Introduction
In the world of LED lighting, consistency is key. However, many users encounter frustrating issues where LEDs vary in brightness or flicker during operation. While there are many variables in a lighting system, the root cause often lies in the internal architecture of the Power Supply Unit (PSU)—specifically the use of Single-Stage PFC (Power Factor Correction).
To provide cost-effective solutions, many LED power supply series utilize a Single-Stage PFC topology. While efficient and economical, this design involves certain technical trade-offs that can affect light quality under specific conditions.
The Challenges of Single-Stage PFC Topology
The primary reason for instability in Single-Stage PFC units is the absence of an input bulk capacitor. In dual-stage systems, this capacitor acts as a buffer; without it, the PSU is more susceptible to the following three issues:
1. AC Line Fluctuation
Because there is no bulk capacitor to store energy and smooth out incoming power, the output becomes a "mirror" of the input. In regions where the AC grid quality is poor or fluctuates, the output voltage and current will follow suit, leading to visible variations in LED brightness.
2. High Output Ripple
Single-Stage units inherently produce significantly larger output ripple compared to Dual-Stage PFC models (see Figure below). If the "trough" (the lowest point) of this ripple falls below the minimum operating voltage of your LED driver IC, the system will lose power momentarily, resulting in a flicker.
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The Fix: You can often resolve this by slightly increasing the output voltage so the ripple’s lowest point remains above the driver's threshold, or by selecting a PSU with a higher rated voltage.
3. Current Harmonics & Compatibility
Single-Stage PFC power supplies are optimized specifically for Constant Current (C.C.) driving. If you attempt to use them as a Constant Voltage (C.V.) source—for example, in a system where you are cascading external constant current driver ICs—the harmonic distortion can worsen. This mismatch often leads to instability and interference.
Application Scenarios: When to Choose Carefully
- Ideal Use Case: Single-Stage PFC is excellent for straightforward, cost-sensitive LED installations where the AC grid is stable and the PSU directly drives the LEDs in Constant Current mode.
- When to Avoid: If your project is located in an area with an unstable power grid, or if your design requires a complex setup with multiple downstream driver ICs, we highly recommend switching to a General Application PSU (Dual-Stage PFC).
Conclusion
Flickering and brightness variations are rarely a sign of a "broken" power supply, but rather a sign of a "mismatched" one. While Single-Stage PFC models offer great value, they require a stable environment. For mission-critical lighting or complex driver-based systems, investing in a Dual-Stage PFC unit is the best way to ensure a flicker-free experience.
If you have any technical issues, feel free to contact our team at contact@wellforces.co.nz. We provide professional support and a wide range of solutions.
