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The cheap bulb teardown linked to by indiantinker [1] shows that it contains a 100uf electrolytic cap for smoothing. A quick search shows that 6.3 V 100uf MLCC

The cheap bulb teardown linked to by indiantinker [1] shows that it contains a 100uf electrolytic cap for smoothing. A quick search shows that 6.3 V 100uf MLCC capacitors are readily available for ~20 cents. Maybe you can only afford that sort of thing starting in a "two dollar" bulb but it shouldn't require buying fancy $10 bulbs to ensure that the capacitors live as long as the LED. Or are there other considerations that mean non-electrolytic capacitors are unsuitable? [1] http://rohitg.in/2014/10/28/Dollar-LED-Bulb/ http://rohitg.in/2014/10/28/Dollar-LED-Bulb/

rcxdude 7y ago
Well, for MLCC caps specifically, 6.3V is definitely not going to cut it (that's less than the voltage across 2 LEDs, and there will be more than that in series). You'll find that 100uf in 200V ceramic caps will be substantially more expensive ($10 - $100), plus you get fun effects like ceramic capacitors have less capacitance the higher the DC voltage across them. Electrolytics are used when you have no choice, and if you are trying to store a large amount of charge in a small volume (especially on the cheap), you have precious little options.
- philipkglass 7y ago
  Thanks! I was thinking of a single LED. Looking at other teardowns where the actual light emitting elements are shown, I see that bulbs contain multiple LEDs.
Animats 7y ago
This needs a 100V capacitor. 6.3V ceramic caps are easy to source, but not higher voltage devices. Multilayer ceramic capacitors for high voltages are still quite expensive.[1] Not available in surface mount, either. Energy stored is voltage x capacitance, and capacitor size and cost scales according. You have to store enough energy to light the bulb for half a power line cycle in something. If you used 3-phase power to light bulbs, no need for energy storage. 3-phase is always on; you just need a switching regulator to smooth out the ripple. Some large arena lights work that way. Not worth the trouble at home scale. [1] http://www.chemi-con.co.jp/e/catalog/pdf/ce-e/ce-sepa-e/ce-ntd-e-2019.pdf http://www.chemi-con.co.jp/e/catalog/pdf/ce-e/ce-sepa-e/ce-n...

rcxdude 7y ago

Well, for MLCC caps specifically, 6.3V is definitely not going to cut it (that's less than the voltage across 2 LEDs, and there will be more than that in series). You'll find that 100uf in 200V ceramic caps will be substantially more expensive ($10 - $100), plus you get fun effects like ceramic capacitors have less capacitance the higher the DC voltage across them. Electrolytics are used when you have no choice, and if you are trying to store a large amount of charge in a small volume (especially on the cheap), you have precious little options.

philipkglass 7y ago
Thanks! I was thinking of a single LED. Looking at other teardowns where the actual light emitting elements are shown, I see that bulbs contain multiple LEDs.

Animats 7y ago

This needs a 100V capacitor. 6.3V ceramic caps are easy to source, but not higher voltage devices. Multilayer ceramic capacitors for high voltages are still quite expensive.[1] Not available in surface mount, either. Energy stored is voltage x capacitance, and capacitor size and cost scales according. You have to store enough energy to light the bulb for half a power line cycle in something. If you used 3-phase power to light bulbs, no need for energy storage. 3-phase is always on; you just need a switching regulator to smooth out the ripple. Some large arena lights work that way. Not worth the trouble at home scale. [1] http://www.chemi-con.co.jp/e/catalog/pdf/ce-e/ce-sepa-e/ce-ntd-e-2019.pdf http://www.chemi-con.co.jp/e/catalog/pdf/ce-e/ce-sepa-e/ce-n...