whats the difference between a torroid and a ferrite core?

[Clipped]

they both look like donuts...is one chocolate and the other glazed or what?

i know metal content is different, but other than that..........?

thanx

[Ouroboros]

Toroids can be made out of ferrite, or out of dust-iron. (And you can get amorphous-metal strip-wound small toroids as well, but you're unlikely to use one of those).

Ferrite toroids have a very high permeability. (ie, you get a lot a inductance per turn-squared), but they magnetically saturate quickly. Dust-iron toroid cores are effectively made by bonding lots of tiny iron (or certain magnetic alloys) particles together with epoxy. They therefore have millions of tiny air-gaps so they saturate at much higher flux levels, but the permeability is much lower, so you get a lower inductance per turn).

[Clipped]

thanx, i "think" i understand what you just told me...

umm so which is better? i guess that would depend on the application?

[Ouroboros]

Better? as you say, it depends on the application.

For the choke in a step-down 'buck' regulator (in a 12V to 5V switching regulator for example), then a dust-iron core is commonly used. This is because there is an effective dc current flowing in the inductor, so it would magnetically saturate if a ferrite toroid was used.

For a half or full-bridge SMPSU transformer, you can use a ferrite toroid or an un-gapped ferrite core, as there is no dc component to the current.

For the output inductor in a Class-D amp, things are a bit more complicated. There is a considerable low-frequency (audio) component in the current as well as the high-frequency switching current, so you can't use a ferrite toroid. You could use a dust-iron toroid but the internal core losses would likely be too high. (The losses are due to magnetic hysterersis and eddy currents in the particles of the core). You therefore see gapped ferrite 'E' cores or even open-bobbin ferrites used in Class-D amps.

There are some gapped ferrite toroids available (a single slot sawn through with a diamond blade) which should be ideal for Class-D output filter chokes but I've not tried them.