Esp32 controls a 12v coil relay through PC817 and 2N7000

[paoloros97]

Hello

I need to control a 12v relay with an Arduino nano ESP32.
Can somebody check if the circuit I designed is good?

Components list:
MOSFET: 2N7000
Optocoupler: PC817
Diode: 1N4007
Relay: 40.31.7.012.0000 (coil needs 42mA @ 12V)

Please find attached the picture with the circuit I made. (Updated 13/7/24)

[selcuk]

I guess D2 LED direction is wrong.

[Benta]

I guess D2 LED direction is wrong.

Agreed.

And don't use a 1N4007, but a 24...33 V Zener across Q1 instead.

[paoloros97]

Thank you!

I did a mistake to place the LED in Kicad.

I uploaded a new schematics.

About the:

And don't use a 1N4007, but a 24...33 V Zener across Q1 instead.

may I ask you why?

thx

[kripton2035]

can someone explain to me the need for the pc817 ?

[paoloros97]

It's not really needed but good to have, IMO.

[Benta]

Thank you!

I did a mistake to place the LED in Kicad.

I uploaded a new schematics.

About the:

And don't use a 1N4007, but a 24...33 V Zener across Q1 instead.

may I ask you why?

thx

To protect the relay contacts. Using a normal diode like in your circuit slows down the release time of the relay immensely, potentially causing contact burn.
Allowing the coil a higher voltage when turning off, the contacts will open much faster.

[Doctorandus_P]

When beginning with electronics, it's good to build circuits like this on breadboards.

Gate voltage of the 2n7000 can also be as high as 3V, which is getting uncomfortably close to the 3V3 of most microcontrollers. it works with this circuit (with 12V gate drive) but it's dubious when the gate gets connected directly to the uC. The 2n7002 is more common, and has a maximum threshold voltage of 2V5.