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Power supply system

  • US 4,425,512 A
  • Filed: 04/09/1982
  • Issued: 01/10/1984
  • Est. Priority Date: 04/10/1981
  • Status: Expired due to Term
First Claim
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1. A power supply apparatus comprising:

  • a power supply circuit of a terminal device;

    a polarity-reversing switch for a d.c. power source of a center equipment, connected to said terminal device through a two-wire line including a hook switch and a terminating power supply rectifier;

    a current detector for detecting a current supplied through said polarity-reversing switch;

    an AND gate for performing a logical operation on an output from said current detector, a terminating signal and an originating signal;

    a timer for delaying an output from said AND gate a predetermined time; and

    an exclusive OR gate for performing a logical operation on an output from said timer and said terminating signal to generate an output for switching said d.c. power source polarity-reversing switch.

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