Seoul Semiconductor LED Driver: unusual topology

With incandescent manufacturing now banned it's been interesting to track the rapid technology progress and wide variety of business and technical approaches in the LED bulb market.

A good portion of the CFL bulb market seems to have deteriorated to providing the lowest-possible-initial-cost bulbs... I wonder if the same will happen with LEDs. I was looking at driver IC's and this vendor, Seoul Semiconductor, has a single-chip which requires no external transformer, nor capacitors and resistors. I think it's aimed at enabling lowest-possible-cost bulbs.

I could not find a commercial bulb with this IC in it but I was able to order the component from Digi-key.

It produces high flicker, but it requires no capacitor (which should lead to very good service life if the LEDs can be kept cool). An interesting tradeoff.

The Acrich2 modules are a very efficient design, and should be relatively reliable. The downside, as you note, is the flicker. I've built a nominal 100W replacement using 8 watt Acrich2 modules, and I don't notice the flicker. Works great for me. Pics are here:
http://www.flickr.com/photos/kurtsj00/sets/72157632507952012/

There are others using this method of switching segments of LEDs in and out as the voltage changes. One example is the Supertex CL8801 LED driver. It appears to be similar to the Seoul Semi driver. There are modifications that add caps across the LED strings in order to keep them on for more of the AC voltage waveform, which reduces the flicker, but presumably reduces the power factor.

electronupdate said:

I could not find a commercial bulb with this IC in it but I was able to order the component from Digi-key.

Click to expand...

About a year ago I bought a ceiling light from home depot, when i opened it up i saw that all it was was an acrich module stuck in a standard fixture. There was no heat sink or even any thermal paste / tape between the module and the steel of the fixture. In the end i ended up taking the module out and putting it in the existing fixture that i had planned on replacing...

Specs according to the box are:
998 Lumens
58 Lumens / Watt
16.92 watts
82 CRI
2819K
35k hrs

If i recall properly i think is was ~29.99

Seoul has 4 or so different wattages of these AC arrays. Look on the left of the page for the varieties.
Some as high as 135 Lumens per watt.
http://www.seoulsemicon.com/en/html/Product/product_view_compare.asp?catecode=100204

Lynk Labs is making these "power supply-less" 120 volt AC arrays also. Looks like some of them have a solderless connector on the board, making connection effortless.
Warm dimming is a option also.
Their partner http://www.trpssl.com/ac-120v_round.html
and Lynk Lab's blurb http://www.lynklabs.com/images/SR114-20WD-120 20W Warm-On-Dim Product Summary.pdf

Digikey is advertizing a more conventional Seoul 3v chip that has a 95 CRI and 180Lumens/watt. Amazing!
http://www.digikey.com/product-high...wer-5630-leds/50876?WT.z_Tab_Cat=New Products

Brian

Recently purchased this from Aliexpess price is very cheap INR98 per piece.Can any body know any information about it ?

Steve K said:

The Acrich2 modules are a very efficient design, and should be relatively reliable. The downside, as you note, is the flicker. I've built a nominal 100W replacement using 8 watt Acrich2 modules, and I don't notice the flicker. Works great for me. Pics are here:
http://www.flickr.com/photos/kurtsj00/sets/72157632507952012/

There are others using this method of switching segments of LEDs in and out as the voltage changes. One example is the Supertex CL8801 LED driver. It appears to be similar to the Seoul Semi driver. There are modifications that add caps across the LED strings in order to keep them on for more of the AC voltage waveform, which reduces the flicker, but presumably reduces the power factor.

Click to expand...

Flicker is one of those things were what you can't see can hurt you.

Headaches, eye strain, etc.

I can't say I notice flicker of these AC driven sources without trying, i.e. waving fingers but after a while with them I get a headache.

Semiman

I've had mine for a year or so, used for 5 or 6 hours a day, and no problems of any kind. It's a shame that there aren't published specs for the flicker for all of these devices, but I would expect to see differences between types.

I don't recall the specifics, but I believe someone is bringing out modules that are similar to the Acrich, but with some caps on the LEDs to make the on/off transition more gradual.

Everyone will have different sensitivities. If you buy your light from a store instead of making your own, you can easily return it and get your money back if you aren't happy with it.

SemiMan said:

Flicker is one of those things were what you can't see can hurt you.

Headaches, eye strain, etc.

I can't say I notice flicker of these AC driven sources without trying, i.e. waving fingers but after a while with them I get a headache.

Semiman

Click to expand...

I am still not received the product after receiving i will post detail. But i am using this module for outdoor lighting purpose so flickering not a problem.

Steve K said:

There are others using this method of switching segments of LEDs in and out as the voltage changes. One example is the Supertex CL8801 LED driver. It appears to be similar to the Seoul Semi driver. There are modifications that add caps across the LED strings in order to keep them on for more of the AC voltage waveform, which reduces the flicker, but presumably reduces the power factor.

Click to expand...

TI offers an inductor-less stackable LED string MOSFET driver which uses capacitors, TPS92411: http://www.ti.com/product/TPS92411 Dave

That might be what I was thinking of... neat gadget! I'm tempted to make a light with these, but the datasheet appears to steer the user to composite LEDs with a total Vf of 20v. I was thinking more of the recent Cree LEDs in their little 3 (or 4?) mm package with a Vf of 37v. These just don't seem like they could be used with these T.I. parts when the AC voltage is 120vac.

But... they still have the virtue of letting you select the LEDs that you want to use, instead of being stuck with the Seoul LEDs in the Acrich, for instance.
For those concerned with flicker, this T.I. part breaks the AC waveform(and LED array) into three sections versus the two sections of the Acrich2, so the flicker amplitude will be reduced. Add in the smoothing effect of the capacitors, with the result of making the change in illumination more gradual and less jarring. All in all, this could result in some interesting products showing up in the stores.

The number of sections makes no difference to flicker really. Acriche2 is 4 sections.

It all comes down to storage ... which is not unique to TI.

Different Acrich modules have different number of sections. The little 8W modules that I used only have two different states as far as how many LEDs are lit up.

I don't have any experimental data, but since the manufacturers are moving from the original designs that just had one big block of LEDs that were either on or off, moving towards 2 or 3 or more groups of LEDs that sequentially powered on and off, and now adding caps to the LED groups to gradually turn each group on and off... I'm assuming that they have data showing that it is more pleasing to the user.

The caps make things look better. More sections do not make a lot of difference.