220v=lighting of led(wat resistor use?)

[zer0w1ng]

Yes you are right.

The voltage at the capacitor will become zero at 180 and 360 degrees and discharges the cap thus reversing voltage at this time.
Thanks for the correction and sorry for the confusion.

[TinTopHack]

Ok ra Bay. I am sure na overlook lang yan. It does look confusing sometimes.

[marcelino]

PaOT:
Ngayon ko lang narealized, i should have had powered my "overkill power-on delay" directly from the power lines... nakapag-experiment pa tuloy ako.

[piona]

@TTH

across 220v ac nga pala yong Cap at LEDs + resistor  

i doubt its: (Vpk-to-pk) - (V leds + V resistor) = V cap  

[winn1971]

I am a bit confused here. Have we considered the fact that when the sine wave crosses zero, the voltage across the cap reverses? Let us do this in slow motion.

Let us assume we have a cap connected directly across a 220VAC line. Starting at 0 deg. the voltage across the cap is 0V. As the sine wave rises towards 90 deg peak the voltage across the cap follows with a little lag considering it is a cap  connected directly across the AC line (no resistance except for the negligible wire resistance). At 90 deg the cap voltage will be 220 x 1.414 = +311V. Then beyond 90 the AC starts to drop to zero. The voltage across the cap will also start to drop because it is forced to do so by the source - meaning the cap starts to discharge. This goes on until 180 deg - zero crossing. At this point the AC voltage will be zero and the cap voltage follows. Beyond 180 the voltage reverses and goes down to towards 270 deg peak or -311V. The cap voltage follows also but this time the voltage is reversed (negative). Beyond 270 deg the AC voltage rises back towards zero. The cap voltage follows as well. So if we look at the highest voltage seen by the cap it appears to be just the peak voltage BUT this voltage reverses periodically. From 90 to 270 the cap does not charge to -2VPK because it discharges back to zero at 180 deg. Same thing happens from 270 to 90 deg of the next cycle.
-TTH

This is exactly what i meant when i said the cap will not get 2Vp at any given time because of the "0" crossing.  There's only one "peak" at any given period of time, never summing up together.  I hope we've now reached a common ground.
Thanks tintophack for explaining it better and thanks zerow1ng for the challenge.  this is good stuff!

[TinTopHack]

@TTH

across 220v ac nga pala yong Cap at LEDs + resistor 

i doubt its: (Vpk-to-pk) - (V leds + V resistor) = V cap 

When the cap + resistor + LED are in series, there will be a phase lag due to the cap so the voltage across the cap and the voltage across the resistor and LED will not rise and fall together. The voltage across the cap will lag the voltage across the resistor and LED. So Vpk - (VLED+ Vres) is NOT equal Vcap.

[insomartin]

OT: i love this topic!

[piona]

sino kaya may installed na multisim o proteus para ma-simulate yong circuit para makuha kung ilan dapat ang voltage rating at voltage waveform ng Cap    sana may magpost ng sims nito 

....bagong format kasi pc ko, os lang ang laman 

[rdpzycho]

galing sa post ko dati (almost 2 years ago. )

Non-Isolated, Capacitor Fed, Voltage Step-Down

http://www.hamill.co.uk/pdfs/acfvsdsp.pdf

[piona]

^^ayoss, thanks sir Rd tama pala si sir TTH,  Vpk lang ang gagamitin....

[piona]

teka sir Rd, parehas lang ba yong pdf circuit nyo, sa circuit na ito?



......parang lagpasan lang ang bawat Vpk ng ac source nito a.

[viel_dk]

up ko lng

bakit hindi nalang gumamit ng rectifier para safe tulad ng circuit ng ac/dc adaptor, para di ka makuryente...

balak ko din gawin to, para sa DIY aquarium LED moonlight

any other simple advice please...

thanks

[TinTopHack]

up ko lng

bakit hindi nalang gumamit ng rectifier para safe tulad ng circuit ng ac/dc adaptor, para di ka makuryente...

balak ko din gawin to, para sa DIY aquarium LED moonlight

any other simple advice please...

thanks

It is not the rectifier that prevents you from being kuryente in ac/dc adaptors. It is the transformer that isolates the primary from the secondary that makes it safe.