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Old 13th October 2012, 03:23 PM   #1
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Default usign redundanct power transformer as CLC choke

I have a pair of 300VA toroid. 110V to 60-0-60V secondary. so the secondary has 300/(60+60)=2.5A capability.
If used in parallel the secondary will have 5A current capacity (RMS) without core saturation leaving the primary open.

1. the question is whether i can use it for CLC or CLCLC choke.
CLC two chokes in parallel , or CLCLC using each secondary in turn. ?

2. Can i use it in differnetial/common mode choke using both secondaries connected to C+ to C+ terminal and C- to C- terminal. ???

The supply design is for single ended Class A amplifier so ripple rejection is very critical here.

regards
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Old 13th October 2012, 03:35 PM   #2
DF96 is offline DF96  England
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You might be able to use it as a common-mode choke by wiring the secondaries in opposition so their is no DC flux to cause core saturation.
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Old 13th October 2012, 04:09 PM   #3
AndrewT is offline AndrewT  Scotland
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The 2.5Aac and 5Aac current rating are for AC current.

If you use the transformer as a choke you need to know the DC current rating.
IT WILL NOT BE THE SAME AS THE AC RATING.
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Old 13th October 2012, 04:27 PM   #4
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I would not put these in parallel without some series resistance to help balance the currents. A transformer cannot be used as a choke, because they will most likely saturate with any appreciable DC current.
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Old 13th October 2012, 06:09 PM   #5
DF96 is offline DF96  England
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The DC current rating will presumably be a bit higher than the AC rating, as there will be no skin or proximity effect to increase conductor resistance and no eddy current losses in the core. However, the DC currents will need to be fairly accurately balanced to avoid core saturation. Best to use only in circumstances where the circuit details guarantee DC balance e.g. secondary-rectifier-cap-CM choke - etc. If there are no other connections to the rectifier etc. then DC balance is assured by Kirchoff's current law.
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Old 13th October 2012, 09:39 PM   #6
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I am really a bit confused here. I have seen old school car amplifiers regulard employing iron core small EI chokes for mains filtering at 12V. i.e 80A current is flowing through them how does it work then without saturation.

Ok. I agree the DC rating would be lesser due to conitnoues heating but should it not be same as that of RMS rating of Ac current ???

Help is neeeded i have these two spare toroids in metal cases salvaged from a sony vintage amplifier i hope i can make some good use of them. I am not sure of how to balance the two secondary windings for CMMMR??
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Old 13th October 2012, 09:41 PM   #7
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can some one explain how to balance the secondaries. i have a pair of these from sony amplifiers. they are completely metal encapsulated. how can it be used in CMMR mode?
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Old 13th October 2012, 10:03 PM   #8
sreten is online now sreten  United Kingdom
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Hi,

Simple fact is you should never be doing stuff you don't understand.

Most of the time you won't understand the answers to your questions.

You work out what sort of inductors are used in SMPS's and why.

You work when you can use common mode and when you can't.

You work out the current rating of a transformer used as a choke.

You work out why CLCLC here simply cannot work properly.
(its an interesting problem as to what would actually happen ...)

(One of the answers in this thread is simply wrong .....)
(One of the answers in this thread is very misleading .....)

You work out why I can't be bothered to answer most of your
ill-informed questions, (answer - your not asking the right
questions - problem - work out what that actually means).

rgds, sreten.
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Last edited by sreten; 13th October 2012 at 10:21 PM.
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Old 13th October 2012, 10:52 PM   #9
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agreeed. But i need solution to reduce hum to my pull push class A single ended amplifer.
for that i need to reduce the ripple at the mains. ????? how can i do do it else?
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Old 14th October 2012, 12:15 AM   #10
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Quote:
Originally Posted by muddasirwaheedmalik View Post
I am really a bit confused here. I have seen old school car amplifiers regulard employing iron core small EI chokes for mains filtering at 12V. i.e 80A current is flowing through them how does it work then without saturation.
Presumably the inductance is much much lower (fewer turns, thicker wire) so the core doesn't reach saturation. I just measured the secondary inductance of a 150VA toroid I have to hand. It was around 400mH but I suspect my LCR bridge was driving it into saturation because the loss was a bit on the high side. Does your circuit really need hundreds of mH inductance? That will look very high impedance at audio frequencies.

If you're building chokes then look into some cores based on no.26 material which is designed for this application - they're not at all expensive. It withstands higher magnetisation because its got a distributed air gap (its iron powder, not iron).
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