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Driving P-Channel Mosfet

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Simon:
Logic level only makes sense if you have an N channel MOSFET. Are you trying to PWM this motor or jut turn it on or off?

girishv:

--- Quote from: Simon on June 28, 2020, 05:39:48 pm ---Logic level only makes sense if you have an N channel MOSFET. Are you trying to PWM this motor or jut turn it on or off?

--- End quote ---

I am trying to PWM. I have selected the a logic level N-Channel MOSFET based on suggestions received in this thread.

Siwastaja:
Brushed DC motor drive consists of N-channel MOSFET, freewheeling diode, DC link capacitance and current sense for current feedback. (Motor is more like an LED, so primarily current-controlled.)

Minimize the length of the circuit loop that is formed by the DC link capacitance, MOSFET and the freewheeling diode. I.e., these three parts should be close together.

Current sense is most easily implemented as a small-value shunt resistor between the ground and the source leg of the N FET, amplified using a current sense amplifier. Regulate current by adjusting PWM according to the current signal. For example a PI controller is quite easy to tune for such purpose. Current sets the torque directly.

For small motors, utilizing motor resistance to limit maximum current is acceptable, in this case you can skip current sensing and roughly adjust PWM relative to the desired final velocity. Ramping PWM setpoint up/down gradually decreases maximum current and jerking but isn't as good catching edge conditions than actual current regulation.

For the very smallest FETs, say something rated to like 30V and 5A and "logic level", good to control motors up to say 0.5A nominal without current sense,  you can directly drive the gate from a microcontroller pin and skip gate driving and current sensing completely.

With FETs any larger, you likely want a proper gate driver IC just to supply enough gate current. If you need this component anyway for current, just pick one which allows you to use higher gate voltage supply as well, for example, a 10V gate supply even if the IO is 3.3V or 5V.

Simon:
Depending on the size of the motor and MOSFET you may need a driver rather than rely on the pin of an MCU or other low driving capacity output, this will speed the switching up and reduce heat.

girishv:

--- Quote from: Simon on June 29, 2020, 02:01:56 pm ---Depending on the size of the motor and MOSFET you may need a driver rather than rely on the pin of an MCU or other low driving capacity output, this will speed the switching up and reduce heat.

--- End quote ---

At this moment, I am looking a 1A or less. I suppose, I can drive directly from MCU.

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