Help with 12/24V input, 14.1V output DC/DC Converter

On a sunny day (Mon, 7 Feb 2011 13:46:39 -0800 (PST)) it happened Luis Filipe Rossi wrote in :

I use this as a battery powered lab supply:

Luis Filipe Rossi wrote in news: snipped-for-privacy@y12g2000prf.googlegroups.co m:

If your following the AN note it is for a discountinous design. This will give you a small inductor but large peak currents. If you increase your inductance to opearte in countinous mode this will reduce your peak switch current.

Can you give me any example on how to perform the designe, or some good theory applyed tosome specific IC so i can understand the idea?

Thank you!

AN920-D.PDF

Try the switching regulator search capability at the following web pages.

Howard

l/AN920-D.PDF

I did that search. But could not find a single piece available on high quantity on stack here on Brazil.

Any other sugestion?

Thank you!

Luis Filipe Rossi wrote in news: snipped-for-privacy@k18g2000vbq.googlegroups.co m:

Sure here is a one it is for constant current but it is the same for the CCM inductor.

If you are uncomfortable in designing one without step by step instructions you can use an external switch rather then the internal darlington.External switches are used in the paper I linked to.That would enable you to just follow the app note (DCM)your switches have to be rated to handle the current and voltage. The components around the external switches are to enhance switch turn-off time dont emit them.

Hammy wrote in news:Xns9E8640FE7C9F5Hammyhamsterca@69.16.185.250:

Forgot to add the paper I linked to shows the NCP3063 this is just an upgraded MC34063 faster switching speed. Also I made a spelling mistake "emit" should be "omit".;-)

I could not understand that hehe. Would that not be the same?

The point is that i do not consider my know-how enough to make the project by myself, specialy becouse it is for a real project, and it is not a very important part, just something to make it work with either 12V and 24V.

I will take a look at the the AN, but the converter is getting big haha. That would be a problem becouse i have a reasonable limited space. Not small one but still limited.

Thank you!

Luis Filipe Rossi wrote in news:d9d79b4f-793a-4b93-8192-9b93b67aa547 @f18g2000yqd.googlegroups.co m:

No I'm assuming in DCM that you are exceeding the pk current of the internal darlington 1.5A. Therfore to get around this use an external BJT or Mosfet that can handle the current.

Well if you can only get the MC34063 in your Country in quantities, I'm afraid your going to be limited in what you can achieve size wise.

Even in CCM this will result in a larger inductance but smaller output caps and may eliminate the need for external switch. Where as DCM its the other way around small inductor large output capacitances depending on your ripple requirments.

If you can source a modern controller in quantities they switch up-to 1MHz you can make a tiny 7W SMPS in the 200-500kHz range.The MC34063 is only guarenteed to about 50kHz depending on the model if I remember correctly.Size is related to switching speed the faster it switches the smaller the footprint.

But if thats what your stuck with....Really though if you use surface mount components the gate drive cct should'nt take up to much room.If you dont use the gate drive cct the mosfet gate capicitance will have to discharge through a resistor to turn off resulting in a slow turn-off dissapative for the FET. If you do use external FET's you have to use caution your Vgs is'nt excedded as well.Using BJT's externally you have similiar problems with storage DELAY and they would likely require external drive circuit.

I am not sure if MC34063 is the only one i will find on my Country. It is the only one i fount so far.

I am kind confused. How can i know when my designe is on CCM or DCM? If i just do not use external FETs(or BJTs) and make use of a much higher inductor, will the peak current be reduced? What that would influence on my project?

Thank you!