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I am looking for a transistor that drives an actuator, and the actuator requires 2A and 2.5 kHz PWM. I am using Arduino to generate the PWM to gate the transistor and then the transistor controls the actuator.

I have looked in Mouser to find the transistor. I can easily set the voltage and current to the values that I need (12V, 2A). However, I would like to know how can I set the value of switching frequency of the transistor. Moreover, I wonder which type of transistors are preferred in this situation, BJT or MOSFET?

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  • \$\begingroup\$ So, when the transistor turns on and conducts 2 amps, what is the maximum voltage lost across the transistor that can be tolerated. That answer will likely force you to consider mosfets. \$\endgroup\$ – Andy aka Feb 28 '17 at 22:07
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    \$\begingroup\$ "how can I set the value of switching frequency of the transistor" that's set by the arduino, you just need to find a transistor capable of work at such 'high speed' (i.e. just about everything apart from the first Germanium transistor built in 1948). \$\endgroup\$ – JIm Dearden Feb 28 '17 at 22:29
  • \$\begingroup\$ Switches are designed between defined inputs and applied loads which you have failed to spec . This includes resistance and reactance and any back EMF. \$\endgroup\$ – Sunnyskyguy EE75 Mar 1 '17 at 0:39
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which type of transistors are preferred in this situation, BJT or MOSFET?

MOSFETs are usually preferred because they are driven by voltage and have low on-resistance. Just make sure the FET can be fully turned on by the voltage from the Arduino. Choose 'logic level' FETs, or those which are specified for a Gate drive of 4.5V or less.

Bipolar transistors are current amplifiers. To stay 'saturated' (fully turned on) you need to feed ~1/20th of the Collector current into the Base. The Ardiuno's PWM output can only deliver 20mA reliably, so a typical small power transistor may only be able to switch ~400mA (even if rated for 2A or higher).

I can easily set the voltage and current to the values that I need (12V, 2A)

Transistor voltage and current ratings are the maximum that the device can withstand under controlled conditions (no overshoot, large heatsink with good cooling etc.). For reliable operation you should increase the voltage rating by at least 50%.

For the current rating you should calculate the power dissipation and temperature rise from current draw and on-resistance, or just select RDSON using the rule-of-thumb that it should drop less than 0.1V at the desired current (in your case 0.1V / 2A = 0.05Ω).

You will also need a 'flyback' diode across the actuator, to recirculate current caused by the inductive kick that occurs each time it is switched off. Schottky diodes are usually used because they switch fast and have low voltage drop. The diode should be rated for at least half the peak load current. Without this diode the actuator will produce very high voltage in an attempt to keep the current going, which will quickly destroy the FET.

how can I set the value of switching frequency of the transistor.

Your PWM frequency is quite low, so just about any transistor that meets the other requirements should work.

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