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How Do LED Drivers Work/Understanding the Ins & Outs

LED (light-emitting diode) lights have become extremely popular during the past couple of decades, especially since they’ve become more affordable. They're now being used in a vast number of everyday applications, from general lighting and automotive lights to traffic signal lights and aviation lighting. LEDs are also popular for use in flashlights, emergency lighting systems, holiday lights and decorations, under-counter illumination, landscape illumination and much more.

The advantages of LED lighting compared to the types of lighting they're quickly replacing include low energy consumption, high-quality light production, low maintenance requirements, superior durability and life expectancy, minimal heat production and more.

By design, LEDs are not normally powered by AC voltage but rather by low-power DC voltage. Therefore, a driver is typically required in order to convert available AC power into the needed DC power for proper operation.

Internal or External?

Most household LED lights that screw into a light socket are what are called “self-driven,” since the required driver is built right into the bulb. All LED light sources require a driver for the conversion of AC to DC power. If your LED light does not include an integrated driver, then an exterior driver will be needed.

A driver for an LED light is similar to a ballast used with a fluorescent tube light. Both provide their respective lights with the proper power to operate correctly. LEDs are designed to operate on low (12 to 24) DC voltage. Since most available power supplies are higher-voltage (120 to 277 volts) AC power, a driver is needed to rectify this higher-voltage alternating current to lower-voltage direct current.

LED Drivers Provide Protection

In addition to converting higher-voltage AC current to low-voltage DC power, LED drivers are also responsible for protecting LED light fluctuations in current or voltage. If there's a voltage change in the electricity being supplied to your LEDs, this could alter the amount of current they receive. This, in turn, will change the light output, since LED light output is directly proportional to the supply of current being delivered.

LEDs are rated to operate within a specific current range, which is measured in amps, and too many or too few amps will cause a variance in the LED light output. This is likely to cause a degradation of the LEDs due to higher operating temperatures. For this reason, it's an important function of the driver to maintain the voltage or current flow through the circuit within its rated range.

The two main LED drivers, also called LED power supplies, are constant-current and constant-voltage types. It's important that you have the type that matches the requirements of your LED system. The type of driver you need and how to pick the one you require will be the topic of a future post.

Forward Voltage and Thermal Runaway

An LED driver is a critical power-regulating part of an LED circuit, and to operate your LED system without one is to invite a system failure. Forward voltage, which is the number of volts required by an LED to light up, decreases as temperature increases, causing the LED to draw more current. As the LED continues to heat up and draw more current, it will eventually burn itself out. This is known as thermal runaway.

A constant-current driver helps to avoid this thermal runaway by automatically compensating for changes in forward voltage by providing a constant current to the LED, as output is precisely matched to the electrical requirements of that specific LED system.

Constant-Current Vs. Constant-Voltage

While there's a vast variety of LED drivers out there, they basically each fall into one of two categories: constant-current or constant-voltage. Each of these driver types is designed to do something different, and it's important that you read the details of your LED light or LED array to ensure you're using the proper driver for your specific application. Constant-current and constant-voltage drivers are not designed to be interchangeable.

Constant-voltage drivers are typically used for LEDs requiring a steady, constant DC voltage. In many cases, these LEDs already have an integral driver installed for current management and simply require help in maintaining consistent voltage. This setup is often found in applications where LEDs are configured in strips running parallel from the driver. This allows them all to receive the same amount of voltage. This is often found in landscape illumination, accent lighting or advertising backlighting.

A constant-current driver, rather than regulating voltage, actually regulates the current coming into the LEDs connected to it. This driver will help regulate forward current produced between individual LEDs, too much of which can cause the lights to overheat, malfunction or have a shortened lifespan. A constant-current driver is usually called for when dealing with LED systems in which there is no built-in current driver in order to provide a consistent current running through the entire array.

Now that you know a little bit about how LED drivers work, the next step is to select the correct driver for your particular application. A future post will explain what you need to consider before making your selection.