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PWM for variable pump airflow + EMI question

I am working on an application using an air pump where I need to change the rate of inflation. What I was doing in the past was decreasing the inflation rate by lowering the the voltage to the pump. With this approach I am operating the pump out of spec and sometimes the voltage is too low for a higher load and the pump stops!

I was thinking of changing the duty cycle so that I could account for variable flow rates. My microcontroller is connected to a MOSFET that toggles the power to my 3.3V powered pump. Are there any potential "gotchas" with this this setup?

From a EMI/RFI prospective should I be putting any type of filtering on the line that is going from the microcontroller to the gate of the MOSFET? What about some in-line resistance for ringing? Any caps on the line?

Do pumps in general have any issues being used this way?

Thanks in advance for your thoughts!

-Brad

Reply to
Brad
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You will be definitely generating some noise. Try putting an am radio on the same circuit as the pump, on the line side, not the pump side of course, and tune to a weak station. Turn on the new pump controller and set it for some midpoint pump value and see how bad the radio noise gets.

Capacitors from each side of the power line to a good ground should reduce the noise somewhat. Ferrite beads clamped around the three leads bunched together would also help. You could also buy a premade filter, there are many manufacturers out there.

First I would try to get the circuit to control the pump the way you want it to, then worry about the nose it creates.

Reply to
hrhofmann

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