[Darksky]Phase Cut Dimming of LED traffic signal.
peter
Fri, 7 Feb 2003 17:59:49 -0800
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Hello All list members ;
I am the Director of Engineering at Ecolux International in Thailand. =
Just found and signed up to your good list while surfing. Native NY'er.
There are some list questions about dimming of LED traffic signals. =
Most LED traffic signals use a switching power supply (for line =
isolation and high energy efficiency) to convert 220V/120VAC to 12V or =
similar low voltage to drive the LED's. This power supply does not =
respond well to phase cut dimming. That's why most (but not all) LED =
signals are not dimmable using ordinary phase cut dimming. Then =
normally 3 or 4 LED's are wired in series with one current limiting =
resistor (depending on the voltage drop of the LED's. Voltage for green =
is much higher than red). Super bright LED's last a long time if the =
circuit is properly designed (MTBF > 2,000,000 hours at room =
temperature), and this power supply normally is the limiting factor for =
the MTBF (Mean Time Before Failure) of the traffic signal.
We manufacture a line of traffic signals that are dimmable using =
ordinary phase cut dimmers. These signals do not use a power supply. =
They respond well to phase cut dimming. The only problem you might =
experience is that most triacs in even a small dimmer control are rated =
600 watts or more. Now in simple terms, the triac is normally pulsed =
to switch it to the "on" condition. Then it is held conducting (on) by =
load current. Since an LED traffic light only uses 4-5 watts, the low =
load current may not keep the triac on reliably. This results in severe =
and unacceptable flicker at dimmed settings. One solution (don't laugh) =
is to use another load (like a big power resistor), to hold the triac =
on. Of course this eliminates the benefit of power savings for the LED =
signal, so clearly not recommended. The recommended method is to use a =
dimmer rated for very small loads.
We also do automatic night time dimming by photocell sensor and dimming =
solar flashers. Most of our sales are 220V, but we are starting to get =
120V orders. Our signals lack regulatory approval, which you may need =
(Thailand has no regulatory requirements yet). So just thought you =
might like to know that dimming is very possible. Lots of info, =
reliability info, and specs on our web site. I hope this post is not =
too commercial. Moderator feel free to cut.
Best Regards,
Peter Guagliano
Director of Engineering
Ecolux International Co. Ltd.
www.ecoluxint.com
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<DIV><FONT face=3DArial size=3D2>Hello All list members ;</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I am the Director of Engineering at =
Ecolux=20
International in Thailand. Just found and signed up to your good =
list=20
while surfing. Native NY'er.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>There are some list questions about =
dimming of LED=20
traffic signals. Most LED traffic signals use a switching power=20
supply (for line isolation and high energy efficiency) to =
convert=20
220V/120VAC to 12V or similar low voltage to drive the LED's. This =
power=20
supply does not respond well to phase cut dimming. That's why most =
(but=20
not all) LED signals are not dimmable using ordinary phase cut =
dimming. =20
Then normally 3 or 4 LED's are wired in series with one current limiting =
resistor (depending on the voltage drop of the LED's. Voltage for green =
is much=20
higher than red). Super bright LED's last a long time if the =
circuit is=20
properly designed (MTBF > 2,000,000 hours at room temperature), and =
this=20
power supply normally is the limiting factor for the MTBF (Mean =
Time Before=20
Failure) of the traffic signal.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>We manufacture a line of traffic =
signals that are=20
dimmable using ordinary phase cut dimmers. These signals do not =
use a=20
power supply. They respond well to phase cut dimming. =
</FONT><FONT=20
face=3DArial size=3D2>The only problem you might experience is that most =
triacs in=20
even a small dimmer control are rated 600 watts or more. Now in =
simple=20
terms, the triac is normally pulsed to switch it to the "on"=20
condition. Then it is held conducting (on) by load =
current. =20
Since an LED traffic light only uses 4-5 watts, the low load =
current=20
may not keep the triac on reliably. This results in severe =
and=20
unacceptable flicker at dimmed settings. One solution (don't =
laugh) is to=20
use another load (like a big power resistor), to hold the triac =
on. Of=20
course this eliminates the benefit of power savings for the LED =
signal, so=20
clearly not recommended. The recommended method is to use a =
dimmer=20
rated for very small loads.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>We also do automatic night time dimming =
by=20
photocell sensor and dimming solar flashers. Most of our =
sales=20
are 220V, but we are starting to get 120V orders. Our =
signals lack=20
regulatory approval, which you may need (Thailand has no regulatory =
requirements=20
yet). So just thought you might like to know that dimming is =
very=20
possible. Lots of info, reliability info, and specs on our web =
site. =20
I hope this post is not too commercial. Moderator feel free =
to=20
cut.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Best Regards,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Peter Guagliano<BR>Director of=20
Engineering<BR>Ecolux International Co. Ltd.<BR><A=20
href=3D"http://www.ecoluxint.com">www.ecoluxint.com</A></FONT></DIV></BOD=
Y></HTML>
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