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# 5mm 6 no of led for night lamp to plug in 230v 50hz power supply ? Answered

i want to make 5mm 6no. led night lamp can directly plug in 230 v ac household power supply ? is it possible ..

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## 3 Replies

Jack A Lopez (author)2013-06-29

Is that 6  5mm sized LEDs?  What color(s) are they?

I am thinking this night light thing of yours could be implemented using a capacitor in series with the LEDs, and maybe a small resistor also, although I would rely on the capacitor's impedance to  50 Hz AC to do most of the current limiting.

The formula for this impedance is, X  = 1/(j*2*pi*f*C).  So, for example, a 0.1 uF capacitor, at 50 Hz, has an impedance of  about 3.18e4 = 31800 = 31.8 K ohms.

The really neat trick to this is the capacitor is not dissipating any real power.  In contrast a resistor of the same size would dissipate I^2*R.  For example at 10 mA of current that would be  I^2*R = (10e-3 A)^2*(31800 ohm) = 3.18 watts.

Regarding the capacitor, you kind of have to pick one that can actually withstand having around 230 V AC across it.  An electrolytic, or any polarized type, capacitor will NOT work for this, since those kind of capacitors actually require the mean voltage across them to be DC.

Anyway, if you let me know how many (6?) LEDs, and what color they are, I will try to come up with a circuit diagram for this.

bwrussell (author)2013-06-28

+1 to AndyGadget on using a wall wart but the actual calculated resistance is 90 ohm so I would suggest rounding your resistor up, to 91 ohm, or you will be drawing too much current which will decrease the life of the LEDs and could potentially cause a burn out.

I'm also a fan of THIS wizard for LED arrays because it does the parallel/series calculation for you. Not a huge deal with such a small array but if you ever do something bigger or with an odd number it can save some trial and error on picking the number of strings.

Also note that these calculations we've posted are making an assumption about the forward voltage of your LEDs (one calculator used 3.6 V for white and the other 3.3) and output voltage of the transformer. You will need to rerun the calculations when you've picked out components.