JP2799760B2 - Resonant converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonant converter, and more particularly to a resonant converter operating at a low input voltage, a large power, and a high frequency.

[Problems to be solved by conventional technology and invention]

Resonant converters have low switching loss,
In particular, when the conversion frequency is increased, the effect is large and widely used. However, in the case of a low input voltage and a relatively large current, the circuit design conditions cannot be satisfied unless the resonance inductance is reduced. In this case, the value of the leakage inductance becomes so large that it cannot be ignored compared to the resonance inductance. Therefore, this leakage inductance is used as a resonance inductance rather positively, and a dedicated inductor is omitted, but the inductance value is still larger than a predetermined inductance value. A first object of the present invention is to realize a low inductance, which is a condition for realizing such a resonant converter operating at a low input voltage, a large output voltage, and a high frequency.

In such a high-frequency, high-power resonant converter, the core of the transformer uses a material with a low high-frequency loss. However, the heat generated by the self-loss of the core is still large. Decrease. Therefore, an attempt is made to solve the problem by increasing the cross-sectional area of the core. However, as the cross-sectional area increases, the heat radiation condition is reduced, so that the magnetic flux density of the increased sectional integral cannot be obtained. A second object of the present invention is to obtain a transformer having a minimum necessary core cross-sectional area in a resonant converter.

[Means for solving the problem]

In order to solve the above problems, the present invention connects the primary windings of a plurality of transformers having the same number of turns in parallel with each other in the same polarity, and connects the secondary windings of the transformers in parallel with the same polarity. A series resonance circuit is formed by a total leakage inductance and a capacitor appearing in primary windings of a plurality of transformers connected in parallel. If necessary, provide an independent inductance.

[Action]

Since each primary winding of the transformer is connected in parallel, the leakage inductance is reduced by the number in parallel. In addition, since the secondary windings are also connected in parallel, the leakage inductance is similarly reduced. Therefore, the inductance seen from the primary side decreases by the number of parallel units. Therefore, the equivalent inductance is lower than in the case of a single transformer.

In addition, since a plurality of cores have a larger total surface area than a single core having an equivalent cross-sectional area, the heat radiation effect is improved.

〔Example〕

FIG. 1 shows an embodiment of the present invention. First, the configuration will be described. A DC voltage is received from the input terminals 11 and 12 and half of the voltage is stored in capacitors 21 and 22 having substantially the same value. Diodes 23 and 24 are connected in parallel to these capacitors 21 and 22, respectively. Input terminal 1
1,12 are field-effect transistors 31,3 connected in series with each other.
Also connected to 2. Here, a connection point between the capacitors 21 and 22 is a node 81, and a connection point between the field effect transistors 31 and 32 is a node 82. Transformers 4,5,6 between nodes 81 and 82
The primary windings 41, 51, and 61 have leakage inductance 4
They are connected in parallel via 2,52,62. The secondary windings 43 and 44 of the leakage transformer 4 have the same number of turns with respect to the midpoint 47, and leakage inductances 45 and 46 are present in series, respectively. The same applies to the transformers 5 and 6. The secondary windings of these transformers 4, 5, 6 are connected in parallel at nodes 91, 92, 93, respectively. The lengths of the connecting wires from these nodes 91, 92, 93 to the windings are arranged as short as possible and substantially equal to each other. The node 91 is connected via the diode 71 to the node 92.
Are both connected to the positive terminal of a capacitor 73 via a diode 72. Node 92 is connected to the negative terminal of capacitor 73. Both ends of the capacitor 73 are connected to output terminals 74 and 75.

In the resonant converter thus configured, the transformers 4, 5, and 6 have the respective windings connected in parallel, so equivalently, each of the leakage inductances is connected in parallel.

In other words, the leakage inductance is equivalently divided into three,
If the number of turns of each winding is all equal, it is expressed as LeqＬ (Llp + Lls) / 3. Here, Leq: equivalent total leakage inductance Llp: primary leakage inductance Lls: secondary leakage inductance

A circulating current may flow due to the difference in the induced voltage of each secondary winding, but this circulating current is limited to a low value by the leakage inductance on the secondary side. Since each leakage inductance is one element of the series resonance circuit, it exhibits a high impedance with respect to the operating frequency of the converter due to its resonance action, and has a large effect as a current balancer in a parallel state. In addition, since the secondary windings of the transformers are connected in parallel at the stage of the AC voltage, even if the magnetic demagnetization phenomenon starts to occur, the secondary winding acts in a direction to eliminate the phenomenon.

Further, since there are a plurality of cores, the heat radiation efficiency is higher than in the case of a single core having an equivalent cross-sectional area, so that the overall required cross-sectional area of the core can be reduced.

In the above embodiment, three transformers are arranged in parallel. However, any number of transformers can be arranged in parallel as needed.

Although not shown, the resonance type converter can be configured by providing an independent inductance in addition to the total leakage inductance as the inductance of the resonance circuit if necessary.

〔The invention's effect〕

Since the present invention has the above-described features, the following effects can be obtained in a converter having a low input voltage.

(1) It is possible to obtain a resonance inductance having a predetermined value, particularly a small desired value.

(2) A dedicated inductor may not be required.

(3) Simple structure, high reliability, and economical.

(4) There is little danger of magnetization.

(5) The required cross-sectional area of the core can be kept small,
It is economical.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention. 11,12 …… Input terminal, 21,22 …… Capacitor 23,24 …… Diode, 31,32 …… Field-effect transistor,
4,5,6… Transformer, 41… Primary winding, 42… Primary leakage inductance, 43,44… Secondary winding 45,4
6 …… Secondary leakage inductance, 71, 72 …… Diode, 73
…… Capacitors, 74,75 …… Output terminals

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshio Suzuki 1-18-1 Takada, Toshima-ku, Tokyo Origen Electric Co., Ltd. (72) Inventor Yasuo Ohashi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Within the Telegraph and Telephone Corporation (72) Inventor Yutaka Kuyada Examiner, Nippon Telegraph and Telephone Corporation Masahiko Koike, 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo 58) Fields surveyed (Int.Cl. ⁶ , DB name) H02M 3/00-3/44

Claims (2)

(57) [Claims] 1. A primary winding of a plurality of transformers having the same number of turns is connected in parallel with the same polarity, and secondary windings of the transformer are connected in parallel with the same polarity. And a series resonant circuit formed by a total leakage inductance and a capacitor appearing in primary windings of the plurality of transformers connected in parallel. 2. The primary windings of a plurality of transformers having the same number of turns are connected in parallel with the same polarity, and the secondary windings of the transformers are connected in parallel with the same polarity. And a series resonant circuit formed by a total leakage inductance, an independent inductance, and a capacitor appearing in primary windings of the plurality of transformers connected in parallel.