Flyback Diode

With relay outputs, I might go 4007. The forward conduction doesn't matter much, so the 1000V rating would be better than to 600 volts for 4004.
For PLCs with transistor or MOSFET outputs, there is a diode junction across the output. It's forward conduction will likely be about .7 volts or lower. This is the nominal voltage for a silicon junction.
If the forward conduction voltage is higher with the diode on the coil, it might not conduct at all, because the PLC output will conduct instead. This causes the collapsing voltage to dissipate in the coil as well as the leads running from the PLC to coil.
In most cases, this probably isn't an issue, but can generate noise that would be hard to troubleshoot.
 

Similar Topics

Hi all, I have a couple of solenoids I'm using on a very low temperature application, and the documentation notes that they don't have any...
Replies
31
Views
7,018
Link 1:http://www.drillspot.com/products/152298/Square_D_8501RSD34V53_General_Purpose_Relay...
Replies
1
Views
2,696
I have a SC9-LS24-3 surge protection solenoid cable from automation direct...
Replies
9
Views
1,302
Maybe someone can elaborate, I’ve done some quick googling and haven’t found a good answer. While troubleshooting a 24VDC contactor, I attempted...
Replies
6
Views
3,204
I have an application where one ControlLogix needs to read data from another ControlLogix. The second PLC is part of a validated pharma process...
Replies
9
Views
2,894
Back
Top Bottom