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Auxiliary battery charge control circuit

  • US 5,668,463 A
  • Filed: 07/22/1994
  • Issued: 09/16/1997
  • Est. Priority Date: 07/22/1994
  • Status: Expired due to Fees
First Claim
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1. A circuit for controlling charge upon an auxiliary battery comprising:

  • an auxiliary battery, a main battery and an ac-to-dc converter connected in parallel with each other and in parallel to a load device;

    a main battery charge control circuit connected between said main battery and said ac-to-dc converter for providing a current from said ac-to-dc converter to said main battery;

    an auxiliary battery charge control circuit connected between said auxiliary battery and said main battery for providing current from said main battery to said auxiliary battery and for modulating connectivity therebetween, said auxiliary battery charge control circuit comprises;

    a pair of voltage dividers coupled between a ground potential and said main battery;

    a pair of comparators, each comparator having an output connected to the other comparator output and a pair of inputs connected to a reference voltage and a respective one of said pair of voltage dividers, and wherein at least one of said pair of comparators comprises a power node coupled through a low pass filter to said main battery;

    a switch transistor having a switch transistor base and a switch transistor conductive path, said switch transistor base is connected to said mutually coupled comparator outputs and said switch transistor conductive path is modulated by said switch transistor base and is connected between a current limiting resistor and said ground potential; and

    a battery connect transistor having a battery connect transistor base and a battery connect conductive path, said battery connect transistor base is connected through said current limiting resistor to said switch transistor conductive path, and wherein said battery connect conductive path is connected between said auxiliary battery and said main battery, whereby changes in conductivity of said switch transistor conductive path correspondingly cause changes in connectivity between said auxiliary battery and said main battery.

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