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Old 17th March 2015, 05:25 PM   #1
cags is offline cags  United States
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Smile Filter Choke Selection

Am Setting up power supply for a line stage preamp. I am using a 350-0-350 CT power tranny, 5ar4 as rectifier and planning on a CLC filter section. Will be using a .47uf 630v as first cap. DCR of choke will be in the 200-250 Ohm range. My question is how to calculate for choke size. Circuit B+ will be 300VDC with current draw of approx 47ma.I have looked at several formulas with no luck. I would like a precise formula to go by.
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Old 17th March 2015, 06:12 PM   #2
20to20 is offline 20to20  United States
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Quote:
Originally Posted by cags View Post
Am Setting up power supply for a line stage preamp. I am using a 350-0-350 CT power tranny, 5ar4 as rectifier and planning on a CLC filter section. Will be using a .47uf 630v as first cap. DCR of choke will be in the 200-250 Ohm range. My question is how to calculate for choke size. Circuit B+ will be 300VDC with current draw of approx 47ma.I have looked at several formulas with no luck. I would like a precise formula to go by.
Thanks Cags
Do you mean 47uf cap? What's the purpose of a .47uf cap?

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Old 17th March 2015, 06:27 PM   #3
Magz is offline Magz  United States
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Old 17th March 2015, 06:30 PM   #4
cags is offline cags  United States
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Smile Choke Selection

How would I calculate using a .47uf 630v cap ? I was told by using a .22uf or a .47uf cap That I could tweak B+ a little. In any case use any figure you like as a matter of fact and what would be a solid formula to use in determining choke size. That is what I am looking to find out. CHOKE size.

Thanks again
Cags
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Old 17th March 2015, 07:01 PM   #5
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Originally Posted by Magz View Post
PSUD II is your friend.

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I second that.

However you could also try a capacitor multiplier supply based on a MOSFET.
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Old 17th March 2015, 07:52 PM   #6
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Use Duncan tools PSUD2 - you get to choose what component sizes and ripple you are happy with.
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Old 17th March 2015, 08:08 PM   #7
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F = 1/(2*PI()*SQRT(L*C))

The smaller the first cap the larger the inductor will have to be. Since you are using a 5AR4 you are limited by how large a cap to use so this means a fairly good size choke, 10H with a 47uF is 7Hz.
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Old 17th March 2015, 09:24 PM   #8
cags is offline cags  United States
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Smile Choke Selection

Famousmockingbird,
Will use formula thanks . Now the 7hz I,m guessing is the resonant frequency. Now the lower the frequency the better circuit stability and a smoother DC ripple. Am I close?

Cags
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Old 17th March 2015, 10:05 PM   #9
AllenB is offline AllenB  Australia
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Your 0.47uF capacitor is fine. It should leave you with a choke input filter that wants a minimum inductance of (350/50 - Volts / mA) or 7H. If you don't have at least this then your B+ will climb and you lose the tuning you'd get from the first capacitor, and the filtering will behave differently.

7Hz is also a good frequency to go with when you look at the choke together with the next capacitor.
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Old 17th March 2015, 10:39 PM   #10
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How much voltage do you need ? Unless you need above 300v you will probably be a lot better not using any cap before the inductor. Or as Trobbins already said download Duncan's tools PSUD2 . It's free and easy to use.


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