I am dealing with some pretty tight quarters left in the enclosure. I can squeeze in a board about 15mm square and no more than 6mm deep. I never really thought about LED damage. I was kind of figuring that 100mA average current would determine its life and it would not really matter if it is getting high current short duration pulses. I guess that an inductor is O.K. if we can still come up with something small and with a low parts count and not microscopic components that I will have to place by hand. The enclosure is plastic and I do need something with very low EMI. It will be mounted behind an instrument panel with other avionics. Brian Kraut Engineering Alternatives, Inc. www.engalt.com -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf Of Dave Tweed Sent: Tuesday, December 04, 2007 3:12 PM To: piclist@mit.edu Subject: RE: [EE] Challenge II:: LED driver Brian Kraut wrote: > I wrote: > > Brian Kraut wrote: > > > I need something that has the output current varying linearly with > > > the input voltage. It needs to be inductorless, very small and low > > > parts count, and cost no more than a buck or three. > > > > As others have pointed out, it's very straightforward to build a buck > > regulator that controls its output current based on its input voltage, > > except for the requirement that it be "inductorless". > > > > Where does this requirement come from? > > I don't think that I have the room for an inductor. You can get some pretty substantial shielded power inductors in a 7mm x 7mm SMT package. Is that too big? > It also does not need to be an efficient buck converter, PWM is fine. You're up against some basic physical limitations here. If you don't have the means to store energy, then you must dissipate it one way or another. Can your LED really handle the direct application of 24-28V, no matter how briefly? You'll probably need some sort of current-limiting device even with PWM, and that can either be a resistor or an inductor. The inductor is a big win in terms of efficiency, and is probably no larger than the resistor you'd need anyway. -- Dave Tweed -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist