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Speed control circuit for electric motor

  • US 4,394,606 A
  • Filed: 11/21/1980
  • Issued: 07/19/1983
  • Est. Priority Date: 11/21/1979
  • Status: Expired due to Term
First Claim
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1. An apparatus for cleaning textile floor coverings, said apparatus including a roller shaped brush, an electric motor for rotating said roller shaped brush, and a suction device for evacuating dirt and dust particles from said floor covering, said motor connected to an alternating current supply and having a load current passing therethrough and an adjustable rotational speed, a circuit arranged in the load circuit of the motor to control the rpm of the motor as a function of its load current, comprising:

  • (a) a measuring resistance connected in said load circuit for producing a measuring signal proportional to said load current;

    (b) a thyristor having an anode and a cathode and being connected in at least one branch of said load circuit;

    (c) a control circuit connected to actuate said thyristor, said control circuit comprising a series circuit arranged in parallel to the anode and cathode of said thyristor, said series circuit including a coupling resistor and a switching transistor having an emitter and a collector, said coupling resistor being connected to the collector of said switching transistor;

    (d) said thyristor having a control electrode connected through a diode to the collector of said switching transistor, said switching transistor having a base electrode connected through a resistance to a parallel circuit comprising a capacitor and a variable resistor, and a diode connecting said measuring signal from said measuring resistance to said resistance in series with said switching transistor base electrode.

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