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High-current SMPS LED driver

Discussion in 'LEDs and Optoelectronics' started by Phaedrus2129, Jan 13, 2013.

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  1. Phaedrus2129


    Jan 13, 2013
    High-current SMPS LED driver (32mm diameter PCB)

    So I'm designing a circuit board with some very unusual characteristics. I have somewhat limited circuit design experience, so I was somewhat wary of tackling a project like this, but I gave it a shot. I think it's come out well, but I want to double check.

    The specifications were as such:
    • SMPS for driving high-current LEDs, with battery input
    • Input voltage: 10.8V +/-0.5V
    • Output voltage: 4.2V +/-0.1V
    • Output current: 9A +/- 0.2A
    • Efficiency: >80%
    • Temperature: -20C to 80C
    • Must fit on circular PCB with diameter of 32mm
    • Budget: <$200 including board

    Turns out this was bloody hard, with the tiny circular PCB. This was probably the hardest layout I've ever done and I had to sort of edge up to the, ah, very limits of Good Layout Practice, just a little bit. ;)

    I elected to use a Texas Instruments TPS53319, which I can obtain a free sample of.
    IC PDF:

    After a great deal of searching, headscratching, and frustration I found an inductor that would work for me: HCTR-441

    I'm using a 300kHz switching frequency. I selected 150uF .22ohm ESR Tantalum caps for the output filtering, 0603 ceramic caps for input filtering and signal, and 0402 1% resistors.

    Now I would have built this on a 3-layer board, but ExpressPCB only offers 4-layer boards and I'm going to go with them for simplicity's sake. So I'm treating both internal layers as ground planes, to help filter noise before it reaches the back of the PCB, and they're cross-linked with vias.

    A final note, the "+in", "GND", and "SW" wires will enter from the back of the PCB, while "+out" and "GND" wires will exit from the front of the PCB to go to the LEDs.

    My main concern is the close proximity of traces, vias, and components, and I'm worried that there may be cross-talk or mechanical incompatibilities in places. I'd appreciate any help or advice. :)

    Schematics updated, below.

    Attached Files:

    Last edited: Jan 13, 2013
  2. Phaedrus2129


    Jan 13, 2013
    I took a 1hr break, and when I came back I discovered a few small errors, as usual. Mixed up the RF and MODE resistors, had a resistor on the PCB when there should have been a capacitor. Streamlined a couple traces. Nothing else major that jumped out though.

    Updated versions attached.

    Attached Files:

  3. Phaedrus2129


    Jan 13, 2013
    No input? :(
  4. davenn

    davenn Moderator

    Sep 5, 2009
    hi there

    cant read your diagrams

    when asking for help, it pays to provide info in a common format that most people can read
    so show us a circuit diagram in GIF format :)

    do a google search on DC-DC buck converters

    Last edited: Jan 14, 2013
  5. Phaedrus2129


    Jan 13, 2013
    Figured ExpressPCB would be ok, it's open source. I took some screencaps.


    PCB (Top, bottom, and silkscreen):

    PCB (Top copper layer):

    PCB (Bottom copper layer):
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The main problem I can see is that this appears to be a voltage regulator.

    Or are you using the over current limit to set the output current?
  7. Phaedrus2129


    Jan 13, 2013
    There will be an additional resistor to make it act as a current source for the LEDs. This PCB is to efficiently step down the battery voltage of 10.8V to 4.2V, for LEDs rated for 3.8 - 4.2V.
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