Fan delay control circuit

A fan delay control circuit includes a fan connector connected to a fan of an electronic device, a power supplying module connected to the fan connector, and a rotational speed controlling module connected to the power supplying module. The power supplying module is connected to a fan power source and a stand-by power source. The power supplying module may continue to supply power to the fan when the electronic device including the fan is powered off. The rotational speed controlling module includes a square wave generation circuit which generates a square wave signal to control a rotational speed of the fan even when the electronic device is powered off.

BACKGROUND

1. Technical Field

The exemplary disclosure generally relates to fan control circuits, particularly to fan delay control circuits.

2. Description of Related Art

A typical cooling fan for an electronic device, such as a computer, stops rotating when the electronic device powers off, but remaining heat from the computer dissipates very slowly. Temperature in the electronic device does not go down quickly when the ambient temperature is high.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION

Referring toFIG. 1, an exemplary embodiment of a fan delay control circuit is used to control a fan200of a computer. The fan delay control circuit100includes a fan connector10, a power supplying module20, a power controlling module30, a rotational speed controlling module40, and a rotational speed detecting module50.

The fan connector10is connected to the fan200. The fan connector10includes a power terminal P1, a controlling terminal P2, a detecting terminal P3, and a ground terminal P4. The ground terminal P4is connected to ground.

The power supplying module20includes a first terminal51, a second terminal S2, a third terminal S3, and a fourth terminal S4. The first terminal51is electrically connected to a fan power source V-c1supplied by a motherboard of the computer. The second terminal S2is electrically connected to a first stand-by power source V-s1of the motherboard of the computer. The third terminal S3is electrically connected to the power terminal P1of the fan connector10. The fourth terminal S4is electrically connected to the power controlling module30.

In one embodiment, the voltage of the fan power source V-c1is +12 volts (V). The voltage of the first stand-by power source V-s1is +5V. When the computer is powered on, the power supplying module20supplies the fan power source V-c1to drive the fan200. When the computer is powered off, the fan power source V-c1is shut down. The voltage of the first stand-by power source V-s1is lower than +12V (the working voltage of the fan200), and the power supplying module20increases the first stand-by power source V-s1to +12V to continue driving the fan200.

The power controlling module30detects temperature inside a housing enclosure of the computer, and converts the temperature into a voltage signal. The power controlling module30compares the value of the voltage signal and the value of a predetermined voltage, and controls the power supplying module20to supply power to the fan connector10when the temperature inside the housing enclosure (i.e., internal temperature) is above a predetermined temperature corresponding to the predetermined voltage. The power controlling module30controls the power supplying module20to stop supplying power to the fan connector10only when the temperature in the housing is below the predetermined temperature corresponding to the predetermined voltage.

The rotational speed controlling module40is connected to the controlling terminal P2of the fan connector10, to control the rotational speed of the fan200.

The rotational speed detecting module50is connected to the detecting terminal P3of the fan connector10, to detect the rotational speed of the fan200.

Referring toFIG. 2, the rotational speed controlling module40includes a square wave generation circuit41, a first buffer U1, a second buffer U2, and an electronic switch43. When the computer is powered off, the square wave generation circuit41generates a square wave signal and transmits the square wave signal to the fan200via the first buffer U1and the fan connector10to control the rotational speed of the fan200. When the computer is powered on, the second buffer U2receives a pulse-width modulated (PWM) signal from the computer and transmits the PWM signal to the fan200via the fan connector10to control the rotational speed of the fan200. The electronic switch43is used to enable the first buffer U1to work even when the computer is powered off, and disable the first buffer U1when the computer is powered on. The first and second buffers U1and U2can be voltage buffers.

In the exemplary embodiment, the square wave generation circuit41includes a comparator U3, a pull-high resistor R1, a first resistor R2, a capacitor C1, a feedback resistor R3, a first voltage dividing resistor R4and a second voltage dividing resistor R5. The comparator U3is an LM393 comparator in one exemplary embodiment. The comparator U3includes a first non-inverting input terminal IN1+, a first inverting input terminal IN1−, a first output terminal OUT1, a second non-inverting input terminal IN2+, a second inverting input terminal IN2−, a second output terminal OUT2, a power terminal VCC, and a ground terminal GND.

The pull-high resistor R1is electrically connected between a second stand-by power source V-s2and the second output terminal OUT2. A node between the pull-high resistor R1and the second output terminal OUT2is labeled “A”. The first resistor R2is electrically connected to the second inverting input terminal IN2− and to the node A. The capacitor C1is electrically connected to ground and to a node between the first resistor R2and the second output terminal OUT2. The feedback resistor R3is electrically connected to the node A and the second non-inverting input terminal IN2+. A node between the feedback resistor R3and the second non-inverting input terminal IN2+ is labeled “B”. The first voltage dividing resistor R4is electrically connected between the power terminal VCC and the node B. The second voltage dividing resistor R5is electrically connected between the node B and ground. The power terminal VCC is further electrically connected to the second stand-by power V-s2. In the exemplary embodiment, the voltage of second stand-by power source V-s2is +3.3V supplied by the motherboard of the computer.

When the square wave generation circuit41is working, if the voltage of the second non-inverting input terminal IN2+ of the comparator U3is higher than the voltage of the second inverting input terminal IN2−, the second output terminal OUT2outputs a high level voltage, such as +5V; if the voltage of the second non-inverting input terminal IN2+ of the comparator U3is lower than the voltage of the second inverting input terminal IN2−, the second output terminal OUT2outputs a low level voltage, such as 0V. The first resistor R2, the capacitor C1and the second output terminal OUT2cooperatively form a charging and discharging circuit. The second inverting input terminal IN2− outputs a variable voltage caused by the charging and discharging circuit charging or discharging the capacitor C1. The voltage of the second inverting input terminal IN2− is alternately higher and lower than the voltage of the second non-inverting input terminal IN2+, and thus the second output terminal OUT2generates and outputs a variable voltage which alternates between a high level voltage and a low level voltage, such as +5V and 0V, and this is the square wave signal which is fed to the fan200.

The feedback resistor R3, the first voltage dividing resistor R4and the second voltage dividing resistor R5cooperatively form a voltage dividing circuit which is used to set a threshold voltage of the second non-inverting input terminal IN2+ of the comparator U3. The feedback resistor R3introduces a feedback to make the second non-inverting input terminal IN2+ have different threshold voltages corresponding to the high-level or low-level voltages output by the second output terminal OUT2. The second output terminal OUT2outputs square wave signals with different duty cycles by setting different resistances of the first resistor R2, the feedback resistor R3, the first voltage dividing resistor R4and the second voltage dividing resistor R5and the capacitance of the capacitor C1, to apply different rotational speeds to the fan200.

The first buffer U1includes a power terminal pin11, an input terminal pin12, a ground terminal pin13and a output terminal pin14. The electronic switch43is a p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET). The power terminal pin11is electrically connected to a drain of the PMOSFET, the input terminal pin12is electrically connected to the node A, the ground terminal pin13is grounded, and the output terminal pin14is electrically connected to the controlling terminal P2of the fan connector10. A gate of the PMOSFET is electrically connected to the fan power source V-c1, a source of the PMOSFET is electrically connected to the second stand-by power source V-s2.

The second buffer U2includes a power terminal pin21, an input terminal pin22, a ground terminal pin23and a output terminal pin24. The power terminal pin21is electrically connected to a system power source V-c2, the input terminal pin22is used to receive a PWM signal, the ground terminal pin23is grounded and the output terminal pin24is electrically connected to the controlling terminal P2of the fan connector10. The system power source V-c2is supplied by the motherboard of the computer and the voltage of the system power source V-c2is +3.3V. The PWM signal is supplied by an I/O controlling chip of the motherboard which adjusts the duty cycle of the PWM signal fed to the fan200according to the temperature of the housing.

When the computer is powered on, the voltage of the drain of the PMOSFET is +12V from the fan power source V-c1, the voltage of the source of the PMOSFET is +3.3V supplied by the second stand-by power source V-s2, the electric switch43, (the PMOSFET), is turned off to deactivate the first buffer U1. The system power source V-c2, the PWM signal and the second buffer U2control the rotational speed of the fan200. When the computer is turned off, the voltage of the drain of the PMOSFET is 0V, the voltage of the source of the PMOSFET is +3.3V supplied by the system power source V-s2, the electric switch43, i.e. the PMOSFET is turned on and drives the first buffer U1. The square wave signal output from the square wave generation circuit41controls the rotational speed of the fan200.

The fan delay control circuit100uses the square wave generation circuit41to generate a square wave signal to control the rotational speed of the fan200when the computer is powered off, allowing the fan200to continue rotating at an appropriate speed even when the computer is powered off.