If they are the same type as Mike's, the capacitor is a series current-limiting element on the AC input side instead of a decoupling cap on the rectifier bridge's output.
I think it shouldn't be any worse than the flicker from fluorescent tubes. Are you particularly sensitive to lamp flicker, or do you find these lamps especially bad?
It depends a lot on the effective duty cycle. If you've got a few of those LED filaments in series so that the Vf isn't far from the AC peak voltage, duty cycle is going to be very low with a very steep rise and fall, making flicker much more obvious. I'm not sure what the output waveform of a fluorescent tube would like like, but I suspect it'll have longer rise and fall with a reasonably long on-time, which is why most people aren't much bothered by them.
I've found there seems to be two types of these laps, one has some white plastic near the base. I assume it is there to cover the more electronics built in.
If I move my hand fast, I see 6/7 distinct hands before me. It generally drives me crazy, I cannot stand the light. I might be a bit sensible for this though, I found even a multiplexed LED screen (with MAX7219 500Hz) on lower brightness levels annoying.
It is possible to build these lamps with a smoothing capacitor after the rectifier and that would eliminate the flicker. But it would have to be an (expensive) high voltage electrolytic and it would be an additional possible point of failure, especially if it were a crapxon branded capacitor with a low temperature rating. Possibly such a capacitor could be added as an aftermarket modification?
A base of an E14 fitting is like 14mm x 15 mm (from memory) so you really dont have much space for electronics. What I expect to be happening, is rectifying mains, smoothing capacitor, and constant current linear drive. The two filaments are in series, so it would turn on at 140V.
I dont want to mess with the bulbs and fittings, what I have in mind is to convert my lamp to output DC or at least somewhat smoothed DC. I hope the rectifier inside are properly rated for this. If Mike is right and they have a capacitor on the mains directly, then I'm in trouble, and I'm actually not sure what to do with thees other than break them for the filaLED (made up word, seems apropriate).
Those scope screens are worth a thousand word.
Clive has torn down a bunch of these lamps on his bigclivedotcom YouTube channel. Mostly he finds a series dropper capacitor on one arm of the mains input followed by a bridge rectifier and then the LED string directly on the DC side of the rectifier. So the LED strings will only light up when the mains voltage cycle exceeds the forward voltage of the LEDs. For a large part of the cycle the LEDs will be off, which is consistent with the scope trace Mike showed.
With the series dropper capacitor arrangement the lamps will not work if you feed them DC, since the dropper capacitor will become a blocking capacitor. To make an improvement the lamp would have to be disassembled and the internal electronics modified.
Yes, that is what I was afraid of. Technically, if you would make an external say 150V power supply and a PWM from it at say 1Khz, the series capacitor would be a short circuit, and the parallel would be properly sized but I think it is not really worth my time.
The result was easily foreseeable: between the ballast's inductive nature keeping the arc alive as voltage drops and the phosphor storing UV lights before it can re-emit it as visible, there is not much down-time on FTs with a good ballast and tubes.
The fluorescent waveform is a hell of a lot smoother than I would have expected! What sort of lamp was that?
The shape of the LED waveform is interesting, particularly how slow the decay is. Is that due to the junctions heating up over the course of the on period, lowering the Vf? It would be interesting to see the voltage and current waveforms along side.
The shape of the LED waveform is interesting, particularly how slow the decay is. Is that due to the junctions heating up over the course of the on period, lowering the Vf?
The thermal impedance and specific heat would not have enough bandwidth for LEDs to warm up and cool down that fast.
The reason for the stepped waveform on the LED is most likely simply the LED turning off after the AC peak (rapidly diminishing current through the series cap until IF=0) and the step on the way down must simply be the phosphor layer's stored energy radiating out.
Regardless of exact scale and transfer function, the general shape definitely looks like there is current for about 4ms per half-cycle, then phosphor glow for about 3ms (LED turns off, no more blue, hence the sharp-ish drop to 2/3) and nothing of significance for the remaining 3ms.