Choke Coil Calculation

You've built a classic second order circuit. You must include the series resistance that your actual coil has to the model to be able to accurately model this circuit. Hopefully that description refreshed your memory, and reminded you where on your bookshelf is your circuit analysis textbook. If this is a new concept for you though, then the link I gave you can be an introduction to the world of analog design.

Now for some details to analyze this by adding the transistor you must do some non-linear conditional work. You'll have to substitute the transistor with an ideal voltage source to establish your fundamental load characteristics. You will have to next analyze or finish designing the biasing of your emitter follower circuit you've started to design. While the base to emitter voltage is forward biased, this circuit will operate similarly to how the ideal voltage model predicts. When the emitter base voltage is reversed biased, and this will happen with this circuit, you will have to consider the peak current the ideal voltage analysis revealed as a reverse current source into the emitter.

If this is a homework question, you'll notice I've only presented the entrance to the path you should pursue. If this neither homework or a flashback to homework done long ago, well either formally or informally you have to take the classes.

Wait a minute, what you actually drew was an IGBT not my BJT answer. Well you presumably took this from a switching supply design then. You'll have to know a lot more then about the gate's biasing circuitry, like at what fundamental frequency are you switching to solve for L. You omitted then where output load is and some critical diodes, too. Oh, and that's a much later class.

output voltage should be pure DC

This basic simplified circuit element (it is not a complete circuit and cannot be used as such without additional electrical elements, gate control, feedback monitoring, etc) will never give you a pure DC output or remain stable under varying output load due to its basic switching nature.

This looks very much like a theoretical example from a text book, not a practical circuit. What exactly is the application (or is this a theoretical problem)?

here i using igbt, switching at 2.5Khz and i want to know how to design L ,what value of

L is must to filter around dc. can i use toroid core ?

You didn't even look at the Wikipedia link I gave you about second order circuits did you. If the math on that page didn't make any sense to you then you should realise that you're attempting something beyond your scale. If it did make some sense but you just want a short cut from us, well sorry there's not enough information here for me to do your job. You now offer the information that this supply circuit is supposed to switch at 2.5kHz, well I don't have the patience to ask my remaining nineteen questions in this game of twenty questions to do your job.

I hope that this is a class assignment for you and you can go to your TA, professor or classmate to go over all of the material with you so you can solve this on your own. Unfortunately for you, I suspect that it's part of your end of semester take home exam and you don't even know where to start. So much for this semester, I hope the parties were good. If this is a real job assignment that requires you to control 100 amperes... I won't finish that thought.

i am not a student. .and i am working in the power electronics field .

if you have any idea, try to share with others, but your answer do not discourage

other.

Actually I find your lack of useful information and feedback discouraging. I and several others here have pointed out that you do not have enough information here to design the value of L to do anything. You've not defined if L is the load you will be driving to maintain a magnetic field, or if this is part of a supply circuit that other parts will use to drive your load. You've not even defined what L should be designed to do. Clearly this must be only part of some whole circuit design, for your circuit diagram doesn't even provide a way to turn ON/OFF your IGBT.

Sharing is a two way street.

(Yep, I still have nineteen questions left. )

My first thought was that it will resonate.

I had an IGBT of >100A that I made into a very effective emitter follower linear dropper power supply solely by adding a 9 v batt (PP3) above the main DC (36V in my case) and a 1MΩ pot for the gate drive and it worked a treat. It served me for nearly ten years when my budget wouldn't run to a decent bench supply that would run to the value of the IGBT. Obviously heat-sinking would be neccesary.

Chas