
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
17th April 2012, 09:56 AM  #1 
diyAudio Member
Join Date: May 2005
Location: Johannesburg

Choke formula  Marty Brown
Hi All
I am presently building a 12V to 330V converter and I have been using a book titled Power Supply Cookbook by Marty Brown as a guide. There is a formula that appears within for calculating the output choke value that I am having a tough time grasping as it seems the result is rather big for such a small smps. The smps operates in pushpull config at 50kHz and is rated for 120mA max. Vin(min) = 11V Vin(max) = 15V Can someone please have a look at my calc. and advise if I misunderstood what was required? Thank you Ashraf 
17th April 2012, 01:55 PM  #2 
diyAudio Member
Join Date: May 2005
Location: Johannesburg

Anybody??

17th April 2012, 02:09 PM  #3 
diyAudio Member

The inductor at the output only smoots the voltage, and operates as a low pass filter with the out cap. Assuming a delta I, the choke is easy to calculate. Normally it is assumed as a 10% of I load. I also have this book, but it is a bit confusious the math he use. Read any inductor calculation for buck converter type, in fact the inductor operates in the same way as it.
__________________
If anything can go wrong, it will. If anything just cannot go wrong, it will anyway. 
17th April 2012, 02:39 PM  #4 
diyAudio Member
Join Date: May 2005
Location: Johannesburg

Osvaldo, are you saying that calculating chokes for buck converters are exactly the same as calculating an output choke for a forward converter?

17th April 2012, 02:50 PM  #5  
diyAudio Member

Quote:
http://www.ti.com/lit/ml/slup127/slup127.pdf I hope this be usefully.
__________________
If anything can go wrong, it will. If anything just cannot go wrong, it will anyway. 

17th April 2012, 05:02 PM  #6 
diyAudio Member
Join Date: Sep 2006

The formula is dimensionally correct.
The only point open to debate is the 1.4 factor, it represents the level of ripple you tolerate for the current in the choke, but even if you choose a different trade off, the value will remain in the same range. It is a normal value for a high voltage converter: the inductance value increase as the voltage squared.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪ 
18th April 2012, 12:31 AM  #7 
Banned

can you use the common magnetic chokes or distance magnetic chokes for short the wave?
i think we can solve your question regards Jay 
18th April 2012, 10:58 PM  #8 
diyAudio Member
Join Date: May 2005
Location: Johannesburg

Thanks for your responses.
Osvaldo, I read the TI note and I can't seem to find where it explains how the inductance of the choke was calculated. The inductance value of the choke was provided all that the note said was what type of core, winding etc. Elvee, I came across a somewhat differennt formula for calulating the choke from Col. T. McLyman and when I did the calculation I come up with a value of 74.5mH. Now I am more confused as to which value is the correct one. Jay, I don't understand your question. Please will you rephrase. 
19th April 2012, 08:59 AM  #9 
diyAudio Member
Join Date: Sep 2006

Can you post your schematic, it will make the discussion easier.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪ 
19th April 2012, 12:02 PM  #10 
diyAudio Member
Join Date: May 2005
Location: Johannesburg

Here is the schematic.

Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
26H choke good enough for a grid or anode choke?  speakerfritz  Tubes / Valves  7  2nd December 2011 06:05 PM 
Help replacing a PSU choke  How to choose choke  Hubba  Tubes / Valves  2  10th September 2010 02:33 PM 
Choke rating for choke input duty  cbutterworth  Tubes / Valves  14  9th November 2007 04:43 PM 
Swinging choke vs std. choke in PS  Curly Woods  Tubes / Valves  2  5th March 2007 08:30 PM 
New To Site?  Need Help? 