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I am currently trying to control a simple servo motor using PWM generated by a MCU with a 3.3V output voltage.

However, this servo works with 5V, so I need an IC capable of "converting a 3.3V PWM to 5V". My question is: What are the pros/cons of level shifting an ouput between the 3 methods:

  1. using a MOSFET
  2. using an optocoupler
  3. using a simple 4.7k pull-up to 5V with output of the MCU being open drain.

Many thanks,

Duarte

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  • \$\begingroup\$ 1) Do you mean FET as level shifting pass gate? 2) What kind of optocoupler, with what kind of output stage you mean? It would also depend on what kind of input signal the servo expects. Which servo is it? \$\endgroup\$
    – Justme
    Commented Jan 12, 2021 at 11:30
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    \$\begingroup\$ Some hobby servos will work reliably with a 3.3V PWM signal, even when fed with a 5V or higher power supply; I would check first if yours does. Also see electronics.stackexchange.com/questions/118390/… \$\endgroup\$
    – ocrdu
    Commented Jan 12, 2021 at 11:50
  • \$\begingroup\$ Does this answer your question? Drive a 4.8V servo signal line using 3.3V \$\endgroup\$
    – ocrdu
    Commented Jan 13, 2021 at 0:49

1 Answer 1

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To answer your specific questions for this task:

  1. MOSFET - Pros: None Cons: High gate capacitance could lead to low switching speeds.
  2. Optocoupler - Pros: Electrical isolation Cons: Multiple components
  3. 4.7k Pull Up - Pros: Low cost and easy Cons: Only applicable if MCU has 5V tolerant inputs

You could also try option number 4: Use a discrete logic IC for voltage level translation e.g. NC7WZ17 - Pros: Low cost and easy Cons: None

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  • \$\begingroup\$ Multiple components for an optocoupler? What other than the opto IC? \$\endgroup\$
    – Reinderien
    Commented Jan 20, 2021 at 4:20
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    \$\begingroup\$ I was thinking about LED drive resistor & output open-collector pull-up resistor. \$\endgroup\$
    – Stefan Wyss
    Commented Jan 20, 2021 at 5:56

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