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I am going to scale PWM 24V generated by PLC to PWM +5V by means of optocoupler TLP521 and MOSFET BSP295 in order to control a micro servo motor (MG90S). What I have tried till now is the below circuit:

enter image description here

I have two questions please:
1. Will it work as I expect?
2. Are there any better circuits to tackle my problem (Converting PWM 24V to 5V)?

Edit: (based on comments)
1. Required frequency is 50 Hz.
2. Due to current limitation I am not able to use opto transistor directly.
3. The two sides are going to be isolated.

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    \$\begingroup\$ Why don't you simply just use two resistors? \$\endgroup\$
    – Andy aka
    Jul 30, 2019 at 13:50
  • \$\begingroup\$ Note that when you use the CircuitLab button on the editor toolbar an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don't need a CircuitLab account, no screengrabs, no image uploads, no background grid. \$\endgroup\$
    – Transistor
    Jul 30, 2019 at 13:50
  • \$\begingroup\$ @Transistor I tried to save it but it was unsuccessful and I decided to upload its image. \$\endgroup\$
    – Pana
    Jul 30, 2019 at 13:53
  • \$\begingroup\$ @Andyaka, the two sides are going to be isolated. Sorry if schematic does not illuminate it. \$\endgroup\$
    – Pana
    Jul 30, 2019 at 14:00
  • \$\begingroup\$ You need to use the "Save and Insert" button. I think it has been a bit flakey today. I had trouble trying to save a schematic. \$\endgroup\$
    – Transistor
    Jul 30, 2019 at 14:01

2 Answers 2

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You can simplify the circuit by using a Broadcom ACPL-021L logic-output optoisolator.

The input resistor must be increased, something like 7.5K would work. Just wire the output side to +5/GND and the servo input and add a bypass capacitor.

enter image description here

That particular part is non-inverting, like your circuit (input high = output high). If you can use inverting, then there are other more common options in logic-output optoisolators.

The input signal at the servo input should be a positive 3-5V pulse of width 1.0 to 2.0 milliseconds (1.5ms representing a position at about half travel), repeated at some tens of Hz frame rate (non-critical).

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A circuit that makes everything could be something like ISO 121x

Connecting SENSE PIN to the PWM 24V signal through the Rt resistor (used to set the threshold of the input level)

IN PIN connected to SENSE through a Rsense resistor to set the maximum current limit.

FGND the ground of 24V

VCC1 5V

GND1 Ground of 5V

OUT 5V PWM isolated

the output current limit forces the use of a buffer like MIC4126/27/28

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