Offline Buck Converter - Output Capacitor selection

Thread Starter

Mark Ariel Livelo

Joined Feb 20, 2018

I'm Mark, I have a project using Buck LED Driver constant current to produce 10-Watts with 36 voltage output.
I have tested the below circuit connected to resistive electronic load with the power efficiency of 89-90%. But after I tested with actual LED load, the input power is increased but same output power thus the efficiency is dropped by 5-6%. I tried changing the value of output capacitor ranging from 22uF to 47uF, 88uF, 100uF and 220uF the input power is decreasing as capacitance is increased thus the efficiency is going back to the gathered result. Due to the mechanical design, the size is limiting my capacitor selection. Is it because of impedance mismatch as the LED is not resistive load (I am not sure) ? Can someone explain why is this happening or is there any other components I can change to improve the power efficiency without affecting the PF and THD.

Below is the schematic for your reference.