I've got an application where we need to drive a high power LED. It's rated at 700mA at about 6.5V, but with adequate heat sinking, it's been run up to about 2A with 7V across it. Back when we were looking at 700mA, I was considering the LT1618 boost converter with a 4.8V battery. But, now that they want the higher current, the switch in this part can't handle it. Also, we're now looking at moving from 4 nickle metal hydride batteries down to a single lithium ion, reducing the voltage from 4.8 to 3.7. The great thing about the LT1618 is that it has a current sense amplifier in it so it can regulate based on load current instead of load voltage, which is what we want here. I have not seen any other switchers with a current regulator like this. Anyone know of one? Any thoughts on using the PIC (which will also be in the circuit) for regulating the LED current? Since the LED can float, I could put a small current sense resistor between the bottom of the LED and ground and perhaps have an analog input on the PIC sense the current. The LT part has an oscillator that turns on the switch every 750ns or so. A current sensor turns the switch off when the switch current (and inductor current) hits some limit. This limit is adjusted to produce the desired load voltage or load current with there being an absolute limit on the switch current (about 2A). It seems that the PIC that's handling the rest of the project could also perhaps measure the switch current and the load current and drive the external FET switch to do something like this. However, it seems that I'd need a couple external amplifiers so the current sense resistors could be small. My parts count is going up again! If I go with a standard boost converter chip (or the clever two transistor circuit recently posted), I'd need to convert the load current sample to a feedback voltage to drive the converter chip. Again, parts count goes up. But, I may have no other choice. Any ideas out there? What'd be the simplest way to get a regulated 2A through a 7V LED from a 3.7V battery? Thanks! Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.