JPH05243060A - Chalk and transformer for switching power supply - Google Patents

Abstract

PURPOSE:To reduce loss by reducing alternating current resistance of a chalk and a transformer for a switching power supply. CONSTITUTION:In a winding constructing a chalk 1 or a transformer 4, there are provided a new primary windings 2, 3 and auxiliary windings 5, 6 with a winding material having an alternating resistance less increased than the primary windings 2, 3 and having the same number of windings as that of the primary windings 2, 3. The primary windings 2, 3 and the auxiliary windings 5, 6 are interconnected in parallel in the direction of winding where their inductances do not disappear, and a DC component many currents flowing through the chalk 1 and the transformer 4 chiefly flows through the primary windings 2, 3 while an alternating component chiefly flows through the auxiliary windings 5, 6. Hereby, there is reduced a loss due to alternating current resistance in the case where the chalk or the transformer is employed at a high frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a choke and a transformer for switching power supplies, which are suitable for high frequency switching power supplies and have low loss.

[0002]

2. Description of the Related Art In recent years, a switching power supply has been widely used as a small, lightweight and highly efficient power supply. In order to further reduce the size and weight, the conversion frequency of switching power supplies is increasing. A DC-DC converter, which is one of switching power supplies, uses a choke for a filter circuit as an input / output in order to convert high-frequency ripple inside to high-quality DC. Furthermore, as converter transformers, there are both a flyback transformer that stores energy in the first half cycle and supplies power to the load in the latter half cycle, and a forward type transformer whose main purpose is insulation and voltage conversion. .. Moreover, a choke is used as a voltage conversion means in a chopper, which is another type of switching power supply.

5 to 7 show typical circuit types and current waveforms flowing in chokes or transformers used in the circuits. FIG. 5 is a diagram showing a choke input type filter circuit (a) and a current waveform diagram flowing in a choke (b), and FIG. 6 is a flyback converter circuit diagram (a) and a current waveform diagram flowing in a flyback transformer (b).
7 (c) and FIG. 7 show a boost chopper circuit diagram (a) and a current waveform diagram (b) flowing through the boost choke, respectively.

Here, 21 is a high frequency AC voltage, 22 is a transformer, 23 and 24 are diodes, 25 is a choke, 2
6 is a smoothing capacitor, 27 is a DC power supply, 28 is a smoothing capacitor, 29 is a MOSFET, 30 is a flyback transformer, 31 is a diode, 32 is a smoothing capacitor, 33
Is a MOSFET, 34 is a diode, 35 is a smoothing capacitor, and 36 is a boost choke. Further, i25 is a current waveform flowing through the choke 25, ip30 is a primary winding current waveform of the flyback transformer 30, is30 is a secondary winding current waveform of the flyback transformer 30, and i36 is a boost choke current waveform. In the flyback converter circuit of FIG. 6A, there are a mode in which the current is continuous (b) and a mode in which the current is discontinuous (c). Ia
v indicates the average value of each waveform, and Ip and Is indicate the ripple value of each waveform. The effective current Irms of each current is given by the following equation.

[0005] In ^{Irms = √D√ (Iav 2 + Ip} 2/12) ...... (1) (1) formula, D is the duty ratio, i25,
In the case of i36, it is 1, and in the case of (b) and (c) of FIG. 6, D = τ / T for ip30 and D = τ ′ / for is30.
It becomes T. Therefore, the loss P of each winding of the chokes 25, 36 or the transformer 30 is expressed by the following equation.

[0006] In _{^{P = RIrms 2 = R DC DIav}} 2 + DR AC Ip 2/12 ...... (2) (2) formulas, R winding resistance, DC resistance R _DC windings, R _AC is the winding AC resistance at the fundamental frequency f of the ripple current flowing. Here, the choke 2 of FIG.
5 and the current of the choke 36 in FIG. 7A, the ratio of the normal ripple current Ip to the average current Iav is Ip / Iav = 0.
In the mode of FIG. 6B, Ip / Iav = 0.2 to 2 and in the mode of FIG. 6C, Ip / Iav ≧ 2, and Ip is smaller than Iav. Become very large. Conventionally, a large-capacity switching power supply of several kW or more could not realize a very high frequency due to the power semiconductor element for switching, and was about 10 kHz at most. Therefore, the AC resistance R _AC of the second term of the equation (2) was not so different from the DC resistance, so that it did not cause a problem.

These DC resistance R _DC and AC resistance R _AC are
It actually looks like this: FIG. 8 shows a winding structure of a general choke. The core is omitted here. In the figure, 41 is a bobbin and 42 is a winding. Usually, in the conventional choke that allows a large current to flow, in order to reduce the direct current resistance, a copper plate having a good space factor is used for multi-layer winding. FIG. 9 shows an example of the frequency characteristic of the resistance of the choke by the rate of increase of the AC resistance. The measurement was performed in the air core to remove the magnetic core loss. The characteristics of the flyback transformer 30 shown in FIG. 6A show almost the same characteristics. The frequency characteristics of this choke are BEC of a copper plate 0.3 mm thick, 14 mm wide and 1.2 m long.
The AC resistance was measured in the case where a 90-core bobbin was successively wound in multiple layers.

As shown in the figure, the AC resistance R _AC is the same as the DC resistance R _DC at low frequencies, and increases sharply as the frequency increases, but does not increase so much up to about 10 kHz. The resistance at a frequency of 300 Hz is 5.4.
It was 5 mΩ.

[0009]

By the way, at present, a switching power supply having a large capacity and a high frequency is being realized by the progress of semiconductor technology, and in the near future, a power supply having a frequency f of more than 1 MHz with a frequency of several tens of kW will be realized. It is supposed. In such a case, since a conductor that allows a large current to flow requires a large cross-sectional area, AC resistance rapidly increases due to skin effect, proximity effect, etc., and AC loss cannot be ignored, which is a serious problem.

This means that the AC resistance R _AC is the same as the DC resistance R _DC at low frequencies as shown in FIG.
It is also clear from the sharp increase at higher frequencies.
This tendency becomes more remarkable as the number of windings increases.

Although the above description has been made for the filter choke and the flyback transformer, the AC loss cannot be ignored in the winding loss of the boost chopper choke, the forward converter type transformer and the like. Therefore, if such a choke and a transformer are applied to a converter, the efficiency of the converter is reduced and the loss of the transformer and the choke is increased. Therefore, there is a problem that the transformer and the choke cannot be downsized, and the size is increased, and the price is increased. .. Furthermore, ultimately, there is a problem that the current natural air cooling or forced air cooling cannot cope with it, and a new heat radiation technology such as water cooling has to be adopted, resulting in a significant increase in cost.

Therefore, the present invention has been made to solve such a problem, and an object thereof is to provide a choke and a transformer for a switching power supply which have a reduced AC resistance and a low loss.

[0013]

In order to achieve the above object, in a choke and a transformer for a switching power supply according to the present invention, the windings constituting them have a main winding and an auxiliary winding having the same number of turns. A wire to make the DC resistance of the main winding smaller than the DC resistance of the auxiliary winding, and the AC resistance of the auxiliary winding at the fundamental frequency of the current flowing through the main winding and the auxiliary winding to the main winding. It is characterized in that it is set smaller than the AC resistance of the wire, and that the main winding and the auxiliary winding are connected in parallel in a winding direction in which the inductance does not disappear.

[0014]

In the choke and transformer for the switching power supply according to the present invention, in addition to the main winding similar to the conventional one, the auxiliary winding having the same number of turns as the winding material in which the increase in AC resistance is smaller than that of the main winding. Is newly provided and the main winding and the auxiliary winding are connected in parallel so that the DC component of the current flowing through the choke and the transformer mainly flows through the main winding and the AC component mainly flows through the auxiliary winding. This reduces loss due to AC resistance when used at high frequencies.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention. Here, (a-1) and (a-2) show a circuit diagram, and (a-1) shows the case where the present invention is applied to one winding of the main winding for applications such as a choke. Example (a-
2) is an embodiment when the present invention is applied to the case where the main winding for use in a flyback transformer or a normal transformer has a plurality of windings. (B-1) and (b-2) are respectively (a
1 shows an equivalent circuit diagram of (1) and (a-2). Here, 1 is a choke, 2 is a main winding, 3 is an auxiliary winding of the main winding 2, 4 is a transformer, 5 is a second main winding, 6 is an auxiliary winding of the second main winding, L of the equivalent circuits of (b-1) and (b-2)
Is an inductance, R is a resistance, and the numerical suffixes attached to L and R correspond to the windings shown in (a-1) and (a-2). The black circles in the windings (a-1) and (a-2) indicate the winding start.

The main winding 2 and the auxiliary winding 3 have the same number of turns, and the second main winding 5 and the auxiliary winding 6 have the same number of turns. Also,
The DC resistances of the main windings 2 and 5 are made smaller than the DC resistances of the auxiliary windings 3 and 6, respectively, and the AC resistances of the auxiliary windings 3 and 6 at the basic frequency of the current flowing in these main windings and auxiliary windings are mainly Set smaller than windings 2 and 5. The main winding and the auxiliary winding are connected in parallel in the same winding direction and the same number of turns so that the main winding and the auxiliary winding do not lose inductance. As a result, the function of the choke or the transformer is provided, and the inductance of the main winding and the auxiliary winding connected in parallel therewith become substantially equal, and there is no reduction in inductance due to the addition of the auxiliary winding. Also,
Since the inductance value and the number of turns are the same, the circulating current between the windings in the same core is small and does not have an adverse effect.

FIG. 2 shows the inductance and resistance characteristics of the main winding 2 and the auxiliary winding 3. The inductance and resistance characteristics of the second main winding 5 and the second auxiliary winding 6 are the same as the characteristics explained in this figure, and the effects are also the same. In the figure, (A)
Is the characteristic curve of copper plate, (B) is the characteristic curve of litz wire,
(C) shows the characteristic curve which connected these copper plates and the litz wire in parallel.

FIG. 3 (a) shows a structural diagram of the choke having the above characteristics. Here, 10 is the main winding, 11 is the auxiliary winding, and 12
Is a core and 13 is a bobbin. In this figure, the main winding specification is an 8-layer winding of a copper plate 8 turns of 0.3 mm thickness × 24 mm width × 1.2 m, and the auxiliary winding specification is 0.1 mmφ × 28 wires × 7 wires × 7 wires ( 1372) x 118 cm litz wire 8
It's a turn. Since the copper plate used for the main winding 10 has a higher space factor than other wire rods, it is possible to reduce the DC resistance by using a thick plate, but since the winding has multiple layers, skin effect and proximity Due to the effect, the AC resistance sharply increases as shown in FIG. For the auxiliary winding 11, a litz wire with a small wire diameter that can reduce the number of winding layers and has a small increase in AC resistance is used. Since the Litz wire has a low space factor,
DC resistance is higher than copper plate, but increase of AC resistance is small. Also, since both have the same number of turns, almost the same inductance value (404 μH with core) can be obtained. The schematic diagram of FIG. 3B also shows the inductance and resistance characteristics when the main winding 10 and the auxiliary winding 11 are connected in parallel. As shown in FIG. 3 (b), in the embodiment of the present invention, a resistance of about 1/2 or less is obtained at a frequency of 100 kHz, and two chokes are connected in parallel, as compared with the conventional main winding only structure. As described above, the inductance is not reduced to 1/2, but the same inductance value is obtained.

As described above, the present embodiment can reduce the increase in loss due to the increase in AC resistance, which has been a problem in the prior art, and thus the efficiency of the switching power supply can be improved. It is possible to achieve higher frequencies and downsizing of the switching power supply without improvement of power consumption and special heat radiation measures.

4 (a) to 4 (k) are structural views of another embodiment of the present invention. In each figure, 10 is the main winding, 11
Is an auxiliary winding, 12 is a core, and 13 is a bobbin. (A)
Is a general wire used for the auxiliary winding 11.
(B) is the lower layer of the main winding 10 of the copper plate, (c) is the upper layer,
(D) is the upper and lower layers, and (e) is the intermediate layer, and the auxiliary winding 11 of the wire is wound. Further, in (f), a wide copper plate is used as the main winding 10 and a thin copper plate is wound in parallel as the auxiliary winding 11, and in (g) and (h), a thick copper plate is used as the main winding 10. And a thin copper plate as the auxiliary winding 11,
It is a layered product (g) and an upper layer (h). Furthermore, (i), (j), (k) are
The thick wire is the main winding 10 and the thin wire is the auxiliary winding 11, and the auxiliary winding 11 is wound on the upper layer (i) of the main winding 10, the intermediate layer (j) thereof, or the lower layer (k). is there.

In the description of the first embodiment of the present invention, the combination of the copper plate and the litz wire was explained, but as shown in FIG.
A combination of commonly used wire rods may be used. Also,
The auxiliary winding may be arranged in any of the lower layer, the middle layer and the upper layer of the main winding. Further, the same effect can be obtained whether the winding is wound by sandwich winding, bifilar winding or lap winding. Even if there are multiple windings on the primary side and the secondary side as in a transformer, the same configuration is performed between the main winding and the auxiliary winding for all or some of the windings, and It is clear that the effect can be obtained. As described above, the present invention has various applications in line with its gist,
Various embodiments are possible.

[0023]

As described above, the choke and transformer for a switching power supply according to the present invention can reduce the AC resistance of the windings, so that the switching power supply can be made highly efficient, high frequency, compact and lightweight. There are advantages.

[Brief description of drawings]

1A and 1B are circuit diagrams showing a first embodiment of the present invention, and FIGS. 1A-2 and B-2 are equivalent circuit diagrams thereof.

FIG. 2 is a diagram showing an actual measurement example of AC resistance of the winding structure of the first embodiment.

3A is a structural diagram of the choke according to the first embodiment, and FIG. 3B is a schematic diagram of its resistance characteristic.

4 (a), (b), (c), (d), (e),
(F), (g), (h), (i), (j) and (k) are structural views showing another embodiment of the present invention.

5A is a diagram showing a conventional choke input type filter circuit, and FIG. 5B is a waveform diagram of a current flowing in the choke.

6A is a conventional flyback converter circuit diagram, and FIGS. 6B and 6C are waveform diagrams of current flowing in the flyback transformer.

7A is a conventional boost chopper circuit diagram, and FIG. 7B is a waveform diagram of a current flowing in the boost choke.

FIG. 8 is a winding structure diagram of a conventional general choke.

FIG. 9 is a diagram showing an AC resistance increase rate of a multilayer winding of a copper plate in the conventional general choke.

[Explanation of symbols]

1 ... choke, 2 ... main winding, 3 ... auxiliary winding, 4 ... transformer, 5 ... second main winding, 6 ... second main winding auxiliary winding,
10 ... Main winding, 11 ... Auxiliary winding, 12 ... Core, 13 ... Bobbin.

Claims (2)

[Claims] 1. A main winding and an auxiliary winding having the same number of windings are provided,
The DC resistance of the main winding is made smaller than the DC resistance of the auxiliary winding, and the AC resistance of the auxiliary winding at the fundamental frequency of the current flowing through the main winding and the auxiliary winding is the AC resistance of the main winding. A choke for a switching power supply, characterized in that it is set smaller and the main winding and the auxiliary winding are connected in parallel in a winding direction in which the inductance does not disappear. 2. A main winding and an auxiliary winding having the same number of windings are provided on both or one of the primary winding and the secondary winding, and the DC resistance of the main winding is set to the DC of the auxiliary winding. The resistance of the main winding and the auxiliary winding is set to be smaller than the AC resistance of the main winding at the fundamental frequency of the current flowing through the main winding and the auxiliary winding. A transformer for a switching power supply, in which the transformers are connected in parallel in the winding direction so that the inductance does not disappear.