If space isnt an issue...but I think time was... COULD get a demo board with a switcher on it, if this is a one-off project. Switcher is the better way to go, hands down. Olin Lathrop wrote: Gerhard Fiedler wrote: > Interesting; thanks for sharing. What I wondered when I saw it, though, > is whether that still makes sense e.g. in a low quantity production > unit, after considering the cost of the additional components (5V > bootstrap supply, MOSFET with driver) and the PIC programming -- > compared to one of the simple switcher ICs. > > Did you calculate that for yourself? What's your conclusion? Most of the switcher chips are surprisingly expensive, especially when they contain the switching element. In most switcher designs, the most expensive component is the inductor, then the switching element, then everything else is small except maybe special caps in some cases. Just a switcher chip doesn't contain the inductor nor the caps, so that's a wash. Everything else can be had for well under $1 if you do it yourself. Firmware control also has inherent advantages. You can decide what the longest time the switch can be on is without saturating the inductor, then guarantee that is never exceeded in the firmware. You can also do something totally different for startup, which is an area that the off the shelf chips have limited flexibility if they even tell you what they do at all. Firmware control also allows for customizing the supply in the field. For example, the QuickProto-01 can handle about 30V in, and of course that was taken into account in the switching algorithm to prevent inductor saturation. However, if you know you are supplying a lower voltage (like in a car for example) you can reprogram the switcher to allow the switch to be on longer and getter higher maximum output current. ****************************************************************** Embed Inc, Littleton Massachusetts, (978) 742-9014. #1 PIC consultant in 2004 program year. http://www.embedinc.com/products -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --------------------------------- Do you Yahoo!? Next-gen email? Have it all with the all-new Yahoo! Mail Beta. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist