MC41 PWM out HS+LS flyback diode wiring question

techsupport@posi-plus com 7 years ago in Master modules / MC4x updated by Gustav Widén (System support) 7 years ago 2

I have a MC41 setup where I need to use a bidirectionnal CAM output in PWM mode to drive a bidirectional valve (2 coils). There is a mention to not use a flyback diode in closed loop control but is it ok to add diodes on coils if the outputs are used in PWM mode, not in current output? I tried it and it seems to work just fine.

I want to add diodes as there will be an emergency operation switch installed to directly power the coils. We want the diodes to prevent high voltage spikes to the MC41 module and the switches.

Found on the forum:

With IQAN-MC3 and IQAN-MC43, -MC42 and -MC41, the internal clamping diode is not disconnected when COUT pins are used as open control PWM.

Does that mean that we do not need to add diodes?


That is correct, for these HS+LS combined outputs where the internal diodes are not disconnected, there is no need to add diodes externally to protect the power drivers. 

But as long as you are not using the output as COUT, it will be ok to have an additional diode. The external diode messes with the current measurement, but that is no problem as the PWM HS+LS does not use that current measurement circuit. 

Perhaps a clarification might be good here, as the purpose described in the post was to connect external switches to the coils, one must not forget the series diode that prevents reverse feed of the high-side driver when the external switch is driving the coil.