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In Reply to: RE: Choke input supply for class AB amp posted by swordsman on April 15, 2012 at 23:00:58
I recommend a 400ma rated choke as the first choke actually sees a peak to average current. Too high a current rating and the choke may lose Lcrit and stop acting as a choke resulting in charging up the first capacitor to higher voltage. 40-50% of ratings is usually minimum current requirements for LCrit. 400ma can be found used. You may meet LCrit with a more common rating of 500ma from Hammond Manufacturing. The 193P is a fine choke. The PSUII power supply designer should show calculate LCrit or ask the manufacture.
Older ham radio tube amplifier equipment subject to large current swings used a swinging choke. Some report a swinging choke may affect the audio, but I doubt that.
Follow Ups:
So you are saying I should use a pi choke of 400mA for 50% derating of 200mA idle current load. And it will handle the 300mA peak load without core saturation. Am I right?
I'm getting the choke custom wind so I have no issue sourcing for what I wanted. The problem is my supplier only does pi choke and has never done a choke for choke input supply. Thats why I'm trying to find out how do we derate a pi choke for choke input supply
A good rule seems to be: The choke needs to be handle the worst case DC load current plus the peak current due to the AC voltage across the choke.
The best way to visualize this is to sim it in PSUD, look for the peak choke current, then spec a choke with a DC rating greater than this value.
Using a choke with a higher current rating than necessary will not cause it to lose regulation in choke-input service.
The advice about mechanical integrity is important. Tell the winder the choke has to be able to withstand half the transformer secondary RMS voltage at 120Hz across its terminals.
-Henry
Not so much the electrical de-rating, but the mechanical de-rating you have to worry about. Unless your winder is really experienced with choke load inductors, expect some nice physical hum/buzz from the unit. Make sure your working voltage rating is +800 as the choke gets beaten pretty hard.
Play with DuncanAmps.com PSUII, it will really help you visualize the supply and it will tell you your problems. You can put in stepped current demand to see how the filter works at various draws.
Neff,
Nice post. I only had one experience with swinging chokes, in a pair of modified Fisher 50As, and when I went from stock swinging chokes to fixed chokes, my ears were much much happier. I have no idea what others have experienced in A-Bing, but "swingers" earned an "D" grade for me with the 50As.Jeff Medwin
Edits: 04/16/12
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