TVS diode in series with a freewheel diode?

[smanches]

Why would someone put a TVS diode in series with a freewheel diode for switching an inductive load?

The only thing I can think of is to lower he current through it by raising the voltage to the TVS breakdown value. Any other thoughts?

 

[ericgibbs]

Why would someone put a TVS diode in series with a freewheel diode for switching an inductive load?

The only thing I can think of is to lower he current through it by raising the voltage to the TVS breakdown value. Any other thoughts?

hi,
One use in adding TVS or Zener diode in series with an inductive suppression diode is that it reduces the hold time of the inductor.
Normally the current flowing the clamp diode loop, when the current is switched off , it will continue to keep the inductor current flowing.

If the inductor is a relay or solenoid, the release time with just a diode maybe too long. By using a TVS of the correct avalanche voltage it possible to reduce the inductor current duration, while still protecting the driver, say a transistor.

 

[smanches]

That makes sense. I figured it would increase the voltage and drop the current. The lower current won't be enough to engage the solenoid any longer, which will force it off quicker. I'm assuming one of the main reasons is to stop any sort of "bounce" or "chattering" of the solenoid when the current is right on the edge of the turn on threshold.

Thank you!

 

[Mosaic]

Eric is correct, increasing the voltage of the transient clamp will significantly reduce the time for solenoid response/recovery. If u consider the use of solenoids in automotive fuel injection, the on/off cycle is critical and must be minimised otherwise larger injectors are called for. If the drivers of these solenoids can tolerate a 60V transient max. Then perhaps a 40V transient clamp will work well. Clamping down to 12VDC is unnecessary and can extend the 'freewheel' time by several milliseconds.