JP2004289944A - Switching power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output large power by surely making the power well-balanced at high efficiency by using a plurality of transformers, and to reduce a cost and a size. <P>SOLUTION: This switching power supply device obtains a DC output by DC-DC converting a DC input by using the plurality of transformers T1, T2. The power supply device comprises a primary circuit in which a switching element 7 is further series-connected to a series circuit in which primary windings 2, 3 of the plurality of transformers T1, T2 are series-connected to each other; and a secondary circuit in which one-side ends of secondary windings 4, 5 of the plurality of transformers T1, T2 are connected to each other, and other-side ends of the secondary windings 4, 5 of the transformers are connected to each other via unidirectional elements D2, D3 each having a flyback current direction as a forward direction, and which sets a gap between a connecting point of the one-side ends and a connecting point of the other-side ends via the unidirectional elements D2, D3 as an output end. In the power supply device, DC power is outputted from the output end of the secondary circuit by switching the switching element 7 of the primary circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply, and more particularly to a switching power supply suitable for supplying a large amount of power using a plurality of small transformers.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 2002-325449 discloses a configuration as shown in FIG. 5 regarding a switching power supply device that supplies a large amount of power using a plurality of small transformers. According to the configuration of FIG. 5, primary windings 2, 3 of transformers T1, T2 having separate cores are connected in parallel, and secondary windings 4, 5 are connected in series. One ends of the primary windings 2 and 3 are connected to the positive electrode of the DC power supply 6, the other ends of the primary windings 2 and 3 are connected to one end of the switching element 7, and the other end of the switching element 7 is connected to the negative electrode of the DC power supply 6, respectively. ing. The secondary windings 4 and 5 of the transformers T1 and T2 are connected to a rectifying and smoothing circuit 8. Further, the transformers T1 and T2 are formed such that the primary side and the secondary side of each winding have the same polarity.
[0003]
When the switching element 7 is turned on, the current flows through the primary windings 2 and 3 of the transformers T1 and T2, and the current also flows through the secondary windings 4 and 5 by the induced electromotive force. . In this case, since the secondary windings of the transformers T1 and T2 are connected in series, the currents flowing through the secondary windings 4 and 5 are equal.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-325449
[Problems to be solved by the invention]
However, the above prior art has the following problems. That is, when the switching element 7 is turned off, the circulating current Ic flows between the primary windings 2 and 3 due to the imbalance of the flyback voltages of the windings 2 and 3, as shown in FIG. One of the transformers is reversely excited by the circulating current Ic, and the other transformer is DC-biased. Therefore, since the magnetic flux of each transformer cannot be balanced, the current flowing through the primary winding at the time of turn-on cannot be balanced.
[0006]
In addition, the circulating current causes a power loss in the primary winding, and a DC current is superimposed on one of the transformers, so that an air gap is required and the size of the transformer is increased.
[0007]
Further, when the configuration shown in FIG. 5 is applied to a flyback type switching power supply, the above-mentioned disadvantage becomes more remarkable. In the flyback switching power supply, while the primary circuit is turned on, no current flows in the secondary circuit and energy is stored in the core. When the primary circuit turns off, a current based on the energy stored in the transformer flows through the secondary circuit. Therefore, at the time of turn-on, the exciting current balance is lost due to an error in the primary winding impedance, and at the time of turn-off, the circulating current Ic as shown in FIG. 6 flows due to the imbalance of the flyback voltage, and the magnetic flux becomes unbalanced. As a result, each transformer cannot supply power to the load equally.
[0008]
In order to solve the above-mentioned drawback, a method of inserting diodes D1a and D1b in series with the primary winding to prevent a circulating current from flowing, as shown in FIG. Power loss occurs in each primary winding due to the forward current flowing through D1a and D1b. This power loss becomes heat and hinders miniaturization of the device.
[0009]
In view of the above problems, it is an object of the present invention to provide a switching power supply device capable of outputting a large amount of power by using a plurality of transformers to achieve a high-efficiency and reliable power balance.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the switching power supply device according to claim 1, wherein the switching power supply device is configured by a flyback method, and obtains a DC output by performing DC / DC conversion of a DC input using a plurality of transformers. A primary circuit in which a switching element is further connected in series to a series circuit in which primary windings of the plurality of transformers are connected in series, and one ends of secondary windings of the plurality of transformers are connected together and a flyback current direction is set to a forward direction. The other ends of the secondary windings of the transformers are connected to each other via a one-way element, and the output end is provided between the one-end connection point and the other-end side connection point via the one-way element. Wherein the switching element of the primary circuit is switched to output DC power from an output terminal of the secondary circuit.
[0011]
The switching power supply according to claim 2 is configured by a flyback method, and obtains a DC output by performing DC / DC conversion of a DC input using a plurality of transformers. A primary circuit in which a switching element is further connected in series to a series circuit in which the windings are connected in series; and a unidirectional connection in which both ends of the secondary windings of the plurality of transformers are connected in parallel and the flyback current direction is a forward direction. Elements are connected in series, and a secondary circuit having an output terminal between the one end connection point and the other end side connection point via the one-way element is provided, and a switching element of the primary circuit is switched. DC power is output from an output terminal of the secondary circuit.
[0012]
The switching power supply device according to claim 3 is configured in a forward system, and obtains a DC output by performing DC / DC conversion of a DC input using a plurality of transformers. A primary circuit in which a switching element is further connected in series to a series circuit in which wires are connected in series, and a first unidirectionality in which one ends of secondary windings of the plurality of transformers are connected and a forward current direction is a forward direction. The other ends of the secondary windings of the respective transformers are connected to each other via an element, and the second unidirectional element having a forward direction from the connection point of the one ends to the connection point of the other ends is connected to the one ends of the second unidirectional elements. One end of the inductor is connected to one of the two ends of the second unidirectional element, and the other end of the inductor is connected to the second end of the second unidirectional element. A secondary circuit having an output terminal between any one of both ends of the directional element, and switching the switching element of the primary circuit to output DC power from the output terminal of the secondary circuit. And
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a switching power supply according to the present invention will be described with reference to the accompanying drawings. Note that the same components as those of the conventional switching power supply device 31 are denoted by the same reference numerals, and redundant description will be omitted. Also, the same operation as the switching power supply device 31 will not be described repeatedly.
[0014]
First, a first embodiment in which the present invention is applied to a flyback type switching power supply will be described with reference to FIG.
[0015]
The flyback type power supply device 1 includes transformers T1 and T2 having separate cores. One ends of primary windings 2 and 3 of both transformers T1 and T2 are connected to each other, the other end of primary winding 2 of transformer T1 is connected to the positive electrode of DC power supply 6, and the other end of primary winding 3 of transformer T2 is connected to the other end. The switch element 7 is connected to one end, and the other end of the switch element 7 is connected to the negative electrode of the DC power supply 6. One ends of the secondary windings 4 and 5 of the transformers T1 and T2 are connected to the negative electrode of the storage element C, and the other ends of the secondary windings 4 and 5 of the transformers T1 and T2 are connected to the anodes of the diodes D2 and D3, respectively. The cathodes of the diodes D2 and D3 are connected to the positive electrode of the storage element C. Further, load RL is connected in parallel with power storage element C. The windings 2, 3, 4, and 5 of the transformers T1 and T2 are formed so that the polarities of the primary side and the secondary side are reversed.
[0016]
In this embodiment, the transformers T1 and T2 have the same specifications, and the turns ratio and the number of turns are set to be equal (n1 / N1 = n2 / N2, n1 = n2, N1 = N2). Further, since the number of turns is equal, the exciting inductance is also equal.
[0017]
Next, the operation of the switching power supply 1 will be described. When the switching element 7 is turned on, the voltage E of the DC power supply 6 is applied to the primary windings 2 and 3 of the transformers T1 and T2 connected in series, and an exciting current I1 flows. Since the exciting inductance of each transformer is equal, the voltage applied to each winding is E / 2. Further, since the primary windings of the respective transformers are connected in series, the respective exciting currents are necessarily equal. At this time, since the secondary winding has a reverse polarity voltage, the diodes D2 and D3 are reverse-biased and do not conduct, and the secondary winding of the transformer does not supply current to the load. Next, when the switch element 1 is turned off, the voltage polarities of the secondary windings 4 and 5 are inverted, and the diodes D2 and D3 are biased in the forward direction. Is supplied. In this case, at the time of turn-on, the exciting currents I1 flowing through the primary windings 2 and 3 are the same, so that at the time of turn-off, the load currents I4 and I5 supplied from the secondary windings 4 and 5 always become the same.
[0018]
The present embodiment has the following effects.
(1) Since the primary windings 2 and 3 of the transformers T1 and T2 are connected in series, the exciting currents become equal. As a result, the load currents I4 and I5 of the secondary windings 4 and 5 become equal and the current balance is surely ensured. Will be kept.
(2) Since the voltage applied to the primary windings 2 and 3 of the transformers T1 and T2 is の of the power supply voltage E, the exciting inductance may be １ ／ and the number of turns is reduced to √ (１ ／). Therefore, the current loss of the primary winding is reduced.
(3) Since the secondary windings 4 and 5 of the transformers T1 and T2 are connected in parallel via the diodes D2 and D3, the winding resistance is reduced and the current loss is also reduced.
(4) Since the present switching power supply device 1 can use transformers having the same specifications, the number of types of components can be reduced and cost can be reduced.
[0019]
Next, a second embodiment in which the present invention is applied to a flyback type switching power supply device will be described with reference to FIG.
[0020]
The configuration of FIG. 2 is different from the configuration of FIG. 1 in that the secondary windings 4 and 5 of the transformers T1 and T2 are connected in parallel and the diode D3 is omitted.
[0021]
According to this configuration, similarly to the first embodiment, when the switching element 7 is turned on, the exciting currents I1 flowing through the primary windings 2 and 3 of the transformers T1 and T2 become the same, so that the switching element 1 is turned off. Sometimes, the load currents I4 and I5 flowing through the secondary windings 4 and 5 of the transformers T1 and T2 always become the same. Therefore, since the circulating current of the secondary windings 4 and 5 does not flow, the secondary windings 4 and 5 can be connected in parallel, and the diode D3 in FIG. 1 can be omitted.
[0022]
According to this embodiment, the circuit can be simplified and the number of components can be further reduced as compared with the first embodiment, thereby contributing to cost reduction and size reduction of the device.
[0023]
Next, a third embodiment in which the present invention is applied to a forward-type switching power supply will be described with reference to FIG.
[0024]
The transformers T1 and T2 having separate cores are formed such that the primary windings 2 and 3 and the secondary windings 4 and 5 have the same phase, and the power storage inductor L and the commutation diode D4 Except for the addition, the configuration is the same as that of FIG. 1, and a detailed description thereof will be omitted. In this embodiment, the transformers T1 and T2 have the same specifications, and the turns ratio and the number of turns are set to be equal (n1 / N1 = n2 / N2, n1 = n2, N1 = N2). Further, since the number of turns is equal, the exciting inductance is also equal.
[0025]
Next, the operation of the forward-type switching power supply 21 configured as described above will be described. When the switching element 7 is turned on, the DC voltage source 6 is applied to the primary windings 2 and 3 of the transformers T1 and T2 connected in series, and a current I1 flows. The voltage generated in the primary windings 2 and 3 of the transformers T1 and T2 is E / 2 because the exciting inductances are equal. Since the configuration of this device is of a forward type, each secondary winding has (E / 2) × (N1 / n1) and (E / 2) × (N2 / n2) due to the induced electromotive force at turn-on. Voltages are respectively generated to supply current to the load through the diodes D2 and D3 and to excite L. At this time, since the currents I1 flowing through the primary windings 2 and 3 of the transformers T1 and T2 are the same as in the first embodiment, the currents I4 and I5 flowing through the secondary windings 4 and 5 of the transformers T1 and T2 are equal. Is also equal.
[0026]
Next, when the switching element 7 is turned off, a reverse voltage is generated in the secondary windings 4 and 5 of the transformers T1 and T2, the diodes D2 and D3 are reverse-biased, and the commutation diode D4 is forward-biased. Becomes conductive. At the time of turn-on, the energy stored in the power storage inductor L is supplied to the load through the commutation diode D4. At this time, a flyback voltage for resetting the excitation energy is generated in the primary windings 2 and 3 of the transformers T1 and T2. However, since the primary windings 2 and 3 are connected in series, a circulating current may flow. There is no.
[0027]
The present embodiment has the following effects.
(1) Since the currents I1 of the primary windings 2 and 3 of the transformers T1 and T2 are equal, the load currents I4 and I5 of the secondary windings 4 and 5 of the transformers T1 and T2 are also equal, and the current balance is reliably maintained. .
(2) Due to the flyback voltage when the switching element 7 is turned off, no circulating current flows, and the magnetic flux balance in the transformers T1 and T2 is maintained.
(3) Since the voltage applied to the primary windings 2 and 3 of the transformers T1 and T2 is の of the power supply voltage E, the number of turns of the primary windings 2 and 3 of the transformers T1 and T2 may be で. The power loss can be reduced by reducing the winding resistance.
(4) Since the secondary windings 4 and 5 of the transformers T1 and T2 are connected in parallel via the diodes D2 and D3, power loss can be reduced by lowering the combined winding resistance.
(5) Since the present switching power supply device 21 can use transformers having the same specifications, the number of types of components can be reduced and cost can be reduced.
[0028]
The embodiment is not limited to the above. For example, as shown in FIG. 4, each primary winding is connected in series using three or more (N) transformers, and each secondary winding is connected. May be connected in parallel.
[0029]
Further, the value of the turns ratio (n1 / N1, n2 / N2) of each of the primary winding and the secondary winding of the transformers T1 and T2 may be different.
[0030]
Further, as the switching element 7, a bipolar transistor or an FET can be used. In addition, as the one-way elements D2, D3, and D4, a switch element such as an FET may be used in addition to a diode, or a one-way element and a switch element may be connected in parallel. Furthermore, the insertion position of the unidirectional element may be any position as long as the direction of the forward current matches.
[0031]
【The invention's effect】
As described above, according to the first to third aspects of the present invention, when a large amount of power is output using a plurality of small transformers, the balance can be reliably maintained with a simple configuration, and the switching power supply device It is possible to realize high efficiency, low cost, and miniaturization of the device.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing a second embodiment of the present invention.
FIG. 3 is a circuit diagram showing a third embodiment of the present invention.
FIG. 4 is a circuit diagram showing another embodiment of the present invention.
FIG. 5 is a circuit diagram showing an embodiment of the related art.
FIG. 6 is a diagram showing a path through which a circulating current flows in the related art.
FIG. 7 is a diagram in which a circulating current preventing diode is added to the circuit of the related art.
[Explanation of symbols]
1, 21, 31, 41 Switching power supply 2, 3 Primary winding 4, 5 Secondary winding 6 DC power supply 7 Switching element C Capacitor D1a, D1b Diode D2, D3 Rectifier diode D4 Commutation diode L Power storage inductor RL Load T1, T2 Transformer

Claims (3)

In a switching power supply device that is configured by a flyback method and obtains a DC output by performing DC / DC conversion of a DC input using a plurality of transformers,
A primary circuit in which a switching element is further connected in series to a series circuit in which primary windings of the plurality of transformers are connected in series;
One ends of the secondary windings of the plurality of transformers are connected to each other, and the other ends of the secondary windings of the transformers are connected to each other via a unidirectional element having a flyback current direction as a forward direction. A secondary circuit having an output terminal between the connection point and the other end side connection point via the one-way element,
A switching power supply device, wherein a switching element of the primary circuit is switched to output DC power from an output terminal of the secondary circuit. In a switching power supply device that is configured by a flyback method and obtains a DC output by performing DC / DC conversion of a DC input using a plurality of transformers,
A primary circuit in which a switching element is further connected in series to a series circuit in which primary windings of the plurality of transformers are connected in series;
The two ends of the secondary windings of the plurality of transformers are connected in parallel with each other, and a unidirectional element having a flyback current direction as a forward direction is connected in series. A secondary circuit having an output terminal between the terminal side connection point,
A switching power supply device, wherein a switching element of the primary circuit is switched to output DC power from an output terminal of the secondary circuit. In a switching power supply device configured by a forward method and performing DC / DC conversion of a DC input using a plurality of transformers to obtain a DC output,
A primary circuit in which a switching element is further connected in series to a series circuit in which primary windings of the plurality of transformers are connected in series;
The other ends of the secondary windings of each transformer are connected via a first unidirectional element having a forward current direction as a forward direction while connecting one ends of the secondary windings of the plurality of transformers, Connecting a second unidirectional element having a forward direction from one end connection point to the other end connection point between the one end connection point and the other end connection point; A secondary circuit in which one end of an inductor is connected to one of both ends of the one-way element, and the other end of the inductor and one of the other ends of the second one-way element are output terminals. With
A switching power supply device, wherein a switching element of the primary circuit is switched to output DC power from an output terminal of the secondary circuit.

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