How to Convert AC110V to 3.2V 200mA without transformer?
Trying to replace lamp with 10 White LED (Extreme Light LED).
Put the LEDs in series so they drop 32 volts - that way they each get
the same current (LEDs) aren't going to drop exactly 3.2 but a range
from 3.2 to 3.8 (for white ones).. In parallel some will hog more
current than others.
Use a point six (0.6) microfarad non polarized (polyester is good) cap
with at least a 300 VDC rating or 120 VAC rating in series with one
leg of the full wave bridge rectifier that serves the LED string, The
rectifier only has to carry 20 ma but use something like a 1N4003 or
so. Add a 100 ohm 1/4 watt resistor in series (serves as fuse and to
limit inrush currents - in series with the cap)
You use ohms law to decide what capacitive reactance you need. In the
above example I used 4.4 K, at 120 volts AC 60 HZ, to drop 88 volts,
at 20 milliamps.
The formula to solve for Capacitance in Microfarads is
159200
C= ---------------------------
F Xc
F is frequency (your power mains)
Xc is capacitive reactance in ohms (to drop the required voltage)
Can't find a point six cap? a .56 will work it isn't too critical
There are several schemes for using caps to run LEDs from the power
mains. I like the FWB, but you could just put a shunting diode around
the string to keep the wrong polarity from frying the LEDs in their
reverse breakdown mode - the downside of that approach is it takes a
larger cap to get 40 ma through the string - at half wave power - and
the LEDs flicker a little bit, and the cap will cost more.
You could, of course, put a separate circuit for each LED and use the
appropriate cap for each (~.40 uf) but that costs more and takes up
more room.
I have an LED night light that's been on for around ten years now
(three red LEDs)
