fan circuits

[stj]

so i have a bit of kit with 5v fans that have a tacho output.
and you cant get them cheaply.

so i got some 12v fans.
but the tacho output is 12v.
datasheet says max output is 4ma

how to not damage the circuit.
i was thinking putting the tacho through a 3k3 resistor and then puting a 5v1 zener between the ground and tacho pins on the board connector.

any other idea's?

[momaka]

Re: fan circuits

If you run the fan on 5V, I think the tachometer output wire should also have, at the most, 5V on it.

Now if you are running the fan on 12V and want it to output a signal of max. 5V on tacho, then yeah, you would need something to clamp down the signal. The 5v1 zener might work. A simple resistive divider might also work too if the 12V rail doesn't go too high.

I'm not all too familiar with the signal on the tachometer wire (whether the signal is pulsed or continuous), but the above two methods should work IMO.

[budm]

Re: fan circuits

Can we see the spec of the fan?

[stj]

Re: fan circuits

no you cant, they are cheap chinese crap.

but the fan tacho is pretty standard so if you look at a datasheet from delta for example, you will get the idea.
the output is from the magnetic sensor usually that is used to syncronize the motor poles.


i'm including the datasheet of the original failed fans.

the replacements will be running at 12v, they are needed for a reason and i need the airflow.
infact the tacho is for a safety circuit that kills the power to the chip if the fan stalls!