Fan control circuit

1. A control circuit set in a server, the control circuit controls a fan to cool an integrated baseboard management controller (iBMC) in the server, the control circuit comprising:

a state determination module connected to the iBMC and a power supply unit (PSU) of the server, for determining states of the iBMC and the PSU;

wherein when the server is powered off and the iBMC is operating, the state determination module receives a low level signal from the PSU and a low level signal from the iBMC, the state determination module connects the PSU and the fan, such that the fan is operating;

when the server and the iBMC are powered off, the state determination module receives a low level signal from the PSU and a high level signal from the iBMC, the state determination module disconnects the PSU from the fan, such that the fan is powered off; and

when the server is operating, the state determination module receives a high level signal from the PSU, the state determination module disconnects the PSU from the fan, such that the fan is powered off.

2. The control circuit of claim 1 , wherein the state determination module includes an OR gate, an inverter, and a first electronic switch, two input terminals of the OR gate are respectively connected to the iBMC and the PSU, for respectively receiving state signals from the iBMC and the PSU, an output terminal of the OR gate is connected to an input terminal of the inverter, an output terminal of the inverter is connected to a control terminal of the first electronic switch, a first terminal of the first electronic switch is connected to the PSU, a second terminal of the first electronic switch is connected to a power pin of the fan.

3. The control circuit of claim 2 , wherein the first electronic switch is a field effect transistor (MOSFET), a gate of the MOSFET is the control terminal of the first electronic switch, a source of the MOSFET is the first terminal of the first electronic switch, and a drain of the MOSFET is the second terminal of the first electronic switch.

4. The control circuit of claim 1 , further comprising:

a temperature measurement module connected to the iBMC and the state determination module, wherein when the server is powered off, and the iBMC is operating, the state determination module receives the low level signal from the PSU and the low level signal from the iBMC, the state determination module further connects the fan and the temperature measurement module, the temperature measurement module measures a temperature of the iBMC, the iBMC outputs corresponding pulse-width modulation (PWM) signals according to the temperature; and

a speed adjustment module connected to the iBMC and the fan, for adjusting the fan according to the PWM signals from the iBMC.

5. The control circuit of claim 4 , wherein the temperature measurement module comprises at least one temperature sensor, a data pin of the temperature sensor is connected to a data pin of the iBMC through a first resistor, a clock pin of the temperature sensor is connected to a clock pin of the iBMC through a second resistor, a power pin of the temperature sensor is connected to the state determination module, an alert pin of the temperature sensor is connected to the state determination module through a third resistor, first to third input/output pins of the temperature sensor are connected to the state determination module through fourth to sixth resistors respectively, a ground pin of the temperature sensor is grounded.

6. The control circuit of claim 4 , wherein the speed adjustment module comprises:

a second electronic switch comprising a control terminal connected to a pulse-width modulation pin of the iBMC, a first terminal grounded, and a second terminal connected to the state determination module through a seventh resistor; and

a third electronic switch comprising a control terminal connected to the second terminal of the second electronic switch, a first terminal grounded, and a second terminal connected to the state determination module through an eighth resistor, and connected to a control pin of the fan.

7. The control circuit of claim 6 , wherein the second electronic switch is a bipolar junction transistor (BJT), a base of the BJT is the control terminal of the second electronic switch, a collector of the BJT is the second terminal of the second electronic switch, and an emitter of the BJT is the first terminal of the second electronic switch.

8. The control circuit of claim 6 , wherein the third electronic switch is a bipolar junction transistor (BJT), a base of the BJT is the control terminal of the third electronic switch, a collector of the BJT is the second terminal of the third electronic switch, and an emitter of the BJT is the first terminal of the third electronic switch.