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Do I need a Flyback diode?

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One of our customers is complaining that some outputs of his IO-D16A3-TO16 modules are holding stuck ON.

This is a transistor output module, so there is something really wrong.

He is driving 96 solenoids, each one that draws 4W at 24VDC (167mA).

The IO-D16A3 provides 24V to solenoid, which is also connected to ground.

This is a PNP connection, and in this mode the module can handle 500mA per port, 4A total.

Next thing I thought of was back emf from the solenoid when it is shut off.

Question: Does the IO-D16A3 have diode protection?

Is there any specifcation for inductive loads? maximum inductance in mH?

I told him to put a flyback diode in parallel to solenoid.



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A flyback diode on an inductive load in a DC application is always a really good idea.

Is the 167 mA the inrush current or the holding current? Have him measure the actual current going to the solenoid. Also have him remove the wire of one of the units while it is stuck on and then re-connect it to see if it comes back on. Transistor outputs almost always stay shorted when they fail.

Joe T.

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