LED Drivers Constant Current vs Constant Voltage



When it comes to LEDs, LED Strips or LED modules it is a good idea to use a LED Driver to keep the brightness the same.

There are two types of drivers.

Constant Voltage - This type of driver will have a Fixed Voltage Output. This will depend on the LED voltage rating. It will be a fixed output. The current output for the driver will have a max rating. If the circuit does not draw more that what is required it will work.

Constant Current - This type of Driver will have a Fixed Current Output. This is determined by the current for the LEDs. The Voltage output will be variable. The Voltage can change due to the number of LEDs that are used. Make sure the voltage range will be for the voltage that is required.

The LED Drivers can be either a Board Mount style or External/Internal - Off Board style.

In some cases, depending on the LEDs being used, a AC/DC power supply can also work.
Just check on the Data sheet for the LEDs to see the Voltage needed as well as how much current is needed.

Choosing the correct LED and LED Driver

Here are some additional notes on typical uses for the constant current and constant voltage applications.

Constant current drivers typically provide longer LED lifetime expectancy and better lighting consistency, especially when dimming is a requirement. LEDs are a non-linear device, which make them inconsistent. A small increase in the voltage can cause an exponential increase in current, and this can sometimes damage an LED if not properly regulated. Thermal runaway is also less prevalent in constant current circuits which improves the reliability of LED’s that are on for extended periods of time. Thermal runaway is the term used when a component’s internal or externally produced heat self induces its bias, decreasing forward resistance (lowered voltage drop), and increases the current through the device. Although a constant voltage driver is voltage regulated, the LED voltage drop itself may fluctuate as the LED turns on or heats up. Constant current drivers are more common in true series circuits, they can also be found in some series-parallel combinational circuits. Keep in mind when an LED(s) burns out, gets damaged, or is cut from a strip in a combinational constant current circuit that the remaining LEDs may be damaged, as the fixed current may be too high for the remaining LEDs.

Constant voltage drivers are more common in multi-color displays, and series-parallel combinational LED strips with built in resistors or some other current limiting device. Constant voltage drivers are also usually the requirement for addressable LEDs, as these types usually have a constant current driver chip built within each LED. Constant voltage drivers are easier to work with as you can add or remove LEDs from the circuit as long as the current of the driver is equal or higher to that of the total LED current.

Although LED drivers are recommended for LED lighting, it is common to see industrial power supplies like these to “drive” LED lighting. Although these have a very tight voltage output tolerance, they may not provide certain specifications for LED lighting such as THD (total harmonic distortion), and ripple specification. Industrial power supplies may have relevant THD and ripple compared to drivers, but since they are not specified on the datasheet it is unknown. For further reference, please see Constant Voltage LED Driver vs AC/DC Power Supply.

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