Hi, i'd like to make the PWM regulator for Luxeon III using PIC microcontroller. Something very similar to this: http://www.trsoft.info/sections/elektro/regluxeon_b.png . But I have read here at this forum, that it wouldn't be very efficient, therefore it's better to use a coil and capacitor to smooth the current. And that's my question - if i connect an inductor in series with the Luxeon and a shunt capacitor, would it be allright? And is there any formula to find out the value of the capacitor and inductor? Thank you.
3 W Luxeon and PWM regulation
- Thread starter werkov
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That sort of plain PWM regulation is a really rubbish way to supply an LED for all sorts of reasons. If you add a coil and a capacitor (and also a reverse diode) you make a switching regulator, which would work a lot better - provided you do make a proper buck regulator http://en.wikipedia.org/wiki/Buck_converter
However a PIC is a really poor choice to use for making a buck convertor, since the PWM frequency is much lower than with a specialist chip - hence you need much larger inductors and capacitors to reduce the ripple. Also analogue electronics are much better in this sort of application than digital.
However a PIC is a really poor choice to use for making a buck convertor, since the PWM frequency is much lower than with a specialist chip - hence you need much larger inductors and capacitors to reduce the ripple. Also analogue electronics are much better in this sort of application than digital.
Yes, I have read that article before, but there's no formula i.e. of this type: L=(1/f)*(Iout/Iin) (it's nonsense, only example). ANd I can't find any site where this formula could be...
And about the PIC PWM frequency, it can be set from 1 kHz to 200 kHz - it's not enough?
And about the PIC PWM frequency, it can be set from 1 kHz to 200 kHz - it's not enough?
Choosing inductors and capacitors isn't that simple - it all depends how much ripple you're prepared to put up with. Fairly straightforward to work out from first principles, but I'm on holiday, and that would make my brain hurt, so I'll leave it to somebody else - sorry! The best way to select these though is to use the datasheet of a proper switching regulator - eg an LM2575, where you'll get reference circuits and also good guidance.
Yes you can get a PIC PWM running at 200kHz, but the resolution will suffer - to get full 10 bit resolution you're limited to 20kHz on those I'm aware of, which will require you to use bigger external components.
Yes you can get a PIC PWM running at 200kHz, but the resolution will suffer - to get full 10 bit resolution you're limited to 20kHz on those I'm aware of, which will require you to use bigger external components.
Nereus
Enlightened
Small boost circuits suitable for flashlight use run somewhere around 200 000 Hz. Like stated above, lowering the frequency leads to bigger components.
Somehow it seems to me that you are about to re-invent the wheel. There are many good ready-to-run converters designed for leds, no need to build your own. If you want adjustable output, see e.g. http://www.taskled.com/ . Those converters are very liked by people here in CPF. See also http://theledguy.chainreactionweb.com/index.php for some nice converters too.
-N
Somehow it seems to me that you are about to re-invent the wheel. There are many good ready-to-run converters designed for leds, no need to build your own. If you want adjustable output, see e.g. http://www.taskled.com/ . Those converters are very liked by people here in CPF. See also http://theledguy.chainreactionweb.com/index.php for some nice converters too.
-N
