What's inside a white LED night light?

[Jeff Wisnia]

I'm interested in finding out what the circuit inside a GE white LED
"night light" looks like, but I'd prefer not to have to bust open one of
the two we use in out bedroom and bathroom to find out.

I'm guesing that it may be just the LED, with a diode across it and a
series cap, and maybe a little series resistance to absorb transients.
But perhaps it's something entirely different.

The reason I'm asking is to satisfy my curiousity about what's happening
to the night light in our bathroom. It is plugged into an outlet fed by
the same circuit as the bathroom's exhaust fan. Fan operation is
controlled by a spring driven wind up timer which AFAIK provides just
mechanical switching of the circuit it controls.

The fan is driven by a shaded pole motor which probably draws far less
than an amp when it's running.

What's bugging me is that *sometimes* as I turn the fan on the
nightlight blinks OFF for a fraction of a second, and once I saw it do
that when the timer switch clicked off. The LED looks like it's going
dark for perhaps 1/4 second, but definitely long enough to notice.

I tried whacking the wall in the area of the switch and the outlet to
see if a "loose disconnection" might be the culprit, but I couldn't get
the LED to blink off by doing that.

I has all the symptoms of switching the current to the motor through a
set of mechanical contacts causing a transient which charges a capacitor
in the night light in a direction that turns the LED off until things
equalize again.

My curious mind wants to know wot's happening...

Thanks guys,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

http://home.comcast.net/~jwisnia18/jeff/

"Truth exists; only falsehood has to be invented."

 

[Spehro Pefhany]

I'm interested in finding out what the circuit inside a GE white LED
"night light" looks like, but I'd prefer not to have to bust open one of
the two we use in out bedroom and bathroom to find out.

I'm guesing that it may be just the LED, with a diode across it and a
series cap, and maybe a little series resistance to absorb transients.
But perhaps it's something entirely different.

The reason I'm asking is to satisfy my curiousity about what's happening
to the night light in our bathroom. It is plugged into an outlet fed by
the same circuit as the bathroom's exhaust fan. Fan operation is
controlled by a spring driven wind up timer which AFAIK provides just
mechanical switching of the circuit it controls.

The fan is driven by a shaded pole motor which probably draws far less
than an amp when it's running.

What's bugging me is that *sometimes* as I turn the fan on the
nightlight blinks OFF for a fraction of a second, and once I saw it do
that when the timer switch clicked off. The LED looks like it's going
dark for perhaps 1/4 second, but definitely long enough to notice.

I tried whacking the wall in the area of the switch and the outlet to
see if a "loose disconnection" might be the culprit, but I couldn't get
the LED to blink off by doing that.

I has all the symptoms of switching the current to the motor through a
set of mechanical contacts causing a transient which charges a capacitor
in the night light in a direction that turns the LED off until things
equalize again.

My curious mind wants to know wot's happening...

Thanks guys,

Jeff

I'd guess the same as you did for the circuit (maybe even just a
resistor and two back-to-back LEDs or an LED and a diode). How
flickery is the light?

However, there are some sophisticated off line chips that are becoming
available. *possibly* it could be a protection feature of such a chip.
They would certainly cost more than a capacitor, but would likely be
less bulky.

Is this a particularly thin package? How much is this thing worth? ;-)


Best regards,
Spehro Pefhany

 

[Jeff Wisnia]

I'd guess the same as you did for the circuit (maybe even just a
resistor and two back-to-back LEDs or an LED and a diode). How
flickery is the light?

However, there are some sophisticated off line chips that are becoming
available. *possibly* it could be a protection feature of such a chip.
They would certainly cost more than a capacitor, but would likely be
less bulky.

Is this a particularly thin package? How much is this thing worth? ;-)


Best regards,
Spehro Pefhany

I paid about $6 per for them at one of the box stores maybe 3 years ago.
They each have a different pattern "sculptured" fan shaped clear plastic
"light spreader" sticking out above them. They do a good job of
performing their intended function and IIRC they are warranted by GE
"forever", but probably not against forced intrusive entry. <G> The
"guts" are about an inch and a half square by half an inch thick, but
that's probably just so you can grab it to unplug it when needed.

Not as much light as a 6 watt bulb, but enough to find your way once the
lights have been out for a while and your eyes have cranked up their
gain. And they probably don't use enough juice to overcome the stiction
of a stopped meter. <G>

I probably won't rest until I find the answer to this. I can't imagine
there's much energy in whatever transient is causing this, given that
wimpy little fan motor, but there's probably 75 feet of romex between
that location and the panel, so there's *some* inductance there too.

I may have to dust off and lug my scope up two flights and try and catch
what's driving this effect.

Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

 

[Jeff Wisnia]

I'd guess the same as you did for the circuit (maybe even just a
resistor and two back-to-back LEDs or an LED and a diode). How
flickery is the light?

However, there are some sophisticated off line chips that are becoming
available. *possibly* it could be a protection feature of such a chip.
They would certainly cost more than a capacitor, but would likely be
less bulky.

Is this a particularly thin package? How much is this thing worth? ;-)


Best regards,
Spehro Pefhany

Well I swapped in the other night light and couldn't get it to blink off
no matter how much I diddled the fan motor switch. I plugged the "funny"
night light back it, it lit, and when I flipped the fan motor switch it
went dark and stayed that way, deader than a doornail.

I figured out how to open up the thing without busting anything and
found a small pc board inside with four discrete components on it; the
white LED, two 9.1K one watt resistors and a 1N004 diode. The four parts
were all in series across the 120 volt line plug.

I would have expected to find a resistor across the LED to make sure the
1N1004 took all the reverse voltage, but there wasn't one.

Anyway, it appears that the LED went bad and even though measurements
show it's drawing about 5 ma it isn't producing light anymore. I didn't
have any white LEDs in my hell box so I swapped in a red one and it lit
as expected.

So, the white LED must have been on its last legs and started blinking
off when it got pinged by transients when the fan motor switch did its
thing, just before it gave up the ghost completely.

It probably just started doing that blinking off thing in the last few
days as I'm sure I wouldn't have missed it occuring before because I
twist that fan motor timer switch knob every time I take a shower and
the night light is located less than six inches away from it.

End of story...

Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"