1. Field of the Invention
The present invention relates to a magnetic leakage transformer.
2. Description of the Related Art
A magnetic leakage transformer is used, for example, in a discharge lamp operating device used to operate a discharge lamp such as a fluorescent lamp. The magnetic leakage transformer is used in the device not only to generate a high voltage necessary to light a discharge lamp but also to limit a discharge current to be supplied to the discharge lamp as a current-limit inductance while the discharge lamp is operating.
If a nonmagnetic leakage transformer is used instead of the magnetic leakage transformer in the discharge lamp operating device, a choke coil to be used as a current-limit inductance must be associated with the nonmagnetic leakage transformer. In this case, the construction of the circuit of the discharge lamp operating device is complicated, the number of components of the discharge lamp operating device is increased so that its assembling is complicated, and the entire discharge lamp operating device is increased in size.
FIG. 1 schematically shows a conventional magnetic leakage transformer used in a discharge lamp operating device. The conventional magnetic leakage transformer has, as shown in FIG. 2, a core unit 14 in which a pair of cores 10, 12 each having E-shaped plane are combined in a state that extending ends of three legs 10a, 10b, 10c and 12a, 12b, 12c are opposed. A pair of central legs 10a, 102a of a pair of the cores 10, 12 of the core unit 14 are covered with a primary winding spool 16a and a secondary winding spool 18a, and a primary winding 16b and a secondary winding 18b, both of which are consisted of an insulated wire, are respectively wound on the primary and secondary winding spools 16a and 18a. The primary winding spool 16a and the primary winding 16b constitute a primary winding unit 16, and the secondary winding spool 18a and the secondary winding 18b constitute a secondary winding unit 18. The primary and secondary winding spools 16a and 18a respectively have supporting bases 16c and 18c extending along the lower surfaces of a pair of the corresponding cores 10 and 12, and the above-described conventional magnetic leakage transformer is mounted at a predetermined position on a circuit board of a discharge lamp operating device through the bases 16c and 18c.
In the above-mentioned conventional magnetic leakage transformer, a pair of side legs 10b and 10c of the three legs 10a, 10b, 10c of one core 10 have the same length, and a pair of side legs of the three legs 12a, 12b, 12c of the other core 12 also have the same length. The central legs 10a and 12a are shorter than the pair of side legs 10b, 10c or 12b, 12c disposed at both sides thereof. As shown in FIG. 1, a pair of the side legs 10b, 10c and 12b, 12c of a pair of the cores 10, 12 are abutted at their extending ends against each other in a state that the pair of cores 10, 12 are associated with each other as described above, and a magnetic leakage gap "G" is created between the extending ends of the central legs 10a and 12a.
When a current is supplied to the primary winding 16b of the conventional magnetic leakage transformer constructed as described above, a magnetic flux directed from the central leg 10a of one core 10 corresponding to the primary winding 16b to the central leg 12a of the other core 12 corresponding to the secondary winding 18b is generated in the core unit 14, and this magnetic flux is passed through a magnetic passage returned to the central leg 10a of the one core 10 through the pair of side legs 12b, 12c of the other core 12 and the pair of side legs 10b, 10c of the one core 10. A current having a predetermined relationship to the current supplied to the primary winding 16b is generated in the secondary winding 18b by the magnetic flux. A magnetic resistance generated in the magnetic leakage gap "G" between the central legs 10a and 12a of the pair of cores 10 and 12 constitutes a leakage inductance for limiting a discharge current while the discharge lamp connected to the secondary winding 18b is operated.
The transmission efficiency of magnetic energy to be transmitted from the primary winding 16b to the secondary winding 18b in the above-described conventional magnetic leakage transformer is determined by the interlinkaging number of exciting magnetic fluxes generated by the primary winding 16b to the secondary winding 18b. Thus, the lesser the magnetic resistance in the magnetic circuit is and the higher the permeability of the core unit 14 is, the higher the transmission efficiency of the magnetic energy becomes and hence the reduction in size of the transformer can be promoted.
However, in the above-mentioned conventional magnetic leakage transformer, the magnetic leakage gap "G" increases the magnetic resistance. The magnetic leakage gap "G" is necessarily indispensable to prevent magnetic saturation of the above-described conventional magnetic leakage transformer in an inverter operation, but the size of the gap "G" required therefor is smaller than that of the gap "G" necessary to obtain the leakage inductance.
In order to obtain a desired discharge starting voltage for starting the operation of the discharge lamp by compensating a large decrease in the transmission efficiency of magnetic energy generated by the large gap "G" necessary to obtain a leakage inductance, in the above described conventional magnetic leakage transformer the numbers of turns of the primary and secondary windings 16b and 18b are larger than those in the above described conventional magnetic leakage transformer. Accordingly, the primary and secondary winding units 16 and 18 are large in size, and hence the entire magnetic leakage transformer is large in size and weight.
In order to obtain a desired discharge lamp starting voltage by the above-mentioned conventional magnetic leakage transformer having large magnetic resistance, the value of the exciting current to be supplied to the primary winding 16b must be increased as compared with that of the nonmagnetic leakage transformer.