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  1. #1
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    NCP3065 LED Driver Acting Very Strange. Will not work with filter caps.

    I have setup an LED regulator (NCP3065 - http://www.onsemi.com/pub_link/Collateral/NCP3065.PDF ) using On Semiconductors design tool and it seems to have some serious issues, if anyone could take a look and give some feedback?

    Schematic: http://i.imgur.com/70YVN.png (Current circuit will not work with R3, C1, or C2) Works "flawlessly" without them.

    The design is on a breadboard, but should be fine since the frequency is only in the kHz range.

    C3 consists of ceramic capacitors (C0G I believe) for a total of 7nF

    L1 is a 120uH inductor as it is the closest I had.

    D2 is MB2060CT (http://www.fairchildsemi.com/ds/MB/MBR2060CT.pdf)

    Ipk is .333Ohms

    LED Sense is set at 0.5 Ohms

    Input: 11v @ 110mA (Using a BK Precision 9110 Power Supply)

    Output: 0.151v @ 265mA (Output into 3 Silicon Diodes for a load)

    Scope Output using low inductance ground directly across the power supply rails: http://i.imgur.com/H3Hag.jpg (5v/div, 5uS/div)

    As soon as I put a capacitor across the rails the oscillations die down and the chip heats up incredibly fast while dropping the output down to ~70mA (exact same as input current)

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  2. #2
    Advanced Member level 4
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    Feb 2011
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    Re: NCP3065 LED Driver Acting Very Strange. Will not work with filter caps.

    I've used this device in the past, and it worked well, using just the calculated values from the spreadsheet
    (buck topology). I picked a value higher for the inductor, to ensure it would work due to tolerances.
    Your inductor value looks low - is that what the spreadsheet calculated for you?
    For my particular application at the time, the inductor value was higher (and I was operating at 150kHz).
    I don't know if breadboard is good or not - the design was PCB based.
    Last edited by sky_123; 18th August 2012 at 20:12.

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