POWER SOURCE APPARATUS

Abstract: The present invention relates to a non-contact type power supply unit intended for use in electronic equipment, aiming at the realization of a small size and low cost and successful achievement in an enhanced capability of electric power transmission. In order to achieve the foregoing objectives, the non-contact type power supply unit comprises a primary coil(11) that is fed with pulsated currents, a secondary coil(13) mounted opposite to the primary coil(11) in an enclosure that is different from an enclosure wherein the primary coil(11) is mounted, whereby electric power is transferred from the primary coil(11) to the secondary coil(13) and wherein a ferrite core(12) is disposed so as to extend from the primary coil(11) towards the secondary coil(13), thus achieving efficient electric power transmission from the primary coil(11) to secondary coil(13).

Description: The present invention relates to a non-contact type power supply unit for use in small portable equipment such as cordless telephones, portable telephones, PHS phones, video cameras, personal computers and the like. Reference JP-A-07 106 170 describes a non-contact type power supply using primary coils and secondary coils. The primary coils and an additional coil element extend from a flat surface. The secondary coils are arranged, when mounted, around the extended portion including the primary coils and the additional coil element. Alternatively, only the additional core element is extending from the flat surface into the surface of the secondary coil element. A non-contact type power supply unit is characterized by transferring electric power from a primary side to a secondary side, and since the primary side circuit and secondary side circuit are packaged in separate enclosures that are completely independent from each other, it is very important to establish magnetic coupling between a primary transformer and a secondary transformer of the non-contact type power supply unit for efficient transfer of electric power. In order to achieve an improvement in the magnetic coupling, use of E-E cores is considered effective. Also, it has been a usual practice to make the opposing area between the primary coil and the secondary coil of the transformers as large as possible for better magnetic coupling. An explanation will be given to prior art technologies in the following with reference to Fig. 4 to Fig. 6. Fig. 4 shows a structure wherein E type cores are used as a primary core 1 and also a secondary core 5. A primary coil 2 is placed in the slot of the primary core 1 (E type core), thereby forming a primary transformer 4. Also, a secondary coil 6 is placed in the slot of the secondary core 5 (E type core), thereby forming a secondary transformer 8. Reference numerals 3 and 7 indicate a primary bobbin and a secondary bobbin, respectively. Next, how the foregoing structure works will be explained. When high frequency currents flow in the primary coil 2 formed of windings wound concentrically, magnetic fluxes are produced in the primary coil 2 and primary core 1. The foregoing magnetic fluxes are propagated to the secondary core 5 and secondary coil 6 and converted to electric power, which is then supplied to load. Fig. 5 shows a structure wherein the opposing area between the primary coil 2 and the secondary coil 6 is made large in order to intensify the magnetic coupling between windings. Also, in order to increase the foregoing magnetic coupling, an arrangement is made to dispose the secondary coil 6 and the primary coil 2 concentrically as shown in Fig. 6(a). Further, there has been provided a structure, wherein a mechanical switch 8a and a magnetic switch 9a are used together in order to enable the primary coil to tell whether what receives electric power from the primary coil is the secondary coil or some other foreign objects and also to reduce a supply of electric power to the foreign objects, thereby preventing an abnormal heating of the foreign objects from taking place, and when a magnetic field generator 10a installed on a secondary enclosure 5a comes close to the magnetic switch 9a, the magnetic switch 9a is turned on and even when the mechanical switch 8a installed on a primary enclosure 4a is turned on by an object other than the secondary enclosure 5a, an arrangement is made so that electric power is not applied to the primary coil, as shown in Fig. 6(b). However, with the structure of Fig. 4, wherein open magnetic circuits are formed, the magnetic fluxes from the middle leg 9 of the primary core 1 (E type core) are returned to the outer legs 10 by short circuiting, thus resulting in a reduction of magnetic fluxes that are propagated to the secondary side and ending up with a poor efficiency. On the other hand, with the structure of Fig. 5, wherein the opposing area between both coils is made large, the dimensions of the primary side and secondary side including the enclosures become extremely large, thereby hindering a unit, wherein this structure is incorporated, from achieving a downsizing. When the secondary coil 6 and the primary coil 2 are disposed concentrically as shown in Fig. 6(a), the magnetic coupling between the primary coil 2 and the secondary coil 6 is intensified, resulting in an increase of the transmission of electric power. However, the diameter of the primary coil 2 becomes the inner diameter of the secondary coil 6 resulting in the problems of an increase of dimensions of the secondary coil 6 and the like. Furthermore, when the mechanical switch 8a is provided on the primary enclosure 4a to prevent an abnormal heating of foreign objects as shown in Fig. 6(b), electrical contacts once eliminated by employing a non-contact structure are used again, thereby bringing about the danger of failure in contacts and also making it difficult to make the direct current power supply unit in a hermetically sealed construction or a water-proof construction. In addition, use of the magnetic switch 9a such as a Hall effect device and the like has caused such problems as a difficulty for the magnetic switch 9a to tell distinctly the difference between a heat producing object other than the secondary enclosure 5a when the foregoing object is made of a magnetic substance and the like and the secondary transformer that includes the secondary enclosure 5a, and the like. The present invention provides an inexpensive and yet reliable power supply unit whereby the shortcomings of the prior art as described in the above are eliminated, a simpler structure is realized, electric power transmission efficiencies are enhanced and a downsizing of the equipment is made possible. This is achieved by the features of claim 1. Fig. 1 shows a construction of a transformer performing an important function in an exemplary embodiment of a power supply unit. Fig. 2 shows a construction of a transformer performing an important function in an exemplary embodiment of the present invention of a power supply unit. Fig. 3 shows a construction of a transformer performing an important function in another exemplary embodiment of the present invention of a power supply unit. Fig. 4 shows how the primary and secondary coils are constructed in a transformer performing an important function in a prior art power supply unit. Fig. 5 shows how the primary and secondary coils are constructed in a transformer performing an important function in another prior art power supply unit. Fig. 6(a) shows how the primary and secondary coils are constructed in a transformer performing an important function in still another prior art power supply unit. Fig. 6(b) shows how the primary and secondary coils are constructed in a transformer performing an important function in still another prior art power supply unit. (Exemplary Embodiment 1) An exemplary embodiment helpful for the understanding of the present invention will be explained below with reference to Fig. 1. As shown in Fig. 1, a ferrite core 12 is inserted into a primary coil 11 and arranged to extend towards a secondary coil 13, which is wound around the ferrite core 12. The primary coil 11 is mounted inside of a primary enclosure 14 and the secondary coil 13 is mounted inside of a secondary enclosure 15. An explanation will be made on how a non-contact type DC power supply unit constructed as described in the above performs. By the passage of high frequency electric currents through the primary coil 11, magnetic fluxes are produced. Almost all the foregoing magnetic fluxes pass through the ferrite core 12, which penetrates the center of the primary coil 11. By having the above ferrite core 12 extended to the secondary coil 13, it is made possible for the magnetic fluxes produced by the primary coil 11 to be transferred to the secondary coil 13 efficiently. Since the foregoing ferrite core 12 is a rod type core forming an open magnetic circuit, it is extremely difficult for the ferrite core 12 to be magnetized to saturation, thereby enabling the ferrite core 12 to have a small diameter and contributing greatly to a downsizing of the power supply unit. (Exemplary Embodiment 2) Fig. 2 shows an exemplary embodiment of the present invention. In general, the coupling between the primary coil and the secondary coil is very poor with a non-contact type DC power supply unit, and little influence is imposed on the primary coil from the changes in condition of the secondary coil. Therefore, it has been extremely difficult for a primary coil 21 to detect whether a correct secondary coil was mounted or any other foreign object article was placed on the secondary side. However, by installing a detector coil 26 at a position which is off the primary coil 21 and closer to a secondary coil 23 on a ferrite core 22 as shown in Fig. 2 so that the detector coil 26 is hardly influenced by the primary coil 21 and readily affected by the secondary coil 23, the voltage induced in the detector coil 26 reflects the changes in condition of the secondary side since the detector coil 26 is more closely coupled with the secondary coil 23 than with the primary coil 21. Because of the above reason, by monitoring the voltage of the detector coil 26, it can be known that whether what is connected to the DC power supply unit is the secondary coil 23 connected to a rectifying circuit or some foreign object having low impedance like a shorting ring. According to the output voltage of the detector coil 26, the high frequency currents fed to the primary coil 21 can be made low in magnitude or flowing intermittently, thereby preventing a temperature rise of the foreign object. In Fig. 2, the reference numerals 24 and 25 are a primary enclosure and a secondary enclosure, respectively. ( Exemplary Embodiment 3) Fig. 3 also shows still another exemplary embodiment of the present invention. As shown in Fig. 3, a resonance capacitor 27 is connected across both ends of the detector coil 26 that is installed as described in Exemplary Embodiment 2, and the changes in condition of the secondary side are amplified, thereby enabling the detection of foreign objects to be performed readily and reliably. As described in the above, the exemplary embodiments of Fig. 1 to Fig. 3 employ a slender ferrite core simply arranged to extend from a primary coil to a secondary coil and can realize a non-contact type DC power supply unit, whereby efficient transmission of electric power from the primary side to the secondary side is made possible. In addition, with a version that has a detector coil provided to the ferrite core, it is made possible to realize an extremely safe non-contact type DC power supply, whereby detection of foreign objects is performed without using a mechanical switch, a magnetic switch and the like. As described in the foregoing, the present invention can provide a power supply unit that achieves an excellent power transmission efficiency with a simple construction, enables the equipment using the power supply unit to achieve a downsizing, contributes to a cost reduction and operates with a high degree of reliability. Particularly, a version provided with a ferrite core that is inserted in the primary coil and extends towards the secondary coil can transfer efficiently the magnetic fluxes produced in the primary coil to the secondary coil. Another version provided with a tertiary coil that is located on the foregoing ferrite core where no primary coil is in place can detect foreign objects with a high degree of reliability because of the use of the foregoing tertiary coil. Still another version provided with the tertiary coil having a capacitor connected across both ends thereof can amplify the changes in condition of the secondary side, thereby conducting the detection of foreign objects more accurately.

Claims: A non-contact power supply unit comprising: a primary coil (21) in a first enclosure (24), said primary coil (21) is to be fed with high frequency currents, a secondary coil (23) mountable opposite to said primary coil (21) in an enclosure (25) being different from said first enclosure (24), wherein said coils (21, 23) are adapted to transfer electric power from said primary coil (21) to said secondary coil (23), a ferrite core (22) extending from said primary coil (21) to said secondary coil (23), and a detector coil (26) provided on said ferrite core (22) at a position where said ferrite core (22) being not inserted in said primary coil (21). characterized in that by monitoring the voltage of the detector coil it can be known whether or not a corresponding secondary coil (23) is mounted to the primary coil (21). A power supply unit according to claim 1, wherein a capacitor (27) is connected across both ends of said detector coil (26).

Inventors: NAKAI YOSHIYUKI, OKURA HIDEKI, ONO MAKOTO, TANIGUCHI SATORU, NAKAI, YOSHIYUKI, OKURA, HIDEKI, ONO, MAKOTO, TANIGUCHI, SATORU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: H02J17
IPC codes: H02J5, H01F38