Hello everyone! I'm not an engineer but i want to do something special - or so it seems. I want to power 2m of this LED strip (12V, 36W, 3A for 2m (120 LEDs)): http://store.yujiintl.com/products/high-cri-led-ribbon-60-led-m-95-98-cri?variant=808351017 with that Lithium-ion battery (Sony BP-U60, 14.4V, 3.9Ah): http://www.sony.co.uk/pro/product/broadcast-products-camcorders-batteries-power-supplies/bp-u60/specifications/ I want to dim it from 0% to 100% (if possible) without PWM - i will use it for filming purposes and flickering is an absolute no-go. Sometimes i do slow-motion shoots with up to 2000fps - this might be extreme, but flicker-free till around 400fps would be nice. So PWM is out... I tested it with my lab power supply: Around 7V its around 5% (and it doesn't flicker at normal framerates). Additionally, i want to make sure i dont fully drain my batteries. And, it's crucial that the brightness stays always the same - if the batteries can't deliver what i want it should be turned off or at least flash some red LED. As i see it, i need: 1. Adjustable voltage regulator from ±14,4V to 7V - 12V, 3+A 2. Some relais that is triggered when voltage in the battery drops below the adjusted voltage 3. Heat absorber of some sort Questions: Where do i find a voltage regulator with my specifications? Do I have to make my own? If so, does someone know a schematic which withstands 3+ amps? What is that 'relais' part called? Due it beeing dependent on the adjusted voltage, does a combo part exist somewhere? Every though is much appreciated. Thanks!
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Depending on the LED driver you're using, an extremely high PWM frequency (10-20 KHz) might be an option. Dimming white LEDs by reducing voltage/current in general does not work well. Color temperature will change drastically or even shift to a color which could not in a bit be called "white" which makes it completely unusable for photographic lighting. If reducing brightness in discrete steps is acceptable, I'd suggest to find a way to simply switch off every 3rd, 2nd, 2 of 3... LED and keep the remaining LEDs at full brightness. Also applying neutral density foil is a good way to reduce brightness without changing color temperature. Or setting up a mechanical "shutter" (e.g. black wrap) in front of the lamp might work as well.
Fabian L. wrote: > Where do i find a voltage regulator with my specifications? http://www.conrad.ch/ce/de/content/filiale_dietlikon/
thank you all for your thoughts! Joe F. wrote: > Depending on the LED driver you're using, an extremely high PWM > frequency (10-20 KHz) might be an option. > > Dimming white LEDs by reducing voltage/current in general does not work > well. > Color temperature will change drastically or even shift to a color which > could not in a bit be called "white" which makes it completely unusable > for photographic lighting. Sadly i don't have a color meter, and this would indeed destroy the purpose of LEDs with a CRI > 98. But from bare eye i don't see a color shift at all, and i'm kind of trained to detect color shifts in light sources. But i might be wrong of course. > If reducing brightness in discrete steps is acceptable, I'd suggest to > find a way to simply switch off every 3rd, 2nd, 2 of 3... LED and keep > the remaining LEDs at full brightness. this would be the best option, but i can't imagine the nigthmare of wiring 120 LEDs this way. And, if it should really work as a photographic light, it has to have the versitality of dimming in smaller steps. > Also applying neutral density foil is a good way to reduce brightness > without changing color temperature. Of course, that would work, but I want to save energy, too. The battery lasts only around 1.3h @ 12V till completly empty and it would be nice if it would last longer if dimmed down. > Or setting up a mechanical "shutter" (e.g. black wrap) in front of the > lamp might work as well. Well, i build a 'practical' - light source that is in frame. Even though i love black wrap, this isn't the place for it. russia wrote: > Try this: > Ebay-Artikel Nr. 361867758044 this look very promising! If there's no other option than go with just a lot of hertz, 150KHz should be enough. what about cutting power off if the voltage drops?
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russia wrote: > https://www.youtube.com/watch?v=jLia59KfkSw&t=406s oh my god, the internet is fantastic. this is perfect and exactly what i need. thanks a bunch!!