Analyze several types of problems often occurring in LED fluorescent lamp power supply
Currently, the LED fluorescent lamp market is highly competitive. Manufacturers can be broadly categorized into three groups. The first group consists of companies that originally produced LED chips and later moved downstream into manufacturing lamps, but they often lack in-depth knowledge about circuit design and power supply systems. The second group includes traditional lighting manufacturers who have entered the LED market and have limited understanding of the underlying electronics. The third group comprises new entrants who are still learning about LED power supplies and their applications.
The power supply is one of the most critical components of an LED fluorescent lamp. Choosing the wrong power supply can lead to poor performance, excessive heat, or even failure to operate correctly. Therefore, selecting a suitable power supply is essential for ensuring the longevity and efficiency of the LED lamp.
Matching Power Supply with Lamp Board
Some customers design the lamp board first and then look for a compatible power supply, which often leads to compatibility issues. For example, the current may be too high (e.g., I > 350mA) or the voltage too low (e.g., V < 40V), or vice versa (I < 40mA, V > 180V). This can result in overheating, inefficiency, or an insufficient input voltage range. To avoid these problems, it's best to determine the optimal series-parallel configuration so that each LED receives the same voltage and current, maximizing the power supply’s performance. Communication with the power supply manufacturer during the design phase is highly recommended for a customized solution.
LED Operating Current
Most LEDs are rated to operate at around 20 mA. However, some manufacturers initially use this maximum value. In reality, operating at 20 mA can cause significant heat buildup. Through extensive testing, it has been found that setting the operating current to 17 mA provides better thermal management and overall performance.
LED Operating Voltage
The typical operating voltage for general LEDs is between 3.0V and 3.5V. Testing shows that most LEDs perform best at around 3.125V. Therefore, it is reasonable to calculate based on this value for more accurate results.
Series and Parallel Connections for Wide Voltage Range
To ensure the LED fluorescent lamp works across a wide input voltage range (AC 85V–265V), the LED string configuration on the lamp board is crucial. Since most power supplies are non-isolated buck types, the output voltage should not exceed 72V. This limits the number of LEDs in series to no more than 23. The number of parallel connections should also be limited to prevent excessive current and heat. It is recommended to use configurations like 6x8 or 8x12, keeping the total current under 240 mA for optimal performance.
Series-Parallel Connections with PFC and Wide Voltage
There are three main types of power supplies with PFC (Power Factor Correction) on the market. The first type lacks a dedicated PFC circuit and typically has a power factor of around 0.65. The second uses a passive PFC circuit, achieving a power factor of about 0.92. The third uses an active PFC circuit, such as the 7527/6561 chip, which can reach up to 0.99 but is significantly more expensive. Passive PFC circuits, also known as valley-fill PFCs, operate at half the peak AC input voltage. For example, if the input is 180V, the peak is approximately 254V, and the operating voltage would be around 127V. With a 30V drop, the maximum output is 90V, allowing up to 28 LEDs in series. To achieve a good power factor, the number of LEDs in series should not be too high, otherwise, the low-voltage requirements might not be met.
Constant Current Accuracy
Many power supplies on the market suffer from poor constant current accuracy. Popular models like PT4107, HV9910, BP2808, and SMD802 typically have an error margin of ±8% or ±10%. However, the industry standard requires a much tighter tolerance of ±3%. If six channels are connected in parallel, each channel’s error should be around ±0.5%, and for twelve channels, it should be about ±0.25%. While higher accuracy improves performance, it also increases costs significantly.
Isolated vs. Non-Isolated Power Supplies
For isolated power supplies, especially those rated at 15W or higher, the transformer size becomes a challenge when designing LED tubes. This makes it difficult to fit into T6 or T8 lamps, where space is limited. As a result, isolation is typically only feasible for power supplies below 15W, and even then, the cost is quite high.
Size Constraints
Height is a major constraint in LED tube design. T6 and T8 lamps usually require a height of less than 9 mm, while T10 lamps can go up to 15 mm. Longer lengths are more flexible and allow for better heat dissipation, making them easier to manage thermally.
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