Maybe this could help you if the PC fan has a controller embeded on the hub. Increasing input voltage will light it up as the fan starts spinning.Īfter while of looking at schematic i figured, should i use the 2M7000 at all? I made this schematic: Its Vgs Treshold voltage is from 0.8V to 3V, so with a voltage divider R7 and R8 i should have that 0.8V when the input voltage is 4V and while it will be not enough to trigger mosfet the light will be off. In first circuit the 2N7000 mosfet is triggering LED. Because of that I was thinking to make a voltage divider. The 4V is approximately the minimal voltage at which fan starts running. I want to have a LED light signalising if the fan is turned off or its currently running. And lastly there is separate fan fuse and a flyback diode across the fan. I think that the TO220 case + radiator should be fine? Also i added capacitors on in and out of regulator as per datasheed, tho im wondering if i shouldn't move the C2 capacitor "outside" (right now i have 5x C2 capacitor, each of separate fan and im thinking if i shouldnt make just one capacitor for all of them). In this case power dissipated on voltage regulator is from 0.15W to 0.35W. I dont have yet fans im gonna use, but initial tests on other 12V case fan have shown that minimal voltage at which they start moving on their own is 4V and current draw is at 40mA and at max 12V its 110mA. A fixed resistor of 110Ω and potentiometer of 1kΩ should give me full range of regulation from min 1.25V to the max of about 11V (12V - Dropout voltage). The voltage regulator is LM1117 (same as LM317T but its LDO).
On schematic there is only one but it will be cloned 5 times, for each fan controlled. Next the 12V is going to fan speed control section. There i have RC circuit to create a softstart (12kΩ and 47μF should give about 4 seconds before full 12V is reached) in case all 5 fans are set to max speed when the power is triggered.
First there is MOLEX connector with 12V on it, then main fuse (its 4A because ill have 5x fan each max 500mA + some space for other stuff) and next main switch.
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