This is quite an unusual LED array that can be run directly from 240V mains with just a rectifier, SM2087 chip and a current setting resistor.
The circuit uses a technique that involves progressively switching in sections of LEDs in series as the rectified sinewave voltage ramps up and down.
It seems to use a series of current threshold levels as the combined forward voltage of each circuit of LEDs is reached to switch the sections in.
There's a data sheet that may take an unusually long time to download, but it is missing a block diagram of the chips internal function.
http://file1.dzsc.com/product/13/05/23/903845_161908921.pdf
The LEDs on this panel are all 5050 housings with three white LEDs wired in series to make up a large array of series LEDs.
Contrary to the sample circuit given on the data sheet, this module has a 100nF capacitor tacked across the rectifiers output.
Note that these panels which seem quite common on eBay do seem to require heatsinking, as their rated power is 7W.
The ebay link to this module. Note that it is for 220V use. http://www.ebay.co.uk/itm/361102101064
The circuit uses a technique that involves progressively switching in sections of LEDs in series as the rectified sinewave voltage ramps up and down.
It seems to use a series of current threshold levels as the combined forward voltage of each circuit of LEDs is reached to switch the sections in.
There's a data sheet that may take an unusually long time to download, but it is missing a block diagram of the chips internal function.
http://file1.dzsc.com/product/13/05/23/903845_161908921.pdf
The LEDs on this panel are all 5050 housings with three white LEDs wired in series to make up a large array of series LEDs.
Contrary to the sample circuit given on the data sheet, this module has a 100nF capacitor tacked across the rectifiers output.
Note that these panels which seem quite common on eBay do seem to require heatsinking, as their rated power is 7W.
The ebay link to this module. Note that it is for 220V use. http://www.ebay.co.uk/itm/361102101064
APPEARS TO BE A CHEAPSKATE`S POWER FACTOR CORRECTOR
Just an amateur's idea: Is it possible, that they are counting on the voltage to drop due to the load (thus never going beyond what the LEDs can take)?
The oscilloscope can be used. The lighting looks stable because of the long persistence time of the fluorescent material.
Here in the US, we call '_' an 'underscore'
It’s actually really simple. A zero current, all switches are off when the first current limit is reached the first switch opens and the current drops. The chip then acts like a poor mans PWM as long as the on current remain below the first threshold. As the current rises the same thing happens at threshold two, until the waveform reaches threshold four and it just PWM’s at that max current. The same thing happens on the downside of the cycle. Chip is efficient because the switches are either on or off so only switch losses and rdson losses are incurred. Really a neat idea and an elegant design.
I'd have thought that it would be the lower number of LEDs lit first ( lower starting voltage ) to have light for the maximum time in the cycle and reduce flicker !!
Used in down lights
I think the chip expects the power supply to be current limited, so the voltage to the LEDs and chip gets throttled down as the chip turns all the LEDs on.
If you cut open a basic LED replacement for 60 watt lightbulb, you will find this item inside.
I wish I understood what a sine wave was an I don't know why
Boobs…
A simple way to see the action of lights that ride the wave, you'll need: a paper towel tube, a disc of paper (thick) slightly more than 2x the dia. of the tube, a DC motor, batteries and a variable rheostat. Mount the motor at the end of the tube so it can hold the disc over the end. Cut a tube sized hole in the disc so when mounted on the motor it will pass over the tube's endhole. You can see where this goes… rheostat inline with the motor et voila !! You can adjust the speed of the motor to match and kind of flickery light to 'slow it down'… it's interesting to see fluorescent tubes as they go from almost totally off to much brighter than you see them, prolly why some folk get migraines from them… I wonder if it'd work with the iPad like it does the human eye tho…
Any one can help me how to calculate sense resistor and wattage of circuit
Right. Next piece of equipment to get would be a cheap slow motion camera. There's a few kick-starters out there that aim to make low cost high-speed cameras for those who need some high-speed footage, but can't justify the cost of a Phantom and are willing to capture at only 10,000fps as opposed to 250,000fps.