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Combined EMI and Smoothing Filter for TSR AC/DC Stage

IP.com Disclosure Number: IPCOM000052207D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Palmucci, CJ: AUTHOR [+3]

Abstract

This combination common mode and differential filter acts as both an electromagnetic interference (EMI) filter and as a rectifier output DC filter for a "DC Bulk" stage at the input of a transistor switching regulator (TSR).

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Combined EMI and Smoothing Filter for TSR AC/DC Stage

This combination common mode and differential filter acts as both an electromagnetic interference (EMI) filter and as a rectifier output DC filter for a "DC Bulk" stage at the input of a transistor switching regulator (TSR).

Imperfect coupling of the windings 10, 12 in the opposite sides of the circuit of a common mode, common core filter 14 is utilized to produce some differential mode filtering effect. This inductor arrangement is flanked by a pair of capacitors 16, 18, thereby forming a pi filter 16, 14, 18. Additionally, a pair of capacitors 20, 22, providing a center tap to ground, is placed across the line downstream of the pi filter. This center tap connection provides a return path to ground for high frequency common mode noise currents from the TSR switching stage (not shown).

By the placement of the EMI pi filter downstream of the line rectifier 22, capacitors 16, 18 of that filter can be electrolytic, and can replace the capacitor that would be required anyway for "DC Bulk" smoothing. The large capacity available in the electrolytic capacitors 16, 18 provides large attenuation in the noise frequency of interest.

The EMl filter keeps noise originating in the TSR switching stage from intrusion onto the AC line. Moreover, since imperfect coupling is desired between the windings 10 and 12 of inductor 14, the spacing between those windings can be increased over that which would be normally found in a com...