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IC Choice for Boost Converter or Flyback Design

Ilkay
Intellectual 310 points
Other Parts Discussed in Thread: UCC28810, UCC28811, TPS92690

Hi All

I have a new LED luminary design. It is something like big projector. I have 96 pcs MK-R LED's and driving current is 400 mA. We are using 12 V model of MK-R LEDs'. A MCU will control LED drivers via PWM signal. Input voltage is 48 V. I'm thinking about LED driver topology. There will be a lot of string. I thinked about 2 topology.

1 ) Boost Converter : I will increase voltage 48 V to 150 V and make 12 series strings and drive each string with one boost converter and control LED Drivers via PWM. But it is hard to find wide input voltage range, dimmable and output voltage is larger than 100 V boost converters.
I thought about use boost controller with external mosfet and make external Vin 12 V or something with any buck converter. And I will supply boost stage with 48 V. For total luminary we need 8 boost converter.


2 ) DC / DC Flyback Converter : I'm thinking about UCC28810 or UCC28811 to make flyback converter and dim via PWM this. I will make 300 V or something like that output voltage and 24 LED's series. For total luminary we need 4 flyback converter.

Could you make suggestions or which way is more suitable for this application ? If you need further information please let me know.

  • 0
    TI__Expert 3495 points
    IIkay: Boost converter is a simpler solution. David Zhang
  • 0 in reply to David Zhang
    Intellectual 310 points

    Dear David Zhang

    Thank you for your reply. As I wrote in my post, could you make a suggestion for boost converter ?

  • 0 in reply to Ilkay
    TI__Expert 3495 points
    IIkay: I suggest TPS92690. It has wide input voltage range from 4.5V to 76V.
    David Zhang
  • 0 in reply to David Zhang
    Intellectual 310 points
    Thank you for your suggestion but the specification of TPS92690 says the output voltage is up to 72 V. As I said before I need 150 V output voltage. Do you have any suggestion or opinion to do this design ?
  • 0 in reply to Ilkay
    TI__Expert 3495 points
    IIkay:
    The max output voltage is 72V if the IS pin is connected to the drain of the MOSFET. If you connect the IS pin to the source of the MOSFET with a current sense resistor between the MOSFET and the ground, then the IS pin does not see high voltage and the output voltage can be higher.
    David Zhang
  • 0 in reply to David Zhang
    Intellectual 310 points

    David : Thank you for your suggestions and explanations. I ordered samples and demo board. I will try to solve our design with TPS92690.

  • 0
    Intellectual 310 points

    I ordered samples and EVM. I'm thinking about protection devices and EMI filter stages. I draw a block diagram as you can see attached.

    Protection Devices Stage : I'm thinking to use TVS diode and Resettable fuse in this stage. Do you have any other recommandation ? And I'm asking about selecting resettable fuse part.

    EMI Filter Stage : I'm thinking to use pi filter like Cap - Inductor - Cap. What do you think about "Radiated Emission" and "Conducted Emission" about this design ? I know it is hard to say before see any result of test about design but I want to know is it acceptable according your experience ? Or do I need to think about "Common Mode Choke" or something like that ?

    Block_Diagram.pdf

  • 0 in reply to Ilkay
    TI__Expert 3495 points
    IIkay:
    This is DC/DC LED driver. Do you know what EMI standard you are trying to meet?
    David Zhang
  • 0 in reply to David Zhang
    Intellectual 310 points
    David : Thanks for your attention. It would meet this standards. I must decrease output voltage of DC/DC LED Driver from 150 V to 120 V because of safety issue. The luminary will be Class 2.

    Radiated and Conducted Emissions : IEC 55015
    Radiated and Conducted Immunity : IEC 61547
    Harmonics : IEC 61000-3-2 Class C
  • 0 in reply to Ilkay
    TI__Expert 3495 points
    IIkay:
    Those standards are for AC/DC power supplies. I think you are trying to have the whole system comply with those standards. I don't know if what AC/DC front end you are using. If you choose an AC/DC power supply meeting those standards, the whole system is likely to meet the conducted EMI and harmonics. You don't need extra EMI filter between the 48V DC and DC/DC LED drivers. The radiated EMI is more complicated.
    It depends not only on the circuit but also on the mechanical housing. So the important thing is the AC/DC power supply.
    David Zhang
  • 0 in reply to David Zhang
    Intellectual 310 points
    David : Yes, we will use like this first project but we will sell them without AC/DC power supply. I double checked certification issue. We don't need to test our luminary according IEC 61000-3-2. If we want to sell luminary without power supply, we need to DC powered luminary according IEC 55015 and IEC 61547.

    Do you have any idea to pass IEC 55015 with Pi filter ?
  • 0 in reply to Ilkay
    TI__Expert 3495 points

    IIkay:

     

       You have to check with an EMC lab to find out how they test the EMI of DC power supply. If they use an AC/DC power supply as a front end, you probably don't need a filter. If they test EMI directly without AC front end, you may need the filter.

     

    David Zhang

  • 0 in reply to David Zhang
    Intellectual 310 points
    David : I already talked with EMC lab and they said as my previous post. We want to sell luminary without AC/DC powersupply for solar systems. So they will test our luminary with DC 48 V supply and check it for IEC 55015 emissions.

    I want to know there is almost 480 W power and can pi filter handle EMI issue or I have to go another EMI filters ? I know there is hard to say it will pass or not but I think someone will say it could be or no way to pass with pi filter.
  • 0 in reply to Ilkay
    TI__Expert 3495 points
    IIkay: Then you need EMI filter to pass. A pi filter is a good starting point.
    David Zhang
  • 0 in reply to David Zhang
    Intellectual 310 points
    David : Thank you for your time and attention. I will start schematic design and I will try it when EVM arrived.