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The 3021 “BuckPuck” LED Power Modules are a line of true current
regulated drivers for LEDs. Unlike standard power supplies, which
deliver a fixed voltage to the output, the 3021 is designed to vary the
output voltage as required to deliver a constant current to the LED(s),
reliably and with stability
Supertex makes some good LED driving ICs. I have had good results with them driving Lamina LEDs up to 2.1 amps.
Aside from being more expensive, modules can't really be designed to work with a wide variety of input and output voltages unless you have a huge inductor to cover all the possibilities. And they're not going to use huge inductors so regulation may suffer. Even still, the choice of how to drive it (constant on-time vs const freq) depends on the ratio of input to output voltage.
it said that the modules sort of self adjust :?: to the voltage of the LEDs, dont ask me how they do this.. i found the link from an ebay site. which is selling them.. lol
self-adjusting to the LED voltage is just a fancy way of saying it's acting as a current source, as was already pointed out. (by definition, a current source applies whatever output voltage is necessary to supply a certain output current) you can find plenty of info in an electronics textbook on current sources, with anywhere from two to dozens of transistors. you'll probably never see current sources used to drive LED's done with discrete circuits, because it's only really practical when they put it in a nice little IC for you, because populating a board with a whole bunch of transistors and resistors to drive each LED would be a big waste of space :lol:
SuperTex (as well as others I have seen) just latch the on-state of the buck converter until the inductor current reaches a set level, then goes off for the rest of the cycle. The freq is set by an external resistor.
The regulation is as good as the inductor & freq matching. If the inductance*freq is large, then it's smooth. If it's low, the current regulation suffers since there is substantial ripple in the inductor current but the chip only senses peak inductor current for feedback.
ah, didn't notice it was a switching supply type circuit, instead of some sort of basic active current source. probably works a lot better that way. but in any case, it still achieves approximately the same result, attempting to provide constant current regardless of LED forward voltage.
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