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Fan speed control circuit

  • US 5,457,766 A
  • Filed: 05/24/1993
  • Issued: 10/10/1995
  • Est. Priority Date: 05/23/1992
  • Status: Expired due to Term
First Claim
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1. A fan speed control circuit for an electronic device having a ventilation fan for dissipating excess heat, said circuit comprising:

  • a temperature sensing circuit for detecting a temperature within said electronic device, and for generating a temperature dependent voltage in response to the detected temperature;

    a low pass filter for providing a low pass filtered voltage by low pass filtering said temperature dependent voltage;

    triangular wave generating means for generating a triangular wave signal;

    pulse-width modulating means for generating pulse-width modulated pulses by comparing said triangular wave signal to said low pass filtered voltage; and

    driving means for driving said ventilation fan in response to said pulse-width modulated pulses, said driving means being comprised of;

    voltage dividing resistors for generating a divided pulse signal by performing voltage division on said pulse-width modulated pulses generated by said pulse width modulating means;

    a capacitor connected between a node formed between, the dividing resistors, and a reference voltage; and

    a transistor connected between said ventilation fan and said reference voltage, said transistor being turned on in response to said divided pulse signal.

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