DC/DC converter with uC interface

[aix]

Driven by curiosity, I took apart a cheap Chinese 7530 blower fan that I'd managed to kill earlier.

Quality of construction aside, the PCB does have provisions for a third pin, though that part of the PCB is unpopulated.  The pin is labelled "O/P" and — if populated — would have been derived from FG/RD signals, all of which makes me think it's a sense output rather than a PWM input.

[ogden]

I am a hobbyist working on a microcontroller project in which I’d like to control the speed of a 12V BLDC fan by varying its supply voltage (no PWM).

I’d like to power everything from a single 5V USB supply

There is no point to make 5V->12V boost converter for 12V fan when you can just use 5V fan.  There are gazillions of various 5V fans available.

[Simon]

True, I meant to say that and forgot to mention it.

[Simon]

Driven by curiosity, I took apart a cheap Chinese 7530 blower fan that I'd managed to kill earlier.

Quality of construction aside, the PCB does have provisions for a third pin, though that part of the PCB is unpopulated.  The pin is labelled "O/P" and — if populated — would have been derived from FG/RD signals, all of which makes me think it's a sense output rather than a PWM input.

i tried looking for the datasheet for the controller. It's very vague and does not even explain the chip. I am not sure what they mean by single phase motor.

[aix]

There is no point to make 5V->12V boost converter for 12V fan when you can just use 5V fan.  There are gazillions of various 5V fans available.

The fan form factor (7530 blower, I posted a drawing earlier) is a hard constraint for my project.  While 5V versions do exist, they seem to be much less readily available.  Additionally, I'd like compatibility with a pre-existing controller whose replacement I am designing.  That controller requires a 12V fan.

P.S. This is also an opportunity for me to learn some new skills, which is an end in itself.

[aix]

i tried looking for the datasheet for the controller. It's very vague and does not even explain the chip. I am not sure what they mean by single phase motor.

Yeah, that datasheet is a bit of an enigma.  I found several versions branded by different manufacturers but they're all equally mysterious (basically copies of each other).

[Simon]

Yes they are all identical copies.

[aix]

In any event, I won't necessarily be expecting the next fan I use to have the same circuitry (even if it's identical on the outside).

[Simon]

Ah, well this is your problem. They are rated for 12V one may go down to 3V, another may not.

[aix]

Ah, well this is your problem. They are rated for 12V one may go down to 3V, another may not.

That I am happy to live with.  It's not a commercial product; I will be the only user and won't mind recalibrating the voltage limits in software when I get a new fan.