JP2006211875A - Switching power supply apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply apparatus designed to deliver a stable output that is equal to or more than before, while making the configuration of a smoothing circuit smaller in size than before. <P>SOLUTION: A switching power supply apparatus includes a smoothing circuit 4 configured to replace a choke coil portion in a conventional smoothing circuit with a circuit portion 40 having a filter function. The circuit portion 40 has a series circuit 45 consisting of a third inductor 43 and a capacitor 44 connected to a first and a second inductors 41, 42 in series each other. The first and the second inductors 41, 42 are connected to each other in series on a first output side transfer line L2H, and connected magnetically to each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a switching power supply apparatus configured to extract a switching output obtained by switching an input DC or AC voltage to an output winding of a power conversion transformer.

  Conventionally, various types of switching power supply devices have been proposed and put into practical use. In many cases, the input DC voltage is switched by a switching operation of a switch circuit connected to the input winding of the power conversion transformer, and the switching output is taken out to the output winding of the power conversion transformer. Along with the switching operation of the switch circuit, the voltage appearing in the output winding is rectified by the rectifier circuit, then converted into direct current by the smoothing circuit and output.

Non-Patent Document 1 describes a switching regulator used as a switching power supply device. As described in Non-Patent Document 1, a choke-input type configuration using a choke coil and a smoothing capacitor is known as a configuration of the secondary side rectification / smoothing circuit portion. As a type of the switching power supply device having such a rectifying / smoothing circuit portion, for example, there are a forward converter method, a pushbull converter method, and a bridge type device in which a plurality of switching elements are connected in a bridge shape. The basic circuit of the forward converter system is described in P.148 to P.159 of Non-Patent Document 1.
Practical power circuit design handbook CQ Publishing Togawa Jiro (P.72-P.89, P.148-P.159)

  In such a switching power supply device such as a forward converter system, a smoothing capacitor in the smoothing circuit portion plays an important role in order to obtain a required output DC voltage. In many cases, an electrolytic capacitor is used for the smoothing capacitor, and if the capacitor to be used is selected in consideration of the output ripple current, the capacitance must be increased. In order to increase the capacity, it is necessary to have a configuration in which a plurality of capacitors are connected in parallel. However, due to its characteristics, the electrolytic capacitor has a large capacitance change due to temperature change, and its operating life becomes shorter than other components due to the operating temperature, so it is a large factor that determines the performance and life as a switching power supply device. It is a negative factor. Further, as the capacity of the smoothing capacitor increases, the mounting area of the circuit board also increases, and the choke coil combined with the smoothing capacitor also increases in size in consideration of the flowing current. For this reason, the size of the switching power supply device itself becomes a factor. Further, the switching power supply device has a problem that harmonics based on the switching frequency are generated on the output side. This harmonic component may adversely affect load-side equipment driven using the switching power supply as a power source.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a switching power supply apparatus that can obtain a more stable output while reducing the size of the smoothing circuit compared to the conventional one. It is in.

  A switching power supply device according to the present invention includes a transformer for transforming an input voltage, a switching circuit provided on the primary side of the transformer, a rectifier circuit provided on the secondary side of the transformer and rectifying the output voltage of the transformer, And a smoothing circuit provided at a subsequent stage of the circuit and whose output side communicates with a pair of output terminals. The smoothing circuit is connected in series with the first and second inductors connected in series to each other on the first transmission line leading to one of the pair of output terminals and magnetically coupled to each other. A series circuit including a third inductor and a capacitor, one end connected between the first inductor and the second inductor, and the other end connected to a second transmission line leading to the other of the pair of output terminals; It is what has.

In the switching power supply device according to the present invention, by using the smoothing circuit having the above-described configuration instead of the conventional smoothing circuit using the choke coil, the configuration can be downsized and the performance can be improved. For example, when considering a configuration in which the inductance of the entire first and second inductors is the same as the inductance of a conventional choke coil, the smoothing circuit according to the present invention, for example, a bifilar in which two windings are wound around a single core at the same time. If it is wound, the volume can be reduced to about half that of a conventional choke coil. In addition, since the smoothing circuit in the present invention functions as a filter circuit that suppresses noise components as described below, ripple voltage and ripple current are effectively suppressed, and a stable output can be obtained. Thereby, even if a smoothing capacitor is used in combination, the capacity can be reduced as compared with the conventional case.
In the smoothing circuit of the present invention, in the ideal state, when the noise voltage Vi in the normal mode is applied to the first inductor side between the first and second transmission lines, the noise voltage Vi is the same as that of the first inductor. The voltage is divided mainly by the third inductor of the series circuit, and a predetermined voltage in the same direction is generated between both ends of the first inductor and between both ends of the series circuit. Since the first inductor and the second inductor are magnetically coupled to each other, a predetermined voltage is also applied across the second inductor in response to a predetermined voltage generated across the first inductor. appear. Since one end of the series circuit is connected between the first inductor and the second inductor, the direction of the voltage generated between both ends of the second inductor depends on the voltage generated between both ends of the series circuit. The direction is opposite to the direction, and their voltages cancel each other. As a result, the noise voltage Vo in the normal mode on the second inductor side between the first and second transmission lines becomes zero, and the noise voltage Vi does not appear on the output side. Thus, noise components are satisfactorily suppressed by using the voltage generated in each inductor.

  In the switching power supply according to the present invention, the smoothing circuit further includes one end connected to the first transmission line between the first and second inductors and one of the pair of output terminals, and the other end of the series circuit. And the other of the pair of output terminals may include a smoothing capacitor connected to the second transmission line.

In the switching power supply according to the present invention, the switching frequency in the switching circuit is fsw, the capacitance of the capacitor in the series circuit in the smoothing circuit is C0, the inductance of the first inductor is L1, and the inductance of the third inductor is L3. When
fsw = 1 / 2π {(L1 + L3) · C0} ^1/2
It is preferable to be configured to satisfy the above.
Thereby, the smoothing circuit acts more effectively at the switching frequency fsw, and the harmonic components based on the switching frequency are also more effectively suppressed.

In the smoothing circuit, when the inductance of the first inductor is L1, the inductance of the second inductor is L2, and the inductance of the third inductor is L3,
L1 = L2 = L3 is satisfied,
In addition, the first inductor and the second inductor include first and second windings wound in the same direction on the same core, and are configured to satisfy the coupling coefficient k = 1. It is preferable.
Thereby, the performance as a filter in the smoothing circuit functions more effectively.

In the switching power supply according to the present invention, the transformer has a single secondary winding, and a first transmission line is formed between one end of the secondary winding and one of the pair of output terminals. A second transmission line may be formed between the other end of the secondary winding and the other of the pair of output terminals. The rectifier circuit includes a first rectifier diode disposed on the first transmission line such that the anode is on one end side of the secondary winding and the cathode is on the smoothing circuit side, and the secondary winding. An anode may be connected to the second transmission line between the other end and the smoothing circuit, and a second rectifying diode having a cathode commonly connected to the cathode of the first rectifying diode may be included.
Thereby, the switching power supply device according to the present invention can be, for example, a forward converter system.

  According to the switching power supply device of the present invention, instead of the conventional smoothing circuit using the choke coil, the first and second connected in series with each other on the first transmission line and magnetically coupled to each other. And a smoothing circuit having one end connected between the first inductor and the second inductor and the other end connected to the second transmission line. The structure can be reduced in size compared to the conventional one, and more stable output can be obtained over a long period of time.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a configuration example of a switching power supply device according to an embodiment of the present invention. In FIG. 1, the example of a structure as a switching power supply device of a forward converter system is shown. This switching power supply device converts an input voltage Vin output from a power supply device (not shown) through a pair of input terminals T1 and T2 into a desired output DC voltage Vout, and passes through a pair of output terminals T3 and T4. It functions as a DC-DC converter that supplies to a load-side device (not shown). In this embodiment, a DC-DC converter in which a DC voltage is input as the voltage Vin will be described as an example. However, the present invention can also be applied to an AC-DC converter in which an AC voltage is input as the voltage Vin. .

This switching power supply device is provided on a transformer 3 having a primary winding 31 and a secondary winding 32, a switching circuit 1 provided on the primary side of the transformer 3, and a secondary side of the transformer 3. A rectifier circuit 2 and a smoothing circuit 4 are provided. In this switching power supply device, a first input transmission line L1H is formed between one end of the primary winding 31 and one input terminal T1, and the other end of the primary winding 31 and the other input terminal. A second input side transmission line L1L is formed between T2 and T2. A first output transmission line L2H is formed between one end A of the secondary winding 32 and one output terminal T3, and the other end C of the secondary winding 32 and the other output terminal T4. A second output transmission line L2L is formed between the two. One output terminal T3 corresponds to the DC positive terminal DC + of the load side device, and the other output terminal T4 corresponds to the DC negative terminal DC−. The first input transmission line L1H and the first output transmission line L2H are positive lines, and the second input transmission line L1L and the second output transmission line L2L are negative lines.
The first output side transmission line L2H corresponds to a specific example of “a first transmission line” in the present invention, and the second output side transmission line L2L is a specific example of “a second transmission line” in the present invention. Corresponding to

  The switching circuit 1 includes one switching element S0, a controller (not shown) that controls switching, and a peripheral circuit thereof. The switching element S0 is disposed on the second input transmission line L1L between the other end of the primary winding 31 and the other input terminal T2. For example, a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), or the like is used as the switching element S0. Note that a smoothing capacitor may be provided in front of the switching circuit.

  The transformer 3 transforms the alternating voltage converted by the switching circuit 1 and outputs the transformed alternating voltage from the end portions A and C of the pair of secondary windings 32. The degree of transformation in this case is determined by the turn ratio of the primary side winding 31 and the secondary side winding 32.

  The rectifier circuit 2 rectifies the output voltage from the secondary side winding 32 of the transformer 3, and includes first and second rectifier diodes 21 and 22. The first rectifier diode 21 is arranged on the first output transmission line L2H so that the anode is connected to one end A of the secondary winding 32 and the cathode is on the smoothing circuit 4 side. The second rectifier diode 22 has an anode connected to the second output transmission line L2L between the other end C of the secondary winding 32 and the smoothing circuit 4, and a cathode connected to the first rectifier diode 21. Commonly connected to the cathode. As described above, the cathode common connection structure in which the cathodes are commonly connected in the connection portion D is formed.

The smoothing circuit 4 is the most characteristic part of this switching power supply device, and includes a circuit part 40 having a filter function and a smoothing capacitor 5. The circuit portion 40 includes first and second inductors 41 and 42 and a series circuit 45 including a third inductor 43 and a capacitor 44 connected in series with each other. The first and second inductors 41 and 42 are connected in series to each other on the first output-side transmission line L2H and are magnetically coupled to each other. The first inductor 41 includes a first winding 47, and the second inductor 42 includes a second winding 48. For example, the first and second inductors 41 and 42 can be configured by bifilar winding in which two windings 47 and 48 are simultaneously wound around the common core 46 in the same direction.
One end of the series circuit 45 is connected between the first inductor 41 and the second inductor 42, and the other end is connected to the second output side transmission line L2L. The positional relationship between the third inductor 43 and the capacitor 44 in the series circuit 45 may be opposite to the state shown in FIG. That is, in FIG. 1, one end of the third inductor 43 is connected between the first inductor 41 and the second inductor 42, but one end of the capacitor 44 is connected to the first inductor 41 and the second inductor 42. You may make it connect between. The capacitor 44 functions as a high-pass filter that passes a signal having a frequency equal to or higher than a predetermined value.

In the circuit portion 40, when the inductance of the first inductor 41 is L1, the inductance of the second inductor 42 is L2, and the inductance of the third inductor 43 is L3, ideally L1 = L2 = L3
Is preferably satisfied. The magnetic coupling coefficient k between the first inductor 41 and the second inductor 42 is ideally preferably 1. When the circuit is actually manufactured, the coupling coefficient k is generally less than 1. In this case, for example, the value of the inductance L3 of the third inductor 43 is adjusted, or the capacitance value of the capacitor 44 is adjusted. Can be adjusted so that

The smoothing capacitor 5 has one end connected to the first output transmission line L2H between the second inductor 42 and one output terminal T3, and the other end connected to the other end of the series circuit 45 and the other output terminal T4. Are connected to the second output side transmission line L2L.
Note that the smoothing capacitor 5 can be omitted from the components of the smoothing circuit 4 particularly when used as a power supply device for low power.

  In FIG. 1, black circles marked on the inductors in the transformer 3 and the smoothing circuit 4 indicate the polarities of the coils constituting them. The polarities of the primary side winding 31 and the secondary side winding 32 of the transformer 3 are the same as each other in the illustrated direction, for example. The polarities of the first and second inductors 41 and 42 in the smoothing circuit 4 are the same as each other in the illustrated direction, for example.

Here, as a comparative example, a basic configuration of a conventional forward type switching power supply device is shown in FIG. The switching power supply device shown in FIG. 16 differs from the configuration of the switching power supply device shown in FIG. The smoothing circuit 104 in FIG. 16 is connected between the choke coil 140 disposed on the first output transmission line L2H and the first output transmission line L2H and the second output transmission line L2L. And a smoothing capacitor 150. In the conventional switching power supply device, in order to increase the capacity of the smoothing capacitor 150 in terms of performance, it is necessary to configure it with a plurality of capacitors 51 to 54 connected in parallel as illustrated.
Conventionally, as shown in FIG. 17, in addition to the configuration shown in FIG. 16, an LC filter 160 including an inductor 161 and a capacitor 162 is added after the smoothing circuit 104 to reduce harmonics and the like. In some cases, it may be configured.

In the switching power supply device of this comparative example, the on-period of switching is ton, the off-period of switching is toff, the input voltage is Vin, the output DC voltage is Vout, the output DC current is I0, and the capacitance of the smoothing capacitor 150 is C1. When the inductance of the coil 140 is L0, the coil 140 is generally designed to satisfy the following expression when designing a forward converter (see Non-Patent Document 1: P.156 to P.159 of Practical Power Supply Circuit Design Handbook).
L0 = {(Vin−Vout) / (0.3−I0)} · ton
= {Vout / (0.3-I0)}. Toff

The switching power supply according to the present embodiment has a configuration in which the choke coil 140 portion in the conventional circuit of FIG. 16 is replaced with a circuit portion 40 having a filter function. In order to obtain a performance equal to or higher than that of the conventional circuit, if the inductance of the first and second inductors 41 and 42 in the circuit portion 40 is Lt (= L1 + L2), the inductance Lt is equal to the inductance L0 of the choke coil 140. The same value is preferred.
In the switching power supply according to the present embodiment, the switching frequency in the switching circuit 1 is fsw, the capacitance of the capacitor 44 in the series circuit 45 in the circuit portion 40 is C0, the inductance of the first inductor 41 is L1, the third When the inductance of the inductor 43 is L3,
fsw = 1 / 2π {(L1 + L3) · C0} ^1/2
It is preferable to be configured to satisfy the above.

  Next, the operation of this switching power supply device will be described.

  First, the overall operation of this switching power supply device will be described. In this switching power supply device, an input DC voltage Vin supplied from a power supply device (not shown) via a pair of input terminals T1 and T2 is converted into an AC voltage by a switching operation by the switching circuit 1. The AC voltage is supplied to the primary side winding 31 of the transformer 3, and the transformed AC voltage is taken out from the secondary side winding 32. The AC voltage is rectified by the rectifier circuit 2. The smoothing circuit 4 smoothes the rectified output generated between the second output side transmission line L2H and the connection point D of the diodes 21 and 22. The output of the smoothing circuit 4 is supplied as a desired output DC voltage Vout to a load-side device (not shown) via a pair of output terminals T3 and T4. On the secondary side of the transformer 3, when the switching element S0 is on, the current I1 flows through the first rectifying diode 21 through the path shown. When the switching element S0 is off, a current I2 flows through the second rectifying diode 22 through the illustrated path due to the back electromotive force generated in the smoothing circuit 4. In this switching power supply device, since the circuit portion 40 of the smoothing circuit 4 functions as a filter circuit that suppresses noise components as described below, the ripple voltage and the ripple current are effectively suppressed, and a stable output can be obtained. .

  Here, the operation of the circuit portion 40 as a filter circuit will be described with reference to FIG. Here, it is assumed that the inductances of the first to third inductors 41 to 43 have the same value, and the impedance of the capacitor C1 is low enough to be ignored. Further, it is assumed that the magnetic coupling coefficient k between the first inductor 41 and the second inductor 42 is 1.

  In this case, as shown in FIG. 2, when the noise voltage Vi in the normal mode is applied to the input side, the noise voltage Vi is mainly generated by the first inductor 41 and the third inductor 43 of the series circuit 45. The divided voltage generates the same noise voltage Vi / 2 in the same direction between both ends of the first inductor 41 and between both ends of the third inductor 43. Note that the arrow in the figure indicates that the potential ahead is higher. Since the first inductor 41 and the second inductor 42 are magnetically coupled to each other, both ends of the second inductor 42 according to the noise voltage Vi / 2 generated between both ends of the first inductor 41. In the meantime, the same noise voltage Vi / 2 as the noise voltage Vi / 2 is generated. Since one end of the series circuit 45 is connected between the first inductor 41 and the second inductor 42, the direction of the voltage generated between both ends of the second inductor 42 depends on the third inductor 43. The direction of the voltage generated between both ends is opposite to each other, and these voltages cancel each other (Vi / 2−Vi / 2 = 0). As a result, the noise voltage Vi entering the input side becomes Vo = 0 on the output side, and the noise component is removed. Thus, noise components are satisfactorily suppressed by using the voltage generated in each inductor.

  FIG. 3 shows the result of calculating the transmission characteristics of the smoothing circuit 4 in the present embodiment and the smoothing circuit 104 of the comparative example using the choke coil 140 of FIG. The horizontal axis represents frequency, and the vertical axis represents attenuation. A dotted curve indicated by reference numeral 201 indicates the characteristics of the smoothing circuit 4, and a solid curve indicated by reference numeral 202 indicates the characteristics of the smoothing circuit 104 of the comparative example. FIG. 4 shows the result of measuring the transmission characteristics of the circuit portion 40 alone (the circuit portion obtained by removing the smoothing capacitor 5 from the smoothing circuit 4) in the present embodiment. As circuit conditions, the inductances of the first to third inductors 41 to 43 in the smoothing circuit 4 are set to the same value, and the inductance Lt of the entire first and second inductors 41 and 42 and the inductance of the choke coil 140 are set. L0 was set to the same value. The capacitance C1 of the smoothing capacitor 5 was also set to the same value as the smoothing capacitor 150 in the smoothing circuit 104 of the comparative example. 3 and 4, it can be seen that a transmission characteristic that attenuates in the vicinity of the switching frequency fsw is obtained.

  5 to 8 show voltage and current waveforms actually measured at points P1 to P4 in FIG. 1 for this switching power supply device. That is, the measured waveform at the point P1 shown in FIG. 5 corresponds to the output waveform from the rectifier circuit 2. The measurement waveform at the point P <b> 2 shown in FIG. 6 corresponds to the output waveform between the third inductor 43 and the capacitor 44 in the smoothing circuit 4. The measurement waveform at the point P3 shown in FIG. 7 corresponds to the output waveform from the circuit portion 40 in the smoothing circuit 4. The measurement waveform at the point P4 shown in FIG. 8 corresponds to the output waveform from the smoothing circuit 4, that is, the output waveform at the final stage of the switching power supply device. Similarly, FIGS. 9 and 10 show waveforms of voltage and current measured at points P3 and P4 of the circuit of the comparative example of FIG. 5 to 10, the upper waveform indicates a voltage waveform, and the lower waveform indicates a current waveform. The horizontal axis represents time (t), and the vertical axis represents voltage and current. The circuit value conditions are the same as the calculation conditions in FIG.

  From these results, as can be seen from the voltage and current waveforms (FIG. 8, FIG. 10) at the point P4, which is the final stage, in the switching power supply according to the present embodiment, compared to the circuit of the comparative example, It can be seen that the ripple voltage and the ripple current are effectively suppressed.

  Further, FIGS. 11A and 11B show frequency characteristics of attenuation actually measured at a point P3 in the switching power supply device and the circuit of the comparative example. The horizontal axis represents frequency, and the vertical axis represents attenuation. Similarly, the attenuation characteristics at point P4 are shown in FIGS. A curve denoted by reference numeral 301 in FIG. 11A indicates the characteristics of the switching power supply device, and a curve denoted by reference numeral 302 in FIG. 11B indicates the characteristics of the circuit of the comparative example. Similarly, a curve denoted by reference numeral 401 in FIG. 12A indicates the characteristics of the switching power supply device, and a curve denoted by reference numeral 402 in FIG. 12B indicates the characteristics of the circuit of the comparative example. From the results of FIGS. 11A and 11B and FIGS. 12A and 12B, the circuit in the present embodiment is attenuated particularly in the vicinity of the switching frequency fsw as compared with the circuit of the comparative example. It can be seen that such good transmission characteristics are obtained. Further, the harmonic component at a higher frequency of the switching frequency fsw is attenuated more favorably in the circuit in the present embodiment.

  From the above results, when the inductance of each inductor in the smoothing circuit 4 and the capacitance of the smoothing capacitor 5 are set to be equivalent to those in the circuit of the comparative example, the switching power supply according to the present embodiment has the ripple voltage and It can be seen that the ripple current is effectively suppressed. Therefore, when the circuit value is adjusted so as to obtain a necessary and sufficient ripple value, the switching power supply device according to the present embodiment can reduce the capacitance of the smoothing capacitor 5. That is, even if the capacity of the smoothing capacitor 5 is reduced, the same performance as that of the conventional switching power supply device using the choke coil 140 can be obtained.

  In the switching power supply according to the present embodiment, the inductance Lt of the entire first and second inductors 41 and 42 is set to the same value as the inductance L0 of the choke coil 140, as compared with the circuit using the conventional choke coil 140. Even so, the volume of the coil on the line can be reduced by adopting a configuration such as bifilar winding in which two windings are wound around a single core at the same time. The larger the coil itself is, the more expensive it is. Therefore, it is possible to reduce the component cost, board mounting area, and module weight by saving the volume. Further, in the conventional circuit, when a power source having a large electric power is configured, it is necessary to use a large-capacity capacitor using an electrolytic capacitor as the smoothing capacitor 5. In the circuit according to the present embodiment, the ripple improvement effect is obtained. As a result, the capacity of the smoothing capacitor 5 can be reduced, so that it can be changed to a capacitor made of a better material that is superior in terms of temperature characteristics and life. This can save mounting area and improve the performance and life of the switching power supply itself. In particular, in the case of configuring a power supply with low power, there is a possibility that the smoothing capacitor 5 itself can be reduced. Furthermore, the circuit of this embodiment also has an effect of reducing harmonics based on the switching frequency fsw (see FIGS. 11A, 11B, 12A, and 12B). Can reduce the adverse effects of load-side devices driven by the power source and reduce the burden of countermeasure parts on the connected device side. For example, it is not necessary to add the LC filter 160 as shown in FIG.

As described above, according to the present embodiment, the conventional smoothing circuit 104 (FIG. 16) using the choke coil 140 is replaced with the smoothing circuit 4 having a filter function. It is possible to obtain a stable output over a long period of time equivalent to or more than the conventional one while downsizing the configuration compared to the conventional one.
[Modification]

  The present invention is not limited to the above embodiment, and various modifications can be made. In the above-described embodiment, the configuration example of the forward type switching power supply device using the single switching element S0 has been described. However, the characteristic part of the present invention is mainly in the smoothing circuit 4, and the configuration of other parts. Various modifications are possible. In particular, the present invention is applicable to all conventional switching power supply devices using a choke input type smoothing circuit.

<First Modification>
FIG. 13 shows a first modification of the switching power supply device according to the present embodiment. In addition, the same code | symbol is attached | subjected to the component substantially the same as the switching power supply device shown in FIG. The present modification is a configuration example of a full-bridge type switching power supply device using four switching elements S1 to S4 as the switching circuit 1A.

In this switching power supply device, the transformer 3 has two secondary windings 32 and 33. In this switching power supply device, the pair of secondary windings 32 and 33 of the transformer 3 are connected to each other by a center tap C, and the center tap C is connected to the other output terminal T4 via the second output side transmission line L2L. Led. That is, this switching power supply device is of a center tap type. The transformer 3 transforms the AC voltage converted by the switching circuit 1A, and outputs AC voltages that are 180 degrees out of phase from the ends A and B of the pair of secondary windings 32 and 33. The rectifier circuit 2A in the switching power supply device is a single-phase full-wave rectifier circuit including a pair of diodes 51 and 52. The anode of the first rectifying diode 21 is connected to one end A of one secondary winding 32 of the transformer 3, and the anode of the second rectifying diode 22 is connected to one end B of the other secondary winding 33. It is connected. The cathodes of the diodes 51 and 52 are connected to each other at the connection point D and to the first output-side transmission line L2H. That is, the rectifier circuit 2A has a cathode common connection structure, and rectifies each half-wave period of the AC output voltage of the transformer 3 by the diodes 51 and 52, respectively, to obtain a rectified voltage. .
<Second Modification>

  FIG. 14 shows a second modification of the switching power supply device according to the present embodiment. In addition, the same code | symbol is attached | subjected to the component substantially the same as the 1st modification shown in FIG. This modification includes a rectifier circuit 2B in place of the rectifier circuit 2A in the first modification shown in FIG. In the rectification circuit 2B, the cathode of the first rectification diode 21 is connected to one end A of one secondary winding 32 of the transformer 3, and the cathode of the second rectification diode 22 is the other secondary winding. It is connected to one end B of 33. The anodes of the diodes 51 and 52 are commonly connected to each other at the connection point D and connected to the second output transmission line L2L. A connection point (center tap C) between the secondary winding 32 and the secondary winding 33 of the transformer 3 is connected to the first output transmission line L2H and led to one output terminal T3. That is, this switching power supply device has a center tap type anode common connection structure, and rectifies each half-wave period of the AC output voltage of the transformer 3 by the diodes 21 and 22 to obtain a rectified voltage. It has become.

Although FIGS. 13 and 14 show the case where a full bridge type switching circuit using four switching elements is provided, a half bridge type switching circuit may be configured using two switching elements. good.
<Third Modification>

FIG. 15 shows a third modification of the switching power supply device according to the present embodiment. In addition, the same code | symbol is attached | subjected to the component substantially the same as the switching power supply device shown in FIG. This modification includes a rectifier circuit 2C in place of the rectifier circuit 2 in the circuit shown in FIG. In the rectifier circuit 2 </ b> C, the first rectifier diode 21 has a cathode connected to the other end C of the secondary winding 32 of the transformer 13. The second rectifier diode 22 has a cathode connected to one end A of the secondary winding 32 of the transformer 13 and an anode commonly connected to the anode of the first rectifier diode 21. Thereby, it has a structure of anode common connection.
Further, the configuration of the circuit portion 40 of the smoothing circuit 4 is a configuration in which the arrangement relationship is reversed between the first output side transmission line L2H and the second output side transmission line L2L. That is, the first and second inductors 41 and 42 are disposed on the second output-side transmission line L2L.

  In addition to these modifications, the present invention can be applied to a chopper type, pushbull converter type switching power supply device, and the like.

It is a circuit diagram which shows one structural example of the switching power supply device which concerns on one embodiment of this invention. It is a circuit diagram for demonstrating operation | movement of the principal part of the smoothing circuit in the switching power supply which concerns on one embodiment of this invention. It is the figure which calculated the signal transmission characteristic in the switching power supply concerning one embodiment of the present invention by simulation, and made it a graph compared with the conventional circuit. It is the figure which measured and showed the signal transmission characteristic in the circuit part which remove | eliminated the smoothing capacitor from the smoothing circuit in FIG. It is the figure which measured and showed the output waveform from the rectifier circuit (P1) in FIG. It is the figure which measured and showed the output waveform between the 3rd inductor and capacitor | condenser in the smoothing circuit in FIG. 1 (P2). It is the figure which measured and showed the output waveform from the main circuit parts (P3) of the smoothing circuit in FIG. It is the figure which measured and showed the output waveform from the smoothing circuit (P4) in FIG. It is the figure which measured and showed the output waveform from the choke coil part (P3) of the smoothing circuit in the circuit of a comparative example. It is the figure which measured and showed the output waveform from the smoothing circuit (P4) in the circuit of a comparative example. It is the figure which compared the frequency characteristic (A) in the switching power supply concerning one embodiment of the present invention with the frequency characteristic (B) of the conventional circuit, and made it a graph. It is the figure which compared the frequency characteristic (A) in the switching power supply concerning one embodiment of the present invention with the frequency characteristic (B) of the conventional circuit, and made it a graph. It is a circuit diagram which shows the 1st modification of the switching power supply device which concerns on one embodiment of this invention. It is a circuit diagram which shows the 2nd modification of the switching power supply device which concerns on one embodiment of this invention. It is a circuit diagram which shows the 3rd modification of the switching power supply device which concerns on one embodiment of this invention. It is a circuit diagram which shows one structural example of the conventional forward type switching power supply device as a comparative example. It is a circuit diagram which shows the other structural example of the conventional forward type switching power supply device as a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Switching circuit, 2 ... Rectifier circuit, 3 ... Transformer, 4 ... Smoothing circuit, 5 ... Smoothing capacitor, 31 ... Primary side winding, 32 ... Secondary side winding, 21, 22 ... Rectification diode, S0, S1 to S4: switching elements, L1H: first input side transmission line, L1L: second input side transmission line, L2H: first output side transmission line, L2L: second output side transmission line, T1, T2 ... input terminals, T3, T4 ... output terminals, I0 ... output DC current, Vin ... input DC voltage, Vout ... output DC voltage.

Claims (5)

A transformer that transforms the input voltage;
A switching circuit provided on the primary side of the transformer;
A rectifier circuit provided on the secondary side of the transformer and rectifying the output voltage of the transformer;
A smoothing circuit provided at a subsequent stage of the rectifier circuit, the output side leading to a pair of output terminals,
The smoothing circuit is
First and second inductors connected in series to each other on a first transmission line leading to one of the pair of output terminals and magnetically coupled to each other;
A second inductor includes a third inductor and a capacitor connected in series with each other, one end connected between the first inductor and the second inductor, and the other end communicating with the other of the pair of output terminals. And a series circuit connected to the transmission line. The smoothing circuit is
One end is connected to the first transmission line between the first and second inductors and one of the pair of output terminals, and the other end is connected to the other end of the series circuit and the other of the pair of output terminals. The switching power supply according to claim 1, further comprising a smoothing capacitor connected to the second transmission line between the first and second transmission lines. The switching frequency in the switching circuit is fsw,
In the smoothing circuit, when the capacitance of the capacitor in the series circuit is C0, the inductance of the first inductor is L1, and the inductance of the third inductor is L3,
fsw = 1 / 2π {(L1 + L3) · C0} ^1/2
The switching power supply device according to claim 2, wherein the switching power supply device is configured to satisfy the following. In the smoothing circuit, when the inductance of the first inductor is L1, the inductance of the second inductor is L2, and the inductance of the third inductor is L3,
L1 = L2 = L3 is satisfied,
In addition, the first inductor and the second inductor include first and second windings wound in the same direction on the same core, and are configured to satisfy a coupling coefficient k = 1. The switching power supply device according to claim 3, wherein: The transformer has a single secondary winding;
The first transmission line is formed between one end of the secondary winding and one of the pair of output terminals, and between the other end of the secondary winding and the other of the pair of output terminals. The second transmission line is formed in
The rectifier circuit is
A first rectifying diode disposed on the first transmission line such that an anode is on one end side of the secondary winding and a cathode is on the smoothing circuit side;
Between the other end of the secondary winding and the smoothing circuit, an anode is connected to the second transmission line, and a cathode is commonly connected to a cathode of the first rectifying diode. The switching power supply device according to claim 1, further comprising: a diode.

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