0
\$\begingroup\$

I'm trying to design a P-channel MOSFET switch with LED indicator. When the motor will turn on at same time a led indicate the the MOSFET switch is turned on. I could not find such a circuit. Can you verify this circuit is a good design, or can you recommend how a LED indicator should be? Optocoupler is LTV-817. MOSFET is FDT434P.

Note that I want to separate the LED from the Arduino. I don't want to use an Arduino PIN for indicator purpose. enter image description here

\$\endgroup\$
1
  • \$\begingroup\$ What purpose do R5 have? \$\endgroup\$
    – MiNiMe
    Nov 9, 2023 at 13:27

1 Answer 1

0
\$\begingroup\$

The schematic needs to be revised.

  • The maximum source-gate voltage for the selected MOSFET is 8V. When you turn the MOSFET on using the optocoupler the source-gate voltage will be around 12V so the MOSFET may break down. So R2-R3 divider should be revised in order to bring the maximum source-gate voltage to somewhere less than 8V. A Zener might be used but if the input voltage is constant (e.g. 12V ± 10%) then may not be needed.
  • I couldn't understand the purpose of R5 which is in parallel with LED-R4 block. Can be removed.
  • The connection of indicator looks correct – it'll light up when the motor's top-side terminal sees 12V through PMOS' on-resistance. One thing I noticed is that, although I don't know what LED you're going to use, the current therefore intensity/visibility could be low with 10k limiter resistor (R4). For example, for a red LED the forward drop is about 2V, this makes the LED current 1 mA. This may or may not be enough depending on the LED itself. This will get even lower with other LEDs such as green or blue/white. So you may need to play with R4 but without exceeding the LED's and limiter resistor's limits.
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.