JP6701827B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that supplies electric power to a plurality of power supply systems via an insulating transformer having a plurality of secondary windings, and in particular, a switching power supply device with a simple configuration that effectively takes measures against surges. Regarding

  Various electronic devices are required to operate sufficiently reliably and stably even when a lightning surge or an impulse is applied. However, in general, it cannot be said that a sufficient surge countermeasure is necessarily provided for each electronic device. Also, in a switching power supply device that supplies power to various electronic devices, for example, generation of high-frequency switching noise due to ON/OFF operation of a semiconductor switching element such as a MOS-FET is suppressed, and further, input is performed via an insulating transformer. Measures are taken to prevent the common mode current flowing from the power supply side to the load (load device) side.

  FIG. 8 is a schematic configuration diagram showing an example of a conventional general switching power supply device 1. This switching power supply device 1 roughly includes a switching power supply main body 3 for switching an input DC voltage applied to a primary winding P of an insulation transformer 2 via an input capacitor Cin and a secondary winding S of the insulation transformer 2. And a power supply output circuit 4 for rectifying the generated secondary voltage to obtain a DC output voltage. By the way, the switching power supply main body 3 is composed of a semiconductor switching element Q composed of a MOS-FET connected in series to the primary winding P of the insulation transformer 2 and a control IC for driving the semiconductor switching element Q on/off. Further, the power supply output circuit 4 is composed of a rectifying diode D connected to the secondary winding S of the insulation transformer 2 and a DC conversion circuit including an output capacitor Cout for smoothing the output voltage of the rectifying diode D. The switching power supply device 1 having such a configuration is called a flyback converter.

  In the switching power supply device 1 shown in FIG. 8, the insulating transformer 2 has a plurality of secondary windings Sa to Sn arranged in parallel, and a plurality of power sources respectively connected to these secondary windings Sa to Sn. Output circuits 4a to 4n are provided. These power supply output circuits 4a to 4n have a role of supplying electric power of a predetermined voltage to the plurality of power supply systems A to N, respectively.

  With respect to the switching power supply device 1 having such a configuration, for example, Patent Document 1 discloses that the housing structure of the insulating transformer 2 is devised to take electromagnetic/electrostatic shield measures against the outside. At the same time, in Patent Document 1, by devising the winding structure of the primary winding P and the secondary winding S (Sa to Sn), the current flows between the primary winding P and the secondary winding S (Sa to Sn). It is disclosed to suppress common mode current (switching noise current).

  Incidentally, in the technique disclosed in Patent Document 1, consideration is given to protection of the power supply systems A to N from surges accompanying the switching operation of the semiconductor switching element Q. However, no consideration is given to protecting the switching power supply main body 3 and the electronic devices connected to the plurality of power supply systems A to N from a lightning surge or the like. In this regard, for example, in Patent Documents 2 and 3, a surge absorber circuit is provided in the preceding stage of the switching power supply device 1, that is, on the primary side (input power supply side) of the insulating transformer 2 to prevent a lightning surge from entering from the power supply source side Is disclosed.

JP, 2001-68359, A JP, 2002-374620, A JP-A-5-161258

  However, even if the surge countermeasures disclosed in Patent Documents 1, 2, and 3 are taken, lightning that enters from a portion other than the power supply source side, for example, the shield portion between the primary side and the secondary side in the insulating transformer 2 It is difficult to protect the switching power supply main body 3 and the electronic devices connected to the plurality of power supply systems A to N from the surge. Moreover, some of the electronic devices connected to the plurality of power supply systems A to N are relatively strong against surges, but many are weak against surges. Therefore, in the switching power supply device 1, it is necessary to protect each of the power supply systems A to N from a surge in consideration of, for example, the characteristics of electronic devices connected to the plurality of power supply systems A to N.

  The present invention has been made in consideration of such circumstances, and an object thereof is to provide a surge applied from the input power source side through an insulating transformer having a plurality of secondary windings that respectively supply power to a plurality of power source systems. Another object of the present invention is to provide a switching power supply device having a simple structure that can effectively cope with surges directly applied to the isolation transformer.

  The switching power supply device according to the present invention basically rectifies the secondary voltage generated in each of the switching power supply main body for supplying an alternating current to the primary winding of the insulating transformer and the plurality of secondary windings in the insulating transformer. And a plurality of power supply output circuits which respectively output to a plurality of power supply systems.

  In particular, the switching power supply device according to the present invention, in order to achieve the above-mentioned object, the secondary winding and the secondary winding in the power supply system in which the coupling impedance between the primary winding and the plurality of secondary windings in the isolation transformer is the smallest. A feature is that a surge absorber circuit is interposed between the power supply output circuit and the power output circuit.

  Preferably, the power supply system in which the coupling impedance between the primary winding and the plurality of secondary windings in the insulation transformer is the smallest, that is, the power supply system in which the surge absorber circuit is interposed is the primary winding of the insulation transformer. The power supply system has the largest coupling capacitance between the secondary winding and the plurality of secondary windings. Alternatively, the power supply system in which the surge absorber circuit is interposed is a power supply system connected to the secondary winding having the largest number of turns among the plurality of secondary windings in the isolation transformer via the power supply output circuit. .

  Alternatively, the power supply system in which the surge absorber circuit is interposed is the power supply system having the largest power output capacity among the plurality of power supply systems, or the primary winding among the plurality of secondary windings in the isolation transformer. Is a power supply system connected to the secondary winding provided closest to the power supply output circuit via the power supply output circuit.

  Preferably, the power supply system having the smallest coupling impedance between the primary winding and the plurality of secondary windings in the isolation transformer is provided as a power supply system in which the power supply output end is open in the plurality of power supply systems. .. Incidentally, the power supply system in which the power supply output terminal is opened includes a secondary winding added to the isolation transformer and a dummy power supply output circuit connected to the added secondary winding.

  Further, it is also preferable to interpose a common mode noise filter between the output terminal of the power supply output circuit and the load connected to the power supply system in the power supply system in which the surge absorber circuit is installed.

  In the switching power supply device according to the present invention, a surge absorber circuit is provided between the secondary winding and the power output circuit in the power supply system in which the coupling impedance between the primary winding and the plurality of secondary windings in the insulating transformer is the smallest. Is installed. Therefore, not only the surge applied from the input power supply side to the primary side of the isolation transformer, but the surge applied directly to the isolation transformer is directed to the power supply system with the smallest coupling impedance with the primary winding among the multiple power supply systems. Flowing.

  Then, the surge applied to the isolation transformer is inserted between the secondary winding of the power supply system, which has the smallest coupling impedance with the primary winding, and the power output circuit connected to the secondary winding. It flows in and is absorbed by the surge absorber circuit. As a result, it is possible to suppress the outflow of the surge to the other power supply system in the isolation transformer, and it is possible to effectively protect the loads connected to the plurality of power supply systems from the surge. In particular, with a simple configuration in which a surge absorber circuit is provided on the secondary winding side of the power supply system with the smallest coupling impedance with the primary winding, all of the multiple power supply systems provided in the switching power supply device are effective from surge. It is possible to obtain a great effect in practical use, such as the protection.

1 is a schematic configuration diagram of a main part of a switching power supply device according to a first embodiment of the present invention. The principal part schematic structure figure of the switching power supply concerning a 2nd embodiment of the present invention. The principal part schematic structure figure of the switching power supply concerning a 3rd embodiment of the present invention. The figure which shows typically the structure of the insulation transformer for demonstrating the switching power supply which concerns on the 4th Embodiment of this invention. The principal part schematic structure figure of the switching power supply concerning a 5th embodiment of the present invention. The principal part schematic structure figure of the switching power supply concerning a 6th embodiment of the present invention. The schematic block diagram of the principal part of the switching power supply concerning a 7th embodiment of the present invention. FIG. 3 is a schematic configuration diagram of a switching power supply device including a plurality of power supply systems via insulation transformers.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the same parts as those of the conventional device shown in FIG.

  The switching power supply device 1 according to the present invention is basically a secondary winding in a power supply system in which the coupling impedance between the primary winding P and the plurality of secondary windings Sa to Sn in the insulating transformer 2 is the smallest, for example, The surge absorber circuit 5 is characterized in that a surge absorber circuit 5 is interposed between the secondary winding Sn and the power output circuit 4n.

  Specifically, as shown in FIG. 1 which is a schematic configuration diagram of a main part of the switching power supply device 1 according to the first embodiment of the present invention, among the plurality of secondary windings Sa to Sn, The surge absorber circuit 5 is characterized in that the surge absorber circuit 5 is interposed between the secondary winding Sn having the largest coupling capacitance between them and the power supply output circuit 4n.

  Alternatively, as shown in FIG. 2 which is a schematic configuration diagram of a main part of a switching power supply device 1 according to a second embodiment of the present invention, a power supply system having the largest power supply capacity among a plurality of power supply systems A to N, for example, a power supply system. The surge absorber circuit 5 is characterized in that a surge absorber circuit 5 is interposed between the secondary winding Sn that outputs electric power to N and the power supply output circuit 4n. Specifically, when the power supply system A outputs a DC voltage of 5 V at a maximum of 120 mA, the power supply system B outputs a DC voltage of 12 V at a maximum of 50 mA, and the power supply system N outputs a DC voltage of 24 V at a maximum of 500 mA, Since the power supply capacities of these power supply systems A, B, N are 600 mW, 600 mW, and 12000 mW, respectively, the surge absorber circuit 5 is interposed between the secondary winding Sn and the power supply output circuit 4n in the power supply system N.

  Alternatively, as shown in a schematic configuration diagram of a main part of a switching power supply device 1 according to a third embodiment of the present invention in FIG. 3, a secondary winding having the largest number of turns among a plurality of secondary windings Sa to Sn, For example, a surge absorber circuit 5 is interposed between the secondary winding Sn and the power output circuit 4n. Specifically, the number of turns of the secondary winding Sa of the power supply system A is 600 turns, the number of turns of the secondary winding Sb of the power supply system B is 800 turns, and the number of turns of the secondary winding Sn of the power supply system N is 1200 turns. In some cases, the surge absorber circuit 5 is interposed between the secondary winding Sn and the power supply output circuit 4n in the power supply system N.

  By the way, the surge absorber circuit 5 includes a first absorber element 5a interposed between a pair of output terminals of the secondary winding Sn, one output terminal of the secondary winding Sn and ground, and the other. It is composed of second and third absorber elements 5b and 5c which are respectively interposed between the output terminal and the ground. These absorber elements 5a, 5b, 5c are made of, for example, a microgap type or a piezoelectric element or a varistor (ZnO) or the like which utilizes semiconductor characteristics.

Here, the power supply system in which the coupling impedance between the primary winding P and the secondary windings Sa to Sn of the insulating transformer 2 is the smallest among the plurality of power supply systems A to N is basically
(1) Secondary winding with the largest coupling capacity with the primary winding P
(2) Secondary winding of the power system with the largest power output capacity
(3) One of the secondary windings having the largest number of turns with respect to the primary winding P having a predetermined number of turns. Incidentally, the number of turns of each of the secondary windings Sa, Sb to Sn is determined according to the output voltage of the power supply system A, B to N, and the maximum output current is the wire diameter of each of the secondary windings Sa, Sb to Sn. It is decided according to.

  Therefore, of the plurality of power supply systems A, B to N, it is verified which of the above-mentioned conditions the power supply system having the smallest coupling impedance with the primary winding P of the insulation transformer 2 corresponds to, and the power supply system is verified. The surge absorber circuit 5 may be selectively interposed between the secondary windings Sa to Sn and the power supply output circuits 4a to 4n.

  In the switching power supply device 1 configured as described above, the surge applied to the insulating transformer 2 exclusively flows toward the power supply system having the smallest coupling impedance. Since the surge absorber circuit 5 is provided in the power supply system having the smallest coupling impedance with the primary winding P, the surge flows into the surge absorber circuit 5 and is absorbed. As a result, the surge does not flow into another power supply system having a large coupling impedance with the primary winding P. Therefore, it is possible to effectively take a surge countermeasure for the plurality of power supply systems A, B to N included in the switching power supply device 1. In particular, with a simple configuration in which the surge absorber circuit 5 is provided only in the power supply system having the smallest coupling impedance, it becomes possible to effectively implement the surge countermeasure.

  By the way, the insulating transformer 2 has a primary winding P and a plurality of secondary windings Sa through an insulating sheet 2b on a tubular core 2a having a flange, as schematically shown in FIG. 4, for example. When Sn is sequentially laminated and wound, the coupling impedance between the primary winding P and each of the secondary windings Sa to Sn, particularly the coupling capacitance c, is defined by the distance d between the winding layers and the facing area s. To be done. Specifically, when the facing areas (coupling area) between the primary winding P and the plurality of secondary windings Sa to Sn are all equal, the secondary winding having the shortest distance from the primary winding P is provided. The stroke increases the coupling capacitance with the primary winding P.

  Therefore, in the switching power supply device 1 according to the fourth embodiment of the present invention, paying attention to the structure of the above-described insulation transformer 2, among the plurality of secondary windings Sa to Sn, it is closest to the primary winding P. The surge absorber circuit 5 may be provided between the secondary winding provided, for example, the secondary winding Sa and the power output circuit 4a connected to the secondary winding Sa.

The coupling capacitance c between the primary winding P and the secondary winding S is c=εo·εr(s/ when the distance between the primary winding P and the secondary winding S is d and the facing area is s. d)
Becomes Here, εo is the dielectric constant of vacuum, and εr is the dielectric constant of the insulating material between the primary winding P and the secondary winding S. Therefore, in practice, the power supply system for interposing the surge absorber circuit 5 may be determined in consideration of the distance d between the primary winding P and the secondary winding S and the facing area s which are determined by the structure of the insulation transformer 2.

  By the way, although the surge absorber circuit 5 is selectively provided in one of the plurality of power supply systems as described above, it may be difficult for the surge absorber circuit 5 to completely absorb the surge. Therefore, in the case of protecting all of the plurality of power supply systems from a surge, it is effective to open the power supply system provided with the surge absorber circuit 5 in advance as shown in FIG. 5, for example.

  However, in general, the switching power supply device 1 is often designed according to the number of power supply systems and the power capacity thereof. Therefore, in such a case, for example, a secondary winding corresponding to the power supply system to be opened in advance is provided in the insulation transformer 2, and the surge absorber circuit 5 is provided in this power supply system to construct the switching power supply device 1. Just do it.

  When the power supply system provided with the surge absorber circuit 5 is not opened, for example, a common mode noise filter is provided at the output stage of the power supply output circuit 4n incorporating the surge absorber circuit 5 as shown in FIG. 6 in the sixth embodiment. It is also useful to provide 6 to prevent common mode noise from flowing out to the load side. If such a common mode noise filter 6 is provided, the common mode noise filter 6 can block the common mode current flowing to the load side, so that the surge absorber circuit 5 can more reliably absorb the surge. It can be anything. As the common mode noise filter 6, a common mode choke coil having a structure in which a pair of power supply lines are wound around a ring-shaped core so as to face each other, or a pair of power supply lines are penetrated to be mounted on the power supply lines. It is sufficient to use a tubular ferrite core.

  Further, as shown in the seventh embodiment in FIG. 7, it is also useful to interpose the common mode noise filter 6 in all of the power supply systems other than the power supply system incorporating the surge absorber circuit 5. If the common mode noise filter 6 is provided in each of the plurality of power supply systems A to N included in the switching power supply device 1 in this manner, the impedance balance between the plurality of power supply systems A to N will not be lost. The surge applied to the insulation transformer 2 can be reliably guided to the surge absorber circuit 5. Therefore, as compared with the above-described respective embodiments, it is possible to surely implement the surge countermeasure for the plurality of power supply systems Å to N.

  The present invention is not limited to the above embodiment. For example, a power supply system incorporating the surge absorber circuit 5 under the above-described conditions according to the structure of the insulating transformer 2, the number of turns of the plurality of secondary windings Sa to Sn, and the power capacities of the plurality of power supply systems A to N. Is sufficient. Further, the switching power supply main body 3 is not limited to one that constitutes the flyback converter described above. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

1 Switching power supply device 2 Isolation transformer 3 Switching power supply body 4 Power supply output circuit 5 Surge absorber circuit 6 Common mode noise filter P Primary winding Sa to Sn Secondary winding A to N Power system

Claims (3)

A switching power supply body that supplies alternating current to the primary winding of the isolation transformer,
A plurality of power supply output circuits for rectifying the secondary voltages generated in the plurality of secondary windings of the isolation transformer and outputting the rectified secondary voltages to a plurality of power supply systems, respectively.
The scan is interposed a surge absorber circuit between the power supply output circuit and the secondary winding coupled impedance in the smallest power system between a primary winding and a plurality of secondary windings of the insulating transformer switching Power supply ,
The power supply system having the smallest coupling impedance between the primary winding and the plurality of secondary windings in the isolation transformer is a power supply system in which a power supply output terminal is opened among the plurality of power supply systems. Switching power supply. Power supply system the power supply output terminal is open, the secondary winding which is added to the isolation transformer, to claim 1 comprising a dummy power supply output circuit connected to this additional secondary winding The switching power supply described. The switching power supply device according to claim 1,
It is interposed a common mode noise filter between further to a load the surge absorber circuit is connected to the output terminal and the other power supply system of the power supply output circuit in another power supply system other than interposed a power supply system Switching power supply device characterized by.

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