I want to build a Spot light with 18 LEDs Superbright , White, for 220 V (AC), socket GU10.?

Question

It;s cleat that i have to find a socket (an old halogen light), but i think i have to use some resistances or something. Can someoane give an ideea on how can I do it? Thanks

Answer 1

This is not a trivial problem. First, the LEDs emit in a fairly broad forward pattern, not exactly what you want for a spotlight. You will need to arrange them in a tight cluster and place them at the focus of a parabolic reflector, pointing inward toward the reflector, not outward. Perhaps you can salvage such a reflector from a discarded spotlight that used an incandescent lamp. Second, the usual way to power bright white LEDs is with a switching power supply. The 220 VAC line is first full-wave rectified with a diode bridge rectifier, then the DC output is applied as the input to the switching regulator. A transformer is usually required to lower the output voltage, along with an inductor, a capacitor, a fast-switching diode, and the integrated circuit switching power supply controller, and perhaps a power FET to switch the primary of the transformer if the IC doesn’t have the required voltage or current capability.

There are “cookbook” circuits available on-line for this, but it does require some skill and knowledge to implement the circuit correctly and reliably. I would not recommend trying to operate a series string of LEDs directly from the power line. The reverse voltage will kill them. Use a step-down transformer, followed by a full-wave bridge rectifier and filter capacitor, to power a series-connected string of LEDs through a current limiting resistor. This is not very efficient, however.

Answer 2

You're going to need some exotic control circuitry to do this. When an LED is lit, it has at most a 1 volt drop across it. You will have to drop the voltage from 220 to less than 20 volts assuming you put them in series. You might be able to do with with a dropping resistor if you know the current through the diodes. Now, keep in mind that an LED is a diode and only conducts in one direction so it will only conduct during 1/2 the voltage cycle. An LED is meant to operate in the conduction mode and if the diodes are all in series, when the direction of the AC signal reverses, each diode will have over 10 volts of reverse bias across them on the average. This may be sufficient to destroy the diodes. Also since you will only be conducting for 1/2 the cycle, you will probably notice flicker in the light and you will only be producing 1/2 the light compared to having the diodes constantly lit. You may want to use a transformer to drop the voltage to something more manageable and put in a rectifier circuit to get DC out to eliminate the reverse bias problem and the flicker and lower power output.