LED Night light schematics?

[tonyb]

I thought I saw some LED night light schematics here a while back, but I can't seem to find them when doing a search. Did anybody else see these schematics here? It might have been a few years ago. Thanks!

tonyb.

 

[MrAl]

Hi tony,

Here's one that's been built and has been running constantly
for about 2 years now.

Take care,
Al

 

[Lynx_Arc]

You could also use a spare walwart and a resistor, make sure and measure the voltage out of it and use one rated as DC output otherwise you will need a voltage rectifying circuit like MrAl's above.

 

[tonyb]

Thats it! Thanks!

tony.

 

[PEU]

what would you change for 220v operation?

Thanks


Pablo

 

[koala]

So Argentina is 220v? /ubbthreads/images/graemlins/smile.gif same here downunder.

MrAl circuit is pretty cool, I've seen circuits with less parts without the 4 diodes(bridge?). From the circuit above all I can interprete is the capacitor drops the voltage and the resistors limit the current? What about the zener diode connected opposite parallel to the LED, does it act as a reverse voltage protector to the LED?

Also MrAl didn't mention, the capacitor must be a non-polarized type(AC circuit) and must have a voltage rating of 200v(120v AC linne) or 400v(220v AC line).

Vince.

 

[legtu]

How about this one?

 

[PEU]

Yes we share more than just the voltage, we use the same power plugs:

Also in common:

Good wines
Good girls
Good rugby (yours is better)
Good Soccer (ours is better)
Same weather
/ubbthreads/images/graemlins/smile.gif

Pablo

 

[MrAl]

Hello again,

Lynx:
I like the wall wart idea too, because it's so simple and very safe!
Keep in mind however that the power consumption might be as high
as 6 watts just to power a tiny white LED. The capacitor/bridge
circuit uses just about 0.25 watts!

tonyb:
Oh that's ok, you're welcome. If you build one and test it please
let me know how it works out and how you like it. Note that nothing
gets hot either.

Pablo:
All you would have to do is change the cap to about half, 0.33uf
should work fine. I'd use a nice high voltage rating, like 600v
for 220vac line. Of course you can replace the four diodes with
a bridge rectifier, maybe i should draw that over.

koala:
Keep in mind the circuits with less parts require a higher cap value
(twice the value) to get the same light output. The circuits with
a bridge rectifier can deliver 2x light per capacitance value.
The circuit works by shifting the phase of the ac line -- so the
reactance of the cap drops a lot of voltage. The first 100 ohm
is there to limit inrush current if the unit is plugged in
at the peak of the sine wave. The second resistor is to allow
a margin in the voltage getting to the LED, and limits current
through the LED. I'll post a complete analysis with waveforms
if you think it will help.
The zener acts as a clamp, so that if there is a surge or spike
in the line the first 100 ohm resistor and the zener act to
limit peak voltage getting to the 100 ohm resistor on the LED,
which limits peak current.
Yes, the cap must be non-polarized, that's certainly good to
mention.
The fuse is a very fast blow 250ma. In the event the cap blows
out and thus turns into a short, the circuit would quickly
overheat so instead the fuse blows. Cap's often blow out
by shorting, that's the reason for the fuse.
Flame proof resistors (2x100ohm) would also be an improvement.
As mentioned, the four diodes could be a small ic bridge rectifier.
I used one of those small ones, about the size of an 8pin dip.

legtu:
Im surprized those circuits didnt turn up in this forum instead of
that one. The cap values depend on diode configuration (bridge
or half wave rect) to get the desired output current (usually
about 20ma or so).


Take care everybody,
Al

 

[koala]

/ubbthreads/images/graemlins/thumbsup.gif

 

[tonyb]

Just finished the circuit board last night!

dual white L.E.D.'s, circuit board measures 1-7/8" long by 3/4" wide by 1/2" high

 

[MrAl]

Hi Tony,

Wow, that's really nice! How did you wire the two
LED's...in series or parallel?
And...
What size cap did you end up using?

I think i forgot to mention that the zener is 9v when
running one single LED.

Thanks for the pic...

Take care,
Al

 

[vicbin]

Hi Al,

My country is also at 220Volt.

Let "assume" I can find high voltage Zener, is it possible to connect LEDs in series say up to 30 pieces ? /ubbthreads/images/graemlins/grin.gif

Any modification needed ?

Regards,
Vic

 

[MrAl]

Hi Vic,

That's an interesting idea...i'll have to look into this
a bit before i can comment, but it sounds like
maybe a resistor (and bridge rect) might work without
too much problem. I've never tried running that many
in series, but i guess it could work. You'd have to
have a margin in overhead voltage just in case
line voltage went low for a short period.
Peak current could be determined from the peak of the
line and the resistor value.

Very roughly, 120-105=15, and i=15/R, but
low line would be much less current.
Maybe a current regulator?

Take care,
Al

 

[vicbin]

Hi Al,

Thanks, and I don't ask that question without reason ! /ubbthreads/images/graemlins/smile.gif

As you see picture below is my big reason, and planning to replace the FL tube with those el-cheapo white leds which nowday only cost 10 to 20 bucks in 100 pieces ! /ubbthreads/images/graemlins/grin.gif

It has a push & hold and release switch for heating up the filament (22W FL circle tube) and that damn switch is broken into "pieces" ! /ubbthreads/images/graemlins/mad.gif Also the shape of host for the switch is so weird that I gave up on finding the replacement ! /ubbthreads/images/graemlins/frown.gif

I missed it so much since it is no fun playing with SMD stuffs without it ! This one has an approx. 6 inches of high magnification lens ! /ubbthreads/images/graemlins/frown.gif

Regards,
Vic

 

[tonyb]

I wired the leds in series and used a 7.00 volt zener I am using them to illuminate a tread mill display. I ended up using a .47 x 10E-6 Farad capacitor. You could aslo add a MOV either to the high side or low side with the appriate value MOV that would further increase spike protection. Also there is no isolation from the mains so treat the whole thing as if it were line voltage energized or you may receive a shock buy touching any part of the output circuitry, as I found out the hard way!

 

[Lynx_Arc]

I just came across an AC cell phone adapter with a full wave rectifier and filtering circuitry for 50 cents. I figure I can make an LED night light and a reading light with it.

vicbin: you should invest in a variable resistor also on that magnifying lamp while you are at it so you don't oversaturate what you are looking at when you don't need the full light output.

 

[vicbin]

Hi Lynx,

Good idea for the different light output ! Thanks ! Maybe three or four circles of 25 LEDS or more in each circle and switch for every circle ! /ubbthreads/images/graemlins/smile.gif

Although I can use the traditional step-down and CC regulator, this one Mr.Al creation is very appealing since the heat dissipations will be minimal, and my country is 220V, imagine how many LEDs can be connected in series !

It is just my "wild" idea and still have to see if it is practical and of course safe for those long series of LEDS !

Imagine the whole series of LEDs got toasted ! /ubbthreads/images/graemlins/banghead.gif

Regards,
Vic

 

[MrAl]

Hi there,

Just thought i would mention one point with many
LED's connected in series...
It's still a good idea to protect them against
reverse voltage by using a diode in reverse across
the string or some other way. With reverse voltage
applied suddenly (just plugged in) the whole string
could blow due to uneven cap distribution (not all
internal capacitance across each diode the same).
Some led's could be subject to very high rev voltage
which would blow them out quick.

Just keep an eye on power diss.


Take care,
Al