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Constant Current vs. Constant Voltage LED Drivers

Keystone offers both constant current and constant voltage LED drivers, providing LED fixture and sign manufacturers with options and flexibility to optimize LED systems for different applications and environments


These drivers are required when the driver is used to power the LED load directly. With constant current drivers, the output current is fixed by the driver, while the output voltage varies depending on the LED load. The more LEDs the driver is powering, the greater the output voltage will be, up to a maximum as allowed by the driver specifications. In order to correctly select a constant current driver, you need to know the following:

The RECOMMENDED DRIVE CURRENT required by the LED module.

The drive current of the LED module(s) should match the RATED OUTPUT CURRENT of the driver. For example, one 380mA LED module requires one 380mA driver and two 350mA LED modules connected in series require a 700mA driver.

The MAXIMUM FORWARD VOLTAGE of all LEDs in the module.*

The maximum forward voltage required of the LED module must not exceed the MAXIMUM OUTPUT VOLTAGE of the driver.


These drivers are required when another LED current controlling device, such as a built-in resistor or regulating driver is already connected directly to the LED load. With constant voltage drivers, the output voltage remains fixed (typically at 12Vdc or 24Vdc) at any current level, up to a maximum allowable current, as dictated by the maximum output power of the driver. In order to correctly select a constant voltage driver, you need to know the following:

The CONSTANT INPUT VOLTAGE required by the LED module.

The constant input voltage required by the LED module must match the CONSTANT OUTPUT VOLTAGE of the driver.

The MAXIMUM POWER required by the LED modules in the system.**

The total power consumption of the LED modules in the system must not exceed the MAX OUTPUT POWER of the LED driver.

* Maximum forward voltage should be specified by the LED module manufacturer. If not, calculate by taking the maximum forward voltage rating as indicated by the LED manufacturer and multiply by the total number of LEDs in the module.

** Calculate by taking the rated power consumption of the LED module as specified by the manufacturer and multiply by total number of modules in the system.

Dimming Requirements

Keystone offers a wide range of dimmable Constant Current LED drivers, compatible with 3 different types of dimming technologies:

• Phase Control Dimming (FDIM)

• 0-10V Analog Dimming (VDIM)

• Local Dimming (LDIM)

Form Factor Requirements

Because of the variety of applications that employ LED technology, there are often size constraints that LED drivers must meet. Keystone has a large selection of LED driver case styles available to fit virtually every application.