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Full-charge indicator for battery chargers

  • US 4,394,613 A
  • Filed: 01/19/1981
  • Issued: 07/19/1983
  • Est. Priority Date: 01/19/1981
  • Status: Expired due to Fees
First Claim
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1. A circuit for use in a battery charger to indicate when the battery to be charged reaches a full charge state and for protecting said battery from being overcharged, comprisinga control means in the charging current path for providing less than a preselected voltage drop thereacross when the charging current is less than a known level, which is indicative of a full-charge battery state,a transistor connected with its base-emitter junction across said control means, said transistor being switchable to a nonconducting state only when the voltage across said control means is less than said preselected voltage,an indicator connected between the collector and emitter of said transistor, whereby, when said transistor is in a nonconducting state, said indicator is energized,unidirectional conducting means in series with said battery through which charging current is supplied,a voltage dividing network comprising at least first and second series resistors connected between a conductor along which current is conducted into said battery and a source of reference potential for said battery,switching means for reducing the effective resistance of one of said voltage dividing resistors when the voltage drop across said control means is less than said preselected voltage to reduce the charging voltage applied to said battery, said switching means comprising a photocoupler and a photocoupler transistor, the former being connected in series with said indicator between the emitter and collector of said transistor, and the later being connected across one of said voltage dividing resistors.

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