JP4785561B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that achieves high efficiency, miniaturization, and cost reduction.

  As a conventional switching power supply device, as shown in FIG. 14, the primary side has a first primary winding Np1 of a transformer T and a first switch element Q1 connected in series to both ends of a DC power supply. The second primary winding Np2 and the first capacitor C1 are connected in series between the terminals of Q1, and the second switch element Q2 and the second capacitor C2 are connected between the terminals of the second primary winding Np2. A so-called boost half bridge (hereinafter referred to as “secondary winding Ns”) in which a secondary tap is provided with a center tap on the secondary winding Ns and a rectifier circuit is connected to both ends of the secondary winding Ns. A switching power supply device referred to as a “BHB” switching power supply device is known (see Patent Document 1).

As another conventional switching power supply device, as shown in FIG. 15, the primary side is connected to both ends of the DC power source by the primary winding Np1 of the first transformer T1, the primary winding Np2 of the second transformer T2, and the first winding Np2. The first switch element Q1 is connected in series, the second switch element Q2 and the capacitor C1 are connected in series to both ends of the first switch element Q1, and the secondary side is the first diode D1. And the secondary winding Ns1 of the first transformer T1 and the tertiary winding Nr of the second transformer T2 are connected in series, and the first diode D1 and the secondary winding Ns1 of the first transformer T1 are connected in series. A configuration in which a series circuit of a second diode D2 and a secondary winding Ns2 of a second transformer T2 is connected in parallel with the circuit is known (see Patent Document 2).
JP 2003-79142 A JP 2004-320916 A

  However, the former switching power supply can perform zero-volt switching (hereinafter referred to as “ZVS”) by using the leakage inductance current near the rated load, but these currents decrease in the light load region, and ZVS Have difficulty. On the other hand, when the leakage inductance value is such that a current that can be ZVS is allowed to flow even in a light load region, there arises a problem that the dead time becomes long and the efficiency is lowered.

  Moreover, although the latter switching power supply device can obtain the current for ZVS by saturating the first transformer, since it requires two transformers, the cost of the entire device is increased and the installation area is increased. There is a problem.

  The present invention has been made in view of the above problems, and provides a switching power supply device that realizes zero-volt switching and enables reduction in cost and size of the entire device.

To solve the above problems, the switching power supply apparatus of the present invention includes an output transformer having a DC power source, first and second primary winding, and first and second secondary winding and a tertiary winding, A series circuit of the DC power source, the first primary winding having one end connected to the DC power source, and a first switch element having one end connected to the other end of the first primary winding ; A series circuit of a second primary winding having one end connected to one end of one primary winding and a first capacitor connected to the other end of the first switch element; and the second primary winding A series circuit of a second switch element and a second capacitor connected between the terminals of the first rectifier, a series circuit of which one end of the first rectifier element and one end of the first secondary winding are connected , series one end of the second rectifier element and one end of the second secondary winding is connected in parallel with the series circuit Road and, said tertiary winding being connected to the other end of the said first and second respective secondary windings, and the first rectifier element and the first secondary winding and the tertiary winding It has a smoothing capacitor connected in parallel with a series circuit .

An output transformer having a DC power source, a primary winding, first and second secondary windings and a tertiary winding, the DC power source and the first primary winding having one end connected to the DC power source ; A series circuit of a first switch element having one end connected to the other end of the first primary winding, and a series circuit of the second switching element and a capacitor connected between terminals of the primary winding When, a series circuit one end of the first rectifier element and one end of the first secondary winding is connected in parallel with the series circuit of the second rectifying element one end of the second secondary winding a series circuit and one end is connected, said first and second and said tertiary winding is connected to the other end of each of the secondary winding, the first rectifier element and the first secondary winding And a smoothing capacitor connected in parallel with the series circuit of the tertiary winding.

  The rectifying element is a MOSFET or other switching element.

  According to the present invention, since only one transformer is required, the overall cost of the device can be reduced and the size can be reduced as compared with the conventional switching power supply device. In particular, in the BHB type switching power supply device, there is a problem that if the leakage inductance value that allows ZVS to flow in a high input voltage range and a medium load range is set, the dead time becomes long and the efficiency is lowered. According to the present invention, ZVS can be performed while suppressing a decrease in efficiency even in a high input voltage range and a medium load range without increasing the leakage inductance value.

  FIG. 1 shows the best mode for carrying out the present invention. The switching power supply according to this embodiment includes an output transformer T having two primary windings Np1, Np2, two secondary windings Ns1, Ns2, and a tertiary winding Nr. The configuration of the output transformer T will be described later. The switching power supply according to this embodiment employs a BHB switching power supply. Specifically, the first primary winding Np1 and the first switch element Q1 are connected in series to both ends of the DC power supply Vin. Subsequently, the second primary winding Np2 and the first capacitor C1 are connected in series between the terminals of the first switch element Q1. A second switch element Q2 and a second capacitor C2 are connected in series between the terminals of the second primary winding Np2.

  On the secondary side, the first rectifying element D1 and the first secondary winding Ns1 are connected in series, and the second rectifying element D2 and the second secondary winding Ns2 are connected in parallel with the series circuit. Are connected in series. Further, a tertiary winding Nr is connected to one end of the second secondary winding Ns2 constituting this series circuit to constitute a rectifier circuit, and a smoothing capacitor Co is provided on the output side.

  Subsequently, an example of a transformer constituting the switching power supply device according to the present embodiment is shown in FIGS. In the transformer T11 of this embodiment, four magnetic legs are provided in parallel on the bottom plate. The first secondary winding Ns1 is wound around one of the two magnetic legs provided on the inner side, and the second secondary winding Ns2 is wound around the other magnetic leg. A tertiary winding Nr is wound around two magnetic legs provided on the inner side. Further, the second primary winding Np2 and the first primary winding Np1 are wound so as to cover the secondary windings Ns1, Ns2 from the outside.

  Next, another embodiment of the output transformer T will be described with reference to FIG. In the output transformer T12 shown in FIG. 4, the inner magnetic legs 22 and 23 are provided in the same manner as in the above embodiment, only the outer magnetic leg 21 is provided, and a total of three magnetic legs 21, 22, and 23 are provided. The provided core 2 is provided. The winding method of the windings Np, Ns1, Ns2, and Nr is the same as in the embodiment shown in FIG.

  Subsequently, an example of a transformer different from the above is shown in FIGS. In the transformer T13 of this embodiment, four magnetic legs are provided in parallel on the bottom plate. The first secondary winding Ns1 is wound around one of the two magnetic legs provided on the inner side, and the second secondary winding Ns2 is wound around the other inner magnetic leg. A tertiary winding Nr is wound around each of the two magnetic legs provided on the inner side. Further, a second primary winding Np2 and a first primary winding Np1 are wound around each magnetic leg. In addition, the inner ends of the primary windings Np1 and Np2 and the tertiary winding Nr wound around the respective magnetic legs are connected by conductive wires.

  The switching power supply device configured as described above operates as follows. The circuit operation will be described with reference to FIG. 7 which is an equivalent circuit diagram and FIG. 8 which is a voltage and current waveform of each part. The transformer T in the embodiment shown in FIG. 1 can be equivalently expressed as two transformers T1 and T2 shown in FIG.

  First, the first switch element Q1 is turned on at time T0 shown in FIG. 7, but the input voltage is applied to the transformer primary side leakage inductance. Both ends connecting the first primary winding Np1 and the third primary winding Np3 and both ends connecting the second primary winding Np2 and the fourth primary winding Np4 are short-circuited, respectively. No power is supplied to the next side. This is a commutation period in which the first rectifier diode D1 and the second rectifier diode D2 on the secondary side are both conductive.

  Subsequently, as shown in FIG. 8, at time T1, the primary side current reaches the primary conversion value of the secondary side output current, and both ends connecting the first primary winding Np1 and the third primary winding Np3. A voltage is generated across both ends of the second primary winding Np2 and the fourth primary winding Np4. All of the current flowing through both the first rectifier diode D1 and the second rectifier diode D2 on the secondary side is transferred to the first rectifier diode D1, and the first excitation inductance Lp1 and the second excitation inductance are transferred. Charging to Lp2 and power supply to the secondary side from the third primary winding Np3 and the fourth primary winding Np4 are started.

  At time T2, the first switch element Q1 is turned off. At that time, the internal capacitor CQ1 of the first switch element Q1 is charged by the energy stored in the transformer primary side leakage inductance, and the internal capacitor CQ2 of the second switch element Q2 is discharged. At this time, power supply to the secondary side continues.

  At time T3, the parasitic diode DQ2 of the second switch element Q2 becomes conductive. The voltages at both ends connecting the first primary winding Np1 and the third primary winding Np3, and both ends connecting the second primary winding Np2 and the fourth primary winding Np4 become zero volts, respectively. This is a commutation period in which the first rectifier diode D1 and the second rectifier diode D2 on the next side are both conductive.

  At time T4, the second switch element Q2 is turned on. At this time, the second switch element Q2 performs zero volt switching because the parasitic diode DQ2 is in a conductive state.

  At time T5, all the currents flowing through both the first rectifier diode D1 and the second rectifier diode D2 are transferred to the second rectifier diode D2, and the primary side of the transformer is clamped. The energy stored in the excitation inductance Lp1 and the second excitation inductance Lp2 is released from the first primary winding Np1 and the second primary winding Np2, and power supply to the secondary side is started. The first tertiary winding Nr1 current and the second tertiary winding Nr2 current increase and are superimposed on each exciting inductor current, and the second switch element Q2 current increases.

  At time T6, the second switch element Q2 is turned off. The internal capacitor CQ2 of the second switch element Q2 is charged by the energy stored in the second leakage inductance Lr2, and the internal capacitor CQ1 of the first switch element Q1 is discharged. At this time, in this embodiment, due to the influence of the first tertiary winding Nr1 current and the second tertiary winding Nr2 current, the first excitation inductance Lp1 current, the second excitation inductance Lp2 current, and the third excitation inductance. The Lp3 current and the fourth exciting inductance Lp4 current are DC-superimposed over the entire period, and have a current value larger than that of the conventional method. Since the increased current charges the internal capacitor CQ2 of the second switch element Q2 and discharges the internal capacitor CQ1 of the first switch element Q1, the ZVS range can be expanded as compared with the conventional method.

  At time T7, the internal capacitor CQ1 of the first switch element Q1 is sufficiently discharged, and the parasitic diode DQ1 of the first switch element Q1 starts to conduct. When the next cycle starts, since the parasitic diode DQ1 of the first switch element Q1 is in a conductive state, the first switch element Q1 performs zero volt switching.

  The switching power supply according to the present embodiment requires only one transformer due to the above-described operation, and enables the cost and size of the entire apparatus to be reduced as compared with the conventional switching power supply. Also, in the BHB type switching power supply device, there is a problem that if the inductance value is such that ZVS can flow in a high input voltage range and medium load range, the loss due to this current is large and the efficiency decreases. According to the present invention, the parasitic capacitance discharge current of the first switch element increases even in a high input voltage range and a medium load range, and ZVS can be performed while suppressing a decrease in efficiency.

  Subsequently, the present invention can be applied to a forward active clamp type switching power supply apparatus, which is shown in FIG. The switching power supply according to the present embodiment includes an output transformer T having a primary winding Np, two secondary windings Ns1, Ns2, and a tertiary winding Nr. The configuration of the output transformer T will be described later. A primary winding Np and a first switch element Q1 are connected in series to both ends of the DC power supply Vin. Subsequently, a second switch element Q2 and a capacitor C1 are connected in series between the terminals of the primary winding Np.

  On the secondary side, the first rectifying element D1 and the first secondary winding Ns1 are connected in series, and the second rectifying element D2 and the second secondary winding Ns2 are connected in parallel with the series circuit. Are connected in series. Further, a tertiary winding Nr is connected to one end of the second secondary winding Ns2 constituting this series circuit to constitute a rectifier circuit, and a smoothing capacitor Co is provided on the output side.

  Subsequently, an example of a transformer constituting the switching power supply device according to the present embodiment is shown in FIGS. The transformer T21 of this embodiment has four magnetic legs provided in parallel on the bottom plate. The first secondary winding Ns1 is wound around one of the two magnetic legs provided on the inner side, and the second secondary winding Ns2 is wound around the other inner magnetic leg. A tertiary winding Nr is wound around two magnetic legs provided on the inner side. Further, the primary winding Np is wound so as to cover the first secondary winding Ns1 and the second secondary winding Ns2 from the outside.

  Subsequently, an example of a transformer different from the above is shown in FIGS. In the transformer of this embodiment, four magnetic legs are provided in parallel on the bottom plate. The first secondary winding Ns1 is wound around one of the two magnetic legs provided on the inner side, and the second secondary winding Ns2 is wound around the other inner magnetic leg. A tertiary winding Nr is wound around each of the two magnetic legs provided on the inner side, and a primary winding Np is further wound. In addition, the inner ends of the primary winding Np and the tertiary winding Nr wound around the respective magnetic legs are connected by conductive wires.

  The switching power supply configured as described above operates in the same manner as the BHB switching power supply. Therefore, detailed description is omitted. In the embodiments of the BHB type switching power supply device and the forward active clamp type switching power supply device, the diodes D1 and D2 are used as the secondary side rectifying elements, but the synchronous rectifying method using a switching element such as a MOSFET is used. It is also possible to adopt.

  According to the present invention, since only one transformer is required, the overall cost of the device can be reduced and the size can be reduced as compared with the conventional switching power supply device. In addition, the ZVS range can be expanded even in a high input voltage range and a medium load range, which can be used industrially.

It is a circuit block diagram of the best embodiment of the switching power supply device according to the present invention. 1 is a front view of an example of a transformer in the embodiment shown in FIG. It is AA sectional drawing of the trans | transformer shown in FIG. It is a block diagram which shows the Example of a trans | transformer different from FIG. 1 is a front view of another transformer example in the embodiment shown in FIG. FIG. 6 is a cross-sectional view of the transformer shown in FIG. 1 is an equivalent circuit diagram of a switching power supply device according to the present invention. It is operation | movement explanatory drawing of the switching power supply device which concerns on this invention. It is a circuit block diagram of the best embodiment in the switching power supply device of a forward active clamp system. 9 is a front view of an example of the transformer in the illustrated embodiment. It is AA sectional drawing of the trans | transformer shown in FIG. 9 is a front view of an example of another transformer in the illustrated embodiment. It is AA sectional drawing of the trans | transformer shown in FIG. It is a circuit block diagram of the conventional switching power supply device. It is a circuit block diagram of the switching power supply device different from the prior art example shown in FIG.

Explanation of symbols

T transformer Q switch element L choke C capacitor D diode Np primary winding Ns secondary winding Nr tertiary winding

Claims (3)

An output transformer having a DC power supply, first and second primary windings, first and second secondary windings and a tertiary winding; and the DC power supply and one end connected to the DC power supply. Secondly one primary winding and one end a series circuit of a first switching element connected to the other end of the first primary winding, one end to one end of the first primary winding is connected A first circuit connected to the other end of the first switch element and a second switch element connected to a terminal of the second primary winding A series circuit with a first capacitor, a series circuit in which one end of the first rectifying element and one end of the first secondary winding are connected , and one end of the second rectifying element and the second in parallel with the series circuit a series circuit having one end and is connected to the secondary winding, connected to the other end of said first and second respective secondary windings Is the the tertiary winding, said first rectifier element and the first switching power supply unit and having a smoothing capacitor connected in parallel with the series circuit of the secondary winding and the tertiary winding . An output transformer having a DC power source, a primary winding, first and second secondary windings and a tertiary winding, the DC power source and the first primary winding having one end connected to the DC power source ; A series circuit of a first switch element having one end connected to the other end of the first primary winding, and a series circuit of the second switching element and a capacitor connected between terminals of the primary winding When, a series circuit one end of the first rectifier element and one end of the first secondary winding is connected in parallel with the series circuit of the second rectifying element one end of the second secondary winding a series circuit and one end is connected, said first and second and said tertiary winding is connected to the other end of each of the secondary winding, the first rectifier element and the first secondary winding switch, characterized in that it comprises a smoothing capacitor connected in parallel with the series circuit of the tertiary winding and Ring power supply. 3. The switching power supply device according to claim 1, wherein the rectifying element is a MOSFET or other switching element.

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