> I don't think those particular AIC parts employ a quite high enough > switching > frequency to use a 10uH inductor, but the Zetex part isn't bad with 10uH > and > it's available from Digikey, albeit at a fairly handsome price (0.72/100). I was immensely disappointed with the Zetex ZXSC100. I got some from the UK via RS and had great hopes for them. It is not like Zetex to do stupid things, their designs are usually superb, but in this case the design is stupid. It has an unnecessary limitation which cripples its low Vin performance. It is specified to run on as little as one NimH cell, but it does so poorly. The "problem" is that it operates only from Vin and not from the boosted output voltage, which is at least 3 Volts for a single white LED and higher again for a string of them. Every Asian LED driver boost converter takes the obvious approach of bootsrtappiing its supply voltage from Vout when used at under about 3V Vin. This allows eg less severe Vgs specs for an output FET. Many of the Zetex application circuits use their bipolar ZXT13N15DE transistor. This is indeed a superb part, but it needs to be. And while it has good Beta, it doesn't help the efficiency having to drive a bipolar base. Worse, as Vin is lowered the IC runs out of drive and they offer the ability to paralle the internal bipolar PNP hi side driver with an external part. A look at the available driver voltage when you have a high and low side bipolar trying to run on Vin = 1 Volt shows that its going to work about as well as it proves to do at low Vin. Get it up to say 2V and its fine with the bipolar output or a lower than usual Vgs MOSFET. The device looks quite fancy from its block diagram but consideration shows that they have achieved apparent sophistication by using driver current emitter (or source) sensing to terminate the switching cycle. That plus a voltage feedback pin gives better design control than with most Asian parts. Shame you can't have load current control as well. I tried folding load current into the driver current sense and while it looked promising I abandoned the IC due to its low voltage performance. Another interesting Zetex IC is the 3 pin ZXLD381 (and they have a number of similar ones). This does not have genuine closed loop output control but achieves "good enough" operation by controlling max inductor current and assuming that the designer can fiddle the inductor size to achieve approximately constant energy output. The data sheet shows application circuits both with and without an output diode. When the LED is directly connected to the output without even a smoothing resevoir capacitor (as they show) it necessarily beats the stuffing out of the LED. For say a 1 Volt supply and a say 3 Volt LED with say 75% (you can hope) efficiency then Iout average = Iinaverage x Vin/Vout x 75%. Or Iin = Iout average x Vout/Vin x 100/efficiency%. eg for 20 mA average LED current, input current average will be 80 mA. Peak input current will be higher and may be quite a bit higher depending on various factors. SO, when the inductor is turned off at the end of the input cycle the LED MUST take the input current flowing in the inductor. So you have a 20 mA LED taking an 80 mA current pulse - maybe higher. In the long-ago time of LED indicator lights, LEDs were such low power and low efficiency devices that you could often pulse them at 10 or even 100 x their average rating, as long as the average current was OK. People have got used to this idea, and so apparently have Zetex, but it's no longer so. with modern white LEDs. A 20 mA white LED will often have a 30 mA absolute maximum specification. They won't die (usually) at 80 mA pulse, or 100 mA or ... but you can expect their "lumen maintencnace" (light output efficiency with time) to be from reduced to severely-reduced as a consequence. ie driving a modern white LED directly from a pulsed output is a bad idea. Note that LED lifetime degrades with both increasing current AND increasing temperature essentially independently. ie a LED conducting more current will have a shorter life, even if the die temperature is not increased. (this radical heresy is based on LumiLeds app notes) > Any idea of the quantity price of the AIC1595 series (2A buck regulator)? No idea I'm afraid, but think of a good price and halve it and you'll probably be about right. > I'm impressed with a part that contains an "internal precious reference". A fair description in a world of zener diodes. A TL431 / TLV431 will provide a "precious reference" (or a semi precision one(+/-1% nominal) ) for about $US0.03 in moderate manufacturing volume. FWIW, I found that the CE9908B boost converter IC most flexibly met my 1 cell boost converter needs. (Voltage feedback on separate pin, chip enable / Vin low sense, external FET drive, ...) Russell McMahon Applied Technology ltd New Zealand -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist