LED current oscillates (is it bad?)

[eem2am]

Hello,

I have designed an offline LED light and here is the input DC bus voltage and LED current.

DC bus voltage and LED current
(LED current pink, DC Bus volts = green)
************

(https://i26.tinypic.com/k4b7uo.jpg)

DC Bus voltage and LED current (Close-up)
(LED current pink, DC Bus volts = green)
**********

(https://i26.tinypic.com/eukdop.jpg)

As you can see, the LED current suffers an oscillation of some 5KHz..
-this oscillation is about 5mA peak-to-peak.
The average LED current is 280mA.

This oscillation of LED current is not going to cause any visible effect to the LED light.
Also, at 5KHz and 5mA peak-to-peak, that’s far too low a frequency to ever cause a radiated emissions problem. ??

So will it be acceptable to just leave this oscillation there?

I can get rid of this oscillation by increasing the gain and phase margin of the feedback loop,
-however, doing this means that my LED current then deviates by some 30mA peak to peak at the twice_line_frequency , as it cannot overcome the input line voltage variation which I have here.
-I could make the input line voltage “flatter” by using more capacitance at the input, but that just makes the power factor worse, so I can’t do this.

-here is LED current without feedback loop oscillation, -but with the twice-line-frequency apparent due to increased phase and gain margin.

(Pink = DC Bus volts, Green = LED current)
******************

(https://i28.tinypic.com/rhq4uu.jpg)

so in summary , am i ok EMC-wise with the 5KHz oscillation in LED current (5mA pkpk) ?

 

[pauloynski]

No problem at all except that for the fact the led current seems to be fairly high. If it is within the current range of the led this is also OK.