The present invention relates to a resonance type transformer for use in various electronic devices and an electric power supply unit using the same.
Magnetic gap 14 is provided between central magnetic legs 6A, 6B, and primary winding 10 and secondary winding 12 are disposed adjacently with each other in the vicinity of magnetic gap 14. Central magnetic leg 6A is longer than central magnetic leg 6B, and magnetic gap 14 is formed by putting magnetic legs 6A, 6B face to face.
Electric current resonance can be caused by connecting a resonance capacitor and a switching element in series with the leakage inductance of primary winding 10 of the resonance transformer. This type of resonance transformer is disclosed in Japanese Patent Unexamined Publication No. H08-064439, for example.
In the above-described conventional structure, primary winding 10 and secondary winding 12 are disposed adjacently with each other in the vicinity of magnetic gap 14. For this reason, as shown in
The present invention provides a resonance type transformer in which temperature rise in the secondary winding is suppressed and the characteristic is enhanced. The resonance type transformer in accordance with the present invention has an O-shaped magnetic core, a primary winding and a secondary winding. The O-shaped magnetic core is formed of a first split magnetic core and a second split magnetic core and has a first magnetic leg that is provided with a first magnetic gap therein and a second magnetic leg opposite the first magnetic leg. The primary winding is wound around the outer periphery of the first magnetic leg so as to cover at least the first magnetic gap. The secondary winding is wound around the outer periphery of the second magnetic leg. With this structure, a part of the magnetic flux generated by the primary winding and directly interlinking with the secondary winding without passing through the O-shaped magnetic core is decreased. That is, the eddy current generated in the secondary winding is suppressed thus suppressing temperature rise in the secondary winding due to the eddy current.
Resonance type transformer 60 in the exemplary embodiment of the present invention has O-shaped magnetic core 20, primary winding 24, and secondary winding 26. O-shaped magnetic core 20 comprises back portions 201A, 201B, first magnetic legs 202A, and second magnetic leg 202B. O-shaped magnetic core 20 is formed in a manner such that first and second C-shaped magnetic cores 30A, 30B, being first and second split magnetic cores, faces each other with each respective end portion opposing through respective first and second magnetic gaps 32A, 32B. Magnetic leg 202A is provided with magnetic gap 32A therein, magnetic leg 202B is provided with magnetic gap 32B therein and is opposite magnetic leg 202A.
Primary winding 24 is wound on the outer periphery of magnetic leg 202A via first bobbin 22A while secondary winding 26 is wound on the outer periphery of magnetic leg 202B via second bobbin 22B. Primary winding 24 and secondary winding 26 are wound so as to cover magnetic gaps 32A, 32B, respectively. That is, bobbin 22A is disposed between outer periphery of magnetic leg 202A and primary winding 24 and is wound with primary winding 24. Bobbin 22B is disposed between outer periphery of magnetic leg 202B and secondary winding 26 and is wound with secondary winding 26.
Primary winding 24 and secondary winding 26 are litz wires prepared by twisting about 150 copper wires having electrically insulating coating with each end connected respectively to first and second terminals 28A, 28B implanted in bobbins 22A, 22B. Each of terminals 28A, 28B includes a terminal section for wiring and a terminal section for mounting.
C-shaped magnetic cores 30A, 30B are made from manganese based ferrite, nickel based ferrite, or dust core, for example. Bobbins 22A, 22B are made of an electrically insulating resin such as phenol resin, polyethylene terephthalate (PET), and polybutylene terephthalate (PBT).
Furthermore, resonance type transformer 60 has case 36 provided with first and second recesses 34A, 34B which match the outer configurations of bobbins 22A, 22B. Case 36 is made of an electrically insulating resin similar to that of bobbins 22A, 22B. Case 36 covers O-shaped magnetic core 20 and makes bobbins 22A, 22B fit into recesses 34A, 34B. Or, bobbins 22A, 22B are bonded with the case at recesses 34A, 34B respectively. By either of this method, bobbins 22A, 22B and O-shaped magnetic core 20 are positioned and secured in case 36. In case 36, electrically insulating wall 38 is provided between bobbins 22A, 22B for separation and insulation between bobbins 22A, 22B.
In particular, primary winding 24 and secondary winding 26 are wound around mutually opposite magnetic legs 202A, 202B, respectively. As a result, leakage magnetic flux 48 generated by primary winding 24 and directly interlinking with secondary winding 26 is further reduced thereby suppressing temperature rise in secondary winding 26. With the suppression of the temperature rise, the temperature rises in both primary winding 24 and secondary winding 26 are controlled to around 40K, which is lower than the temperature rise in conventional resonance type transformers.
In case 36, insulating wall 38 is provided at a position between primary winding 24 and secondary winding 26. With this arrangement, primary winding 24 and secondary winding 26 are not spatially electrically insulated over a distance in a straight line but along a further longer creeping distance due to insulating wall 38. This is preferable as higher electrical insulation can be maintained.
Beam 39A on the lengthwise side of case 36 extends in the direction to contact O-shaped magnetic core 20 as shown in
O-shaped magnetic core 20 is formed by making C-shaped magnetic cores 30A, 30B face each other, and primary winding 24 and secondary winding 26 are wound on portions including opposing portions of C-shaped magnetic cores 30A, 30B. As a result, leakage magnetic flux 48 without going inside O-shaped magnetic core 20 and leaking from magnetic gaps 32A, 32B provided in the opposing parts is interrupted by primary winding 24 and secondary winding 26. As a result, the influence on other mounted components is suppressed.
As shown in
When the ratio d2/d1 decreases toward 0.5, leakage inductance increases and coupling coefficient decreases as the opposing area between primary winding 24 and secondary winding 26 decreases. Conversely, when the ratio d2/d1 increases toward 2.0, the leakage inductance decreases and the coupling coefficient increases as the opposing area between primary winding 24 and secondary winding 26 increases. A detailed description will be given on this aspect referring to
When the ratio d2/d1 is smaller than 0.5, the climb gradient of the leakage inductance becomes steep as shown in
Although alternating current resistance component of secondary winding 26 increases by driving at a high frequency, the alternating current resistance component can be reduced by using a litz wire for secondary winding 26. So, it is preferable to use a litz wire for secondary winding 26. As the temperature rise in secondary winding 26 can be suppressed as described above, alternating current resistance component associated with a temperature rise can also be reduced. Accordingly, even when the number of copper wires to be twisted into a litz wire is reduced, the characteristics are not impaired. A smaller size and cost reduction can thus be achieved.
Primary winding 24 and secondary winding 26 are wound via bobbins 22A. 22B, and case 36 for securing bobbins 22A, 22B is provided. As a result, positioning of terminals 28A, 28B implanted in bobbins 22A, 22B is made possible thus improving ease of mounting on a circuit board.
O-shaped magnetic core 20 may be formed not only by oppositely facing C-shaped magnetic cores 30A, 30B but also by composing the first and the second split magnetic cores with U-shaped magnetic core 61 and I-shaped magnetic core 62 and making them face each other as shown in
Depending on the configuration of the split magnetic cores used, bobbins 22A, 22B may not be necessary. However, productivity of primary winding 24 and secondary winding 26 may be improved by using bobbins 22A, 22B.
In the resonance type transformer in accordance with the present invention, as the temperature rise in the secondary winding can be suppressed and the characteristics are improved, it can be used in a variety of electronic devices.
Number | Date | Country | Kind |
---|---|---|---|
2005-052851 | Feb 2005 | JP | national |
2006-022031 | Jan 2006 | JP | national |
This application is a U.S. national phase application of PCT International Application No. PCT/JP2006/303118.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2006/303118 | 2/22/2006 | WO | 00 | 6/27/2007 |