SEPIC converter design

[Peter05]

Hello,

i would like to design a SEPIC conveerter with input voltage ranging from 3Volts to 19 Volts . On its output will be connected three DC-DC converters ( 1 boost and 2 buck converters , their image is attached) and the output voltage of the SEPIC should be araound 8.4V.Could you help me with the design ?

Thank you.

 

[MacGyverS2000]

What's stopping you from using one of the myriad of available chips and following their datasheets? Unless you're truly trying to do something different, the datasheets have pretty much everything you need to know to build up a basic converter. The fact that you're hooking up multiple converters the the output of the SEPIC only matters in terms of how much input capacitance they have (i.e., how much output capacitance the SEPIC sees).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Peter05]

My first try is this circuit :

But my circuit presents a strange response.
For pw =4.8u the response on the output is this (about 6.5V):

and the response for greater pw(e.g. 5u) is like this :

Both far away from ~8.4V.