Pi filter at input bulk capacitor
Hi,
I am designing 50W power supply using TOPswitch 271Jx. I want to know that which one is beneficial to use in case of input bulk capacitor from below & also will help to reduce inrush:
1. single capacitor at input.
2. Pi combination (2- 68uF capacitors with 6mH common mode choke).
3. Two 68uF capacitor.
Comments
Thanks PI- Nano for your valueable reply..
I gone through PI expert software during design and there is option that PI filter at input bulk. They have suggested PI filter with 6mH inductor coil. Then what is use of PI filter at input?
Could you please send your PIExpert design file so that I can check your design.
Regards,
PI-NANO
Please find PI expert attached file, In input capacitor selection there it Option of Use Pi filter.
Pi expert file with Pi filter at input capacitor.
Hi,
Thanks for sharing the PIExpert file.
Regarding pi filter arrangement at the input, I saw the schematic and I am assuming that you are designing for a 2 wire input.
Pi filter can be made to work for a 2 wire input design, but EMI filter configuration has to be fine-tuned until you get a passing result.
There is a help section in the PIExpert, where you can see the description for the pi filter configuration. If you double click on EMI filter in your design file, a window will pop up and you can find a help button there. If you click on the help button, it will display a page showing PIExpert recommendations according to power level. I am attaching that help section as a pdf here.
Here are my comments regarding pi filter configuration,
With pi filter configuration you will be depending on the leakage inductance. You will have to make sure that there is not much variation between part to part and generally higher leakage will give you better performance.
You will need 2 electrolytic caps instead of single capacitor, which adds cost to the cost and occupies additional space on the board. If you would like to design with pi filter configuration then I would also suggest to place another high ceramic disc capacitor for high frequency currents.
But with pi filter configuration you can probably use a smaller common mode choke because, the first capacitor peak charges to the input peak voltage.
In my previous reply I have suggested you two reference designs as well. It is up to individual’s choice what to go with. I hope this clears.
Regards,
PI-NANO
How can i make 6mH input choke, i need choke instraction...
and also 3.3 uH output self...
thx;)
Hi,
This is someone else's post. If you have anyy question please post it as a seperate question.
There are two options
1. Order off the shelf componments (These components will be avaialble wildely).
2. Making your own magnetics by getting teh suitable cores.
Regards,
PI-NANO
Hi..as per my knowledge the current remains unchanged irrespective of one capacitor or two capacitors as long as capacitance value remains same.Placing 6mH commonmode choke in between 2 capacitors at that power level is generally not recommended. That will make ethings bad for EMI.
Hi,
Yes, Inrush current remains unchanged irrespective of one capacitor or two capacitors as long as capacitance value and ESR remains same.
Regards,
PI-NANO
Hi,
Inrush current remains unchanged irrespective of one capacitor or two capacitors as long as capacitance value remains same.
Placing 6mH commonmode choke in between 2 capacitors at that power level is generally not recommended.
Here I am posting the link for 2 design examples
http://www.powerint.com/sites/default/files/PDFFiles/der243.pdf
http://www.powerint.com/sites/default/files/PDFFiles/der245.pdf
Please go through the designs and you can modify the design according to your requirements.
Regards,
PI-NANO