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Harmonic distortion of offline Buck LED driver input current waveform

Flyback

Well-Known Member
Thread starter #1
Hi,
The attached is the LED current (green) and mains input current (red) of a 15W offline, non isolated Buck LED driver. There is deliberately no electrolytic input capacitor.
Do you believe that this mains input current would violate THD regulations? I mean, it does have the ringing waveform at the mains voltage zero crossings, as you can see.
(The pink waveform is the mains voltage)

The basic schem is also attached...as you can see, its an extremely simple constant off time Buck
 

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ronsimpson

Well-Known Member
Most Helpful Member
#2
The schematic looks like something I have done many times.
1) You have no current when the line voltage is under +/- 70 volts. You know why.
2) The line current is almost constant at 0.5A when the line voltage is above 70 volts. To get good distortion, normally the line voltage is fed into the current compare to get a sign wave (1/2 sign wave). You are using a IC that was not designed for PFC.
1543782897438.png
 

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