The Origin of LED Driver

In the past, AC-DC power supplies that provided a regulated “constant-voltage” to LEDs were referred to as LED power supplies. Conventional AC-DC power supplies and DC-DC converters provide an output that is regulated to provide a “constant-voltage.” However, LEDs work most efficiently and safest with a “constant-current” drive. As a result, many new devices have been developed to provide this type of LED drive. Today, the terms “LED driver” and “LED power supply” are used interchangeably.

Figure 1. Eiffel Tower Lighting Show with MOONS’ LED

Constant Current LED Drivers and Constant Voltage LED

As we can see above, LED drivers can be sorted into two types: constant current LED drivers and constant voltage LED drivers.

Constant current LED drivers are designed for a designated range of output voltages and a fixed output current (mA). These drivers vary the voltage along an electronic circuit which allows current to remain constant throughout the LED system. MOONS’ “CP” series LED Driver is a good example shown below. As for CP series, once the output current configured by MSSL200, the output current is fixed, and the output voltage is corresponding adjustable as specification shows, but the power will not exceed the maximum.

Figure 2. MOONS’ MU100M105AQ_CP Label

When Do I Need a “Constant-current” LED Driver?

Figure 3. CREE XM-L2 LED Forward Voltage and Forward

From the electrical characteristics of the Cree XM-L2 above in Figure 3, you can see the exponential relationship between the applied forward voltage to the LED and the current flowing through it. When the LED is turned on, even the smallest 3% change in 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.

Figure 4. The maximum forward current in different
ambient temperature conditions

As shown in figure4 above, the maximum forward current is determined by the thermal resistance between the LED junction and ambient. In the example above we would still be alright driving the XM-L2 LED at 1000mA, however, if you don’t have a current limiting device, the LED will draw more current because its electrical characteristics change with increasing temperature. This will cause the current to exceed a defined value, especially in a hotter environment. It is crucial for the end product to be designed in a manner that minimizes the thermal resistance from the solder point to ambient in order to optimize lamp lifespan and optical characteristics.

Constant-voltage LED drivers power LEDs that require a fixed output voltage with limited output current. More information about MOONS’ Constant Voltage LED Drivers please clicks here. In these LEDs, the current is already regulated by a simple resistor or internal constant current driver within the LED module. These LEDs require one stable voltage, usually 12V DC or 24V DC.

Figure 5. LED Strip with Current-limiting Resistor

Do I Need a “Constant-voltage” LED Driver?

The most common LED strips are designed with a group of LEDs in series with a current limiting resistor in line with them. The manufacturer must ensure that the value and position of the resistor are correct so that the led on the strip is not as susceptible to voltage changes as we mentioned in XM-L2. Since their current is already being regulated, all they need is a constant voltage to power the LED(s). It is convenient and safe for customers to install the constant voltage LED drivers and its’ lighting project.


In short, without the right LED driver, the LEDs would become too hot and unstable, causing malfunctions and poor performance. In order to ensure the LEDs function perfectly, the self-contained LED driver needs to provide a constant power supply for the LED. The important thing to keep in mind is whether the output of the power device provides a “constant-voltage” or a “constant current”, they are required by the LED device that is receiving the power.