Need for inductive kickback diode

NO. not necessary - can't hurt, but can't help

Yeah, it is resonant in the MHZ range and very low Q - ignore it.

Waste of time and money, unless you might stick a coil in there.

Relays with snubber diodes across the coils will open more slowly and arc longer - and shorten the relay life in some applications - one of those compromise things again, but only if the relay has to interrupt power on its contacts with some inductance present.

Yes

Mosfets are great devices (they save power and can do what bipolars can't)

Mosfets do require special treatment. A spike on a mosfet may damage it, if the intrinsic diode isn't fast enough. Generally it takes a fast switching diode (reverse biased) between Drain and Source to protect it from a load transient.

You might use a 30 amp mosfet protected by a 15 amp fuse - but the transient caused by the fuse interrupting the 15+ amp short circuit current may still eat the mosfet.

Mosfet gates are very fussy to transients. A long wire run to the gate can have enough inductance to cause the mosfet to go belly-up.

Generally you'd use a resistor in series with the gate (which slows turn-on) to protect it, by dropping the transient across the intrinsic gate capacitance, and may also want diodes to snub transients in extreme cases. And a mosfet once turned on - will stay on if there isn't some discharge path for the gate - only a few pico farads as a rule but still requires a discharge path. (high power mosfets usually have larger gate capacitance but we are still only talking a 100K gate to source (or so depending on transistor, and speed needed - relays are slow in comparison so speed shouldn't be a concern)

I love mosfets. They can really make a lot of otherwise tricky projects go smoothly (like replacing relays with SS devices and no maintenance). But they have some quirks before you can apply them for every application.

Not trying to dissuade you - mosfets are better than bipolars for most things that I do, but they take a little understanding.

No, incandescent is not inductive. It's resistive.

Because those are inductive.

The resistance in the element creates a very low Q, any inductance that may be there isn't going to be much.

The only time you may get inductive fly back is when making and breaking electrical connections. This becomes more prevalent if the control wire is bundled tightly with other control wires that are already passing current. The eddy currents that exist may be caught at the correct time as you're making and breaking. that could generate a transient. if it makes you feel better, go ahead.

As far as i'm concerned, it does not change the answer in your case..

Circuit configuration has a lot to do with what type of protection you require.

You might want to do that. *All* real circuits have at least some inductance from the loop area of the wiring..

No.

Graham

EVERYTING has some inductance.

Graham

What do you think PWM does ? As in many thousandds of times a second typically.

Graham

You really need to learn some basic electronics instead of relying on 'folksy ideas' to get you by.

LOL @ 'eddy currents'.

Graham

Yes, including you obviously

Message stripping again are we?

Yeah, I guess your version of a PWM circuit would be a mechanical timing wheel with a set of points on it.

Stop flaunting and try to impress some one for a change. You're not winning any popularity contests over here. That i'm sure of.

Have a good day sucker.

It is not needed, and would just waste space and increase cost.

Ed

But with an ordinary incandescent bulb, and just ordinary wires, the inductance is negligible.

I'd be more concerned about the thermal response of the filament, and even be inclined to use a parallel capacitor to smooth out the spikes.

Cheers! Rich