Originally Posted by ericgibbs

hi,
I dont know what type of signals you are coupling thru the opto, but be aware adding a 100nF from the base to 0v will significantly reduce the rise and fall times of the signals.!!

EDIT: As you are using a FET to drive the relays, the heat dissipation in the FET's will be increased, also the switching point/times will be delayed.
IMHO it dosnt require a 100nF on the base of the opto, just dont touch the base.

Hi ,
I could still see the humm even with the 100nF . Anyways I removed the Capacitor .

-D

Originally Posted by ericgibbs

hi dark,
If you dont feel easy with the performance of the opto, post the circuit fragment that shows the opto driver and signal, also the FET and relay part.

I can check it with an LTspice simulation.

Hi,
Its just driving a bigger contactor , not very particular regarding switching speed.

Thanks