I think the topology that does both boost an d buck is Sepic but that is
limited to small currents due to the coupling capacitor...

Steve

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
William "Chops" Westfield
Sent: 24 March 2008 06:12
To: Microcontroller discussion list - Public.
Subject: [SPAM][EE] Combining Boost and Buck switchmode converters...


In the attached circuit I've overlaid a standard buck-mode converter  
(SW2, CR2, L1), and a boost mode converter (SW1, CR1, L1) that shares  
the same inductor.

Is there some reason that this doesn't work as a boost/buck variable  
voltage regulator? (for boost, you leave SW2 ON continuously, for  
buck you leave SW1 off all the time.)  I don't think I've ever seen  
this sort of configuration.  (for that matter, I haven't seen many  
switch-mode variable power supplies at all...)  I can forsee "issues"  
trying to run this with a traditional analog feedback path, but if  
I'm using a microcontroller as the regulating element anyway?

Thanks
Bill W



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