Controlling circuit for fan
View Patent ↗A controlling circuit for a fan includes three comparators, a capacitor, and a thermistor. When the temperature around the thermistor changes, the resistance of the thermistor changes. The comparators control the charging and discharging time of the capacitor, thereby generating a corresponding pulse width modulation signal to the fan according to the temperature, to adjust the speed of the fan.
1. A controlling circuit for a fan, comprising:
first to third comparators each comprising an inverting input terminal, a non-inverting input terminal, an output terminal, a power terminal coupled to a first power source, and a ground terminal connected to ground; and
a thermistor;
wherein the inverting input terminal of the first comparator is coupled to a second power source, the output terminal of the first comparator is connected to the non-inverting input terminal of the first comparator through a first resistor, and is also coupled to the inverting input terminal of the second comparator through a second resistor and the thermistor in that order; the non-inverting input terminal of the second comparator is coupled to the second power source, and the output terminal of the second comparator is connected to the inverting input terminal of the second comparator through a first capacitor, the output terminal of the second comparator is coupled to the non-inverting input terminal of the first comparator through a third resistor, the output terminal of the second comparator is coupled to the output terminal of the third comparator through fourth and fifth resistors in that order; the inverting input terminal of the third comparator is coupled to a third power source, the non-inverting input terminal of the third comparator is coupled to a node between the fourth and fifth resistors, the output terminal of the third comparator is coupled to the fan.
2. The controlling circuit of claim 1 , wherein the non-inverting input terminal of the second comparator is connected to ground through a second capacitor.
3. The controlling circuit of claim 2 , wherein the non-inverting input terminal of the second comparator is further connected to ground through a third capacitor.
4. The controlling circuit of claim 3 , further comprising an amplifier, wherein an inverting input terminal of the amplifier is coupled to a fourth power source through a sixth resistor, a non-inverting input terminal of the amplifier is coupled to a fifth power source, a power terminal of the amplifier is coupled to the first power source, a ground terminal of the amplifier is connected to ground, and an output terminal of the amplifier is coupled to the inverting input terminal of the amplifier through a seventh resistor, the output terminal of the amplifier is coupled to the inverting input terminal of the third comparator, to output the third power source.