INTRODUCTION:

In certain lighting applications, LED drivers need to be mounted away from their respective light engines or light fixtures. In that case, it also becomes necessary to ascertain the maximum distance of the driver from the light engine (in other words, how far away can the driver be located from the LED engine).

Application Note 110 (AN-110) on our website addresses that question for both Constant Current and Constant Voltage driver applications by providing explanatory equations and circuit diagrams, and attaching helpful tables that will help fixture designers quickly find the maximum permissible wiring length for their specific installation application.


SUMMARY OF AN-110:

Constant Current Drivers:

For remote mounted applications, the voltage drop along the wires between the driver and the LED light engine will dictate the maximum distance. This is because the driver “sees” the Forward Voltage (Vf) of the LED load as well as the voltage drop along the wires, and the sum of the two cannot exceed the driver’s maximum rated driver output voltage, Vout_max.

See representative circuit diagram below, for a Constant Current driver connected to an LED load.

Vout_max and the maximum Vf are known to the designer because they know which driver they’re going to use and what type of LED load will be connected to the driver. This info—along with the example equations helpfully provided in the application note—can help the designer in computing the maximum allowable voltage drop along the wires between the driver and the load.

AN-110 also provides equations to help you calculate the maximum length of the wire, since the voltage drop along the wire depends on the resistance of the wire, the length of the wire, and the current flowing in the wire from the driver to the LED load.

In addition, AN-110 provides a handy maximum wire length table for constant current drivers using copper wire.


Constant Voltage Drivers:

In constant voltage drivers, the voltage drop along the wires is lost voltage, which means the voltage across the load is reduced—potentially creating issues if the voltage drop along the wires is excessive. That is why limiting the wire length and/or decreasing the wire resistance—by choosing a lower gauge
wire—is important.

See representative circuit diagram below, for a Constant Voltage driver connected to an LED load.

The industry standard for an acceptable voltage drop (Vdrop) for constant voltage power supplies is 3% of the nominal output voltage.

Again, the example equations provided in AN-110 will help the designer in computing the maximum allowable Vdrop along the wires between the driver and the load.

Similarly, AN-110 also provides equations to help you calculate the maximum length of the wire, and a maximum wire length table for constant voltage drivers using copper wire.

In addition to the Application Note 110 posted on our website, please watch ERP Power’s useful and informative webinar (presented by Talal Abdelghany of ERP) on remote mounting of LED drivers HERE.