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Relay switching apparatus

  • US 4,296,449 A
  • Filed: 08/27/1979
  • Issued: 10/20/1981
  • Est. Priority Date: 08/27/1979
  • Status: Expired due to Term
First Claim
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1. A switching circuit for selectively coupling a load to an A.C. power source, said switching circuit comprising:

  • (a) a master relay including a master relay contact and a master relay coil;

    (b) a pilot relay including a pilot relay and a pilot relay coil, said master and pilot relay contacts being coupled in series with each other and being coupled between said load and said power source to cause said power source to be coupled to said load whenever both said master and pilot relay contacts are closed; and

    to cause said power source to be completely disconnected from said load whenever at least said pilot relay contact is open;

    said pilot relay contact being devoid of any additional conductive element thereacross;

    (c) a single commutating diode coupled in parallel only with said master relay contact; and

    (d) timing and control circuit means for performing a switching operation in which;

    (1) said master relay contact is opened during a first half-cycle of the A.C. waveform of said power source during which said single commutating diode is forward-biased;

    (2) the state of said pilot relay contact is changed during a second half-cycle of said A.C. waveform, said second half-cycle being that half-cycle of said A.C. waveform immediately following said first half-cycle, and during which said single commutating diode is reverse-biased.(3) said master relay contact is closed during a third half-cycle of said A.C. waveform, said third half-cycle being that half-cycle of said A.C. waveform immediately following said second half-cycle.

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