Lytswitch 4313E Driver Design

7 posts / 0 new

Hi,

I am working on a 14W, 8-14V, 1A dimmable constant current driver. I have been using DER350 as a reference for the most part. I am trying to figure out what voltage zener diode to use for the overvoltage protection circuit. In DER 350 they use a 33v zener diode, while the output voltage is 36v. The output voltage is sensed via the bias winding which is set to 25v nominally. If I am understanding this correctly the output voltage for the secondary would then be limited to about 47v to protect the output capacitors? Is that a correct assumption?

Thanks,

Alex

AttachmentSize
PI transformer design52.5 KB
Circuit38.32 KB

Hi Alex,
Yes, that would be the correct assumption. You need to size the zener diode depending on the output capacitor voltage rating, and the bias winding to secondary winding turns ratio.

Hi PI-Logan,

Thanks for your reply.

I am also noticing significant flicker on the output. It is not flicker visible to the human eye. We test for flicker at lower frequency <300Hz (per CA title 24 regulations) using a light sensor. I am measuring high amounts of flicker (70%) in the 120Hz area. Is there a way to remove this flicker (down to <20% is the goal.)?

On another note, the output current is much higher than intended, adjusting the FB resistor should change that but I am not entirely sure as to how that is calculated. Any help on this would be great.

Edit: I tested the output current and bias voltage per the design guide instructions. However because the output current is outside the 10% target range, PIXI generates a warning and suggests a 4Mohm resistor for RV. However that change would increase the output current. What are my options to correct this issue?

Thanks,

Alex

TitleSize
Schematic38.32 KB

Hi Alex,
For the flicker issue, in what condition do you see this flicker? Is it during full load non dimming conditions? Or when you use the triac dimming functionality?
For your output current regulation issue, you can try fine tuning it by referring to this application note on LYTSwitch-4 (step 11, page 17):
https://led-driver.power.com/system/files_force/product-docs/an59.pdf

Hi PI Logan,

The flicker issue is during full load under non dimming conditions with an output voltage of nominal 12v led at 1280mA current. The current however is slightly higher than than the intended 1000mA due to the current regulation issue. Based on the output waveform it seems like the output voltage is fluttering at the edge of the minimum Vf for the led (10v).

Hope you are enjoying the holidays.

Thanks,

Alex

Hi Alex,
Sorry for the late reply. Since the flicker issue is at non dimming conditions, we can assume that it has nothing to do with the dimming mechanism. Based on your earlier reply, the flicker is around 120Hz. This is most likely due to the rectified input reflecting onto the output. You can either increase the bulk cap C7 (this may affect PF) and see if the flicker is reduced, or you can tweak R5 and C8 which, according to DER-350, prevents rectified line frequency ripple. Hope this helps.

https://led-driver.power.com/sites/default/files/product-docs/lytswitch-4_family_datasheet.pdf

Hi PI-Logan,

Thanks for getting back to me. I tried both of those options and they seemed to help, but only in small amounts. I increased the capacitance of C6 and that also helped a little. The combination of the two changes and the increase in C6 seemed to have fixed the problem. The measured flicker isn't completely gone but it is under the requirement for our application so that is a plus. Thank you very much for your help in solving this issue.

Alex