4 is not limited to an FET, and various switching elements such as a transistor can be employed. Further, the switch 4 may be connected between the winding end side terminal of the primary winding 3a of the transformer 3 and the winding start side terminal of the primary winding 2a of the transformer 2. In addition, when applied to a forward-type power supply, the connection positions of the diodes 31 and 32 and the choke coil 35 can be changed as appropriate as long as a function equivalent to that of the power supply device 1C can be realized. For example, the choke coil 35 can be connected between the winding start terminals of the secondary windings 2b and 3b and the low potential output section. Also, a diode 31,
32 can be connected between the winding start terminal of each of the secondary windings 2b and 3b and the low potential output section.

[0032]

As described above, according to the switching power supply device of the first aspect, the series circuit of the primary winding of the first transformer and the switching element is connected to the positive output terminal and the negative output terminal of the other rectifier circuit. And the primary winding of the second transformer is connected between the smoothing circuit and the positive output terminal of one of the rectifier circuits, the switching elements are switched, and induced in each secondary winding of both transformers. By rectifying and combining voltages to generate an output voltage, power loss can be reduced because a semiconductor such as a diode is not connected in series to both primary windings, thereby improving conversion gain. Can be. Further, since the second transformer can be reduced in size as compared with the power supply device 41, the size of the device can be reduced, and the cost of parts and the price of the device can be reduced. . Furthermore, as a result of allowing the current to flow into the device over substantially the entire cycle of the input AC, the input power factor is lower than that of the switching power supply device disclosed in Japanese Patent Application Laid-Open No. 7-2222447 having a discontinuous period. Can be sufficiently improved. In addition, the stored energy of the capacitance equivalently connected in parallel to the switching element is regenerated by a resonance phenomenon occurring on the primary winding side of both transformers, so that the power loss when the switching element is turned on is reduced. As a result, the conversion gain of the device can be improved and the short-circuit noise can be reduced.

According to the switching power supply device of the present invention, since one rectifier circuit generates the pulsating voltage and the DC voltage to be supplied to each primary winding of both transformers, two rectifier circuits are used. As compared with the configuration used, the size and cost of the device can be reduced.

Further, according to the switching power supply device of the fourth aspect, the noise filter and the one-way element are connected between the positive output terminal of the rectifier circuit and the series circuit, so that the primary winding of the second transformer is connected. Since the switching noise generated at the time of switching is removed by the noise filter while the backflow of the current from the line to the noise filter is prevented, the amount of noise leakage to the AC input unit side can be reduced.

In addition, according to the switching power supply of the fifth aspect, the secondary circuit of the forward-type switching power supply can be simply configured.

According to the switching power supply of the sixth aspect, the energy stored in the capacitive element equivalently connected to the switching element in parallel is supplied to the DC voltage through the primary windings of both transformers. By controlling the switching element to be in the ON state when the switching element is regenerated to the line side, loss when the switching element is turned on can be reliably reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device 1 according to an embodiment of the present invention.

FIGS. 2A and 2B are waveform diagrams for explaining the operation of the power supply device 1. FIG. 2A is a voltage waveform diagram of an input AC VAC, FIG. 2B is a voltage waveform diagram of a pulsating voltage VR, and FIG. The current waveform diagram of I1, the current waveform diagram of the current I2, the waveform diagram of the input current I1IN, and the current waveform diagram of the input current IIN are shown in FIG.

FIG. 3 is a circuit diagram of a power supply device 1A according to another embodiment of the present invention.

FIG. 4 is a circuit diagram of a power supply device 1B according to still another embodiment of the present invention.

FIG. 5 is a circuit diagram of a power supply device 1C according to still another embodiment of the present invention.

FIG. 6 is a circuit diagram of a power supply device 41 already developed by the applicant.

[Explanation of symbols]

 1, 1A to 1C Power supply device 2, 3 Transformer 2a, 3a Primary winding 2b, 3b Secondary winding 4 Switch 5 Parasitic capacitance 11, 12, 14, 31, 32, 34 Diode 13, 33 Capacitor 21 Diode stack 22 Noise Filter 26 Diode 35 Choke coil VDC DC voltage VO Output voltage VP Ripple

Claims (6)

[Claims] 1. A first and a second transformer having a primary winding and a secondary winding, two rectifier circuits for rectifying an input AC to generate pulsating voltages, respectively, and one of the rectifier circuits. A smoothing circuit for smoothing the generated pulsating voltage to generate a DC voltage, and a switching element, wherein a series circuit of the primary winding and the switching element of the first transformer is the other rectifier circuit And the primary winding of the second transformer is connected between the smoothing circuit and the positive output terminal of the other rectifier circuit, and the switching element A switching power supply unit that generates an output voltage by rectifying and combining voltages induced in respective secondary windings of the two transformers by switching. 2. A first and a second transformer each having a primary winding and a secondary winding, a rectifier circuit for rectifying an input AC to generate a pulsating voltage, and a DC voltage for smoothing the pulsating voltage. A smoothing circuit that generates a current, a unidirectional element that is connected between the rectifier circuit and the smoothing circuit and that conducts only a current from the rectifier circuit to the smoothing circuit, and a switching element. A series circuit of the primary winding of the first transformer and the switching element is connected between a positive output terminal and a negative output terminal of the rectifier circuit, and the primary winding of the second transformer is connected to the smoothing circuit. The rectifier circuit is connected between the positive output terminal and the rectifier circuit, and by switching the switching element, rectifies and combines the voltages induced in the respective secondary windings of the transformers, and outputs the rectified voltage. A switching power supply device for generating a voltage. 3. A first and a second transformer each having a primary winding and a secondary winding, a rectifier circuit for rectifying an input AC to generate a pulsating voltage, and the primary winding in the second transformer. A smoothing circuit for smoothing the pulsating voltage supplied from the rectifier circuit via a line to generate a DC voltage, and a switching element, wherein the primary winding of the first transformer and the switching element A series circuit is connected between the positive output terminal and the negative output terminal of the rectifier circuit, the primary winding of the second transformer is connected between the smoothing circuit and the positive output terminal of the rectifier circuit,
A switching power supply device that generates an output voltage by rectifying and combining voltages induced in respective secondary windings of the two transformers by switching the switching element. 4. A noise filter, and a one-way element for conducting only a current from the noise filter to the series circuit is connected between the positive output terminal of the rectifier circuit and the series circuit. The switching power supply device according to any one of claims 1 to 3, wherein 5. A rectifying first and second rectifying power supply, wherein an anode is connected to a high-potential terminal of each secondary winding in each of the transformers and a cathode is connected to each other. A diode, a smoothing choke coil connected between the cathodes of the two diodes and the high-potential output portion, and connected between one end of the choke coil on the high-potential output portion side and the low-potential output portion. A smoothing capacitor and a commutation diode having an anode connected to the low potential terminal and the low potential output section of each of the secondary windings and a cathode connected to the cathodes of the two diodes. The switching power supply device according to any one of claims 1 to 4, wherein 6. The switching element, after the energy stored in a capacitive element equivalently connected in parallel to the switching element is regenerated to the smoothing circuit side through the two primary windings. The switching power supply according to any one of claims 1 to 5, wherein the switching power supply is controlled to an on state.