I am pulsing a flyback primary with a IRF510 FET. I am trying to figure out what I need to suppress inductive kick and soak up the voltage spikes.

I was going to put an RC snubber (.o1uF and 100K) across the Source and Drain of the FET and put a diode across the primary?

Do I need both of these??? Should I just put the RC snubber across the primary?

 

If you post a schematic here, we can give you precise advice about a solution.

hgmjr

 

You can read up on "Contact protection":
http://www.leachintl2.com/english/english2/vol6/properties/00049.html

 

Usually a simple power diode will work, similar to this...

 

Here's a brief schematic of what I was thinking I needed.

Is this right?

 

The diode is properly placed. Is there some reason you have not placed the coil in the drain circuit instead of the source circuit?

hgmjr

 

In most cases when powering a small motor or relay a signal diode such as the 1N4148 will be plentiful. If you work it out, due to the relatively high resistance of most relay coils and small motors, you will find the diode operates well within its limits. More powerful motors will need much more powerful diodes.

 

Hi electronice123,

It won't "flyback" if you clamp it with a diode. A snubber circuit would also limit the voltage output of the secondary... unless that is your intent. You need to use a driver with a high drain-to-source breakdown voltage, say 500V. The IRFP450 should be okay for Vdds, and ensure current rating is just what you need and no more.

The primary needs to be on the drain side also, because a source follower won't work for this application.

Regards,
Ifixit

 

Ok. Thanks everyone for the input....I guess I need to do some more reading to understand the difference between driving at the source vs the drain.

Is there any way I can calculate the snubber circuit to know how much I could limit the secondary voltage?

 

You could use a zener diode, it will clip the secondary voltage to spec.