Modding 220V LED for 110V - LED rectrofitting

Projects /  Mods  Original post date: 04/04/2017

The LED ceiling light I ordered 2.5 months ago finally arrived. I guess I didn't read the fine prints carefully and missed the 220V in the description. Ooops.

Here is what's inside:

A bit of google later, I found the datasheet. Only problem is that it is in Chinese and a bit skimpy. (Google translate on mobile is useful for this, but it is not needed here.)

A datasheet is a datasheet...

First clue:

That's probably the operating range. There are 18 LED, so anywhere between 54V to 90V is required to drive them. The sample schematic is a bit skimpy and comes without values, so I copy down what's on the PCB: (41K is actually 91K)

Next are the usual operating parameters:

The symbols part are pretty standard:

Vdd_clp = Clamping voltage: 15.8V - 17.2V at 0.8mA. Probably a Zener diode of some kind.
Idd = operating current: 135uA (max)
Vst, Ist: Starting voltage, starting current: 12.8V - 14.2V, 195uA (max)

Vuvlo: Under votlage lock out: 8.1 - 9.1V

Max voltage drop across the two 510K (during start up) = 510K * 2 * 195uA = 199V
Start up voltage (worse case) = 199V + 14.2V = 213V This is a bit too high for 110V.

This is 213V/(220V * 1.414) = 68% of the peak voltage from 220V AC full wave recification
Using same ratio for 110V: 110V * 1.414 * 0.68 = 106.5V
Take off the Vst: 106.5V - 14.2V = 92.3V is what I'll need to drop in the resistor. 
Working backwards: R = 92.3V / 195uA = 473K.


In theory, just one of the 510K would work, but I am going to use a 470K 1/2W resistor (for voltage rating) and add a 0.5A fuse to the input. They have a serpentine PCB trace for a fuse, but I think that thin wires or tiny bridge rectifier would fail first. :P  Safety people don't like component or wires failing first.

I tested it on my bench supply and it starts at around 70V DC. Good.

I did some prep work earlier today with the LED retrofit I did last Dec. I used to be a Halogen lamp and I replaced it with CF at some point.

Originally the drive sits on the two stand off in the middle. I used 2 piece of transformer cores and bend them so that I can mount the driver vertically so that both of them would get similar amount of cooling. The hot air rises and escape from the top vents while drawing in cooler air from the bottom vents. The new LED ring is one size larger.

This is what I have now: 40W of LED lighting if I could believe them. :) This kind of reminds me of those Radar helicopters or The Time Tunnel.

I wired the light switch as follows to gave a half brightness.

The rings comes with a magnetic base as they are designed to be used for the flat surface of a ceiling light. I have replaced the supplied M2 screws with longer ones so that the base can be tilted a bit for better attachment to the concave surface.