JP2015211588A - Switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power loss of a switching power unit.SOLUTION: An input AC voltage is applied between lines L1 and L2. In a positive section in which the potential of the line L1 is positive as compared with the potential of the line L2, a switching element 6 is made to switch and a switching element 7 is turned on. In a negative section in which the potential of the line L1 is negative as compared with the potential of the line L2, the switching element 7 is made to switch and the switching element 6 is turned on. Through the switching thereof, a pulsating voltage of the line L1 in the positive section and a pulsating voltage of the line L2 in the negative section are alternately switched and a transformer 15 is excited in both directions. A desired output voltage Vo is obtained by smoothing a voltage generated across a secondary coil of the transformer 15.

Description

  The present invention relates to a switching power supply device.

  In a switching power supply device using AC power as an input, arbitrary AC or DC power is obtained by switching the input AC power to a pulsating or direct current by half-wave rectification or full-wave rectification. When half-wave rectification or full-wave rectification is performed, power loss occurs in the rectifier diode.

  FIG. 15 shows a block diagram of a switching power supply device using full-wave rectification (see Patent Document 1). The switching power supply apparatus of FIG. 15 includes a noise filter 902 that reduces the noise of commercial AC power from the commercial AC power supply 901, a bridge diode 903 that full-wave rectifies the AC power output from the noise filter 902, and the output power of the bridge diode 903. A power converter 904 that performs power conversion on the power converter 904 and an output unit 905 to which an output voltage of the power converter 904 is applied. In the switching power supply device of FIG. 15, for example, a voltage as shown in FIG. 16 is observed. In the example of FIG. 16, switching is performed after full-wave rectification of the input voltage of AC 100 V by the bridge diode 903, and DC 12 V is obtained by rectifying and smoothing the voltage obtained thereby.

JP 2013-45754 A

  After the input power is pulsated or converted to direct current by full-wave rectification of the bridge diode 903, power conversion is performed by the subsequent power converter 904. At this time, the input current Iin from the commercial AC power supply 901 is It passes through two diode elements in the diode 903. For this reason, power loss occurs in the bridge diode 903 by the amount of power obtained by multiplying the forward voltage of the diode element by (2 × Iin). For example, when the input power to the switching power supply device is 100 W, the input voltage is AC 100 V, and the power factor is 1.0, the input current Iin is 1 A (ampere), so the forward voltage of one diode element is If it is about 1.0 V, the power loss of the bridge diode 903 is 2 W.

  Therefore, if the power conversion efficiency in this case is 90%, the total power loss of the switching power supply device is 10 W, and the ratio of the power loss (2 W) of the bridge diode 903 is as large as 20%. . Needless to say, it is better for the switching power supply to have lower power loss. Technology for reducing the forward voltage of the bridge diode has been actively developed to reduce the power loss, but if the bridge diode is not used, a significant improvement in power loss can be expected. In the above numerical example, the total loss is 10%. Therefore, if it is not necessary to use a bridge diode, the total loss is suppressed to 8%. That is, the power conversion efficiency is improved from 90% to 92%.

  Accordingly, an object of the present invention is to provide a switching power supply device that contributes to reduction of power loss.

  A switching power supply according to the present invention includes first and second input lines to which an input AC voltage is applied, and a transformer in which a primary coil is indirectly disposed between the first and second input lines. A switching power supply device that generates an output voltage on the secondary side of the transformer by performing power conversion on the input AC voltage, the pulsating flow in the first input line as seen from the potential of the second input line The power conversion is performed by alternately switching a voltage and a pulsating voltage on the second input line as viewed from the potential of the first input line to excite the transformer bidirectionally.

  According to the present invention, it is possible to provide a switching power supply device that contributes to reduction of power loss.

It is a figure which shows the structure of the switching power supply device which concerns on embodiment of this invention. It is a figure which shows the structure of the switching power supply device which concerns on 1st Embodiment of this invention. It is a figure which shows the structure of N-channel type FET. It is a figure which shows the on / off state of the switching element which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the electric current which concerns on 1st Embodiment of this invention and flows into the primary side of a trans | transformer. It is a figure which shows the electrical property of the body diode of FET. It is a figure which shows the waveform of the voltage observed with the switching power supply device of 1st Embodiment of this invention. It is a figure which shows the structure of the switching power supply device which concerns on 2nd Embodiment of this invention. It is a figure which shows the ON / OFF state of the switching element and rectifier which concern on 2nd Embodiment of this invention. It is a figure for demonstrating the electric current which concerns on 2nd Embodiment of this invention and flows into the secondary side of a transformer. It is a figure which shows the waveform of the voltage observed with the switching power supply device of 2nd Embodiment of this invention. It is a figure which shows the structure of the switching power supply device which concerns on 3rd Embodiment of this invention. It is a figure which shows the ON / OFF state of the switching element and rectifier which concern on 3rd Embodiment of this invention. It is a figure which shows the structure of the switching power supply device which concerns on 4th Embodiment of this invention. It is a figure which shows the structure of the conventional switching power supply device. It is a figure which shows the waveform of the voltage observed with the switching power supply device of FIG.

  Hereinafter, an example of an embodiment of the present invention will be specifically described with reference to the drawings. In each of the drawings to be referred to, the same part is denoted by the same reference numeral, and redundant description regarding the same part is omitted in principle. In this specification, for the sake of simplification, information, signals, physical quantities, and state quantities corresponding to the symbols or signs are described by writing symbols or signs that refer to information, signals, physical quantities, state quantities, or members. Or names of members, etc. may be omitted or abbreviated.

  FIG. 1 shows a configuration of a switching power supply apparatus according to an embodiment of the present invention. The switching power supply device includes a noise filter 2, lines L 1 and L 2 that are input lines to the power converter 4, and the power converter 4. An output unit 5 is connected to the power converter 4. However, it may be considered that the output unit 5 is also included in the components of the switching power supply device. Reference numeral 1 represents a commercial AC power source. A commercial AC voltage from the commercial AC power source 1 is input to the noise filter 2, and the noise filter 2 removes noise in the input commercial AC voltage, and uses the commercial AC voltage (hereinafter referred to as input AC voltage) after noise removal. Output between lines L1 and L2.

  The power converter 4 is connected to the lines L1 and L2, and generates an output voltage Vo by power-converting an input AC voltage applied between the lines L1 and L2. At this time, the power converter 4 generates the AC or DC output voltage Vo by directly switching the input AC voltage without full-wave rectification or half-wave rectification of the input AC voltage. The output voltage Vo is supplied to the output unit 5 connected to the power converter 4. The output unit 5 includes, for example, a pair of output terminals to which the output voltage Vo is applied.

  Hereinafter, a configuration example of the switching power supply device will be specifically described. The above description of the switching power supply device of FIG. 1 is also applied to the switching power supply devices of the following embodiments.

<First Embodiment>
A switching power supply device according to a first embodiment of the present invention will be described. FIG. 2 is a configuration diagram of the switching power supply device according to the first embodiment. The switching power supply device of FIG. 2 includes a power converter 4 </ b> A as the power converter 4. The power converter 4A includes first and second switching elements 6 and 7, a smoothing circuit 10A, first and second control circuits 11 and 12, a transformer 15, and a feedback circuit 16.

  Each of the switching elements 6 and 7 is composed of an N-channel field effect transistor (hereinafter referred to as FET). The FET is particularly preferably a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), for example. FIG. 3 shows the configuration of an N-channel FET. The N-channel type FET includes an FET main body 19 composed of a source, a drain and a gate, and a body diode 20 connected in parallel between the source and the drain and having a forward direction from the source to the drain. Each of the switching elements 6 and 7 has the same structure as the N-channel FET including the FET main body 19 and the body diode 20, and each of rectifier elements 8 and 9 (see FIG. 8 and the like) to be described later. It shall have.

  The transformer 15 has a primary side coil and a secondary side coil. Hereinafter, the primary side coil and the secondary side coil refer to the primary side coil and the secondary side coil of the transformer 15 unless otherwise specified. The drain of the switching element 6 is connected to the line L1, while the source of the switching element 6 is connected to one end 31 of the primary side coil. The drain of the switching element 7 is connected to the line L2, while the source of the switching element 7 is connected to the other end 32 of the primary coil.

The control circuits 11 and 12 perform switching control for the switching elements 6 and 7, respectively. Switching control for the switching element 6 is control for turning on or off the switching element 6 through control of the gate-source voltage V _GS of the switching element 6. Switching control for the switching element 7 is control for turning on or off the switching element 7 through control of the gate-source voltage V _GS of the switching element 7.

In the switching element that is the switching element 6 or 7, the switching element is turned on when the gate-source voltage V _GS of the switching element is equal to or higher than a predetermined threshold voltage and the drain and source of the switching element are in a conductive state. That is, when the switching element is turned off, the gate-source voltage V _GS of the switching element is less than the threshold voltage, and the drain and source of the switching element are in a non-conductive state. A state in which the switching element is on and off is also referred to as an on state and an off state, respectively. The gate-source voltage V _GS of a switching element refers to the gate voltage as viewed from the source potential of the switching element.

  The control circuits 11 and 12 monitor the polarity of the voltage of the line L1 as viewed from the potential of the line L2, and can determine whether the current time belongs to the positive section or the negative section based on the monitoring result. In order to realize this monitoring, the combined circuit of the control circuits 11 and 12 is connected to the lines L1 and L2, and the control circuits 11 and 12 are also connected to each other. The positive section refers to a section in which the potential (voltage) of the line L1 is positive as viewed from the potential of the line L2, and the negative section refers to the potential (voltage) of the line L1 as viewed from the potential of the line L2. The section which becomes. Although there is a timing at which the potential difference between the lines L1 and L2 becomes zero, the timing is ignored (the timing may be considered to belong to the positive interval or the negative interval). The polarity of the voltage of the line L1 viewed from the potential of the line L2 is alternately positive or negative in the cycle of the input AC voltage (that is, for example, the reciprocal of 50 or 60 Hz). Therefore, the positive interval and the negative interval alternate according to the period of the input AC voltage.

  In the positive section, the control circuit 11 controls the switching element 6 to cause the switching element 6 to perform a switching operation, while the control circuit 12 always turns on the switching element 7. In the negative interval, the control circuit 12 controls the switching element 7 to cause the switching element 7 to perform a switching operation, while the control circuit 11 always turns on the switching element 6. This is shown in FIG. In the positive section, the sections in which the switching element 6 is on and off are called sections P1 and P2, respectively. In the negative section, the sections in which the switching element 7 is on and off are sections P3 and P4, respectively. Call.

  With respect to the switching element 6 or 7, the switching operation of the switching element or simply switching refers to an operation in which the switching element switches, that is, an operation in which the ON state of the switching element and the OFF state of the switching element are alternately repeated. The switching frequency that is the reciprocal of the period is considerably larger than the frequency of the input AC voltage (for example, several tens of kHz to several hundreds of kHz). When the switching element performs a switching operation, a drain current as a switching current flows between the drain and the source of the switching element.

  By the above switching operation, during the positive interval (more specifically, in the interval P1), as shown in FIG. 5A, the switching current 110P flows between the drain and the source of the switching element 6, and the switching current 110P flows through the body diode 20 of the switching element 7 via the primary side coil of the transformer 15 (the same applies to each embodiment described later). During the negative interval (more specifically, in the interval P3), as shown in FIG. 5B, a switching current 110N flows between the drain and source of the switching element 7, and the switching current 110N is the primary of the transformer 15. It flows through the body diode 20 of the switching element 6 via the side coil (the same applies to each embodiment described later).

An example of electrical characteristics of an N-channel FET used as the switching elements 6 and 7 is shown in FIG. 6, curve 401 and 402, respectively, the gate of the N-channel type FET - definitive when the source voltage V _GS is 0V, 10V (volts), the forward current I _F and the body diode 20 of the body diode 20 it represents the relationship between V _F (source potential as seen from the drain) of the forward voltage of. When the voltage V _GS is 0V, the body diode 20 has the same characteristics as the single diode element, a substantial current flows through the first body diode 20 forward voltage V _F is equal to or greater than about 0.6V. On the other hand, when the voltage V _GS is 10 V, the forward voltage V _F becomes extremely small compared to when the voltage V _GS is 0 V. For example, when the forward current I _F is 10A (ampere), whereas V _GS = forward voltage V _F at 0V is about 0.8 V, V _GS = 10V in the forward voltage V _F is 0 Less than 1V.

The state in which the voltage V _GS is 10 V is a state in which the switching element 6 or 7 as an N-channel FET is turned on. Therefore, for example, the control circuits 11 and 12 have the characteristics of the switching elements 6 and 7 so that the body diode 20 of the switching elements 6 and 7 has the characteristic of the curve 402 at the timing when the switching elements 6 and 7 should be turned on, respectively. The gate-source voltage V _GS is controlled. The control circuits 11 and 12 can flow the switching current 110P to the body diode 20 of the switching element 7 by turning on the switching elements 6 and 7 in the section P1, and turn on the switching elements 6 and 7 in the section P3. Thus, the switching current 110N can be passed through the body diode 20 of the switching element 6.

  In the positive section, the voltage in the line L1 viewed from the line L2 is a positive pulsating voltage, and in the negative section, the voltage in the line L2 viewed from the line L1 is a positive pulsating voltage (of course, these pulsating currents. The voltage is obtained without rectifying the input AC voltage). The switching element 6 switches the positive pulsating voltage on the line L1 viewed from the line L2, while the switching element 7 switches the positive pulsating voltage on the line L2 viewed from the line L1 (this will be described later). The same applies to each of the embodiments). The transformer 15 is excited in one direction by the switching current 110P, and the transformer 15 is excited in the reverse direction by the switching current 110N. That is, the switching currents 110P and 110N alternately flow in the primary coil, thereby exciting the transformer 15 in both directions. The control circuits 11 and 12 have a function of exciting the transformer 15 bidirectionally by alternately performing a switching operation by the switching element 6 and a switching operation by the switching element 7 (this is described in each of the embodiments described later). The same applies to the form).

  The voltage generated in the secondary coil by the bidirectional excitation is input to the smoothing circuit 10A connected to one end 41 and the other end 42 of the secondary coil. The smoothing circuit 10A smoothes the input voltage from the secondary coil, and outputs the voltage obtained by the smoothing to the output unit 5 as the output voltage Vo. With reference to FIG. 7, a waveform 421 is an example of a voltage waveform obtained by directly switching an input AC voltage by the method of the present embodiment, and a waveform 422 is an example of a waveform of the output voltage Vo of the smoothing circuit 10A. It is. The waveform 421 may be considered to be a similar waveform of the voltage generated by the secondary side coil (and hence the input voltage to the smoothing circuit 10A) depending on the turns ratio of the primary side coil and the secondary side coil of the transformer 15. In FIG. 7, for convenience of illustration, the switching frequency is shown as if it is about 20 times the frequency of the input AC voltage, but the actual switching frequency is considerably higher than that shown in FIG. (The same applies to FIG. 11 described later).

  The smoothing circuit 10A generates an AC output voltage Vo by removing a switching frequency component included in the input voltage from the secondary coil.

  The feedback circuit 16 detects the voltage value (for example, effective value) of the output voltage Vo of the smoothing circuit 10A, and controls the control circuits 11 and 12 so that the output voltage Vo becomes a predetermined target AC voltage. The magnitude of the target AC voltage is arbitrary (however, it is different from the magnitude of the input AC voltage). In the example of FIG. 7, the input AC voltage is AC 100 V (that is, an AC voltage having an effective value of 100 V), and the target AC voltage is AC 12 V (that is, the AC voltage having an effective value of 12 V).

  The control circuits 11 and 12 can use pulse width modulation for switching control. The control circuits 11 and 12 cooperate with the feedback circuit 16 to turn on the switching elements 6 and 7 (that is, the rate at which the switching element 6 is turned on in the positive interval) if the output voltage Vo is smaller than the target AC voltage. If the output voltage Vo is larger than the target AC voltage, the on-duty is reduced. As a result, the output voltage Vo of the smoothing circuit 10A is stabilized at the target AC voltage.

  In the present embodiment, the switching current 110 </ b> P in the positive section flows through the low-resistance channel (between the drain and source) in the switching element 6 and also flows through the low-voltage body diode 20 in the switching element 7. The switching current 110N in the negative section flows through the low-resistance channel (between drain and source) in the switching element 7 and also flows through the low-voltage body diode 20 in the switching element 6. As a result, in comparison with the conventional configuration using a bridge diode as shown in FIG. 15 (configuration with power loss for two diode forward voltages), the configuration in FIG. Loss can be reduced (eg, power loss can be reduced by 20%). Further, the reduction of the bridge diode and the reduction of the power loss contribute to the cost reduction and miniaturization of the switching power supply device. Furthermore, an arbitrary AC voltage can be generated through on-duty adjustment. Needless to say, in this embodiment using switching, the transformer can be greatly reduced in size compared to a configuration in which a desired AC voltage is generated from a commercial AC voltage by simply adjusting the winding ratio of the transformer.

  In the above description (see FIG. 4), the switching element 7 is always on in the positive interval and the switching element 6 is always on in the negative interval. However, at the timing when the switching element 6 is off in the positive interval, the switching element 7 May be turned off, or at a timing when the switching element 7 is turned off in the negative interval, the switching element 6 may be turned off.

Second Embodiment
A switching power supply device according to a second embodiment of the present invention will be described. The second embodiment is an embodiment based on the first embodiment. Regarding matters not specifically described in the second embodiment, the description of the first embodiment applies to the second embodiment as long as there is no contradiction. Is done.

  FIG. 8 is a configuration diagram of the switching power supply device according to the second embodiment. The switching power supply apparatus of FIG. 8 includes a power converter 4B as the power converter 4. The power converter 4B includes first and second switching elements 6 and 7, first and second rectifying elements 8 and 9, a smoothing circuit 10B, first to fourth control circuits 11 to 14, a transformer 15, And a feedback circuit 16.

  In the second embodiment, the connections of the lines L1 and L2, the switching elements 6 and 7, and the primary coil are the same as those described in the first embodiment.

  Each of the rectifying elements 8 and 9 is composed of an N-channel FET, as is the switching element 8 or 9. In the rectifying element 8, the source is connected to one end 41 of the secondary side coil of the transformer 15, and the drain is connected to the line L3. In the rectifying element 9, the source is connected to the other end 42 of the secondary side coil of the transformer 15, and the drain is connected to the line L3. The line L3 is connected to the first input terminal 51 of the smoothing circuit 10B. A tap (center tap) 43 is provided at the center of the secondary coil, and the tap 43 is connected to the second input terminal 52 of the smoothing circuit 10B via a line L4.

The control circuits 13 and 14 control on / off of the rectifying elements 8 and 9, respectively. That is, the control circuit 13 turns on or off the rectifying element 8 through control of the gate-source voltage V _GS of the FET as the rectifying element 8, and the control circuit 14 sets the gate-source voltage of the FET as the rectifying element 9. The rectifying element 9 is turned on or off through the control of V _GS .

Each of the rectifying elements 8 and 9 acts so that a current flows only in the forward direction of its body diode 20. The forward direction of the rectifying element 8 (the forward direction of the body diode 20 of the rectifying element 8) coincides with the direction from the source to the drain of the rectifying element 8, and the forward direction of the rectifying element 9 (the forward direction of the body diode 20 of the rectifying element 9). ) Coincides with the direction from the source to the drain of the rectifying element 9. When the gate-source voltage V _GS of the FET as the rectifying element is equal to or higher than a predetermined threshold voltage and the drain and source of the FET are in a conductive state, the rectifying element is on and the gate of the FET as the rectifying element _{-When the} source-to-source voltage V _GS is less than the threshold voltage and the drain and source of the FET become non-conductive, the rectifying element is off. The state where the rectifying element is turned on and off is also referred to as an on state and an off state, respectively. The gate-source voltage V _GS of the FET indicates a gate voltage viewed from the source potential of the FET.

  Switching control by the control circuits 11 and 12 is the same as that described in the first embodiment. Therefore, as shown in FIG. 9, in the positive section, the control circuit 11 controls the switching element 6 to perform the switching operation of the switching element 6, while the control circuit 12 always turns on the switching element 7. In the negative interval, the control circuit 12 controls the switching element 7 to cause the switching element 7 to perform a switching operation, while the control circuit 11 always turns on the switching element 6. Thereby, like the first embodiment, the transformer 15 is excited in both directions, and a voltage due to the excitation is generated in the secondary coil.

  The control circuits 13 and 14 monitor the voltage appearing in the secondary coil, determine which section the current time period P1 to P4 belongs based on the monitoring result, and based on the determination result, the rectifying element as shown in FIG. Control 8 and 9 states. In order to perform this monitoring, each of the control circuits 13 and 14 is connected to the lines L3 and L4, and the control circuit 13 is connected to the line L5 to which the one end 41 of the secondary coil and the source of the rectifying element 8 are connected. The control circuit 14 is connected to a line L6 in which one end 42 of the secondary coil and the source of the rectifying element 9 are connected. Specifically, the control circuits 13 and 14 turn on and off the rectifying elements 8 and 9 in the section P1, respectively, turn off both the rectifying elements 8 and 9 in the section P2, and in the section P3. The rectifying elements 8 and 9 are turned off and on, respectively, and both the rectifying elements 8 and 9 are turned off in the section P4.

  When the potential at one end 31 viewed from one end 32 of the primary coil is positive, a positive potential appears at one end 42 viewed from one end 41 of the secondary coil and a positive potential appears at one end 42 viewed from the tap 43. Thus, the transformer 15 is formed. Accordingly, the current 120P in FIG. 10A flows in the section P1 in which the switching current 110P (see FIG. 5A) flows. The current 120P passes from the terminal 52 via the line L4, the tap 43 in the secondary coil, the winding between the tap 43 and one end 41, the one end 41 of the secondary coil, the body diode 20 of the rectifier 8 and the line L3. Current flowing through the terminal 51. In a section P3 in which the switching current 110N (see FIG. 5B) flows, the current 120N in FIG. 10B flows. The current 120N passes from the terminal 52 via the line L4, the tap 43 in the secondary coil, the winding between the tap 43 and one end 42, the one end 42 of the secondary coil, the body diode 20 of the rectifying element 9, and the line L3. Current flowing through the terminal 51.

  When the current 120P flows during the section P1, the power transmitted to the secondary side coil during the section P1 is supplied to the smoothing circuit 10B through the rectifying element 8, and when the current 120N flows during the section P3, The electric power transmitted to the secondary coil is supplied to the smoothing circuit 10B through the rectifying element 9. In the sections P2 and P4, no current flows through the secondary coil.

  The smoothing circuit 10 </ b> B generates a DC voltage as the output voltage Vo by smoothing power generated by the currents 120 </ b> P and 120 </ b> N supplied from the secondary coil, and outputs the DC voltage to the output unit 5. As understood from the above description, in the second embodiment, power is transmitted to the secondary side of the transformer 15 when the switching element 6 or 7 is turned on. That is, the switching power supply according to the second embodiment is a forward switching power supply. For this reason, the smoothing circuit 10B includes a choke coil that accumulates power supplied from the secondary side coil. In the smoothing process, electric power is accumulated by the choke coil.

  Referring to FIG. 11, a waveform 423 is an example of a voltage waveform obtained by directly switching an input AC voltage by the method of the present embodiment, and a waveform 424 is a primary side coil and a secondary side coil of the transformer 15. It is an example of a similar waveform of the output voltage Vo of the smoothing circuit 10B depending on the winding number ratio. The waveform 423 may be considered as a waveform of the voltage generated by the secondary coil.

  The feedback circuit 16 detects the output voltage Vo of the smoothing circuit 10B and controls the control circuits 11 and 12 so that the output voltage Vo becomes a predetermined target DC voltage. The magnitude of the target DC voltage is arbitrary. In the example of FIG. 11, the input AC voltage is AC 100 V (that is, the AC voltage having an effective value of 100 V), and the target DC voltage 424 is DC 12 V (that is, the DC voltage of 12 V).

  The control circuits 11 and 12 can use pulse width modulation for switching control. The control circuits 11 and 12 cooperate with the feedback circuit 16 to turn on the switching elements 6 and 7 (that is, the rate at which the switching element 6 is turned on in the positive interval) if the output voltage Vo is smaller than the target DC voltage. If the output voltage Vo is higher than the target DC voltage, the on-duty is reduced. As a result, the output voltage Vo of the smoothing circuit 10B is stabilized at the target DC voltage.

  In the second embodiment, as in the first embodiment, the diode forward voltage is compared with the conventional configuration using a bridge diode as shown in FIG. 15 (configuration with power loss corresponding to two diode forward voltages). The power loss can be reduced by two (for example, the power loss can be reduced by 20%). Further, the reduction of the bridge diode and the reduction of the power loss contribute to the cost reduction and miniaturization of the switching power supply device. Furthermore, an arbitrary DC voltage can be generated through on-duty adjustment.

  In the above description (see FIG. 9), the switching element 7 is always on in the positive interval and the switching element 6 is always on in the negative interval. However, at the timing when the switching element 6 is off in the positive interval, the switching element 7 May be turned off, or at a timing when the switching element 7 is turned off in the negative interval, the switching element 6 may be turned off.

<Third Embodiment>
A switching power supply device according to a third embodiment of the present invention will be described. The third embodiment is an embodiment based on the first and second embodiments. For matters not specifically described in the third embodiment, the description of the first and second embodiments is the first unless there is a contradiction. This also applies to the third embodiment.

  FIG. 12 is a configuration diagram of a switching power supply device according to the third embodiment. The switching power supply device of FIG. 12 includes a power converter 4 </ b> C as the power converter 4. The power converter 4C includes first and second switching elements 6 and 7, first and second rectifying elements 8 and 9, a smoothing circuit 10C, first to fourth control circuits 11 to 14, a transformer 15, The feedback circuit 16 is basically the same as the corresponding portion of the power converter 4B (FIG. 8).

  In the third embodiment, the connections of the lines L1 and L2, the switching elements 6 and 7, and the primary coil are the same as those described in the first embodiment, and the secondary coil, the rectifying elements 8 and 9, the line The connection relationship between L3 to L6 and the control circuits 13 and 14 is the same as that described in the second embodiment. The first and second input terminals 51 and 52 of the smoothing circuit 10C perform the same function as the input terminals 51 and 52 of FIG. The drain of the FET as the rectifying element 8 is connected to the input terminal 51 of the smoothing circuit 10C through the line L3, and the tap 43 is connected to the input terminal 52 of the smoothing circuit 10C through the line L4.

  FIG. 13 shows the states of the switching elements 6 and 7 and the rectifying elements 8 and 9 in each section of the third embodiment. In the positive section, the control circuit 11 controls the switching element 6 to switch the switching element 6 to perform a switching operation, while the control circuit 12 turns on the switching element 7 in the section P1 and turns on the switching element 7 in the section P2. Turn off. In the negative interval, the control circuit 12 causes the switching element 7 to perform a switching operation by controlling the switching of the switching element 7, while the control circuit 11 turns on the switching element 6 in the interval P3 and turns on the switching element 6 in the interval P4. Turn off. Thereby, like the first embodiment, the transformer 15 is excited in both directions, and a voltage due to the excitation is generated in the secondary coil.

  The control circuits 13 and 14 also have the same function as in the second embodiment, and control on / off of the rectifying elements 8 and 9. However, the on / off timings of the rectifying elements 8 and 9 are different from those of the second embodiment. The control circuits 13 and 14 monitor the voltage appearing in the secondary coil, determine which section P1 to P4 the current time belongs to based on the monitoring result, and based on the determination result, as shown in FIG. Control 8 and 9 states. That is, the control circuits 13 and 14 in the power converter 4C turn off both the rectifying elements 8 and 9 in the section P1, and turn on and off the rectifying elements 8 and 9 in the section P2, respectively. , Both the rectifying elements 8 and 9 are turned off, and in the section P4, the rectifying elements 8 and 9 are turned off and on, respectively.

  In the section P1 in which the switching current 110P (see FIG. 5A) flows, since the rectifying elements 8 and 9 are off, a current loop passing through the secondary coil is not formed. Therefore, in the section P1, no current flows through the secondary coil, and magnetic energy generated by the switching current 110P is accumulated in the transformer 15. The accumulated magnetic energy is released from the secondary coil as electric power by the current 120P (FIG. 10A) when the rectifier 8 is turned on in the section P2. That is, the above-described current 120P flows in the section P2 (the electric power due to the current 120P is supplied from the secondary coil to the smoothing circuit 10C through the rectifier 8).

  In the section P3 in which the switching current 110N (see FIG. 5B) flows, since the rectifier elements 8 and 9 are off, a current loop passing through the secondary coil is not formed. Accordingly, in the section P3, no current flows through the secondary coil, and magnetic energy generated by the switching current 110N is accumulated in the transformer 15. The accumulated magnetic energy is released from the secondary coil as electric power by the current 120N (FIG. 10B) when the rectifying element 9 is turned on in the section P4. That is, the above-described current 120N flows in the section P4 (the electric power from the current 120N is supplied from the secondary coil to the smoothing circuit 10C through the rectifying element 9).

  The smoothing circuit 10 </ b> C generates a DC voltage as the output voltage Vo by smoothing the electric power generated by the currents 120 </ b> P and 120 </ b> N supplied from the secondary coil, and outputs the DC voltage to the output unit 5. As understood from the above description, in the third embodiment, when the switching element 6 or 7 is turned on, electric power (magnetic energy) is accumulated in the transformer 15, and the stored power is turned off in the switching elements 6 and 7. At the time of discharge from the secondary coil. That is, the switching power supply according to the third embodiment is a flyback switching power supply. Therefore, the transformer 15 according to the third embodiment is a transformer that combines both power storage and power transmission. Generally, the second embodiment is more suitable for power conversion than the third embodiment. Is possible.

  The feedback circuit 16 detects the output voltage Vo of the smoothing circuit 10C and controls the control circuits 11 and 12 so that the output voltage Vo becomes a predetermined target DC voltage. The magnitude of the target DC voltage is arbitrary. The waveform 424 in FIG. 11 described above is also an example of the waveform of the output voltage Vo of the smoothing circuit 10C. In the example of FIG. 11, the input AC voltage is AC 100V (that is, the AC voltage having an effective value of 100V), and the target DC voltage is DC 12V (that is, the DC voltage of 12V).

  The control circuits 11 and 12 can use pulse width modulation for switching control. The control circuits 11 and 12 cooperate with the feedback circuit 16 to turn on the switching elements 6 and 7 (that is, the rate at which the switching element 6 is turned on in the positive interval) if the output voltage Vo is smaller than the target DC voltage. If the output voltage Vo is higher than the target DC voltage, the on-duty is reduced. As a result, the output voltage Vo of the smoothing circuit 10C is stabilized at the target DC voltage.

  Also in the third embodiment, as in the first embodiment, the diode forward voltage is compared with the conventional configuration using a bridge diode as shown in FIG. 15 (configuration with power loss for two diode forward voltages). The power loss can be reduced by two (for example, the power loss can be reduced by 20%). Further, the reduction of the bridge diode and the reduction of the power loss contribute to the cost reduction and miniaturization of the switching power supply device. Furthermore, an arbitrary DC voltage can be generated through on-duty adjustment.

  In the above description (see FIG. 13), the switching element 7 is turned off in the section P2 and the switching element 6 is turned off in the section P4. However, the switching element 7 is always on in the positive section and the switching element 6 is always turned on in the negative section. It may be turned on.

<Fourth embodiment>
A switching power supply device according to a fourth embodiment of the present invention will be described. The fourth embodiment is an embodiment based on the first to third embodiments, and the matters described in the fourth embodiment are not described in the first to third embodiments unless there is a contradiction. This also applies to the fourth embodiment.

  FIG. 14 is a configuration diagram of a switching power supply device according to the fourth embodiment. The switching power supply device of FIG. 14 includes a power converter 4D as the power converter 4. The power converter 4D is the same as the power converter 4B in FIG. 8 or the power converter 4C in FIG. Therefore, in the fourth embodiment, the same operation and effect as in the second or third embodiment can be obtained. The smoothing circuit in the power converter 4D is referred to by the symbol “10D”. When the power converter 4D is the power converter 4B, the smoothing circuit 10D is the same as the smoothing circuit 10B of FIG. 8, and when the power converter 4D is the power converter 4C, the smoothing circuit 10D is the smoothing circuit of FIG. This is the same as the circuit 10C.

  The switching power supply according to the fourth embodiment includes a second power converter 17 in the subsequent stage of the power converter 4D, and the output voltage Vo of the power converter 4D (that is, the output voltage Vo of the smoothing circuit 10D) is the power converter 17. Is input. The power converter 17 generates a second output voltage Vo ′ having an arbitrary voltage value by performing power conversion (power conversion different from the power conversion performed by the power converter 4D) on the output voltage Vo. The output voltage Vo ′ is supplied to the output unit 5.

  In a configuration in which AC power is half-wave rectified with a diode or full-wave rectified with a bridge diode and then supplied to the power converter, generally, a half-wave rectifier diode or a full-wave rectifier bridge diode is used. A large capacity capacitor is required between the power converter (for example, between the bridge diode 903 and the power converter 904 in FIG. 15). When such a large-capacitance capacitor is mounted, the phase of current advances from the voltage and the power factor decreases. In the switching power supply device of the fourth embodiment, since a large-capacitance capacitor is not required before the power converter 17, an improvement in power factor can be expected compared to a configuration in which a large-capacity capacitor is mounted. Due to the improvement of the power factor, the switching power supply device of the present embodiment can be applied even to a strict device such as a lighting fixture.

<Consideration of the present invention>
Consider the present invention.

  In the switching power supply according to the present invention, a primary coil is indirectly disposed between the first and second input lines (L1, L2) to which an input AC voltage is applied and the first and second input lines. And a transformer (15) for generating an output voltage (Vo) on the secondary side of the transformer by performing power conversion on the input AC voltage, from a potential of the second input line The transformer (15) is bi-directionally excited by alternately switching the pulsating voltage on the first input line as seen and the pulsating voltage on the second input line as seen from the potential of the first input line. Thus, the power conversion is performed.

  A conventional configuration in which rectification by a bridge diode or the like is essential before switching by switching the input AC voltage directly without rectification and exciting the transformer bidirectionally to perform power conversion (for example, the configuration of FIG. 15). Compared with, for example, power loss can be reduced by two diode forward voltages. In addition, the reduction of bridge diodes and the like and the reduction of power loss contribute to cost reduction and size reduction of the switching power supply device.

  The fact that the primary coil is indirectly arranged between the first and second input lines does not mean that the primary coil is connected in series to the first and second input lines. This means that some component (such as a switching element) is interposed between the input line and the primary coil.

  Specifically, for example, a first switch that is disposed between the first input line and one end of the primary coil and switches a pulsating voltage in the first input line as viewed from the potential of the second input line. The switching element (6) is disposed between the second input line and the other end of the primary coil, and switches the pulsating voltage in the second input line as viewed from the potential of the first input line. A switching control circuit (11, 12) that excites the transformer bidirectionally by alternately performing a switching operation by the second switching element (7), the first switching element, and a switching operation by the second switching element. ) May be provided in the switching power supply device.

  By providing the first and second switching elements and causing them to perform switching operations alternately, bidirectional excitation of the transformer is possible, and rectification before switching is not required.

  In each of the embodiments described above, the switching control circuit may be considered to be configured by the control circuits 11 and 12, or may be considered to be configured by the control circuits 11 and 12 and the feedback circuit 16. .

  In addition, for example, in the switching power supply device, an output AC voltage different from the input AC voltage may be generated as the output voltage (Vo) by smoothing a voltage generated in the secondary coil of the transformer (15).

  This makes it possible to generate an arbitrary output AC voltage with low power loss.

  Alternatively, for example, a first rectifier element (8) connected to one end of the secondary side coil of the transformer (15), and a second rectifier element (9) connected to the other end of the secondary side coil of the transformer. May be further provided in the switching power supply. In this case, the switching power supply rectifies the power output from the secondary coil by the excitation using the first and second rectifying elements, It is preferable to generate a DC voltage as the output voltage by smoothing.

  This makes it possible to generate an arbitrary output DC voltage with low power loss.

  More specifically, for example, the first and second switching elements (6, 7) are composed of field effect transistors, and the switching control circuit is configured such that the potential of the first input line viewed from the potential of the second input line. The first switching element is switched in a positive interval in which is positive, and when the first switching element is turned on in the positive interval, the second switching element is also turned on, thereby switching the first switching element. A current is passed through the body diode (20) of the second switching element, and the second switching element is switched in a negative interval in which the potential of the first input line viewed from the potential of the second input line is negative. The first switching element is also turned on when the second switching element is turned on during the negative interval. The switching current of the switching element may flow through the body diode (20) of the first switching element.

  As a result, the switching current in the positive section flows through the low-resistance channel (between the drain and source) in the first switching element and also flows through the low-voltage body diode in the second switching element. The switching current in the negative section flows through a low-resistance channel (between drain and source) in the second switching element and also flows through a low-voltage body diode in the first switching element. As a result, power loss can be reduced by, for example, two diode forward voltages, compared to a conventional configuration (for example, the configuration of FIG. 15) in which rectification by a bridge diode or the like is necessary before switching.

  Further, for example, the switching power supply device that generates a DC voltage as the output voltage (Vo) is a forward-type switching power supply device, and each of the first and second rectifying elements (8, 9) each composed of a field effect transistor. It is preferable to further include a rectifying element control circuit (13, 14) for controlling on / off of). In the forward-type switching power supply device, for example, the switching control circuit (11, 12) may be configured such that the first switching is performed in a positive section in which the potential of the first input line viewed from the potential of the second input line is positive. Switching the element (6) and switching the second switching element (7) in a negative interval in which the potential of the first input line viewed from the potential of the second input line is negative, the rectifying element control In the positive section, the circuits (13, 14) turn on and off the first and second rectifier elements when the first switching element is turned on, while the first switching element is turned off. When both the first and second rectifying elements are turned off, the smoothing circuits (10B, 10D) smooth the power from the secondary coil. In contrast, when the second switching element is turned on in the negative section, the first and second rectifying elements are turned off and on, respectively, while the second rectifying element is turned on and off. By turning off both the first and second rectifier elements when the switching element is turned off, the power from the secondary coil is supplied to the second rectifier element to the smoothing circuit (10B, 10D). Good to supply through.

  This makes it possible to generate an arbitrary output DC voltage with low power loss.

  Alternatively, for example, the switching power supply that generates a DC voltage as the output voltage (Vo) is a flyback switching power supply, and each of the first and second rectifying elements (8, It is preferable to further include a rectifying element control circuit (13, 14) for controlling on / off of 9). In the flyback switching power supply device, for example, the switching control circuit (11, 12) may be configured such that the first input line is positive in a positive interval when the potential of the first input line viewed from the potential of the second input line is positive. Switching the switching element (6), and switching the second switching element (7) in a negative interval in which the potential of the first input line viewed from the potential of the second input line is negative, the rectifying element The control circuit (13, 14) turns off both the first and second rectifier elements when the first switching element (6) is turned on in the positive section, while the first switching element A smoothing circuit (10C) that smoothes the power from the secondary side coil by turning on and off the first and second rectifying elements when turned off. 10D) through the first rectifying element, and turning off the first and second rectifying elements when the second switching element (7) is turned on in the negative section, When the second switching element is turned off, the first and second rectifying elements are turned off and on, respectively, so that power from the secondary coil is supplied to the smoothing circuit (10C, 10D). It may be supplied through the second rectifying element.

  This makes it possible to generate an arbitrary output DC voltage with low power loss.

  Further, for example, in the switching power supply device, another DC voltage (Vo ′) may be generated by performing a second power conversion different from the power conversion on the DC voltage (Vo) obtained by the smoothing. good.

  According to this switching power supply device, since it is not necessary to arrange a large-capacity capacitor in front of the power converter that performs the power conversion, the power factor is improved in comparison with the conventional configuration in which a large-capacitance capacitor is required. Can be expected.

<Deformation, etc.>
The embodiment of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims. The above embodiment is merely an example of the embodiment of the present invention, and the meaning of the term of the present invention or each constituent element is not limited to that described in the above embodiment. The specific numerical values shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values.

  In the switching power supply device of each of the embodiments described above, the circuit configuration may be modified so that the switching elements 6 and 7 are formed using a P-channel FET, or the rectifier element using a P-channel FET. The circuit configuration may be modified so that 8 and 9 are formed.

DESCRIPTION OF SYMBOLS 1 Commercial AC power supply 2 Noise filter 4, 4A-4D Power converter 5 Output part 6, 7 Switching element 8, 9 Rectifier 10, 10, 10A-10D Smoothing circuit 11-14 Control circuit 15 Transformer 16 Feedback circuit 17 2nd power conversion vessel

Claims (5)

A first input line to which an input AC voltage is applied, and a transformer in which a primary coil is indirectly disposed between the first and second input lines, and performs power conversion on the input AC voltage. A switching power supply that generates an output voltage on the secondary side of the transformer by performing,
The transformer is configured by alternately switching a pulsating voltage at the first input line as viewed from the potential of the second input line and a pulsating voltage at the second input line as viewed from the potential of the first input line. The switching power supply device performs the power conversion by bi-directionally exciting the power. A first switching element that is disposed between the first input line and one end of the primary coil and that switches a pulsating voltage in the first input line as viewed from the potential of the second input line;
A second switching element that is disposed between the second input line and the other end of the primary coil, and switches a pulsating voltage in the second input line as viewed from the potential of the first input line;
The switching control circuit for exciting the transformer bidirectionally by alternately performing a switching operation by the first switching element and a switching operation by the second switching element. The switching power supply device described in 1. The switching power supply according to claim 2, wherein an output AC voltage different from the input AC voltage is generated as the output voltage by smoothing a voltage generated in a secondary coil of the transformer. A first rectifier connected to one end of the secondary coil of the transformer;
A second rectifier connected to the other end of the secondary coil of the transformer,
The DC voltage as the output voltage is generated by rectifying the electric power output from the secondary coil by the excitation using the first and second rectifying elements and further smoothing the power. 3. The switching power supply device according to 2. The first and second switching elements are field effect transistors,
The switching control circuit includes:
The first switching element is switched in a positive section in which the potential of the first input line viewed from the potential of the second input line is positive, and the first switching element is turned on in the positive section. By turning on the second switching element, the switching current of the first switching element flows through the body diode of the second switching element, and
When the second switching element is switched in a negative interval in which the potential of the first input line viewed from the potential of the second input line is negative, and the second switching element is turned on in the negative interval 5. The switching power supply device according to claim 2, wherein a switching current of the second switching element is caused to flow through a body diode of the first switching element by turning on the first switching element.

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