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Bus to Bus Short Circuit Protection in an N+1 Power System

IP.com Disclosure Number: IPCOM000014448D
Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-19

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Randhir Malik


Problem In all N+1 or redundant power systems the over-voltage (OV) is sensed before the OR-ing diode. This is done to prevent shutdown of the whole power system in case of an over-voltage on any one of the outputs of any power supply in parallel. For example, if +5V Bus goes OV due to a fault in power supply 1, the other power supplies in parallel will not shutdown because their individual OV sense point is on the anode side of the OR-ing diode. The good power supplies never see the OV fault because OR-ing diode is reverse biased for an OV fault condition on the Bus. Now if one of the Bus voltage e.g.+12V shorts +5V bus or +3.3V bus, the power system will not shutdown because the OR-ing diodes on +5V and +3.3V are reverse biased by the OR-ing diodes and therefore the OV condition is not detected by the individual power supplies. It could mean damage to expensive hardware such as memory, processors and other chip sets in a computer or communication system! Problem solved