Level shifting 3.3V to 5V for PWM output to servo

Question

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:

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

Many thanks,

Duarte

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 https://electronics.stackexchange.com/questions/118390/drive-a-4-8v-servo-signal-line-using-3-3v — ocrdu, Jan 12 '21 at 11:50
Does this answer your question? Drive a 4.8V servo signal line using 3.3V — ocrdu, Jan 13 '21 at 00:49

score 2 · Answer 1 · answered Jan 12 '21 at 11:58

2

To answer your specific questions for this task:

MOSFET - Pros: None Cons: High gate capacitance could lead to low switching speeds.
Optocoupler - Pros: Electrical isolation Cons: Multiple components
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

answered Jan 12 '21 at 11:58

Stefan Wyss

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Multiple components for an optocoupler? What other than the opto IC? – Reinderien Jan 20 '21 at 04:20
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I was thinking about LED drive resistor & output open-collector pull-up resistor. – Stefan Wyss Jan 20 '21 at 05:56

Level shifting 3.3V to 5V for PWM output to servo

1 Answers1