On Fri, Jun 27, 2008 at 4:54 AM, Olin Lathrop wrote: > Xiaofan Chen wrote: >> Typically Buck Converter works better when duty ratio is >> between 0.2 to 0.8 (or 0.1 to 0.9). The efficiency will get >> worse when the duty ratio is above 0.9 or below 0.1. > > There is nothing in basic physics that says this needs to be true, which is > why it isn't. This may be true for some types of converters with particular > properties, but to say this broadly applies is just wrong. There is. I've done theoretical steady state analysis, albeit simplified, to show that at very low and very high duty ratio, the buck converter efficiency will suffer. And it is in line with my past experiences since I have developed two universal input sensor (20V-240V DC and AC) using a buck converter which converts the high voltage to And quite some PWM controllers actually limit the minimum and maximum duty ratio. The value of 0.1-0.9 is a ball-park value. The following article http://www.powermanagementdesignline.com/howto/207500488 "If you have a 24-volt input and 1.2-volt output, for example, you need a duty ratio of 0.05. But it's not optimized for efficiency or performance. And in the common buck converter, a very low duty ratio often isn't easily achieved." Xiaofan -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist