Help identifying an LED.  I think its a 3528 or a 2835 - Page 1
Forum section: electronics / beginners

author: TT_Vert
author_rank: Regular Contributor
timestamp: March 12, 2019, 01:22:48 am
content: I believe dimension wise they are the same correct? is it just the efficiency that separates them? Reason I ask is i have an LED light fixture that I want to swap the lights out for a cool white led. I checked my my adjustable power supply and at 20mA it is around 8.2V which confuses me. If it has multiple LEDS on one chip would it still only have 2 solder pads? Is there any way to visually ID one that has multiple LEDS on the chip? If it was 3 LEDS that means that each had an average Vf of 2.73V which seams low and if two, 4.1V sounds high. Any input would be appreciated. I always seem to get stumped by these things. This particular light has 15 of these in series and has 120Vac rectified and 110Vdc is coming out to an 8 pin chip which I think is a constant current drive but the numbers don't come back to anything. here is also an N channel mosfet in there.Sorry for the basic question here.Dave

author: mariush
author_rank: Super Contributor
timestamp: March 12, 2019, 01:30:04 am
content: Make sure the LEDs are fully open, it could be that at 20mA, the led is still partially closed, so you see a lower voltage. May be 8.5v..9v at 50-100mA.A led can have multiple diodes in series internally, so you'd get only two terminals.Besides opening one led to visually see the diodes, you could limit the current to a very low amount, like 1-5mA and use a microscope or some camera in macro mode to see each diode in the led light up (at a level that your eyes may not detect)

author: tooki
author_rank: Super Contributor
timestamp: March 12, 2019, 07:05:44 pm
content: I think 3528 vs 2835 means the contacts are on different sides.

author: TT_Vert
author_rank: Regular Contributor
timestamp: March 19, 2019, 01:30:33 pm
content: I can not get them even close to 100mA. I did gradually start to increase current w/ my power supply and i didn't really see multiple LEDS but I was looking w/ my naked eye.

author: TT_Vert
author_rank: Regular Contributor
timestamp: March 21, 2019, 11:23:44 pm
content: Can anyone else offer any insight? I'd really like to swap in new LEDS but I'm not sure exactly what to replace these with given the apparent Vf.Dave

author: TT_Vert
author_rank: Regular Contributor
timestamp: March 23, 2019, 08:57:34 pm
content: Last night I was able to increase current mA by mA and I did determine it is 3 LEDs in series which makes sense I suppose. So I believe this thishttps://www.digikey.com/product-detail/en/bridgelux/BXEN-50E-13H-9B-00-0-0/976-1621-6-ND/6618668is what I need. Any opinions? One thing that I am concerned about is that the LED i tested was very bright at 20ma @8.2V and this LED is rated at 9.2V @ 100 mA. I didn't find anything else that was a 3led in series in this form factor.

author: Jwillis
author_rank: Super Contributor
timestamp: March 23, 2019, 10:38:40 pm
content: SMD 2835 Chips look very much like 3528 chips, but they are 4.6 times brighter.Contacts are on the same side. 2835 typically operate at 100mA and 3528 typically operate at 65mA .Sorry tooki

author: tooki
author_rank: Super Contributor
timestamp: March 24, 2019, 09:43:30 pm
content: Quote from: Jwillis on March 23, 2019, 10:38:40 pmThe LED numbers literally are the dimensions in 1/10mm. So 3528 means 3.5x2.8mm, and 2835 means 2.8x3.5mm. You don’t have to believe me, but I’ve seen them specifically with the contacts on different edges by this system, since the contacts are normally on the edge of the second (y) dimension.

author: Jwillis
author_rank: Super Contributor
timestamp: March 24, 2019, 10:31:04 pm
content: Quote from: tooki on March 24, 2019, 09:43:30 pmI don't doubt you have seen them but its not the defining characteristic of the chip. The 2835 are re-engineered 3528 with an increased light-emitting surface area and better heat sinking that allows for increasedr output.

author: tooki
author_rank: Super Contributor
timestamp: March 25, 2019, 12:45:30 pm
content: Quote from: Jwillis on March 24, 2019, 10:31:04 pmWhile I am sure I saw them somewhere in the way I described, I think you're right, in that it sure does seem that your description what's widely used now. (It'd been a while since I bought LED strips.) Even if it deeply offends the pedant in me that the 2835 designator violates the convention of using the second dimension as the one with the contacts!

author: TT_Vert
author_rank: Regular Contributor
timestamp: March 25, 2019, 03:22:49 pm
content: I've seen the same thing the said the difference was the pads. Bickering aside, can someone perhaps answer my question above regarding current draw discrepancies of what I had vs. the item I'm ordering?

author: Jwillis
author_rank: Super Contributor
timestamp: March 25, 2019, 07:53:26 pm
content: Phosphor-converted LEDs such as the 2835 have one single chip that emits Short wave length High energy Blue or UV .The phosphor coating converts some of the blue or UV photons by colliding them with the phosphorous in the coating thereby decreasing the some of the photons energy to Yellow.Mixing Yellow photons with Blue or UV photons produce White light.Higher power pcLeds may have multiple chips which can be observed by dimming the led with lower voltages.Even multi pin pcLeds like the 5050s I have work with the same principle as single pcLEDs but have 3 chips .This gives a higher intensity of light. Since the chips emit Blue or UV they have forward voltages around 3 - 3.5V. The higher the energy of photon required means the higher the energy needed to excite that photon emitted from the chip.15 series chips supplied by 110v-120v means that each chip receives around 7-8 volts. Each chip requires a minimum of 3-3.5 volts (forward voltage) to turn on.This would mean that each chip are rated for at the very least 9v but are most likely rated for 12V . 12V PLCC (Plastic Leaded Chip Carrier) LEDS are the most common used. So a 2835 rated 12V with a kelvin of between 5000 and 6500 would give cold white light