Home made fan controller?
For manual control, a very cheap way to regulate fans without PWM wires would be to use a linear regulator with low dropout voltage.
Here's just some of those regulators that would fit the bill : https://www.digikey.com/short/3wdr1b
You feed them with 12v and they can output anything between the internal reference voltage (the most common being 1.25v) and the input voltage, minus 0.1-0.5v ... so you could have for example a range between 5v and 11.8v (and the fan will naturally vary its speed accordingly). Some industrial fans may not start at 5v, only at something like 7v, but once they start they could be lowered down to 5v.
For example see this one: https://www.digikey.com/product-detail/en/stmicroelectronics/LDFPT-TR/497-14663-1-ND/4844090
Pins 1 and 2 go to +12v, pin 3 (broken one in the PPAK package) or the TAB go to ground, pin 4 is the output voltage and pin 5 is the adjust pin ... the reference voltage is 0.8v and you can adjust output voltage with the resistor ... formula is Vout = 0.8 x ( 1 + R1/R2) .. so you'd use a 100ohm resistor for R2 and a 470 ohm resistor in series with a 1kohm potentiometer where you see R1 and that will give you a minimum of 0.8 x (1 + 470/100) = 4.6v and a maximum of 0.8 x (1+1470/100) = 12.5v
Another method of controlling a fan without pwm wire would be to use a npn transistor in the state between fully off and fully on to limit the amount of current going through it.
So for example, a npn transistor with a hFe value of 100 would allow 100mA to go between collector and emitter if there's 1mA of current on the base pin .. so if you want to adjust the current between 100mA and 500mA on the fan, you'd adjust the base current on the transistor between 1mA and 5mA ... you can do it with a potentiometer
Then of course you can use a led driver IC to control the current going through the fan .. it's easy. You set the led driver IC to allow maximum 500mA as the fan is rated for, and then you can adjust the maximum current with the pwm control pin of the led driver, or by sending it i2c commands. It's overkill for the job, but it would work.
Here's some suggestions : https://www.digikey.com/short/3wdfz8
For example, looking at AL8861 :
You power it with 12v (and that's the maximum voltage the fan will see), you pick an inductor and a Rs resistor according to the datasheet (around 47-68uH for max 500mA according to the pretty graphs in datasheet and default output current is set with formula 0.1 / Rs so for a default of 500mA so for example you'd use a 0.2 ohm resistor, or 2 x 0.1 ohm resistors in series), a generic diode like 1n4007 (or any 1n4001, 1n4002 all the way up to 4007 the only difference between them is the maximum voltage they can handle, all support at least 50v which is above 12v the fan uses) and you place the fan where the leds are shown in schematic.. 12v wire on top, ground wire where it's connected to L1
With Vset you can adjust the amount of current using your microcontroller (it likes up to 3.3v but will work with up to 5v):
Quote
Multi-Function On/Off and Brightness Control Pin:
* Leave floating for normal operation
* Drive to voltage below 0.2V to turn off output current
* Drive with DC voltage (0.3V < VSET < 2.5V) to adjust output current from 0 to 100% of IOUTNOM. Linear adjustment range from 5% to 100% of IOUTNOM
* Drive with PWM signal from open-collector or open-drain transistor, to adjust output current.
Linear adjustment range from 1% to 100% of IOUTNOM for f < 500Hz
* Connect a capacitor from this pin to Ground to increase soft-start time. (Default soft-start time = 0.1ms. Additional soft-start time is approximately 1.5ms/1nF)
Other led driver ICs work pretty much the same.
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now