Filter circuit and power supply unit

• US 7,209,024 B2
• Filed: 03/16/2006
• Issued: 04/24/2007
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: TDK Corporation
• Original Assignee: TDK Corporation
• Inventors: Nakahori, Wataru
• Primary Examiner(s): Nguyen; Tuyen T.
• Application Number:
  US11/376,145
• Publication Number:
  US 20060221655A1
• Time in Patent Office: 404 Days
• Field of Search: 336/65, 336/83, 336/170, 336/212, 336213-215, 336/220, 336221-222, 323/355, 323/356, 323/361, 333181-183, 363/39, 363 44- 48
• US Class Current: 336/170
• CPC Class Codes: H02M 1/14 Arrangements for reducing ripples from dc input or output

Abstract

The present invention provides a filter circuit realizing reduction in the number of magnetic cores on a circuit board and a space occupied by the magnetic cores, and a power supply unit using the filter circuit. A filter circuit includes a first filter part and a second filter part which are connected in series. The first filter part includes a center leg coil and a capacitor, and the second filter part includes an outer leg coil and a capacitor. The center leg coil is wound around a center leg of a magnetic core including the center leg, a first outer leg part configuring a loop magnetic path in common with the center leg, and a second outer leg part configuring another loop magnetic path in common with the center leg. The first and second outer leg parts share the center leg. The outer leg coil is wound around the outer leg parts in a manner such that magnetic fluxes generated in the outer leg parts by current flowing in the outer leg coil cancel each other in the center leg.

Claims

1. A filter circuit comprising a first filter part and a second filter part which are connected in series each other, the first filter part including a first inductor and a first capacitor, the second filter part including a second inductor and a second capacitor,

wherein the first inductor includes a center leg coil wound around a center leg of a magnetic core including the center leg and a plurality of outer legs, each of the outer legs configuring a loop magnetic path in common with the center leg while sharing the center leg,

the second inductor includes an outer leg coil wound around the outer leg of the magnetic core,

the outer leg coil includes a first outer leg coil part and a second outer leg coil part which are connected in series each other, the first outer leg coil part being wound around the outer leg configuring one of the loop magnetic paths, the second outer leg coil part being wound around the outer leg configuring the other loop magnetic path,

the winding directions of the first and second outer leg coil parts are the same in polarity direction, the number of turns of the first outer leg coil part and that of the second outer leg coil part are equal to each other, and

the outer leg coil is wound around the outer legs in a manner such that magnetic fluxes generated in the plurality of outer legs by current flowing in the outer leg coil cancel each other in the center leg part.

2. A power supply unit comprising:

a transformer configured to transform an input AC voltage and to output the resultant as an output AC voltage;

a rectifying circuit operable to rectify the output AC voltage; and

a smoothing circuit operable to smooth an output of the rectifying circuit,

wherein the smoothing circuit is configured by using the filter circuit according to claim 1.