What Limits the Maximum Voltage for Powering an LED Light?

In the last article, we learned how to accurately select LED drivers among 12V, 24V, 36V, and 48V. Therefore, we also know that the greater the voltage of the lamp, the higher the brightness and efficiency of the lighting, especially when used in some large-scale lighting demand projects. High voltage lighting abounds. So why are no constant voltage lighting fixtures exceeding 48V on the market? What limits the maximum voltage of LED light power supply? Next, we introduce it in detail:

1. LED voltage withstand limit

Each LED chip has a maximum forward voltage (VF) it can tolerate. However, LED itself is a low-voltage component and the forward voltage withstand limit of most ordinary LED chips does not exceed 4V. Therefore, it is a common practice to use multiple chips in series to increase the withstand voltage. However, exceeding the forward voltage withstand limit of the LED may cause overcurrent, rapidly heat up, and damage the chip structure, causing the LED to permanently fail. To prevent overvoltage, voltage limiting and current stabilizing circuits are usually designed in LED drivers.

When multiple high-power LED chips are combined in the same package, they are often connected in series and parallel to achieve higher voltage withstand limits to meet the needs of high-power and long-distance applications, such as outdoor lighting, high-power floodlights, etc. However, the overall voltage tolerance depends on its internal structure and chip count. The forward voltage tolerance of a single LED chip is limited, so most LED lights are driven by constant current rather than directly increasing the voltage.

Connecting multiple LED chips in series can increase the overall voltage. For example, when three LEDs with a forward voltage of 3V are connected in series, the total voltage withstand limit is 9V. This approach is common in constant-voltage drives, where the current remains constant while the voltage increases.

The total amount of current is increased by parallel connection, but the voltage remains unchanged, which is used in low voltage scenarios. Although this connection method does not increase the withstand voltage, it increases the driving current and power.

2. Overheating problem

As the voltage increases, the current increases accordingly, producing more heat. LED lights are very sensitive to temperature. An increase in temperature will cause the forward voltage of the LED to decrease slightly, by about 2-3 millivolts per degree Celsius. Excessively high temperatures will accelerate chip aging, resulting in decreased brightness or shortened lifespan. Therefore, LED applications are usually designed to operate at a moderate forward voltage to balance luminous efficiency and thermal stability.

With good heat dissipation design, high voltage may not immediately cause overheating problems, but in actual applications, excessive voltage often leads to insufficient heat dissipation, causing the driver or lamp to overheat. To prevent overvoltage and temperature-induced voltage fluctuations, the driver usually Current stabilization and protection circuits will be designed to ensure stable operation and long life of the LED. Therefore, increasing voltage is limited by the device's ability to dissipate heat.

3. Driver design limitations

LED drivers are usually designed as constant current drives because the luminous efficiency and lifespan of LEDs perform better in a constant current state. The constant current design can keep the current stable and avoid brightness changes or overcurrent damage caused by current fluctuations. If the voltage is too high, the constant current mechanism of the LED driver may not be able to maintain a stable current output, thus affecting the life of the lamp.

High-voltage driver design requirements are also higher. High voltage also means high efficiency. However, high-efficiency driver design can usually achieve an efficiency of more than 85% to avoid excessive power conversion into heat. However, designing an efficient driver also increases the design difficulty and cost. Therefore, most drives are designed within reasonable limits to ensure safety and stability.

4. Security requirements

Excessively high voltage power supply brings high safety risks, especially in humid, outdoor or high-temperature environments. As supply voltage increases, the risk of electric shock increases significantly. In the event of direct contact, higher voltages may result in serious injury or even fatal hazards. Generally, low-voltage (less than 50V) power supply systems are considered safer because low voltage does not cause severe currents to pass through the human body. Especially in the lighting design of public places, low-voltage LED lamps are more popular because they have lower risks in emergencies (such as fire or leakage) and are easy to manage safely.

Many LED lighting systems use safety extra-low voltage (SELV) designs, usually in the 12V or 24V range, to ensure that there is no risk of electric shock even if people come into direct contact. The SELV system is an isolated power supply, ensuring that the power output is completely isolated from the mains to reduce the probability of accidents.

5. Electrical standards and certification requirements

The electrical safety standards of many countries and regions have clear requirements for the safety of low-voltage and high-voltage systems. Standards usually specify that the voltage of LED lighting systems used in public places, homes and handheld devices should be limited to a certain range to avoid the possibility of personnel exposure to electric shock.

Certification agencies such as UL (United States), CE (European Union), and CSA (Canada) have stipulated voltage limits for LED lamps and drivers to ensure that products will not cause safety hazards to users when they malfunction. These safety certification requirements usually limit the supply voltage of LED lamps to a safe range to meet the safety access standards of each market. Especially in homes and public places, limiting voltage can reduce the risk of electric shock and electrical accidents.

6. Insulation and isolation design requirements

As voltage increases, so do the quality and thickness requirements for insulating materials to prevent current leakage. Different materials of LED strips have different band gap widths, resulting in differences in LED forward voltage. Typical LED materials include gallium nitride (GaN), gallium arsenide (GaAs), indium phosphide (InP), etc. The larger the band gap width, the higher the required voltage. However, for high-voltage driving, insulation materials and designs must reach higher withstand voltage levels, thereby increasing design difficulty and cost.

In LED drivers, high-voltage systems require strict isolation design to ensure safe isolation between the power side and the load side to avoid the risk of electric shock. In order to reduce design complexity and cost, many LED drivers use low-voltage DC power supply, which can simplify the isolation design and make the system safer and more reliable.

7. Power efficiency and cost issues

Providing high-voltage power supplies results in higher system power consumption, increasing energy consumption and costs. At the same time, high voltage has higher requirements on circuit design, insulation, protection, etc., which increases production and use costs.

Constant-voltage LED drivers have more energy efficiency advantages at lower voltages, so efficient and stable designs usually prioritize low-voltage rather than high-voltage power supply.

8. Cable and wiring requirements

High-voltage power supply systems have higher requirements on cables and require thicker insulation layers and grounding protection to prevent leakage. Low-voltage power supply allows the use of thinner cables, reducing wiring costs, and does not require too much additional protection during wiring.

In outdoor or high-altitude installations, the wiring process of low-voltage LED lamps is simpler and safer, reducing the risk of electrical accidents and making installation and maintenance easier for non-professionals.

Summarize

The supply voltage of LED lamps is limited by LED tolerance, heat dissipation, driver design, safety, regulatory requirements, etc., especially in terms of preventing the risk of electric shock, electrical accidents and complying with various safety standards. Constant current is usually used and controlled within a low voltage range to ensure the safety, reliability, and long life of LED lamps.