LC filter for noisy power: diode needed?

[PeteAU]

Hi,

I want to add a little LC filter to a noisy power supply (car!) and am wondering if I need a flyback diode?
Is D2 necessary or superfluous?

[uncle_bob]

Hi,

I want to add a little LC filter to a noisy power supply (car!) and am wondering if I need a flyback diode?
Is D2 necessary or superfluous?

Hi

Simply for noise, both diodes are technically "superfluous". They are there to take care of fairly normal spike events. I would include both of them, but a lot depends on exactly what the problem is. I also would put a fuse in front of the diodes that is rated at much less than the diode's current rating.

Bob

[danadak]

Its dependent on load and value of L. Basically when you disconnect
an active load the catch diode will prevent high V transients. So for the
pennies a diode costs I would add it. Also consider a zener on output
to catch load disconnect transients.

Regards, Dana.

[PeteAU]

Yep, that's what I figured. But, should I put the diode in parallel with the inductor instead of going down to GND?

[uncle_bob]

Yep, that's what I figured. But, should I put the diode in parallel with the inductor instead of going down to GND?

Hi

They are fine as shown.

Bob