Analyze several types of problems often occurring in LED fluorescent lamp power supply
Currently, the LED fluorescent lamp market is highly dynamic. Manufacturers are mainly divided into three categories. The first group consists of companies that originally produced LED chips and later expanded into downstream lighting products. These firms often lack deep knowledge of circuit design and power supply systems. The second category includes traditional lighting manufacturers who have entered the LED field, with limited understanding of circuitry. The third type is new startups that have some familiarity with LED power supplies but may not have extensive experience in the entire system.
The power supply is one of the most critical components of an LED fluorescent lamp. If it's not chosen properly, the lamp may fail to perform optimally or even malfunction. Selecting the right power supply ensures efficiency, longevity, and safe operation.
Matching Power Supplies with LED Lamp Boards
Some customers design the light board first and then look for a compatible power supply. However, they often face challenges such as mismatched current and voltage levels. For example, the current might be too high (e.g., >350mA) while the voltage is too low (<40V), or vice versa (e.g., <40mA and >180V). This can lead to excessive heat, poor efficiency, or even failure. To avoid this, it’s best to plan the string and parallel configuration carefully so that each LED receives the same voltage and current. This ensures optimal performance. It’s also advisable to collaborate directly with the power supply manufacturer for a tailored solution.
LED Operating Current
Most LEDs are rated for a standard operating current of 20 mA. Some manufacturers initially use this value, but testing has shown that 17 mA provides better thermal management and longer lifespan. Designing at a slightly lower current reduces heat generation and improves reliability over time.
LED Operating Voltage
The typical operating voltage for general LEDs ranges between 3.0V and 3.5V. Testing has revealed that most LEDs operate efficiently around 3.125V. Therefore, using 3.125V as a baseline for calculations is both practical and accurate.
Series-Parallel Configuration for Wide Voltage Range
To ensure the LED fluorescent lamp works across a wide input voltage range (AC 85–265V), proper series and parallel connections on the lamp board are essential. Since most power supplies are non-isolated buck types, the output voltage should not exceed 72V. This limits the number of LED strings to around 23. Parallel connections should be kept reasonable—ideally 6 or 8 in parallel, or 8 to 12—to avoid excessive current and overheating. A total current of no more than 240 mA is recommended for optimal performance.
Series-Parallel Connections with PFC and Wide Voltage
There are three common types of power supplies with PFC (Power Factor Correction): those without PFC, which typically have a PFC of about 0.65; passive PFC designs, offering a PFC of around 0.92; and active PFC solutions using circuits like 7527/6561, which can achieve up to 0.99. While active PFC is more efficient, it comes at a higher cost. Passive PFC circuits, also known as valley-fill designs, operate within half the peak AC input voltage. For example, if the input is 180V, the peak is about 254V, and the working voltage would be around 127V. With a 30V drop, the maximum output voltage is 90V, allowing up to 28 LED strings. To maintain a good power factor, the number of strings shouldn’t be too high, otherwise, the minimum voltage requirement won’t be met.
Constant Current Accuracy
Many power supplies on the market have poor constant current accuracy, with errors ranging from ±8% to ±10%. For better performance, a ±3% accuracy is preferred. If you have six parallel channels, each channel can tolerate about ±0.5% error. For 12 channels, the error per channel would be around ±0.25%, which is sufficient. However, extremely high accuracy increases costs significantly, so a balance must be struck based on application needs.
Isolated vs. Non-Isolated Power Supplies
Isolated power supplies are commonly used for 15W and above, but they require larger transformers, making them difficult to fit inside LED tubes, especially T6 or T8 models. Isolation is generally only feasible for power supplies under 15W, and these tend to be more expensive due to the additional components required.
Size Constraints
Height is a major limitation when designing LED tubes. For example, T6 and T8 lamps must be under 9 mm in height, while T10 tubes can go up to 15 mm. Longer lengths allow for better heat dissipation, making them more suitable for higher-power applications.
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