NCP3065 Step-down

This was one of my first designs when I started designing power LED circuits. The DC/DC controller is ON-Semi NCP3065. It requires power inductor, schottky diode and some other passives. NCP3065 is PWM controller suitable for many topologies, including buck, boost or sepic. Circuit presented here is classical step down buck (click to enlarge):

NCP3065 is nice circuit with internal power switch capable of switching up to 1A currents. For step-down and power LEDs in 700mA-900mA range it is enough. I designed circuit with Coilcraft “DO” series power inductor:

Coilcraft DO3340 power inductor datasheet

First prototype was ugly, but it run when plugged for the first time:

Complete altium project is here: NCP3065 Step down (BUCK) altium project

And documentation in PDF is here (full schematic and PCB assembly drawings): NCP3065 step down project

I still have some professionally manufactured PCB circuit on-stock. Anyone interested just send me an email:

Circuit shown in schematic above has additional PWM control input for LED dimming purposes. PWM frequency could not be too high. I tested with 15kHz, which is above average hearing limit and it works well. Circuit was used to build some sports lamps for MTB. Also my kids were happy with lamps for winter activities.



  1. Digvijay says:

    Hi, I am Digvijay from India designing same circuit without external PWM.
    Design Specifications:
    Input Voltage: 32-34 V AC ( direct 230V AC is not available for me. 230V AC is converted to 32V AC with the help of Transformer)
    Output : 5W,17V,350mA COB LED
    Can you guide for the same?

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