Quote Originally Posted by john swift View Post
Hi Voicecoil

The diagram in post 40 shows the signal path through the circuit after the HCPL-2631 opto isolators

the only diode is within the NTR5198NL-D FET

hence my comment in post 30

“Its a pity they had not used a DIL (dual in line ) octal transistor array like the ULN2803
or a new FET array
like the Toshiba TB D62381A series DMOS transistor array
that would enable the user to plug in a replacement “

the Gecko G540 has the same issue with a FET that's soldered in

John
Well in that case the manual really should show a clamp diode in parallel with the relay coil IMHO. The intrinsic body diode in the FET will be sod-all use for a coil that's connected between the output and +24 as it'll shoot a long way positive when the FET switches off and over-voltage it in the process. The great thing about drivers like the ULN2803 you mentioned is that they have the clamp diodes built into the chip which makes it a lot less likely that they'll blow. I'll be adding some diodes to all my relay outputs tomorrow.