What happened to toroid power transformers?

They have poorer line-to-output AC isolation the conventional types with separated split windings. They usually have lower leakage inductance, which is bad for direct bridge-rectifier storage-capacitor setups as it leads to higher peak currents. Plus, they don't welcome adding a grounded primary-secondary inter-winding shield. But hey, what the hell, I like their low ac magnetic fields spreading into sensitive electronics.

In one of our products, we use a primary-side resistor-triac as both a surge limiter and a crude bang-bang regulator, to reduce the stress on downstream stuff as line voltage changes.

John

This was for an nmr gradient amp, in a rack with lots of stuff that doesn't like 60 Hz fields. We finally talked them into letting us use switchers - it took about 10 years - and they work great.

John

Diagram, please (c:

We use toroids almost exclusively for medical. A shield layer is no problem at all. I also use them here in the office and in the lab for

Joerg wrote in news:uryKh.8079$ snipped-for-privacy@newssvr12.news.prodigy.net:

While following this thread, I saw a couple of people mention R-cores. Would they not be better?

I'd once seen one and thought it was some eccentric variant on a toroid that someone made so they could mount it where their design once called for a chassis mounted E/I type, or had some other odd space restriction. I was so wrong. :)

From what I saw via Google once I'd seen the name 'R-core', I see that easy fitting of split bobbins directly round the straight long sections allows either a commercial firm OR a hobbyist to not only build their windings quickly and easily, but to modify them, as an assembled bobbin can rotate freely if wanted. Electrical isolation between windings can be better than in a toroidal type, which could be important for use in a medical device. The efficiency is good, and the flux well-contained, and they'd probably run as quietly as toroidals. Waste heat can escape from them more efficiently that either E/I types or toroidals. I'm surprised they aren't much more widespread than toroidals.

They used to be quite popular in TV sets. I believe I still have a few cores. Nowadays often just called U-U cores. For those who haven't seen them yet:

One challenge with these is proper clamping. You can't inspect how snug the core halves are joining because it is inside the packets.

BTW your follow-up settings aren't right, was missing three NGs. That would have broken the thread for those folks.