Fan speed control circuit
First Claim
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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Accused Products
Abstract
A speed control circuit for a ventilation fan of an electronic device, such as a laser printer, adaptively varies a speed of the ventilation fan depending upon an internal temperature of the device. The speed control circuit has a temperature sensing circuit for generating a voltage depending upon the temperature, a triangular wave generator for generating a triangular wave signal having fixed period, a pulse width modulator for comparing the triangular wave signal with the voltage generated by the temperature sensing circuit and generating pulse-width modulated pulses, and a driving circuit for controlling the speed of the ventilation fan in response to the pulse-width modulated pulses so that the speed of the ventilation fan will be increased in response to an increasing temperature, for example.
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Citations
12 Claims
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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:
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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. - View Dependent Claims (2)
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3. A fan speed control circuit for an electronic device having a ventilation fan for dissipating excess heat, said circuit comprising:
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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, said temperature sensing circuit being disposed in close proximity to a heater for heating a fuser unit in said electronic device in order to exhibit a thermal response to said heating of the fuser unit; 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.
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4. A speed control circuit for a ventilation fan of a printer, said circuit comprising:
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temperature sensing means for generating a detected temperature dependent voltage in response to an internal ambient temperature of said printer, said temperature sensing means comprising a resistor and a thermistor connected in series between a supply voltage and a reference voltage, said thermistor being positioned near a heater, said heater being utilized for heating a fixing device of said printer, said detected temperature dependent voltage being generated at a junction between said resistor and said thermistor; low-pass filter means for generating a low-pass filtered temperature dependent voltage by low pass filtering said detected temperature dependent voltage; triangular wave generator means for generating a triangular wave signal from an oscillator signal; pulse-width modulator means for making a comparison of said triangular wave signal from said triangular wave generator means with said low-pass filtered temperature dependent voltage from said low-pass filter means, and for generating pulse-width modulated pulses corresponding to said comparison; and driving means for controlling a voltage supplied to said ventilation fan in response to said pulse-width modulated pulses. - View Dependent Claims (5)
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6. An apparatus for controlling a ventilation fan in an electronic device, said apparatus comprising:
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a first resistor connected at a first node to a thermistor, said resistor being further connected to a voltage source and said thermistor being further connected to a reference voltage, wherein a temperature dependent voltage is generated at said first node in response to a change in a resistance value of said thermistor in response to ambient heat in said device; a low pass filter connected between said first node and a second node, said low pass filter filtering said temperature dependent voltage and providing a filtered temperature dependent voltage to said second node; a relaxation oscillator generating a square wave signal; an integrator converting said square wave signal into a triangular wave signal; a pulse width modulator having a first input terminal connected into said second node for receiving said filtered temperature dependent voltage and having a second input terminal connected to an output of said integrator for receiving said triangular wave signal, said pulse width modulator generating a pulse width modulation signal by comparing said filtered temperature dependent voltage and said triangular wave signal; and a driver for controlling a speed of the ventilation fan in dependent upon said pulse width modulation signal. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A method for controlling a ventilation fan in an electronic device, said method comprising the steps of:
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generating a temperature dependent voltage in response to a change in a resistance value of a thermistor in response to ambient heat in said device; providing a filtered temperature dependent voltage by filtering said temperature dependent voltage; generating a square wave signal; converting said square wave signal to a triangular wave signal; generating a pulse width modulation signal by comparing said filtered temperature dependent voltage and said triangular wave signal; and controlling a speed of said ventilation fan in dependence upon said pulse width modulation signal.
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Specification