Designing/chosing components for PT4115 led driver

Discussion in 'The Projects Forum' started by Sindre Brun, Feb 14, 2018.

  1. Sindre Brun

    Thread Starter New Member

    Oct 23, 2017
    1
    0
    Hi

    I'm designing a driver to control 10 3W LEDS. They all have a forward voltage of 3.2V - 3.4V and expect a 700mA current. Since I want to learn PCB design and SMD soldering, I want to design my own driver. The proposed driver will be used to drive 5 of the LEDs, and so I'll use two of them.

    The leds will be used in a WakeUp light, ie I'll gradually increase the light over a period of 15-45 minutes. Because of this, it has to be dimmable. I've settled on the PT4115 driver, because I can find them dirt cheap on aliexpress.

    The circuit I'm using is the reference design in the datasheet, but I just want to make sure that I'm chosing the correct parts. Aside from an intro class to circuits about 2 years ago, I don't really have much experience with electronics.

    This is the reference schematic/"typical application" from the datasheet:
    Typical application.PNG

    My LEDS are rated for 700mA, and I = 0.1/Rs, and so I was thinking I would use a 0.15ohm resistor. This would give a 666mA current, just to be safe. A standard SMD 0805 sized resistor should do the trick?

    The diode D is a Schottky SS24 diode. [Link]
    The inductor is a 68uH with a saturation current of 2A [Link]
    The capasitor is a 100uF tantalum capasitor [Link]

    In addition, I read that the DIM pin is sensitive, and that is should be protected. Therefore I'm adding a Zener diode of 5.1V with a 10k resistor as a clamp is that would work? I'm not quite sure if this is right.

    Zener diode is this one [Link]

    My circuit (designed in KiCad) looks like this:

    My circuit.PNG

    Note that the resistor value is wrong in the schematic, it should be 0.15.

    So my question is, does this look like the right components, and/or are there any other errors with my design? I'm thinking that I have to drive this with a 24V supply, as this is the easiest supply to get hold of, while 18V would be to little?

    The DIM pin will be driven by a Wemos or other micro controller. Here is the entire solution:
    Schematic.PNG

    So does this look like it will work?

    This is my first post, so feel free to give me feedback on the format of the post as well, but preferably in my message box instead of cluttering the thread. :)
     
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