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Old 14th June 2001, 06:12 AM   #1
dorkus is offline dorkus  United States
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hi,

i know chokes (inductors) have long been used in tube power supplies, where the benefits (good ripple rejection, better regulation and smaller cap size than capacitor-only supplies) outweigh the drawbacks (higher power supply impedance, size and weight of chokes), but recently i've noticed some solid stage gear (the Musical Fidelity stuff in particular) using chokes in the supply to seemingly good effect. so i'm considering trying a choke-regulated supply in a solid-state preamp project i'm working on.

does anybody know any good references on designing choke power supplies? all of the information i've found so far pertains to high-voltage (tube) supplies and i'm trying to figure out how to optimize such a supply for the low-voltage rails i would use (e.g. +/- 24V). basically i'm looking for design tips, rules of thumb, basic formulas - anything to help me find optimum component values (i'm an EE so i can deal with the math). also, are there any good sources for the kinds of chokes i would need? they seem rather hard to find.


thanks,
marc
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Old 14th June 2001, 11:02 AM   #2
Geoff is offline Geoff  United Kingdom
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Section 7 of the Rectifier Applications Handbook (HB214/D), available for download at the ON-Semi site, gives design details for choke input filters. This handbook is long (300+ pages)and takes an age to download, but is one of the most comprehensive publications on power supply design that I have seen.
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Old 14th June 2001, 01:57 PM   #3
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Marc,
And they're quiet, too...
Inductors are out of fashion, due to weight and cost. I've had trouble finding larger current capability units, myself.
One option is to strip an old transformer core and wind your own. Look up the current capability of various wire gauges, derate somewhat due to the fact that the wire will be in a confined space, and start winding. (If you use heavy enough gauge wire, the R of the inductor can be quite low.) Use ordinary shellac to cement layers in place. If you want to isolate layers from one another (lower capacitance), use kraft paper (i.e. grocery bags) to wrap each layer.
Yes, it's a pain in the ***, but since inductor values for power supplies are not as critical in value as they would be in the signal path, you have plenty of latitude as to final H values. The values calculated from the formulas for ripple are minumum values; anything over is gravy.
Anyone who's been fiddling with electronics for a while ends up with a few dead power transformers in a dusty box somewhere. Why not put them to good use? Think of it as recycling...you're helping the environment.

Grey
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Old 14th June 2001, 03:23 PM   #4
tvi is offline tvi  Australia
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Inductance For Your Supply design
by Fernando Garcia Viesca
Audio Amateur 4/87 pages 22-26

"We place the inductor before the rectifier, and therefore the core is AC powered and reset every half cycle.
Core saturtion is no longer a problem and we are free to include as much or as little inductance as the circuit requires"

Also Onkyo use an inductors prior to the bridge recifier in some of their amps, they call it a "Real Phase Power Supply"

Regards James
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Old 14th June 2001, 03:55 PM   #5
dorkus is offline dorkus  United States
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thanks for the info guys, i'll look into that ON Semi handbook and so forth. incidentally, i've only found one source for power supply chokes, this esoteric tube audio shop in switzerland:

http://www.audio-consulting.ch/chokes.htm

they look very expensive but pretty hard-core. anyway, i'm sure if i keep looking hard enough i'll be able to find one in the states (sorry grey, i'm too lazy to wind my own... =p).

thanx,
marc
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Old 14th June 2001, 10:10 PM   #6
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...aw, come on, Marc...
Just think--silver wire, Teflon insulation, use poly foam to lock down the layers...
Okay, okay...like I said, it's a pain.
(Got any dead transformers you don't want???)

Grey
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Old 14th June 2001, 10:35 PM   #7
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Search the web for "psu designer" + "Duncan" and you will find PSUD2 which is a great amateur power supply design package that I was involved in betatestin for. I really like it -- and it supports inductors.

You can get some pretty good chokes in various flavours from http://www.hammondmfg.com -- but I had custom toroids made up. It seems http://www.plitron.com are planning to make chokes as well.

Petter
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Old 14th June 2001, 11:16 PM   #8
jam is offline jam  United States
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Default Chokes

Marc,

I believe that Toroid of Maryland will build chokes to your specifications. They used to advertise a lot in Audio Electronics.

Jam
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Old 15th June 2001, 03:00 AM   #9
dorkus is offline dorkus  United States
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hmm yeah, i've actually had Toroid Corp. of maryland build me a couple power xformers for my amp project last year, i saw that they could do chokes too. i've also heard (though i could be completely wrong) that traditional E-core inductors/xformers have better performance characteristic than toroids, other than EMF radiation. anybody care to comment on that?
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Old 15th June 2001, 09:45 AM   #10
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Default Can of worms -- toroids versus traditional core

I am opening up a can of worms here. Technically, the Toroid is always superior to a traditional form factor. Space, leakage etc.

However, many claim that toroids don't sound as good as EI's etc. Having separated windings does seem to make sense + the small air-interruptions/gaps in the magnetic path may actually be useful.

I went with toroids myself from a space/cost/availability consideration.

Petter
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