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Preventing Core Saturation in Parallel Power Transformers in a Switching Converter

IP.com Disclosure Number: IPCOM000043490D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-04

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Spreen, JH [+details]


If a switched mode power supply contains two power transformers with the primary windings connected in parallel, then a circulating current will be established, as shown, for example, in the dual switch primary circuit of Fig. 1. Such a circulating current may be large enough to cause saturation of a transformer core. The circulating current is caused by an unintentional difference between voltages applied to the primary inductances Lp1 and Lp2 . Both primary windings are connected to a common source, vB, during Ton, the time interval when both transistors Q1 and Q2 are simultaneously conducting. Similarly, both windings fly back to a common reset voltage (-vB) when Q1 and Q2 turn off and reset diodes DR1 and DR2 conduct.