Constant voltage vs Constant current - LED strip for longer run lengths
Constant voltage vs IC Integrated - what is the difference?
This article will explain the difference between the physical components of constant voltage and IC Integrated for constant current LED strip and also applications of when it is best to use either format in an installation.
Component elements of both strips -
Constant voltage LED strip
A 12 volt constant voltage LED strip has multiple arrays of 3 x light emitting diodes in series and one fixed value current limiting resistor. When fed with a 12 volt supply, in every array 3 volts will be used for each of the LED's and 3 volts for the current limiting resistor (3V being the optimum working voltage for an LED chip to give full brightness when drawing around 120mA).
Therefore, in order to maintain the 3 volts required by each LED to operate at its full potential, it is important to have a consistent 12 volt supply level along the whole length of the strip from beginning to end.
But what if the supply voltage drops to 11 volts due to resistance in run length?
Each LED array will now be fed with 11 volts, reducing in essence each individual array's supply voltage by 1 volt. This will lead to each LED now having a working voltage of 2.75 volts and not the original 3 volts (0.25V less per LED and resistor).
What effect will this have on brightness?
2.75 volts across an LED will draw 40 to 50 mA and not the original 120mA required for full brightness, therefore the LED strip will still illuminate, albeit though at a reduced level of brightness.
If voltage drop was to increase further to say a 10 volt supply level (2 volts below original 12 volt supply) then each LED would now be supplied with 2.5 volts, which would draw little or no current resulting in the output brightness being dim or even not visible at all.
Integrated circuit for constant current & zero voltage drop
With reference to the operating elements of the constant voltage example above, in comparison to this the IC LED strip does not have a fixed current limiting resistor, but instead uses an IC chip to perform this function and compensate for voltage drop along the length of the strip.
For example, a reduction in the supply voltage to 11 Volts will not have the same effect on this strip as it does on the constant voltage type, due to the integrated circuit compensating for the voltage reduction and keeping the 3 Volt supply to each diode; therefore maintaining consistent brightness along its entire potential 20 metre length. Part number: LSP24-120.
Supply Cable effects:
Supply cable length is also a contributing factor to voltage drop due to it adding resistance to the circuit. Therefore, if your LED power supply is housed some distance from the LED assembly - for example if you group your drivers in a central supply cupboard - this could cause the voltage to drop significantly. If the voltage drop is envisaged to be anything more than circa 2 volts below the supply voltage, then the constant current IC integrated LED option may be preferable for your installation.
In summary:
For LED strip run lengths of 5 to 20 metres, IC integrated is the better option because it can cater for voltage drop whilst consistently maintaining the brightness of the LED strip to the farthest end of the run.
For LED strip runs up to 5 metres the constant voltage option, used for the rest of our LED strip range is a viable choice as voltage drop along this length less likely and the cost of purchase less that that of the IC variety.