Mains-powered led night-light 2012-11-09

[alec_t]

alec_t submitted a new article:

Mains-powered LED night-light - I'm probably re-inventing the wheel, but here are a few variations of a mains-powered night-light f

I'm probably re-inventing the wheel, but here are a few variations of a mains-powered night-light for 230-250V, adaptable for 110-120V.
View attachment 55863
The component values given are for 240V 50Hz operation with an LED current of ~ 7mA. I've found that quite sufficient for a night-light for a child's bedroom.
If you do need a brighter light the current can be increased in proportion to the value of the capacitor C (e.g. double the capacitance gives 14mA), or additional LEDs (or...

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[peterlonz]

Nice simple circuit.
I have found it very difficult to obtain reliable designs for Mains powered LED's.
I have a few comments:
1) I disagree that a 7mA LED will be adequate for a nightlight anywhere.
I recently found that a 20mA, 12mcd, 5mm Diam, Red Led set up to operate as a pilot was nearly useless in the outdoor sunlight. Remedy replace with 2000mcd which I can see from a distance in bright sunlight. Generally I'd suggest designing (IE offering values for) a 20 mA supply to 5000mcd LED units for night lighting. What has been provided here is more applicable as a pilot IMHO.
2) Why do we need such a high Resistance to bleed off charge, 1MOhm is a bit hard to find. Would a 1K or 5K wire wound, 5W, resistor do the job?
3) why is the fuse as high as it is if we plan to use only a few 7mA LEd's?

 

[alec_t]

I disagree that a 7mA LED will be adequate for a nightlight anywhere

I have two of them giving perfectly adequate night-time lighting of a stairway and child's bedroom. We're talking nightlight, not searchlight!

I recently found that a 20mA, 12mcd, 5mm Diam, Red Led set up to operate as a pilot was nearly useless in the outdoor sunlight

I'm not in the least surprised.

Why do we need such a high Resistance to bleed off charge, 1MOhm is a bit hard to find. Would a 1K or 5K wire wound, 5W, resistor do the job?

No. The high resistance is to minimise power loss. A 1 meg resistor is readily available (in the UK at least) and dissipates only ~ 52mW on a 230V mains supply. A 1k resistor would be totally unsuitable as it would dissipate ~ 52W !! Even a 5k resistor would waste ~10W.

why is the fuse as high as it is

Partly to handle the surge current when the capacitor charges initially if the light happens to be switched on at the peak of the mains cycle, and partly because it's readily available. By all means use a lower rating fuse if you prefer.

I'd suggest designing (IE offering values for) a 20 mA supply

I suggested how to increase current, by increasing the capacitor value. Do the sums if you want 20mA.

 

[shripsacharya1]

Dear alec_t
How can I Light a single 10mm LED lamp 220V AC. Please guide me with a clear circuit diagram and with commercial name of items used for this (as I am not from engg. background.) It will be great help to me. Actually I want to decorate our wooden Temple and want to fix lamps several points.My mail ID is
Regards

 

[alec_t]

On safety grounds I would NOT recommend using a capacitor as a voltage dropper (as per my circuit) for your intended purpose of lighting a wooden Temple with several lamps. It would be safer/better to use a regulated low-voltage power supply or commercially-available LED supply.
The choice of supply would depend on the characteristics of your LEDs (what is their maximum current?, what is their forward voltage drop?).