At present, LED lights and accessories occupy more than 1/3 of the total lighting market, being especially popular in commercial applications due to the lower power consumption, longer lifespan, and environment-friendly. LED light requires a device that could control the current to prevent fluctuations in output, flickering, and even burnout. To avoid these problems, as well as to enhance performance in the application such as dimming and color-changing, a control device called a “driver” is needed.
Before explaining the questions mentioned in the title, we must know the concept that LEDs are constant current devices with a forward voltage drop. This means the electrical current flow through the LEDs as soon as voltage supply exceed that fixed voltage drop, and by controlling the current, you control the lighting intensity.
The forward current vs. forward voltage of CREE XM-L2 LED is shown in Figure 1. As we can see above, the XM-L2 will turn on above 2.6V. When the LED is turned on, even the smallest 3% change in the voltage (2.95V to 3.05V) can create a 50% increase in current driven to the XM-L2 as you can see at the red marks in curve move from 1000mA to 1600mA. If the voltage changes frequently, the visible light changes synchronizing.
As for constant current LED drivers itself, it varies the voltage across the electronic circuit in order to maintain a constant current. This guarantees that no matter the fluctuation in voltage, or electrical resistance changes in LEDs due to the temperature rise, the current is driven to the LED will be maintained at the specified level. Constant current drivers are designed for LEDs that require a fixed output current and a range of voltages. Constant current drivers usually list their specifications on the device, with only one output current rating and a range of voltages that vary based on the wattage of the LED.
If you are building your own LED lighting project with high power, constant current LED drivers are the best choice. Because their current is limited, the life of the luminaire can be extended at lower temperature with rated output current. In general, the LED driver has a Tc point, which is the position of the highest temperature on the drive’s shell. Designers often find these drives easier to control in the project, and they achieve a more consistent brightness level in the LED group and have less power consumption than the constant voltage power supply used.
However, a constant voltage driver is more flexible when it used in low power application like cabinet light, Christmas tree light. It does not matter when it refers to power consumption as it is a low power application. Sometimes, a constant voltage is first stage power source to drive DC/DC LED drivers, like landscape light, because the output voltage is fixed, usually either 12VDC or 24 VDC that is lower than ELV (Extra-low voltage) to keep from the risk of dangerous electrical shock.
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