Quote Originally Posted by Dave View Post
No. It is better to place the diode in the same polarity but across the relay to shunt the back emf when the relay is disabled by the opto. If you notice you are just paralleling the internal diode on the opto.
Hi Dave, thanks for your answer! Yes, I already have a diode across the relay, I forgot to draw it on the diagram.

I am just not sure if the interval diode in the opto can resist a punch from the fly-back voltage/current from the relay or it will give way and render the opto useless after a few switching cycles. I am not experienced but hold basic knowledge about this and could not really find anything in the data sheet to give me some confidence towards removing the parallel diode from the opto.