Drivers for LEDs
Most LED modules require specially adapted drivers that convert mains voltage (230V) into suitable direct current or direct voltage. The driver also has built-in safety features that cut the power in the event of a failure.
Two different operating modes
There are two different operating modes: constant current or constant voltage. Most luminaires are operated with constant current. Constant voltage drivers are typically used for LED strips or LED tape, for example, usually 24 V DC. With constant current operation, several LED products can be connected in parallel to a common driver, provided this can manage the connected load. The voltage drop in long cables is calculated in the same way as for traditional extra-low voltage installations.
No matter the type of operation, the driver must be matched correctly to the type of LED luminaire or luminaires to be powered. A driver that can handle more load than needed results in lower efficiency, which affects the energy efficiency (lm/W) of the luminaire. Choosing incorrectly when replacing the driver can damage the LED module, pose a risk of injury, and reduce the efficiency of the luminaire.
SELV / Non-SELV
The total output voltage of the LED circuit and the luminaire design determine whether the driver is SELV* or Non-SELV. In luminaires with a Non-SELV driver, touching the LED modules can cause injury. A cover that requires tools to open, is therefore placed over the LED modules. In luminaires with SELV, the voltage level is considered safe to touch and no cover for the modules is required.
*SELV = Safety/Separated Extra Low Voltage: voltage system with touchable electrical parts with max. 60V DC. Information on the driver and in the data sheet indicates whether the driver is SELV.
Dimming technology
The drivers have two built-in dimming technologies: amplitude modulation (AM) or pulse-width modulation (PWM). Amplitude modulation means that the electricity to the LED module is reduced during dimming. This is the most commonly used method. In pulse-width modulation (PWM) the electricity is kept constant, whereas during dimming it is pulsed. The load is switched on or off, as applicable, using a high frequency which is perceived as a change in the light level. The recommendation is for the highest possible frequency: at least 300Hz and preferably above 500Hz.
Fagerhult mainly uses dimmable drivers with amplitude modulation. Exceptions are constant voltage products and RGBW products.