For an LED to properly operate, the power supply must have a high enough voltage to turn on (illuminate) the LED and it must provide a controlled constant amount of current to the LED.
This means a dedicated power supply would need to be implemented to drive any LEDs in a circuit.
Every LED light source requires a driver. However, some LEDs, particularly those designed to fit in small areas, contain internal drivers rather than separate, external drivers. Household luminaires usually include an internal driver because it makes replacing old incandescent or CFL bulbs easier.
LEDs that typically require an external driver include cove lights, downlights, and tape lights, as well as certain fixtures, panels, and outdoor-rated lights. Sometimes, LEDs will come equipped with a separate driver. Other times, manufacturer datasheets will specify whether or not an LED requires a separate driver, along with the type of driver it requires if necessary.
Constant-current drivers power LEDs that require a fixed output current and a range of output voltages. There will be only one output current specified, labeled in amps or milliamps, along with a range of voltages that will vary depending on the load (wattage) of the LED.
Constant Current LEDs are wired in series to give a constant amperage to each LED on the LED power supply. Common amperages are 350mA and 700mA although many other mA versions are on the market. Constant current LEDs are mainly used for spotlight type lights.
A constant voltage power supply receives standard line voltage (120-277VAC). This is the type of power that is typically output from your wall outlets around the home. Constant Voltage Drivers switch this alternating current voltage (VAC) to a low direct current voltage (VDC). The driver will always maintain a constant voltage no matter what kind of current load is put on it.
Constant-voltage drivers power LEDs that require a fixed output voltage with a maximum output current. In these LEDs, the current is already regulated, either by simple resistors or an internal constant-current driver, within the LED module. These LEDs require one stable voltage, usually 24V DC.
Constant Voltage LEDs are wired in parallel to give a constant voltage to each LED on the LED power supply. Common voltages are 24V. These LEDs are used mainly in LED tape and strips although you can find these in other types of light fitting.