Download Constant Current Technology explained

 TECHNICAL INFORMATION BULLETIN
Constant Current Technology explained
All SloanLED products feature Constant Current Technology designed to protect the module and
control the drive current through the LED’s.
For clients without an electronic background it is not easy to understand what CCT is, what
advantages this technology offers and why you should buy only LED systems that feature it.
This document explains the advantages of CCT in simplified terms.
A LED is an electronic semi-conductor device that converts electrons into photons (light). The
process requires an electrical current to run through the LED with the light output of the LED being
directly related to the amount of current flowing through it. The higher the current, the more light
the LED emits. Each and every LED has a maximum current rating, specified by the diode
manufacturer, which must not be violated.
Also specified by the manufacturer is a maximum operating temperature measured at a junction
point inside the LED. This junction temperature must also be kept below the manufacturer’s
maximum rating.
Excessive current or Excessive junction temperature causes irreparable damage to the LED and
results in either total failure or a reduction in the expected lifetime of the LED.
The LED industry uses the term L70 as an indication for the expected lifetime in hours at which
point the brightness of the LED reaches 70% of the original brightness of the LED on day one. For
current generation white LED’s the L70 is usually between 50.000 – 60,000 hours.
As we stated before the current through a LED is directly related to the light output of the LED. See
graph below. This graph shows that brightness will continue to increase even after the maximium
drive current and maximum junction temperature have been violated. If an LED is driven in this
range, it will be brighter than one driven properly, but will fail prematurely.
SloanLED Europe b.v. – Rotterdamseweg 388F – 2629HG Delft – The Netherlands Tel +31 15 3641569 – Fax +31 84 2297252 – Email: [email protected] – www.sloanled.com TECHNICAL INFORMATION BULLETIN
Most LED systems sold today are powered by a constant voltage power supply, in our case 12 Volt
DC. With this type of system there are two common ways of controlling the current that drives the
LED’s.
The first way is by use of a simple fixed resistor connected in series with one or more of the LED’s.
This is the cheapest solution as the component and manufacturing cost is very low. Most low cost
LED systems use this method. The disadvantage being that for the system to work the system
needs a fixed voltage for example 12V. For those of you who remember Ohm’s law, you will recall
that the current (I) is directly related to the Voltage (V) over the resistor (R). V = I x R. Therefore if the
voltage varies, so does the current.
A fixed voltage in any type of LED system measuring more than a couple of meters long is simply
not possible as for each and every meter of cable or connector added into the circuit comes
resistance which will lower the voltage before it reaches the LED modules. This is called voltage
drop and on a typical LED signage installation the voltage can drop from 12V at the beginning of the
circuit to 9V at the end. This has an effect on the light output of a string of LED modules with this
design, as we will see later.
SloanLED uses a Constant Current Driver in each module to electronically control and limit the
current through the LED’s in that module. The electronics regulate the current to be set within the
LED manufacturer’s maximum values and at safe junction temperatures. Even when the voltage over
a string of LED modules with CCT drops, this technology ensures that the current running through
the LED’s in the first and last module of the string is the same. Thus the brightness of the first and
last module will be the same.
CCT ensures that the LED’s are all driven by a controlled current meaning that the entire system will
perform as expected and achieve the L70 performance criteria as designed by the LED
manufacturer.
SloanLED Europe b.v. – Rotterdamseweg 388F – 2629HG Delft – The Netherlands Tel +31 15 3641569 – Fax +31 84 2297252 – Email: [email protected] – www.sloanled.com TECHNICAL INFORMATION BULLETIN
The final benefit CCT offers is that it also aids installation as longer strings of modules can be
connected in series, even with remote mounted power supplies. For example using our 14AWG hook
up cable a 60W psu can be mounted more than 15 meters away from the first module in the chain
and in the case of our new V180 system the power supply can go on to power 150 modules
connected together in series. That’s over 34 meters of circuit without any noticeable brightness
variation.
Obviously this technology adds more cost to a LED module than the simple current limiting resistor.
When SloanLED introduced this technology back in 2004 we believed that this extra cost was a
small price to pay to enable us to offer the signage world a reliable and safe LED system that was
built to last.
The effect of voltage drop over the cables connecting LED modules in a string without CCT can be
quite dramatic. The module below has a simple current limiting resistor (arrow).
The manufacturer specifies that 160 modules can be connected to a 60W power supply in one
string. We put this to test and connected just one tray of 100 modules to a 12 V DC regulated
laboratory power supply and measured the brightness of the first and last module in the string.
The first module measured 308 cd/m2 in our test box, the last 231 cd/m2. Giving a brightness drop
over just 100 modules of 25%.
As in the product example above it can be easy to see if a module features CCT. For modules that
are covered in an over moulding or housing some destructive action may be required, although this
can be quite interesting as you will also get an idea of other quality aspects of the module.
SloanLED Europe b.v. – Rotterdamseweg 388F – 2629HG Delft – The Netherlands Tel +31 15 3641569 – Fax +31 84 2297252 – Email: [email protected] – www.sloanled.com TECHNICAL INFORMATION BULLETIN
A module with CCT usually has a lot more electronic components, as in the SloanLED example
below. Of course you wouldn’t normally see this as in the case of our Great White 4 product below
the finished module features a moulded body designed to protect the electronic components.
There are more aspects than CCT that make the difference between a LED module that will operate
with minimal brightness loss during its expected life time or a LED module that will start to reduce in
brightness quite rapidly. CCT is however a major contributing factor to a LED module’s performance.
Many low cost LED system manufacturers drive their LED’s hard to make their modules appear
bright when they are first presented. However once out in the field these modules will start to lose
their brightness quite rapidly. If the junction temperature is close to the maximum rating set by the
LED manufacturer at room temperature, it is likely to exceed that limit and reach dangerous levels
when the module is operating in real climatic conditions.
SloanLED does not follow this “close to maximum” practice regards drive currents and or junction
temperatures. Backed by our industry leading five year warranty our products are designed for
global demand and are reliably performing in some of the world’s toughest environments. Put simply
our products are built to last and designed to exceed your clients expectations.
We at SloanLED see CCT as a must have technology featured in all of our LED modules since 2004
when we pioneered its use. We hope that this document helps you and your clients understand the
importance of CCT.
SloanLED Europe b.v. – Rotterdamseweg 388F – 2629HG Delft – The Netherlands Tel +31 15 3641569 – Fax +31 84 2297252 – Email: [email protected] – www.sloanled.com