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Safety Circuit for Line Frequency Leakage Current

IP.com Disclosure Number: IPCOM000042783D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Kapur, KN: AUTHOR

Abstract

An inductor and the equivalent input capacitance of a filtered input switching regulator (SR) are configured as a parallel resonant circuit to mitigate line frequency leakage current in the ground return. In SRs using a single- or multiple-phase input house supply, it is customary to provide a half-section type LC filter in each phase input to attenuate any RFI noise, which is generated by the SR, and thus prevent its propagation into the house supply, as required by FCC and/or other regulatory bodies. For example, in the illustrated single-phase application, RFI half-section filter L1C1 is connected between the single-phase 60-cycle house supply 1 and SR 2. C1 is connected to the return wire GWG (green wire ground) which is also grounded to the machine frame 3.

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Safety Circuit for Line Frequency Leakage Current

An inductor and the equivalent input capacitance of a filtered input switching regulator (SR) are configured as a parallel resonant circuit to mitigate line frequency leakage current in the ground return. In SRs using a single- or multiple-phase input house supply, it is customary to provide a half-section type LC filter in each phase input to attenuate any RFI noise, which is generated by the SR, and thus prevent its propagation into the house supply, as required by FCC and/or other regulatory bodies. For example, in the illustrated single-phase application, RFI half-section filter L1C1 is connected between the single-phase 60-cycle house supply 1 and SR 2. C1 is connected to the return wire GWG (green wire ground) which is also grounded to the machine frame 3. As long as GWG remains in tact, the RFI noise from SR 2 is safely filtered by L1C1 from supply 1. If GWG should become open as at A, for example, the line frequency current and/or its harmonics also passing through C1 presents a safety hazard to anyone contacting the grounded machine frame. To overcome this potential hazard, an inductor L2 is connected in parallel with C1 and forms a parallel resonant circuit with the equivalent input capacitance represented by the combination of the RFI half-section filter capacitor C1, the DC filter capacitor C2 via rectifier D1, the effective snubber capacitance C3 and the effective transformer shield capacitance C4 ass...