On Thursday, October 9, 2014 9:23:34 AM UTC-4, Frank Pittelli wrote: > > Agreed. I would never drive an inductive load directly with an > opto-isolator. Fortunately, there are plenty of cheap FETs with > built-in protection now that can be used. >
I disagree. I always use an opto-isolator between a microprocessor that reads RC servo signals and an inductive load. The opto-isolator protects the microprocessor from nasty inductive spikes. 1) small inductive loads (<150 mA steady-state current) Drive the LED side of the opto-isolator with the microprocessor. The Darlington side can safely drive a small inductive load directly. 2) medium inductive load (<2 A steady-state current) Drive the LED side of the opto-isolator with the microprocessor. Use the Darlington side to drive a BJT or MOSFET for the load. 3) large inductive loads (<40 A steady-state current) Drive the LED side of a solid-state relay (SSR = big ass opto-isolator) with the microprocessor. The SSR output is a very large MOSFET with heat sinks that can drive the load. Driving an FET directly from the microprocessor does not protect it from large inductive spikes because there must be a common connection between the microprocessor GND, the FET source pin and low-side power for the load. Joe -- -- You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups "R/C Tank Combat" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
