Surely you want a self resonant freq. as high as possible, this means the lowest parasitic cap possiblle? ----- Original Message ----- From: "Dave Tweed" To: Sent: Tuesday, September 23, 2003 6:02 PM Subject: Re: [PIC:] Stealing power from the phone line update > michael brown wrote: > > Don't get me wrong, I am intrigued by the idea of using a switching > > supply for the rest of the circuit. > > Just out of curiosity, I worked out the numbers for a simple buck regulator > that would convert 50V at 10uA to 5V at 100uA, just to see if it is doable. > > I chose a switching frequency of 100 kHz for a good balance between being > easy to filter out of the audio and good efficiency. I came up with a coil > value of 100mH, which is rather large. In fact, I couldn't find any 100mH > coils that didn't have a self-resonant frequency that was less than 100kHz! > > Any ideas, or is this a lost cause? Is it possible to build a resonant > converter that can work with nonideal coils with good efficiency? It sounds > like things could get very complicated very quickly. > > -- Dave Tweed > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu