PT4115 LED-Square

Availability: design files


A small 50x50mm board with 6 high-efficiency Nichia LEDs driven by a PT4115 buck regulator. Total light output was about 180lm for the first version (see below), the upgraded version is essentially twice the brightness. It runs with 24V and consumes about 100mA (first version) / 200mA (upgraded version).

Some images from older versions:

10 Responses to PT4115 LED-Square

  1. Arun says:

    Do I need a zener diode and 1k resistor for DIM pin when using arduino pwm ? or 1k resistor enough ?

    • robert says:

      From personal experience I recommend using a Zener diode plus resistor.

      • Arun says:

        My PT4115 worked well for around 24 hours doesn’t get hot. Now it gets too hot, turns off and on the LEDs alternatively. What would be the reason bad caps or inductor spiking?

        • robert says:

          It’s dead. I had a few die like this before I used the Zener protection. You can measure the dim pin input resistance once you’ve taken out the chip. Should be high when chip OK.

          What supply voltage & LED current were you using?

          • Arun says:

            it is around 37.1 Kilo-ohms . I left DIM pin float . it gets hot even with no load .
            my 2nd chip faced this same problem after 2 weeks.

            • robert says:

              The chips I killed had about 6 Ohm to GND. Symptons: LEDs always ON (no switching, very high current) or always OFF.

              Still, 37.1k is rather low for an input pin. All my boards died by touching them with my fingers while they were on. I guess either ESD or I somehow bridged VCC to DIM. Once I had the Zener-Diode protection on the layout, not a single one has died so far.

          • Arun says:

            which type of decoupling capacitor do you recommend for this IC ?

            • robert says:

              I used 1x 4.7µF ceramic X5R next to the chip and 4x on the bus connectors. This works for my board (200mA, 24V from a clean DC power supply). I don’t remember if I ever measured ripple voltage, it worked in this case. YMMV. There are some hints in the datasheet on page 12.

  2. abies says:


    which uC are you using for the input of your input pin?
    I have been trying an ATMega328p and since at startup, the pwm pins are configured as inputs, the PT4115 drives the LED for a short amount of time (75 ms without a bootloader, a lot more with).
    The PT4115 datasheet indicates a pullup resistor of 200 kO, I have tried a 10 kO pulldown on the PWM pin, it still blinks briefly :(
    On your github page, your schematic states C6 should not be used with a 5V pwm signal which would be my next try. Can you elaborate a bit on this statement?

    Best regards

  3. robert says:

    If I remember correctly, C6 was used as a soft-start option (extreme low pass rc filter). Just on/off. Dimming should still work, but not very responsive.

    You need to look at the PWM output of your micro with a scope. There’s probably some funny business during initialization of the PWM. Try 1k pull down. If it still blinks, the PWM pin is configured as output at some point in time, not just internal pull up.

    If you do your own PWM configuration on register level, make absolutely sure the pin is set to 0 to begin with & input & no pull up & there is no funny business with the compare match registers for the PWM timer (or inverted output). That can generate a 1 tick long blip on the PWM.

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