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DiscoverCircuits.com -- Hobby Corner
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Tuesday, June 01, 2021 03:06 PM
Hobby Circuits List
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More
Flashers & Blinkers
LED's |
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Line Powered White LED Array
February 27, 2010
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| There has been a lot of
excitement lately in the lighting industry. Some companies are beginning to
manufacture general lighting fixtures, which replace incandescent and fluorescent
lamps, using LED lights. When proper heat management is designed
into the
light fixtures, these LED lights can produce more light with less electricity and
last much longer than other devices. They can also operate well in cold
temperatures. Some of these new lighting fixture designs use a large number of
white LEDs, wired into long series wired string arrays. The circuit below is
designed
to provide a regulated DC voltage for these strings. |
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Examples of LED Lights Using an Array
of Small Devices |
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circuit begins operation by first rectifying the AC voltage with a bridge rectifier. The
pulsating DC output of the rectifier is fed to a switch circuit. This circuit operates
as an intelligent voltage switch. The NPN transistor Q1 in concert with the
n-channel MOSFET Q2, routes a specific peak voltage to the storage capacitor C2.
The voltage is selected to be 5 to 7 volts higher then the total forward voltage of the
LED series string. The capacitor C2 should be sized based on the rule of thumb of
4000uF per Amp of current. If the LED string requires 20ma of current, the
capacitor should be at least 80uF. Select the voltage rating of the capacitor to
be higher than the peak voltage. I would also suggest using a quality capacitor
with a 105C temperature rating. |
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15v zener diode limits the voltage to the gate of the n-channel FET Q2 and also limits
the voltage across the transistor Q1. This circuit will also operate with 240vac
power lines, however, the transistor Q2 should be one with a 400v rating. The
circuit works best when the LED array voltage is above 30v and the total current does
not exceed 1/2 Amp. |
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Click on Circuit Below to view PDF of Schematic |
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