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Old 12th January 2006, 02:51 PM   #1
Cassiel is offline Cassiel  Libya
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Default Choke current

Hi,

I did order the wrong choke. It is a Hammond max current 100 mA DC.
The amp i am building (pp6v6 stereo) needs 140mA DC. I am going to try it anyway...see if am lucky.But i would like to know what happens when the choke saturates, what kind of problems should i expect?

Thanks
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Old 12th January 2006, 06:38 PM   #2
poobah is offline poobah  United States
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Your heating in the choke will approximately double because of I squared. Your ripple at the output will increase; as the inductor saturates, the inductance value decreases.

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Old 12th January 2006, 06:40 PM   #3
cerrem is offline cerrem  United States
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According to standard textbook approach, you don't normally design a choke for saturation mode....
But there are cases in aerospace, due to size restriction that I have operated a choke in sat mode.... you get a bit more heat and losses but sometimes it don't mean much...
For example: if you examine the L vs I curve .....your L will creep up when applying increasing DC current..then hit a peak at sat point then the L will start to come down quickly....
If your minimum required L is say 7H , and your peak L is 10H ...the you will see the 7H twice....once on the way up to sat. and once on the way back down after your in sat. but this time with more DC current.... You will make for more current harmonics, but not to worry since these are higher order intervals and will average out in the filtering .... Will work in power supply..But not a good idea in RF filter circuits ...
You would need to first plot your L vs I curve and then see what you have will fit....
Depending on the value of this choke....you can re-gap it to handle a bit more DC current at the expense of lossing a few Henries....But you still might end up with enough Henries to get the job done..

Chris
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Old 12th January 2006, 07:38 PM   #4
Cassiel is offline Cassiel  Libya
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Quote:
Your heating in the choke will approximately double because of I squared. Your ripple at the output will increase; as the inductor saturates, the inductance value decreases.
Uff, doesn't sound good.

Quote:
Will work in power supply
This sounds better .

Ok i get the picture it can be done but better not doing it. I'll order another and keep this for future projects. Another week of delay. This amp is taking forever!!!

Thanks for the replies, been a help.
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Old 13th January 2006, 01:24 AM   #5
anatech is offline anatech  Canada
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Hi stalker,
Modify the power supply and use one choke per channel?

-Chris
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Old 13th January 2006, 03:06 AM   #6
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Quote:
Originally posted by anatech
Hi stalker,
Modify the power supply and use one choke per channel?

-Chris
Certainly more economical than a high current choke and better channel isolation.
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Old 13th January 2006, 10:08 AM   #7
dhaen is offline dhaen  Europe
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Default My suggestion...

.
Consider supplying only the output stages (where regulation is critical) through the choke. Supply the other stages through their own RCRC smoothing.
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Old 13th January 2006, 10:17 AM   #8
dhaen is offline dhaen  Europe
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Default And another thing.....

A overrun choke sometimes buzzes. I don't think this has been mentioned...
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Old 13th January 2006, 10:17 AM   #9
Cassiel is offline Cassiel  Libya
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Quote:
Modify the power supply and use one choke per channel?
That, unfortunately, is not an option. I need a choke input filter to bring the voltage down.
Anyway when i said i may be lucky i was thinking that the core may not saturate. If the specs say 100mA it can possibly take more, maybe 140mA?
I have read Hammond are pretty conservative with their numbers.
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Old 13th January 2006, 10:54 AM   #10
SY is offline SY  United States
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Quote:
If the specs say 100mA it can possibly take more, maybe 140mA?
This is the very definition of an optimist.

Your earlier instinct was correct- just go get the right part.
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You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
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