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DC motor speed controller having protection

  • US 4,873,453 A
  • Filed: 10/19/1988
  • Issued: 10/10/1989
  • Est. Priority Date: 10/27/1987
  • Status: Expired due to Fees
First Claim
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1. Speed controller for a DC motor connected in series with a switching device that controls the average DC current of the motor by controlling the switching duty cycle, said switching device having an input control terminal, comprising:

  • oscillator means for generating an AC signal having controllable duty cycle;

    means for communicating said AC signal to said input control terminal of said switching device;

    undervoltage protection means for producing an under voltage signal upon occurrence of a low-battery condition below a predetermined threshold voltage level;

    override circuit means communicating said undervoltage signal to said input control terminal of said switching device, for turning off said switching device irrespective of the AC signal of said oscillator means upon an undervoltage condition;

    and wherein said undervoltage protection means comprises one operational amplifier circuit having;

    means for establishing a first battery voltage threshold corresponding to said predetermined threshold voltage level and a second battery voltage threshold which is higher than said first threshold;

    means for providing said undervoltage signal when battery voltage is below said first threshold and withholding said undervoltage signal when battery voltage exceeds said second threshold; and

    ,means for providing or withholding said undervoltage signal when the batter voltage is between said first and second thresholds, depending upon whether the battery voltage entered between said thresholds when said undervoltage signal was already being provided on already being withheld, respectively;

    whereby said operational amplifier circuit performs both (a) a threshold comparator function and (b) a hysteresis function.

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