Hi all,
I'm playing around with a bunch of white power LEDs (the 3W version, with
0.7A current), and now I'm looking for an efficient step-down converter to supply up to three of these from approximately 5V (four NiMH cells).I designed stepdown converters before, but most of these were based on regulator chips which required a rather higher supply voltage (e.g. UC3842); also, they featured Schottky diodes to ground instead of a MOSFET, which is less efficient. Last but not least, the output should be a stabilized current, instead of a stabilized voltage.
Now before setting out and reinventing the wheel, I realized that there must be countless suitable designs out there -- all those cheap LED torches must have a built-in boost converter; also, every modern computer has several low-voltage high-current switchmode step-down circuits. So my question is if anyone could point out an actual circuit design, or at least an SMPS controller chip capable of handling voltages as low as 3-4V. I considered the good 'ole TL497, but that one has a minimum Vcc of 4.5V, which is too close for comfort to the 5V battery voltage (I've had some nasty latch-ups with that one, lacking an undervoltage lockout).
Thanks for any advice already, best regards,
Richard Rasker