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Green Wire Ground Current Attenuation Circuit

IP.com Disclosure Number: IPCOM000044253D
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Carroll, LB: AUTHOR

Abstract

This attenuation circuit substantially eliminates green wire ground (GWG) current (IGWG) resulting from the line-to-frame ground capacitors C1-C2 of an electromagnetic interference filter (EMI). Such EMIs are often used with the switching regulator (SW REG) of a computer system or the like. In general, the circuit technique involves reproducing the voltage waveform at a preselected one of the EMI input terminals 1A or 3A with respect to the frame ground (FRAME GND), feeding it to the input winding of a transformer (TX) and applying the resultant voltage at the TX's output winding between the EMI node 2 and FRAME GND. As a result, the line or utility voltage across either of the capacitors C1 and C2 is approximately zero and hence the IGWG is also substantially zero.

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Green Wire Ground Current Attenuation Circuit

This attenuation circuit substantially eliminates green wire ground (GWG) current (IGWG) resulting from the line-to-frame ground capacitors C1-C2 of an electromagnetic interference filter (EMI). Such EMIs are often used with the switching regulator (SW REG) of a computer system or the like. In general, the circuit technique involves reproducing the voltage waveform at a preselected one of the EMI input terminals 1A or 3A with respect to the frame ground (FRAME GND), feeding it to the input winding of a transformer (TX) and applying the resultant voltage at the TX's output winding between the EMI node 2 and FRAME GND. As a result, the line or utility voltage across either of the capacitors C1 and C2 is approximately zero and hence the IGWG is also substantially zero. Because the return side of the input winding of TX cannot be directly connected to FRAME GND as it would contribute to the current IGWG, a virtual ground connection (VIRTUAL GND), for example, C4-C6. is provided at the return side of the input winding. It can be shown that for the illustrated dot polarity of TX, it is immaterial to the operation of the circuit whether switch S2 is closed on terminal 1A, as shown, or alternatively on terminal 3A. The circuit technique is applicable to single and/or multiple phase utility input systems, such as the schematically shown three-phase input system. For example, when a three-phase wye input system having its center or neutral terminal grounded to EARTH GND is used, the attenuation circuit consists of components C3-C6/TX with switch S1 in its closed position. As such, the AC voltage input waveforms appear at terminal 1A (for the shown closed position of S2) with respect to F...