I've actually googled the heck out of this several times but can't seem to get a definitive answer on what is REALLY going on inside a typical 120v LED bulb.
Is it --
** a capacitor to limit current and a power resistor plus a series stack of leds? (and 60hz flicker isn't noticed?)
** a bridge rectifier (couldn't use a half wave could you?), plus the above?
** or just the rectifier and resistor (no cap)
or?
does anyone know?
I would imagine the same scheme is used with pretty much all manufacturers. Certainly there aren't sophisticated drivers in a lamp (maybe just some higher priced ones?)
I should have mentioned also -- the LED bulbs that are trying to replace conventional medium base bulbs I'm particularly interested in. Popular LED replacements for standard 40w, 60w etc.
conventional medium base bulbs I'm particularly interested in. Popular LED replacements for standard 40w, 60w etc.
B22 is the light bulb standard - at least in OZ. You only asked what they have inside which is pretty irrelevant to what kind of base it has.
This one would easily replace a 40W and perhaps even a 60W. I think the white of the light fools the brain into thinking it is much brighter - in any case it is easy to read under. I think it also comes in ES and if not there is an adapter.
--
We have failed to address the fundamental truth that endless growth is
impossible in a finite world.
Well, this is going to be a really crappy light. it will have a lot of flicker as I assume it generates either 100 or 120 short pulses a second. The better lamps have a switching power supply set up for constant current, and maybe even a PFC circuit that maintains power to the converter through most of the mains cycle. So, it would give constant brightness throughout almost the entire line cycle, with maybe a short dip at the voltage crossing.
That circuitry WILL cost a bit more, but ought to be worth it to the end user. What you describe is basically a strobe light!
Maybe not by manufacturer of the complete lamps, but the makers of the control chips all publish reference designs that are likely VERY close to what is in the lamps using those particular chips. There are ENTIRE magazines devoted to LED lighting circuits, applications, etc. right now!
With plenty of voltage available (during AC peak) and a relatively high series impedance, why would the conduction angle be very short ?
A white LED has a threshold voltage about 2.7 V, so with 30 LEDs this would be 81 V. With US mains peak voltage of 170 V, the threshold voltage would be about 48 % of peak voltage. Thus, some light would be produced between 30 and 150 degrees each half cycle, thus 2/3 of the time. How does this differ very much from fluorescent lamps with 100/120 pulses/s ?
People also tolerated 50 or 60 pulses/second from CRTs for decades (admittedly at a lower surface brightness).
** I just tried a 3mm and a 5 mm white led on a 4 volt, 50Hz source - with a 100 ohm resistor to limit current to 20 mA peak, conduction time was 6mS in each 20mS cycle.
The 5mm LED ( bluish white) appeared to flicker slightly and the 3mm one ( paper white ) did not visibly flicker at all.
3mm green and red LEDs also did not appear to flicker.
"David Lesher" wrote in message news:jcube0$8vf$ snipped-for-privacy@reader1.panix.com...
Might be risky if one LED in one string opens.
The real problem with the circuit using a series capacitor is the high = surge=20 at turn-on (depending on phase angle), and line voltage surges. Plus the = LED=20 current varies quite a bit with input voltage. Why not use a FWB and a=20 simple current regulator? One circuit that should work is as follows. It =
uses a high voltage MOSFET but it's probably cheaper than a big film=20 capacitor. For instance, the BSP125 is 600V 120mA for about $0.35 = each/100.=20 I simulated a string of white LEDs with zeners and one LED. For greater=20 efficiency and usability at lower voltages a switching supply with = inductors=20 may be required. But a circuit like this is dimmable, at least with a=20 variable transformer type control. TRIACs and SCRs, not so much.
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