Constant Current LED Fixtures

It's common in the household environment that we need to install a dimmable lighting fixture a reading room or a children's room. Since most LED lights require constant current LED drivers, this would mean that we need to select a compatible LED dimmable driver for a particular lighting fixture. However, this can be more involving than doing the same for constant voltage LED strips. Thus, in the following discussion, let's assume that we need to change a non-dimmable driver to a dimmable version for a downlight. Let's also first assume that we already have chosen a compatible dimmer and driver (to exclude another possible incompatibility factor), the next step is to select the LED drivers with appropriate output conditions (operating voltage and current) to match a COB downlight. While choosing non-dimmable LED drivers is much easier, doing the same for dimmable applications requires additional considerations.

Dimming Principle and Implications with LED Drivers

The concept of constant current reduction (CCR) is straightforward to understand. Let's consider the rated current of a dimmable driver as the maximum output current to the LED light. The purpose of a dimmable driver is to reduce the output current into the light, which results in the brightness intensity reduction. We know that LEDs are semiconductor diodes with a non-linear relationship between the operating voltage and current. So, by the CCR principle, we know that as we continue to drop the output current, so does the operating voltage of the driver. Since each LED driver has a rated operating voltage range for the constant current output, the driver would likely be working in a stage below the rated minimum operational boundary; this can result in flickering at a low level, etc. So, improper dimmable driver selection can also cause flickering in LED dimming.

Understand the Downlight's Electrical Specifications

So, our basic strategy is to understand the downlight's operating voltage and current range, then select a dimmable driver with the right constant current output range. When we combine the two sets of data on a single graph, our matching task becomes straightforward.

Using the downlight shown on the right as our example, we can use a workbench or programmable power supply to investigate the operating range of the downlight. In this case, the downlight operates at 38V at 300mA or rated current; on the other hand, it remains operational at 30V, below which the lamp will switch off. With this data set, we'd understand the target DC output range of the dimmable LED driver we need. Note that today's LED lights can operate at shallow operating currents.

Application Notes

In practical dimming projects, we'd encounter various types of LED lighting fixtures. It is inevitable for Electricians or Lighting Professionals to involve dimmable driver selection to match a light on-hand.

To share the experience of choosing dimmable drivers to match some randomly chosen LED downlights, we formulated an LED Dimmable Drivers Selection Application Notes for interested prospects to review further. In particular, we also used LED drivers with selectable current outputs in the discussion. It's a good starting point to help customers and prospects save time for trial-and-errors.