Technical information

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LED
Technique
Cable routing
It is important that the polarity is followed. Incorrectly connected
LEDs can be destroyed or damaged. Usually a maximum cable
length is stated for PWM units. Longer cables can create problems
with control or generate EMC issues and downtime. The voltage
drop must be taken into consideration in constant voltage circuits.
Heat development
In spite of an LED being physi-
cally very small, great demands
are made on correct cooling,
either through the use of heat-
sinks or through other smart
design solutions. We apply the
same high temperature margin
demands during the develop-
ment of LED products as for
other products containing elec-
tronics in one form or another.
Ballasts
LEDs require specially designed ballasts, usually known as drivers,
that convert 230 V mains voltage to appropriate parameters to run
the LED. One type of LED operation is known as constant current,
where the LED is powered with a constant current, usually 350 or
700 mA, but there are LEDs that can be run on higher currents. The
voltage must be kept lower than 48 V DC. This type of operation per-
mits LEDs to be connected in series, however, the total output per
circuit must be adapted to the size and specification of the driver.
Systems consisting of strips, or self-adhesive tapes, accommodat-
ing a large number of LEDs are usually powered by a constant volt-
age of 8, 10, 12 or 24 V. Several strips can be connected in parallel to
a common driver. It is important to rememberthat the voltage drop
in cables is calculated in the same way as for traditional extra-low
voltage lighting installations.
Irrespective of the type of operation it is important that the
driver is matched correctly to the type of LED. The polarity is also
important as it is direct voltage (DC) that powers the LED. Incorrect
driver selection will damage or destroy the connected LED. A driver
also needs to ensure electrical separation/isolation from the mains
voltage, LED modules without protective isolation can therefore be
touched without risk of electric shock.
Dimming
LED dimming is carried out through the use of drivers with pulse
width modulation (usually abbreviated PWM). The LED is then
powered using a technique consisting of square waves with vary-
ing frequency. The connected LED is switched on and o at a high
frequency, which reduces the light level. Ballasts with PWM are
available with dierent types of control interface including DALI,
DSI, DMX512 and switchDIM.
The LED is connected in parallel to the driver in constant voltage operation.
Constant current operation is chosen when the LED is connected in series to the
driver.
The picture has been taken using a heat
camera and illustrates thermal develop-
ment from an LED assembly.
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