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Assuming that one just want to control a single power transistor or MOSFET with a microcontroller and that one is using an intermediary transistor(s) between the microcontroller and the power MOSFET to get the full range of allowed voltages to the gate. What are the issues of just using the analog output of a microcontroller to control a power transistor or MOSFET instead of using digital pins and PWM?

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    \$\begingroup\$ Which Arduino? On many Arduinos, the "analog" output is in fact merely a PWM signal whose duty cycle is set by the "analog" value written to it. \$\endgroup\$ – JRE Jul 18 at 16:04
  • \$\begingroup\$ Well I am talking of any microcontroller in general, but what you are saying is very important one has to 'take a look inside' the specific microcontroller is using to see how the DAC is implemented. \$\endgroup\$ – Sirius Fuenmayor Jul 18 at 16:22
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    \$\begingroup\$ By 'what are the issues', are you looking at the problems in designing the electrical interface or problems in operation, such as the heat dissipation in the transistors? I hope you don't reply 'all of them' because that's far too generic. Please set a specific area of interest for your question. \$\endgroup\$ – TonyM Jul 18 at 17:01
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There's no problem at all with what you're suggesting. Some DACs have buffered outputs, some don't. Some are rail-rail, some aren't. As long as you design for the DAC's actual output voltage capability and provide buffering as needed all will work fine.

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The problems are related to MOSFET gate trigger voltage, gate parasitic capacitance, and microcontroller output voltage level and current driving capability.

For switching "digital" mosfet direct connection will be fine, for driving IRF840 for example it won't do very well.

For driving power MOSFETS in high frequency PWM applications i strongly recommend using dedicated gate driver IC like MIC4428 or one of many similar ICs

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