JP5450212B2 - Multi-output switching power supply - Google Patents

Description

  The present invention relates to a multi-output switching power supply.

  Conventionally, a multi-output switching power supply having a plurality of outputs has been proposed (see, for example, Patent Document 1).

[Configuration of Multi-Output Switching Power Supply 100]
FIG. 15 is a circuit diagram of a multi-output switching power supply 100 according to a conventional example. The multi-output switching power supply 100 is connected to a DC power supply VIN and loads Load1 and Load2, and supplies DC power to each of the loads Load1 and Load2 using DC power supplied from the DC power supply VIN.

  The multi-output switching power supply 100 includes a transformer T100 that insulates the DC power supply VIN from the loads Load1 and Load2, a switch element Q100 composed of N-channel MOSFETs, diodes D111, D112, D121, and D122, and capacitors C110 and C120. Inductors L110 and L120 as output chokes and a control unit 120 are provided. The transformer T100 includes a primary winding NP100, a first secondary winding NS110, a second secondary winding NS120, the primary winding NP100, the first secondary winding NS110, and a second secondary winding NS110. A core (not shown) around which the secondary winding NS120 is wound.

  One end of the primary winding NP100 is connected to the positive electrode of the DC power source VIN, and the other end of the primary winding NP100 is connected to the drain of the switch element Q100. The negative electrode of the DC power source VIN is connected to the source of the switch element Q100.

  A rectifier circuit formed by diodes D111 and D112, an inductor L110, and a capacitor C110 is connected to the first secondary winding NS110. Specifically, the anode of the diode D111 is connected to one end of the first secondary winding NS110, and the cathode of the diode D112 and one end of the inductor L110 are connected to the cathode of the diode D111. The inductor L110 is magnetically coupled to the inductor L120. One end of the capacitor C110 and one end of the load Load1 are connected to the other end of the inductor L110. The other end of the first secondary winding NS110 is connected to the anode of the diode D112, the other electrode of the capacitor C110, and the other end of the load Load1.

  A rectifier circuit formed of diodes D121 and D122, an inductor L120, and a capacitor C120 is connected to the second secondary winding NS120. Specifically, the anode of the diode D121 is connected to one end of the second secondary winding NS120, and the cathode of the diode D122 and one end of the inductor L120 are connected to the cathode of the diode D121. One end of the capacitor C120 and one end of the load Load2 are connected to the other end of the inductor L120. The other end of the second secondary winding NS120 is connected to the anode of the diode D122, the other electrode of the capacitor C120, and the other end of the load Load2.

  A control unit 120 connected to the gate of the switch element Q100 is connected to one end of the load Load1.

[Operation of Multi-Output Switching Power Supply 100]
The multi-output switching power supply 100 having the above configuration is configured such that the control unit 120 switches based on the output voltage of the rectifier circuit formed by the diodes D111 and D112, the inductor L110 and the capacitor C110, that is, the voltage generated in the load Load1. PWM control of Q100 is performed to stabilize the DC power supplied to the load Load1, so that the DC power supplied to the load Load2 is also stabilized.

  Here, suppose that the inductor L110 and the inductor L120 are not magnetically coupled. The current flowing through the inductor L110 includes a ripple that is determined according to its own inductance. Then, the average current of the inductor L110 decreases as the load of the load Load1 becomes lighter. For this reason, when the load Load1 becomes a light load, a period in which the current flowing through the inductor L110 is “0” occurs, which may be discontinuous.

  When the current flowing through the inductor L110 becomes discontinuous, the control unit 120 determines the voltage generated in the load Load1 by narrowing the ON width of the switch element Q100 as compared with the case where the current flowing through the inductor L110 is continuous. Value. When the ON width of the switch element Q100 is narrowed, the time for storing energy in the inductor L120 is shortened. As a result, the voltage generated in the load Load2 is decreased.

  On the other hand, in the multi-output switching power supply 100 described above, the inductor L110 and the inductor L120 are magnetically coupled. For this reason, the sum of the respective voltages of the second secondary winding NS120 and the inductor L120 and the forward voltage of the diode D121 is equal to the voltage generated in the load Load2. For this reason, if the voltage generated in the load Load1 is constant, the voltage generated in the load Load2 is constant regardless of the current flowing through the load Load1.

JP 2000-341949 A

  In the above-described multi-output switching power supply 100, it is necessary to magnetically couple the inductor L110 and the inductor L120, which may increase the component mounting area and increase the cost.

  Thus, instead of magnetically coupling the inductor L110 and the inductor L120, a method of connecting a resistor in parallel with the load Load1 and a method of increasing the inductance of the inductor L110 are conceivable.

  According to the method of connecting a resistor in parallel with the load Load1, the average current of the inductor L110 is equal to the sum of the current flowing through the load Load1 and the current flowing through the resistor. For this reason, even at the minimum load of the load Load1 determined by the power supply specifications, it is possible to suppress a decrease in the current flowing through the load Load2 by flowing the current through the resistor so that the current flowing through the inductor L110 is continuous. However, if a resistor is provided as described above, power is always consumed by the resistor, so that the efficiency of the power supply decreases.

  In addition, according to the above-described method for increasing the inductance of the inductor L110, the ripple included in the current flowing through the inductor L110 can be reduced. For this reason, a decrease in the current flowing through the load Load2 can be suppressed by designing the inductance of the inductor L110 so that the current flowing through the inductor L110 is continuous even at the minimum load of the load Load1 determined by the power supply specifications. However, when the inductance of the inductor L110 is increased, the outer dimension of the inductor L110 is increased.

  Therefore, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a multi-output switching power supply that can realize downsizing, cost reduction, and suppression of reduction in efficiency.

  The present inventor has intensively studied to achieve the above-described object. Here, among the plurality of secondary windings provided in the transformer, the one that detects the output voltage of the connected rectifier circuit, such as the first secondary winding NS110 in FIG. A line that does not detect the output voltage of the connected rectifier circuit, such as the second secondary winding NS120 in FIG. 15, is referred to as a second secondary winding. Then, the present inventor provides a plurality of legs on the core of the transformer, a center tap on the first secondary winding, and the primary winding so as to surround all the legs around which the secondary winding is wound. When winding, connecting the center tap of the first secondary winding to one end of the load, and connecting both ends of the first secondary winding to the other end of the load via the rectifying element of the rectifier circuit The present invention is completed by finding that even if the load connected to the first secondary winding becomes a light load, the voltage drop generated in the load connected to the second secondary winding can be suppressed. It came to.

  (1) The present invention is a multi-output switching power supply that supplies power to each of a plurality of loads using power supplied from a DC power supply, and includes a primary winding, a plurality of secondary windings, A transformer having a primary winding and a core around which the plurality of secondary windings are wound, a first switch element for turning on and off an output current of the DC power supply, and a first switch element used for releasing excitation energy of the transformer. Two switch elements, a capacitor connected in series with the second switch element, a plurality of rectifier circuits connected to each of the plurality of secondary windings, and an output voltage of one of the plurality of rectifier circuits And control means for controlling respective conduction times of the first switch element and the second switch element according to a detection result, and the core includes a plurality of legs, and the primary Winding the front The plurality of legs are wound so as to surround all of the windings of the secondary winding, and the plurality of secondary windings connected to a rectifier circuit that detects voltage by at least the control means, A center tap is provided, the center tap is connected to one end of the load, and both ends of the secondary winding provided with the center tap are connected to the other end of the load via a rectifier element included in the rectifier circuit. We propose a multi-output switching power supply characterized by

  According to the present invention, a multi-output switching power supply that supplies power to each of a plurality of loads using power supplied from a DC power supply includes a transformer, a first switch element, a second switch element, a capacitor, a plurality of A rectifier circuit and control means were provided, and the transformer was provided with a primary winding, a plurality of secondary windings, and a core for winding the primary winding and the plurality of secondary windings. Then, the output current of the DC power source is turned on / off by the first switch element, and the second switch element is used for releasing the excitation energy of the transformer. A capacitor was connected in series with the second switch element. Each of the plurality of rectifier circuits was connected to each of the plurality of secondary windings. Further, the control means detects one output voltage of the plurality of rectifier circuits, and controls the conduction times of the first switch element and the second switch element according to the detection result. Furthermore, the core was provided with a plurality of legs, and the primary winding was wound so as to surround all of the plurality of legs around which the secondary winding was wound. A center tap is provided on at least one of the secondary windings connected to a rectifier circuit that detects the output voltage by the control means. Then, the center tap was connected to one end of the load, and both ends of the secondary winding provided with the center tap were connected to the other end of the load via a rectifier element included in the rectifier circuit.

  For this reason, among the secondary windings provided in the transformer, the one that detects the output voltage of the connected rectifier circuit by the control means is called the first secondary winding, and the output voltage of the connected rectifier circuit If the load that is not detected by the control means is called the second secondary winding, even if the load connected to the first secondary winding becomes a light load, the second secondary winding It is possible to suppress a decrease in voltage generated in the connected load.

  Here, the multi-output switching power source of (1) does not include magnetically coupled inductors (for example, equivalent to the inductors L110 and L120 of FIG. 15) as shown in FIG. Can be suppressed. For this reason, since it is not necessary to magnetically couple a plurality of inductors, it is possible to reduce the size of the multi-output switching power supply by suppressing an increase in the component mounting area, and to reduce the cost of the multi-output switching power supply.

  Moreover, the multi-output switching power source of (1) can suppress the voltage drop as described above without connecting a resistor in parallel with the load Load1 as described above. For this reason, since no power is consumed by the resistor, power consumption does not increase, and a decrease in efficiency of the multi-output switching power supply can be suppressed.

  Further, the multi-output switching power source of (1) can suppress the voltage drop as described above without increasing the inductance of the output choke (for example, equivalent to the inductors L110 and L120 in FIG. 15). For this reason, the enlargement of a multi-output switching power supply can be avoided.

  Furthermore, the multi-output switching power source of (1) can function as an output choke (for example, equivalent to the inductors L110 and L120 in FIG. 15) by a transformer. For this reason, since it is not necessary to provide an output choke, the size can be further reduced and the cost can be reduced.

  (2) In the multi-output switching power source according to (1), the rectifier circuit has one end of the plurality of secondary windings excluding the secondary winding provided with the center tap. A multi-output switching power supply is proposed in which one end of the load is connected via an element and the other end is connected to the other end of the load.

  According to the present invention, in the multi-output switching power source of (1), one of the plurality of secondary windings excluding the secondary winding having a center tap is connected to one end via the rectifying element of the rectifying circuit. One end of the load was connected and the other end was connected to the other end of the load. For this reason, about the thing except a secondary winding provided with a center tap among several secondary windings, a structure can be simplified compared with the secondary winding provided with a center tap. Therefore, the size can be further reduced and the cost can be further reduced.

  (3) In the multi-output switching power source according to (1) or (2), the secondary winding including the center tap includes a first winding portion and the first winding via the center tap. A second winding portion connected to a portion, wherein the first winding portion is wound around any of the plurality of legs, and the second winding portion is connected to the first of the plurality of legs. A multi-output switching power supply has been proposed in which the winding portion is wound around any one except the one wound.

  According to the present invention, in the multi-output switching power source of (1) or (2), the secondary winding including the center tap is connected to the first winding portion and the first winding portion via the center tap. And a second winding part. Then, the first winding part is wound around any of the plurality of legs, and the second winding part is wound around any one of the plurality of legs excluding the one wound with the first winding part. . According to this, an effect similar to the effect mentioned above can be produced.

  (4) In the multi-output switching power supply according to any one of (1) to (3), the core includes at least three legs, and at least two of the at least three legs include an air gap. We propose a multi-output switching power supply characterized by

  According to the present invention, in the multi-output switching power supply of any one of (1) to (3), the core is provided with at least three legs, and at least two of the at least three legs are provided with an air gap. . For this reason, the excitation inductance value can be changed according to the distance of the air gap.

  ADVANTAGE OF THE INVENTION According to this invention, the multi-output switching power supply which can implement | achieve size reduction, cost reduction, and suppression of the fall of efficiency can be provided.

1 is a circuit diagram of a multi-output switching power supply according to a first embodiment of the present invention. It is a schematic diagram of the transformer with which the multi-output switching power supply is provided. It is sectional drawing of the said transformer. It is a figure which shows the current-voltage characteristic of the said multiple output switching power supply. It is a mimetic diagram of a transformer concerning a 2nd embodiment of the present invention. It is a mimetic diagram of a transformer concerning a 3rd embodiment of the present invention. It is a mimetic diagram of a transformer concerning a 4th embodiment of the present invention. It is sectional drawing of the said transformer. It is a mimetic diagram of a transformer concerning a 5th embodiment of the present invention. It is a mimetic diagram of a transformer concerning a 6th embodiment of the present invention. It is a circuit diagram of the multiple output switching power supply which concerns on 7th Embodiment of this invention. It is a circuit diagram of the multiple output switching power supply concerning the modification of this invention. It is a circuit diagram of the multiple output switching power supply concerning the modification of this invention. It is a circuit diagram of the multiple output switching power supply concerning the modification of this invention. It is a circuit diagram of the multi-output switching power supply which concerns on a prior art example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the constituent elements in the following embodiments can be appropriately replaced with existing constituent elements, and various variations including combinations with other existing constituent elements are possible. Accordingly, the description of the following embodiments does not limit the contents of the invention described in the claims.

<First Embodiment>
[Configuration of multi-output switching power supply 1]
FIG. 1 is a circuit diagram of a multi-output switching power supply 1 according to the first embodiment of the present invention. The multi-output switching power source 1 is connected to a DC power source VIN and loads Load1 and Load2, and supplies DC power to each of the loads Load1 and Load2 using DC power supplied from the DC power source VIN.

  The multi-output switching power supply 1 includes a transformer T, a switch element Q1 as a first switch element, a switch element Q2 as a second switch element, a capacitor C1, rectifier circuits REC1 and REC2, and control means. And a control unit 20. Switch elements Q1 and Q2 are formed of N-channel MOSFETs. The rectifier circuit REC1 includes diodes D11 and D12 and a capacitor C11, and the rectifier circuit REC2 includes diodes D21 and D22 and a capacitor C21.

[Configuration of transformer T]
The transformer T includes a core 10, a primary winding NP, a first secondary winding NS1 (see FIG. 2), and a second secondary winding NS2 (see FIG. 2). The core 10 includes a first outer leg 11, a first middle leg 12, a second middle leg 13, and a second outer leg 14. The first middle leg 12 and the second middle leg 13 each have an air gap. The transformer T will be described below with reference to FIGS.

  FIG. 2 is a schematic diagram of the transformer T. 3 is a cross-sectional view of the transformer T at AA in FIG.

  The first secondary winding NS1 includes a first winding portion NS11, a second winding portion NS12, and a center tap provided between the first winding portion NS11 and the second winding portion NS12. , Composed of. The second secondary winding NS2 includes a first winding portion NS21, a second winding portion NS22, and a center tap provided between the first winding portion NS21 and the second winding portion NS22. , Composed of.

  The first secondary winding NS <b> 1 is wound around the first middle leg 12 and the second middle leg 13. Specifically, of the first secondary winding NS1, the first winding portion NS11 is wound around the upper portion of the first middle leg 12, and the second winding portion NS12 is wound around the second middle leg 13. It is wound.

  The second secondary winding NS <b> 2 is wound around the first middle leg 12 and the second middle leg 13. Specifically, in the second secondary winding NS2, the first winding portion NS21 is wound in a region below the first middle leg 12 where the first winding portion NS11 is not wound. The second winding portion NS22 is wound in a region below the second middle leg 13 where the second winding portion NS12 is not wound.

  The primary winding NP includes a first secondary winding NS1 and a second secondary winding NS2 among the first outer leg 11, the first middle leg 12, the second middle leg 13, and the second outer leg 14. Is wound so as to surround all of the wound ones, that is, so as to surround the first middle leg 12 and the second middle leg 13. Specifically, the primary winding NP includes the first winding leg NS11 and the first winding part NS21 in the first middle leg 12 and the second middle leg 13 in the second winding. It is wound around the region where the winding portion NS12 and the second winding portion NS22 are wound without passing between the first middle leg 12 and the second middle leg 13. Therefore, as shown in FIG. 3, the portion of the primary winding NP that is wound around the first middle leg 12 and the second middle leg 13 forms one annular winding portion. The first middle leg 12 and the second middle leg 13 are present inside one winding part. Note that the term “annular” includes not only a perfect circle shape but also an elliptical shape or a substantially rectangular shape as shown in FIG.

  Returning to FIG. 1, one end of the primary winding NP is connected to the positive electrode of the DC power source VIN and one electrode of the capacitor C1. The drain of the switch element Q2 is connected to the other electrode of the capacitor C1, and the capacitor C1 and the switch element Q2 are connected in series. Further, the other end of the primary winding NP and the drain of the switch element Q1 are connected to the source of the switch element Q2, and the switch element Q1 and the switch element Q2 are connected in series. The negative electrode of the DC power source VIN is connected to the source of the switch element Q1.

  One end of a load Load1 is connected to the center tap of the first secondary winding NS1, and a diode D11 or a diode D12 as a rectifying element included in the rectifier circuit REC1 is connected to both ends of the first secondary winding NS1. The other end of the load Load1 is connected. Specifically, in the first secondary winding NS1, one end of the capacitor C11 is connected to one end of the first winding portion NS11 and one end of the second winding portion NS12 via the center tap described above. Are connected to one end of the load Load1. The other end of the first winding part NS11 is connected to the cathode of the diode D11, and the other end of the second winding part NS12 is connected to the cathode of the diode D12. The other electrode of the capacitor C11 and the other end of the load Load1 are connected to the anode of the diode D11 and the anode of the diode D12.

  One end of a load Load2 is connected to the center tap of the second secondary winding NS2, and a diode D21 or a diode D22 as a rectifying element included in the rectifier circuit REC2 is connected to both ends of the second secondary winding NS2. And the other end of the load Load2 is connected. Specifically, of the second secondary winding NS2, one end of the first winding portion NS21 and one end of the second winding portion NS22 are connected to one end of the capacitor C21 via the center tap described above. Are connected to one end of the load Load2. The other end of the first winding part NS21 is connected to the cathode of the diode D21, and the other end of the second winding part NS22 is connected to the cathode of the diode D22. The other electrode of the capacitor C21 and the other end of the load Load2 are connected to the anode of the diode D21 and the anode of the diode D22.

  One end of the load Load1 is connected to the control unit 20 connected to the gate of the switch element Q1 and the gate of the switch element Q2.

[Operation of multi-output switching power supply 1]
In the multi-output switching power supply 1 having the above configuration, the control unit 20 performs PWM control of the switch elements Q1 and Q2 based on the output voltage of the rectifier circuit REC1, that is, the voltage generated in the load Load1, and supplies it to the load Load1. By stabilizing the DC power, the DC power supplied to the load Load2 is also stabilized.

  When the switch element Q1 is turned on while the switch element Q2 is turned off, the output current of the DC power supply VIN flows through the primary winding NP, the output voltage of the DC power supply VIN is applied to the primary winding NP, A voltage is generated in each of the first secondary winding NS1 and the second secondary winding NS2. Further, excitation energy is accumulated in the transformer T. A current from the DC power source VIN flows through each of the first secondary winding NS1 and the second secondary winding NS2. The current flowing through the first secondary winding NS1 is rectified by the diodes D11 and D12, smoothed by the capacitor C11, and supplied to one end of the load Load1. The current flowing through the second secondary winding NS2 is rectified by the diodes D21 and D22, smoothed by the capacitor C21, and supplied to one end of the load Load2.

  Thereafter, when the switch element Q1 is turned off, the output current of the DC power source VIN is cut off. A voltage between terminals of the capacitor C1 is applied to the primary winding NP, and a voltage is generated in each of the first secondary winding NS1 and the second secondary winding NS2. The capacitor C1 is charged through the source-drain diode parasitic on the switch element Q2 by the current generated by releasing the excitation energy accumulated in the transformer T. The switch element Q2 is turned on with this current flowing. Further, the current due to the excitation energy accumulated in the transformer T flows through the first secondary winding NS1 and the second secondary winding NS2 via the primary winding NP. The current flowing through the first secondary winding NS1 is rectified by the diodes D11 and D12, smoothed by the capacitor C11, and supplied to one end of the load Load1. The current flowing through the second secondary winding NS2 is rectified by the diodes D21 and D22, smoothed by the capacitor C21, and supplied to one end of the load Load2.

  FIG. 4 is a diagram showing current-voltage characteristics of the multi-output switching power supply 1. The horizontal axis represents the current Iout flowing through the load Load1, and the vertical axis represents the voltage Vout generated at the load Load2.

  The solid line indicates the voltage Vout when the current Iout is changed when the positive voltage Vin of the DC power supply VIN is equal to the lower limit value determined by the power supply specifications. The broken line indicates the voltage Vout when the current Iout is changed in the case where the positive voltage Vin of the DC power supply VIN is equal to the intermediate value in the range determined by the power supply specifications. The alternate long and short dash line indicates the voltage Vout when the current Iout is changed when the positive voltage Vin of the DC power supply VIN is equal to the upper limit value determined by the power supply specifications.

  According to the above multi-output switching power supply 1, the following effects can be produced.

  In the multi-output switching power supply 1, four legs of a first outer leg 11, a first middle leg 12, a second middle leg 13, and a second outer leg 14 are provided on the core 10 of the transformer T. A center tap is provided in the next winding NS1. The primary winding NP is wound around the first middle leg 12 and the second middle leg 13 around which the first secondary winding NS1 and the second secondary winding NS2 are wound. The center tap of the first secondary winding NS1 is connected to one end of the load Load1, and both ends of the first secondary winding NS1 are connected to the load Load1 via the diode D11 or D12 of the rectifier circuit REC1. Is connected to the other end. For this reason, even if the load Load1 becomes a light load, it is possible to suppress a decrease in the voltage Vout generated in the load Load2.

  Further, the multi-output switching power supply 1 does not include a magnetically coupled inductor as shown in FIG. 15 (for example, equivalent to the inductors L110 and L120 in FIG. 15), and the voltage Vout generated in the load Load2 is a load. It can suppress that it falls at the time of light load of Load1. For this reason, since it is not necessary to magnetically couple a plurality of inductors, an increase in component mounting area and an increase in cost can be avoided in configuring the circuit of the multi-output switching power supply 1.

  Further, the multi-output switching power supply 1 can suppress the voltage Vout generated in the load Load2 from being reduced when the load Load1 is light, without connecting a resistor in parallel with the load Load1 as described above. For this reason, power is not consumed by the resistor, so that power consumption does not increase and a reduction in efficiency can be suppressed.

  Further, the multi-output switching power supply 1 does not increase the output choke (for example, equivalent to the inductors L110 and L120 in FIG. 15) as described above, and the voltage Vout generated in the load Load2 is low when the load Load1 is light. It can suppress that it falls. For this reason, the multi-output switching power supply 1 can be reduced in size.

  Here, in the multi-output switching power supply 100 according to the conventional example shown in FIG. 15, the DC power supply VIN and the loads Load1 and Load2 are insulated by the transformer T100, and the output choke is configured by the inductors L110 and L120. On the other hand, the multi-output switching power supply 1 insulates the DC power supply VIN and the loads Load1 and Load2 by the transformer T and constitutes an output choke. For this reason, the multi-output switching power source 1 does not need to separately provide a configuration for insulating the DC power source VIN and the loads Load1 and Load2 and a configuration as an output choke, so that it can be further reduced in size and cost. Can be reduced.

Second Embodiment
[Configuration of Trans TA]
FIG. 5 is a schematic diagram of a transformer TA according to the second embodiment of the present invention. The transformer TA differs from the transformer T according to the first embodiment of the present invention shown in FIG. 2 in the manner of winding the primary winding NP. In the transformer TA, the same components as those of the transformer T are denoted by the same reference numerals, and the description thereof is omitted.

  In the transformer T, the primary winding NP includes a first winding portion NS11 and a first winding portion NS21 in the first middle leg 12 and a second winding in the second middle leg 13. The wire portion NS12 and the second winding portion NS22 were wound around the region where the wire portion NS12 and the second winding portion NS22 were wound without passing between the first middle leg 12 and the second middle leg 13. On the other hand, in the transformer TA, the primary winding NP includes the first middle leg 12 in the region where the first winding part NS11 and the first winding part NS21 are not wound, and the second middle leg 13. Among them, the second winding part NS12 and the second winding part NS22 are wound around the area where the second winding part NS22 is not wound without passing between the first middle leg 12 and the second middle leg 13.

  Specifically, the primary winding NP is wound on the upper portion of the first middle leg 12, and the first winding portion NS11 is disposed below the region where the primary winding NP is wound. Is wound, and the first winding portion NS21 is wound below the region where the first winding portion NS11 is wound. Further, in the upper part of the second middle leg 13, the primary winding NP is wound, and the second winding part NS12 is wound below the region where the primary winding NP is wound. The second winding portion NS22 is wound below the region where the second winding portion NS12 is wound.

  When the above transformer TA is provided in the multi-output switching power source 1 shown in FIG. 1 instead of the transformer T, the same effect as that of the multi-output switching power source 1 including the transformer T can be obtained.

<Third Embodiment>
[Configuration of transformer TB]
FIG. 6 is a schematic diagram of a transformer TB according to the third embodiment of the present invention. The transformer TB differs from the transformer TA according to the second embodiment of the present invention shown in FIG. 5 in the manner of winding the primary winding NP. In the transformer TB, the same constituent elements as those of the transformer TA are denoted by the same reference numerals, and the description thereof is omitted.

  In the transformer TA, the primary winding NP is wound around the upper part of the first middle leg 12 and the upper part of the second middle leg 13. On the other hand, in the transformer TB, the primary winding NP is wound around the upper part and the lower part of the first middle leg 12 and the upper part and the lower part of the second middle leg 13.

  When the above transformer TB is provided in the multi-output switching power source 1 shown in FIG. 1 instead of the transformer T, the same effect as the multi-output switching power source 1 including the transformer T can be obtained.

<Fourth embodiment>
[Configuration of transformer TC]
FIG. 7 is a schematic diagram of a transformer TC according to the fourth embodiment of the present invention. FIG. 8 is a cross-sectional view of the transformer TC at BB in FIG. The transformer TC is different from the transformer T according to the first embodiment of the present invention shown in FIG. 2 in that a core 10A is provided instead of the core 10. In the transformer TC, the same components as those of the transformer T are denoted by the same reference numerals, and the description thereof is omitted.

  The core 10 </ b> A is different from the core 10 in that a second outer leg 14 </ b> A is provided instead of the first outer leg 11 and the second outer leg 14. The cross-sectional area of the second outer leg 14 </ b> A is equal to the sum of the cross-sectional area of the first outer leg 11 provided on the core 10 and the cross-sectional area of the second outer leg 14 provided on the core 10.

  When the above transformer TC is provided in the multi-output switching power source 1 shown in FIG. 1 instead of the transformer T, the same effect as the multi-output switching power source 1 including the transformer T can be obtained.

<Fifth Embodiment>
[Configuration of transformer TD]
FIG. 9 is a cross-sectional view of a transformer TD according to the fifth embodiment of the present invention. The transformer TD is different from the transformer T according to the first embodiment of the present invention shown in FIG. 3 in that a core 10B is provided instead of the core 10. In the transformer TD, the same components as those of the transformer T are denoted by the same reference numerals, and the description thereof is omitted.

  The core 10B is different from the core 10 in that the third middle leg 15 is provided. The third middle leg 15 exists inside one annular winding portion formed by the primary winding NP. That is, the primary winding NP is connected to the first middle leg 12, the second middle leg 13, and the third middle leg 15, and each of the first middle leg 12, the second middle leg 13, and the third middle leg 15. It is wound without passing between.

  When the above transformer TD is provided in the multi-output switching power source 1 shown in FIG. 1 instead of the transformer T, the same effect as that of the multi-output switching power source 1 including the transformer T can be obtained.

<Sixth Embodiment>
[Configuration of transformer TE]
FIG. 10 is a cross-sectional view of a transformer TE according to the sixth embodiment of the present invention. The transformer TE is different from the transformer T according to the first embodiment of the present invention shown in FIG. 3 in that a core 10C is provided instead of the core 10. In the transformer TE, the same components as those of the transformer T are denoted by the same reference numerals, and the description thereof is omitted.

  The core 10 </ b> C is different from the core 10 in that the third middle leg 16 and the fourth middle leg 17 are provided.

  The third middle leg 16 and the fourth middle leg 17 exist inside one annular winding portion formed by the primary winding NP. That is, the primary winding NP is connected to the first middle leg 12, the second middle leg 13, the third middle leg 16, and the fourth middle leg 17, and the first middle leg 12, the second middle leg 13, and the third middle leg NP. It is wound without passing between the middle leg 16 and the fourth middle leg 17.

  Further, the first winding leg NS11 is wound around the first middle leg 12, the second winding leg NS12 is wound around the second middle leg 13, and the first middle leg 16 is wound around the first middle leg 16. The winding part NS21 is wound, and the second winding part NS22 is wound around the fourth middle leg 17.

  When the above-described transformer TE is provided in the multi-output switching power supply 1 shown in FIG. 1 instead of the transformer T, the same effects as those of the multi-output switching power supply 1 including the transformer T can be obtained.

<Seventh embodiment>
[Configuration of Multiple Output Switching Power Supply 1A]
FIG. 11 is a circuit diagram of a multi-output switching power supply 1A according to the seventh embodiment of the present invention. The multi-output switching power supply 1A is different from the multi-output switching power supply 1 according to the first embodiment of the present invention shown in FIG. 1 in that it includes a rectifier circuit REC2A instead of the rectifier circuit REC2, and a second secondary winding. The configuration is different from that of NS2. In the multi-output switching power supply 1A, the same constituent elements as those of the multi-output switching power supply 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the multi-output switching power supply 1, the second secondary winding NS2 includes a first winding portion NS21, a second winding portion NS22, and between the first winding portion NS21 and the second winding portion NS22. And the center tap provided in the. On the other hand, in the multi-output switching power supply 1A, the second secondary winding NS2 is configured by the second winding portion NS22.

  The rectifier circuit REC2A includes a diode D23 and a capacitor C21. One electrode of the capacitor C21 and one end of the load Load2 are connected to the cathode of the diode D23. The other end of the second winding part NS22 is connected to the other electrode of the capacitor C21 and the other end of the load Load2, and one end of the second winding part NS22 is connected to the anode of the diode D23.

  According to the above multi-output switching power supply 1A, in addition to the same effects as the multi-output switching power supply 1, the following effects can be obtained.

  The rectifier circuit REC2A included in the multi-output switching power supply 1A has a simpler configuration than the rectifier circuit REC2 included in the multi-output switching power supply 1. Further, the second secondary winding NS2 provided in the multi-output switching power supply 1A has a simpler configuration than the second secondary winding NS2 provided in the multi-output switching power supply 1. As described above, the multi-output switching power supply 1A can be further reduced in size and cost can be further reduced as compared with the multi-output switching power supply 1.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made without departing from the gist of the present invention.

  For example, in the first embodiment described above, in the multi-output switching power source 1, one electrode of the capacitor C1 and the positive electrode of the DC power source VIN are connected, the other electrode of the capacitor C1, and the drain of the switch element Q2 , And the switch element Q1 and the switch element Q2 are connected in series. However, the present invention is not limited to this. For example, a multi-output switching power supply 1B shown in FIG. 12 or a multi-output switching power supply 1C shown in FIG. 13 may be connected.

  In the multi-output switching power supply 1B shown in FIG. 12, the negative electrode of the DC power supply VIN is connected to one electrode of the capacitor C1 instead of the positive electrode of the DC power supply VIN. In the multi-output switching power supply 1B, the same components as those of the multi-output switching power supply 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the multi-output switching power supply 1C shown in FIG. 13, the switch element Q2 is formed of a P-channel MOSFET. One electrode of the capacitor C1 is connected to the other end of the primary winding NP and the drain of the switch element Q1. The drain of the switch element Q2 is connected to the other electrode of the capacitor C1. The negative electrode of the DC power source VIN is connected to the source of the switch element Q1 and the source of the switch element Q2. In the multi-output switching power supply 1C, the same components as those of the multi-output switching power supply 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the first embodiment described above, the N-channel MOSFET is used as the switching elements Q1 and Q2 in the multi-output switching power supply 1. However, the present invention is not limited to this. For example, an NPN BJT (Bipolar Junction Transistor) may be used as the switch elements Q1 and Q2 as in the multi-output switching power supply 1D shown in FIG. In the multi-output switching power supply 1D shown in FIG. 14, IGBTs (Insulated Gate Bipolar Transistors) may be used as the switch elements Q1 and Q2 instead of the NPN type BJT.

  In the multi-output switching power supply 1D shown in FIG. 14, the cathode of the diode D1 is connected to the collector of the switch element Q1, the anode of the diode D1 is connected to the emitter of the switch element Q1, and the diode D1 is connected to the switch element Q1. Connected in parallel. Further, the cathode of the diode D2 is connected to the collector of the switch element Q2, the anode of the diode D2 is connected to the emitter of the switch element Q2, and the diode D2 is connected in parallel to the switch element Q2. In the multi-output switching power supply 1D, the same components as those in the multi-output switching power supply 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the first embodiment described above, the multi-output switching power supply 1 supplies DC power to the two loads Load 1 and Load 2. However, the present invention is not limited to this, and three loads or four loads are used. DC power may be supplied. For example, when DC power is supplied to four loads, two first secondary windings NS1 and two rectifier circuits REC1 may be added to the multi-output switching power supply 1.

  In each of the above embodiments, the diodes D11 and D12 are provided in the rectifier circuit REC1, and the diodes D21 and D22 are provided in the rectifier circuit REC2. However, the present invention is not limited to this. For example, instead of the diodes D11, D12, D21, and D22, a rectifying element different from the diode, or a switching element represented by a MOSFET or a bipolar transistor may be provided.

1, 1A, 1B, 1C, 1D, 100; multi-output switching power supply 10, 10A, 10B, 10C; core 11; first outer leg 12; first middle leg 13; second middle leg 14, 14A; Legs 15 and 16; 3rd middle leg 17; 4th middle leg 20; Control part C1, C11, C21, C110, C120; Capacitor D1, D2, D11, D12, D21-D23
Load1, Load2; Load NP, NP100; Primary winding NS1, NS110; First secondary winding NS2, NS120; Second secondary winding NS11, NS21; First winding section NS12, NS22; Second Winding part REC1, REC2, REC2A; Rectifier circuit Q1, Q2, Q100; Switch element T, TA, TB, TC, TD, TE, T100; Transformer VIN; DC power supply

Claims (4)

A multi-output switching power supply that supplies power to each of a plurality of loads using power supplied from a DC power supply,
A transformer having a primary winding, a plurality of secondary windings, and a core around which the primary winding and the plurality of secondary windings are wound;
A first switch element for turning on and off an output current of the DC power supply;
A second switch element used to release the excitation energy of the transformer;
A capacitor connected in series with the second switch element;
A plurality of rectifier circuits connected to each of the plurality of secondary windings;
Control means for detecting an output voltage of one of the plurality of rectifier circuits and controlling respective conduction times of the first switch element and the second switch element according to a detection result;
The core includes a plurality of legs,
The primary winding is wound so as to surround all of the plurality of legs around which the secondary winding is wound,
Of the plurality of secondary windings, at least the control means connected to a rectifier circuit that detects an output voltage includes a center tap,
The center tap is connected to one end of the load, and both ends of a secondary winding provided with the center tap are connected to the other end of the load via a rectifier element included in the rectifier circuit. Output switching power supply.   One of the plurality of secondary windings excluding the secondary winding provided with the center tap is connected to one end of the load via a rectifying element included in the rectifier circuit, and the other end is connected to the second winding. The multi-output switching power supply according to claim 1, wherein the multi-output switching power supply is connected to the other end of the load. The secondary winding with the center tap is
A first winding part;
A second winding part connected to the first winding part via the center tap, and
Winding the first winding part around any of the plurality of legs,
3. The multi-output switching according to claim 1, wherein the second winding portion is wound around any one of the plurality of legs excluding the one wound around the first winding portion. Power supply. The core comprises at least three legs;
The multi-output switching power supply according to any one of claims 1 to 3, wherein an air gap is formed in at least two of the at least three legs.

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