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Motor speed control circuit

  • US 4,605,883 A
  • Filed: 02/05/1982
  • Issued: 08/12/1986
  • Est. Priority Date: 02/05/1982
  • Status: Expired due to Term
First Claim
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1. A motor speed control circuit for use in controlling the speed of an electric motor of a household electrical appliance comprising;

  • tachometer means located in proximity with a plurality of blades of a fan in driven connection with an electric motor and producing a tachometer signal when said electric motor rotates said fan blades past said tachometer means, clipping means connected to said tachometer means to produce a clipped tachometer signal having a preselected maximum amplitude, comparator means connected to said clipping means, and producing a rectangular wave signal in response to said clipped tachometer signal received from said clipping means, differentiating means connected to said comparator and receiving said rectangular wave signal therefrom and producing a differentiated pulse signal in response thereto, integrator means connected to said differentiating means and receiving said differentiated pulse signal from said differentiating means and producing a speed signal having an amplitude indicative of a speed of rotation of said electric motor, means for comparing said speed signal to a reference signal and producing an error signal indicative of a difference between said reference signal and said speed signal, isolation means receiving said error signal and producing an isolation error signal in response thereto, timing means receiving said isolation means error signal and producing a signal having a selected amplitude after a period of time proportional to a magnitude of said error signal, and a triac connected to said timing means to receive said selected amplitude signal therefrom and to change state in response thereto to control a flow of electric current received from an external power source through said electric motor of said household electric appliance.

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