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RGB LED bulb design issue

Rajendra Khope38
Prodigy 20 points
Other Parts Discussed in Thread: TPS92518, TPS92515, UCC28810, LM3463
We are designing smart WiFi controlled LED bulb with R,G,B cool white & warm white LEDs.

This is a bulb with three colored leds (RGB) each with 10 in series.
Also 10  each LEDs for Warm white and Cool white in single assembly.
total number of LEDs will be 50.

We need to have total 5 channel PWM dimming possible.
We'll be using suitable WiFi microcontroller for dimming purpose and connectivity.

LED specs: max current 350ma
Forward Voltage: 2.4 to 3.1 v (different for R, G, and B LEDs)
LEDs in each string 10
total strings 5 (R,G,B,CW,WW)


Please suggest TI solution for atleast 5 channel dimming of LEDs.
Total possible Wattage of bulb should be 10 to 12 watt.



Kind request to direct us to some TI integrated solution or reference design for above problem

  • 0
    TI__Mastermind 28655 points

    Hello,

    What topology are you interested in using.  Are you planning on a PFC device to create a voltage rail for these five channels of LEDs to run from?

    Does it need to be isolated?

    Does it need to interface to a triac dimmer?

    Are you looking for a linear regulator for the five channels or switching regulators?  If you plan on using switching regulators would they be buck, boost or other?  Linear will not be as efficient with the different LED stack voltages.

    Is space/size a concern?  We have a two channel buck converter, TPS92518 as well as other parts but need to know what you plan on building.

    What frequency are you considering for PWM dimming?

    Is the total power 10-12 watts meaning that the total current through all strings is about 350 mA?

    Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points

    Hi,

    Thanks for quick reply! 

    As I already mention, what I'm planning for retrofit RGB LED bulb.

    With following design requirement.

    1) Input Voltage 110 to 230 (95 to 260v), Frequency 50HZ (India)

    2) Might Need mostly transformerless design to get approx 40vDC from 230v AC.

    3) I want have 3 sets of Red, Green and Blue 3030 type LEDs string each containing 10 LEDs for each color.

    (These are not single RGB chip. These are separate R,G,B LEDs)

    Total 30 LEDs

    4) Also on same panel need 2 strings of Cool White and Warm White LEDs for getting additional Luminance. 10 LED each.

    Total 20 LED (10 WW and 10 CW)

    5) Total LEDs including R,G,B,CW & WW with each string of 10 LEDS will become 50 LEDs. 

    6) Each LED has forward current max of 350ma and forward voltage max of 2.6v to 3.4 v

    check out specs: 

    LEDs type are :


    if topology you mean is about LED connection arrangement & configuration!

    A) then probably series-parallel is better. each color will be having 10 LEDs in series so that each channel can be dimmed separately.

    So if I can understand this each string will need 350ma current and forward voltage will be 34v Max.

    B) You asked about Power Factor correction , but i'm not sure about this.

    C) Isolation - Isolation can be avoided to keep design simple, but i'm not sure if it's better to have as I've WiFi microcontroller on board.

    D) Interface - No! absolutely not! no triac dimming, What I need is to be dimmable to control from microcontroller. I'll be including wifi microcontroller along with this design

    to control this dimming external from Mobile App. This mostly will be PWM dimming.

    E) regulators - switching regulators will be prefered with buck.

    F) Space concern is there as its Incandescent Bulb form factor.what we want is retrofit bulb.

    But it's not that hard, I'm free to change Bulb design and size if better suitable solution is available.

    G) PWM freq - currently I'm working with 5000 Hz LED base freq in my test firmware for dimming. But microcontroller offers me to change it as per need.

    H) total watt:  I'm also really concerned about this. Each string is going to consume 350 mA leading to 1.75A. Considering Voltage for each string 34 volt

    total wattage goes up to 59 watt. But I want to keep the total wattage in between 15 to 10 watt. Considering that not all LED string will be at

    max operating voltage/current always. As per the specification each LED has different Flux o/p for different Vf voltages, So i'm thinking of

    if it can be controlled through proper biasing as per max flux needed for each color and different intensity of each color leading to less or

    more voltage/current in each string to keep watt consumed in desired range. Also managed from firmware programming to generate always a 

    color combination to keep watt in range. For White color we already using White LEDs so no need to use full power RGB to get white.

    I hope i'm satisfying what clarification you are expecting. Let me know if you need additional information.

  • 0 in reply to Rajendra Khope38
    TI__Mastermind 28655 points

    Hello,

    You could look at using the UCC28810/11 as a buck or a buck/boost to create 40 volts.  Then TPS92515 or TPS92518 for buck converters, there are other buck converter parts available as well.  There's also the LM3463 that would be a linear solution that can be dimmed.  I imagine you will have to create lower voltage from the 40 volts for the micro.  Isolated versus not shouldn't matter for the micro if it is wireless.  You won't be able to run all the strings at 350 mA since there will be too much heat in the bulb and the 40V buck converter will have to be design for that much power.  You'll have to figure out what worst case is before deciding the design for the buck converter.

    Regards,