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Battery protection circuit employing active regulation of charge and discharge devices

  • US 6,313,610 B1
  • Filed: 08/21/2000
  • Issued: 11/06/2001
  • Est. Priority Date: 08/20/1999
  • Status: Expired due to Term
First Claim
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1. A battery protection circuit, comprising:

  • a pair of back-to-back connected metal-oxide-semiconductor field-effect transistors (MOSFETs) M1 and M2;

    a first gate voltage regulating circuit operative in response to a first enable signal EN1 to control the gate voltage VG1 of M1 such that (i) when EN1 is de-asserted, VG1 is sufficient to enable M1 to strongly conduct current in either direction, (ii) when EN1 is asserted, VG1 is a function of the polarity of drain-to-source voltage VDS1 of M1 so as to prevent M1 from conducting when VDS1 has a charging polarity and to allow M1 to conduct when VDS1 has a discharging polarity, the conducting of M1 preventing VDS1 from achieving a value sufficient to forward bias a parasitic diode associated with the source and drain terminals of M1;

    a second gate voltage regulating circuit operative in response to a second enable signal EN2 to control the gate voltage VG2 of M2 such that (i) when EN2 is de-asserted, VG2 is sufficient to enable M2 to strongly conduct current in either direction, (ii) when EN2 is asserted, VG2 is a function of the polarity of the drain-to-source voltage VDS2 of M2 so as to prevent M2 from conducting when VDS2 has a discharging polarity and to allow M2 to conduct when VDS2 has a charging polarity, the conducting of M2 preventing VDS2 from achieving a value sufficient to forward bias a parasitic diode associated with the source and drain terminals of M2; and

    detection circuitry operative to detect the charge condition of a battery connected to the protection circuit and to generate the signals EN1 and EN2 such that;

    (i) in a normal charge condition, both EN1 and EN2 are de-asserted, (ii) in an overcharged condition, EN1 is asserted and EN2 is de-asserted, and (iii) in an over-discharged condition, EN1 is de-asserted and EN2 asserted.

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