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TPS92411 increased current drive

Adam Reed
Prodigy 250 points
Other Parts Discussed in Thread: TPS92411

I have an LED driver  design challenge and need some further information.  I need around 22 watts for a large volume cost-sensitive room fan lighting design.

I've gone over the TPS92411 data sheet and EVM manuals, and if I look at the TPS92411EVM-001 reference design,  it seems to me that if I simply doubled up on the number of Cree LEDs and connected each respective new string in parallel  to the strings on the EVM board (in other words 8 for 8, 4 for 4, 2 for 2), that's about all I would need to double output  power.

Is this a valid assumption?  There is  a note in the 110V analog-regulator 92411 modeling software that says basically "this design is good for about 25 watts".  But I need some details about the right way to do this.

Thanks!

Adam Reed

Dendera Partners

  • 0
    TI__Guru 50190 points

    HI Adam,

    On our website we have a excel spreadsheet calculator which can help you to optimize your design:

    http://www.ti.com/product/TPS92411/toolssoftware

    We also have a Tina model if you want to try different configurations.

    Are you finding parallel LED's to increase current is more cost effective than using fewer higher current LED's?

    Regards,

  • 0 in reply to JCHK
    TI__Intellectual 2540 points

    Adam,

    Only adding LEDs in parallel will not double the power or light output.  Actually the total current in the linear regulator will remain the same and you will have half flowing in each string.  The result being more LEDs used, but not 2x the light output.  To get 2x output, you will need to change the current sense resistor (Rcs) by following the guidance on page 14 of the datasheet or using the Excel calculator John mentioned.

    The Cree LEDs used in this EVM are capable of handling more current than we have set as the default on the EVM board.  Without changing LEDs, you can probably achieve 2x output simply by changing Rcs.

    John

  • 0 in reply to JCHK
    Prodigy 250 points

    Perhaps not more cost effective, but my customers really dislike optical hot spots, so I am more inclined to use a lot of smaller, lower power LEDs if there is space.  More LEDs also means more contact area with the heat sink, so gives more efficient transfer of heat.  And if you want to improve lifetime, add even more LEDs and don't run them so close to full capability.

    Your answer about it being OK to simply double up on the LED count for double the power may seem obvious in this context, but for us poor blokes who have had to mostly deal with switching supplies as current regulators, this just seemed to good to be true!  So thanks for that verification. 

    cheers

    Adam