Pulse-width modulation speed controllable DC brushless cooling fan
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United States of America Patent
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Mar 24, 1992
Grant Date -
N/A
app pub date -
May 3, 1991
filing date -
May 3, 1991
priority date (Note) -
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Abstract
A cooling fan for use inside a circuit system, especially a pulse-width modulation speed controllable DC cooling fan which can automatically vary its speed according to the internal temperature of the circuit system. An object of the invention is to control the rotation speed of the fan by a pulse-width modulation fan speed control circuit composed of a plurality of resistors, capacitors, diodes, Zener diodes, ICs and a thermistor, which is installed inside a circuit system in combination with a DC brushless fan. The control circuit in turn outputs control signal pulse following a monostable IC of said circuit continuously triggered by a phase changing cycle timing pulse signal transmitted of the fan motor. The pulse width of the control signal pulse is determined by a resistor element within a set of monostable pulse width timing resistor-capacitor (RC). The resistor element is a thermistor which is characterized in that it can vary the resistance depending on the temperature resulting in the variation of the output pulse width as the temperature changing to control the OFF time of the phase changing cycle of the fan motor for the purpose of controlling the rotation speed of the fan.
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