Currently, the LED fluorescent lamp market is quite dynamic. LED driver manufacturers can be broadly categorized into three types. First, there are companies that produce LED chips or LED lights and then move downstream to develop drivers. Second, there are traditional lighting manufacturers that have transitioned into producing LED power supplies. Lastly, there are new ventures that previously focused on other products or power solutions and now specialize in LED drivers.
The LED driver plays a critical role in the performance of an LED fluorescent lamp. Choosing the wrong power supply can lead to poor lighting quality, reduced lifespan, or even failure. Below are some practical tips for selecting and using LED fluorescent lamp power supplies, based on real-world experience and testing.
1. Why is constant current important for LED fluorescent lamps?
LEDs are sensitive semiconductor devices. Their performance is affected by temperature and voltage fluctuations. When temperature rises, the current through the LED increases, which can damage the device over time. A constant current power supply ensures stable operation by maintaining a consistent current, regardless of environmental changes, thus protecting the LEDs from overheating and extending their lifespan.
2. How should the power supply match the lamp board?
Some users design the lamp board first and then look for a compatible power supply, but this often leads to mismatches—either too high voltage and low current or vice versa. This can result in excessive heat, low efficiency, or improper operation. The best approach is to plan the series-parallel configuration carefully so that each LED receives the same voltage and current. It’s also recommended to work directly with the power supply manufacturer to tailor a solution that fits your specific needs.
3. What is the ideal working current for LED fluorescent lamps?
Most LEDs are rated for 20 mA, but operating at this level can cause significant heat. Through testing, it's been found that 17–19 mA provides better thermal management. Ideally, 18 mA is recommended as it balances performance and longevity effectively.
4. What is the appropriate working voltage for LED drivers?
The typical operating voltage for an LED is between 3.0V and 3.5V. After testing, most LEDs operate efficiently around 3.125V. Therefore, when designing a circuit, the total voltage for M LEDs in series would be 3.125 × M volts.
5. What is the optimal series-parallel configuration for wide voltage range?
To support a wide input voltage range (AC 85–265V), the LED string configuration is crucial. Non-isolated buck power supplies typically have an output limit of around 72V. This means no more than 23 LEDs in series. Using too many parallel strings can increase current and cause overheating. It’s recommended to use 6, 8, or 12 parallel strings with a total current not exceeding 240 mA. Another option is to use a two-stage power supply system, but this is costly and less common in the market.
6. How does series-parallel configuration affect PFC and wide voltage?
There are three types of PFC circuits: passive, active, and none. Passive PFC offers a power factor of around 0.92, while active PFC can reach up to 0.99 but at a higher cost. For passive PFC, the voltage range is limited to half the peak AC input. To achieve a good power factor, the number of LEDs in series shouldn’t be too high, otherwise, the low-voltage requirement might not be met.
7. What is the best constant current accuracy for LED drivers?
Many commercial drivers have a constant current error of ±8% or ±10%, which is not ideal. Most applications require a precision of ±3%. With multiple parallel channels, the error per channel can be reduced significantly, making it sufficient for most LED applications. Too much precision increases costs unnecessarily, and for LEDs, small current variations don’t make a big difference.
8. Isolated vs. non-isolated power supplies
Isolated power supplies are generally larger and more expensive, especially for low-power applications like 15W LED tubes. In T6/T8 lamps, it’s almost impossible to fit an isolated transformer due to space constraints. Non-isolated designs are more compact, efficient, and cost-effective, provided proper safety measures are in place.
9. Power efficiency of LED drivers
Efficiency is calculated as (output voltage × output current) / input power. Low efficiency means more energy is lost as heat, which can reduce the lifespan of internal components. High efficiency helps maintain lower temperatures, ensuring longer life for both the driver and the LEDs. A minimum efficiency of 80% is recommended, and this depends on how well the lamp board is matched with the driver.
10. Size considerations for LED drivers
Height is a key constraint, especially for T6 and T8 lamps, where the driver must be under 9 mm tall. T10 lamps can be slightly taller, up to 15 mm. Longer length allows better heat dissipation, which is beneficial for performance and reliability.
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