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Phase shift mains AC to de-flicker LEDs
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Zero999:
Yes, I do remember Big Clive doing a video now, but he didn't reverse engineer the schematic.

Looking at the photograph, there appears to be a full wave bridge rectifier on the top right hand side of the board. Adding a suitable 400V rated capacitor across the DC side should reduce the ripple greatly, as well as increase the duty cycle, hence the brightness. The downside is it will get hotter more quickly. Hopefully the driver will have some over temperature protection and reduce the current, otherwise it will fail more quickly.


A better approach would be to power it off a DC power supply with a lower voltage, than the mains peak voltage but, it's still more sensible to use a higher quality LED lamp, rather than cheap crap.
tunk:
Diodegonewild have also looked at them (including schematic):
Zero999:
Oh, I also forgot to say:

The metal circuit board must be earthed for safety's sake. It's also quite likely they don't meet the bare minimum safety standards as they will lack sufficient insulation between the live parts and earth. If you mush use them, then I repeat, ensure the aluminium board is properly grounded!
Lupin III.:

--- Quote from: richard.cs on March 20, 2020, 02:52:36 pm ---I've attached a very simplified LTSPICE model.

The LED is modelled as having a forward voltage of 250 V, an on-resistance of 100 Ohms and an active circuit limiting the forward current to 200 mA. You would need to tweak this to match your LED and drive. Run the model and plot V(line,neutral) and I(I1).

I find that if I put a capacitor in series then about 4u7 will shift the conduction earlier by around 1.2 ms, which is only 22 degrees. A smaller capacitor shifts it further but also significantly limits the LED current. A series inductor of around 500 mH (huge!) will shift it about 1.5 ms, around 27 degrees, the other way before the LED current starts to drop.

--- End quote ---

Thanks Richard. I'll try that out. Even a 22° shift may already make a difference, since the "dark time" will be shorter. The flicker is at 100Hz, assuming the LEDs conduct about half of those 10ms, so 5ms, a 1.2ms shift is considerable.



--- Quote from: Zero999 on March 20, 2020, 04:18:17 pm ---Oh, I also forgot to say:

The metal circuit board must be earthed for safety's sake. It's also quite likely they don't meet the bare minimum safety standards as they will lack sufficient insulation between the live parts and earth. If you mush use them, then I repeat, ensure the aluminium board is properly grounded!

--- End quote ---

I know this, which is why the heatsink IS already earthed. And not only that, the COB is in a plastic/glass lamp housing (with vent holes for airflow), so the heatsink can't even be touched unless you poke throuh the holes with a screwdriver.
Prehistoricman:
May not be possible, depending on the driver. Some turn off the entire array when the voltage gets too low. More efficient ones will switch in various banks to drop more voltage as the input voltage rises. If you have one of these, then supplying a lower DC voltage will be fine and won't overheat the driver. If you have the former, then you may risk overheating it by running on DC.

Getting 230V or 120V DC isn't particularly easy. Perhaps a dimmer circuit into a bridge rectifier + cap would work, but the peak current might kill the dimmer.

Your phase shift idea is an interesting one but I don't think there's an easy way to do it. Phase shift by inductor or capacitor implies an attenuation in the signal (see any RC or LR bode plot). Then again consider overpowering the module; if you use a diode to switch over to your shifted AC, then you're power the module for more % of the time.


As for questions about why this project should exist, I agree with Lupin that they're unhelpful. I see this all the time on the forum. Some people just want to hack things, and they don't need to justify that to the world.
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