Many engineers and enthusiasts are eager to understand how transformers and inductors in LED power supplies are applied. Starting from this article, we will introduce their applications in different power supply systems. Today, we focus on the LED driver and its essential magnetic components.
The example below shows a 100W LED driver PCBA (without potting for clarity). In the image:
Label 1: Common Mode Inductor
Label 2: PFC Inductor
Label 3: Transformer
Label 4: Output Filter Inductor (Drum Core Type)
1. Common Mode Inductor in LED Power Supplies (Label 1)
The first component is a UU9.8 common mode choke built with MnZn ferrite. Compared to toroidal types, this inductor can be mass-produced at lower cost. However, its EMI suppression is weaker due to limited core material options.
In higher-performance LED drivers, toroidal common mode inductors are preferred. These allow broader material choices such as MnZn, nanocrystalline, amorphous, or NiZn cores. For better waveform control, some LED power supplies use multiple common mode inductors for multi-stage filtering.
2. PFC Inductor in LED Power Supplies (Label 2)
The Power Factor Correction (PFC) inductor uses a PQ2620 ferrite core. Its role is to smooth harmonics and make the current waveform closer to a sine wave, improving power factor and efficiency while reducing grid pollution.
By regulation, LED drivers above 75W must include a PFC stage (except for bridgeless totem-pole PFC). Aside from ferrite, powder cores are also widely used in LED PFC inductors. (For further reading, check our article: PFC Inductor Design).
3. Transformer in LED Power Supplies (Label 3)
The transformer here is designed for flyback topology with a PQ3220 core. It converts high-voltage DC into low-voltage AC before rectification. For LED power supplies, minimizing leakage inductance is essential, often achieved with sandwich winding techniques.
When designed properly, the transformer helps achieve up to 90% efficiency in a 100W LED power supply. Wide tape is used for insulation to meet safety requirements.
4. Output Filter Inductor in LED Power Supplies (Label 4)
The drum core inductor works with two capacitors to form a π-type filter circuit, suppressing output noise and interference. When paired with synchronous rectification, it reduces losses and improves the efficiency of the LED driver.
Conclusion: Why Transformers and Inductors Are Essential in LED Power Supplies
As we can see, transformers and inductors in LED power supplies play critical roles:
- Common mode inductors filter EMI.
- PFC inductors improve efficiency and comply with regulations.
- Transformers handle voltage conversion.
- Output filter inductors ensure clean, stable output.
With proper design and core material selection, LED drivers can achieve both high efficiency and reliability. In future articles, we will explore how these magnetic components are applied in other types of power systems.
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