LED Driver Design with On-Bright Controllers
LED Driver Fundamentals
LEDs require constant current drive for stable light output and long lifetime. LED drivers must provide regulated current regardless of input voltage variations, LED forward voltage variations, and temperature changes. Key specifications include output current accuracy, current ripple, efficiency, and power factor.
Isolated vs Non-Isolated Topologies
Isolated flyback drivers use a transformer for safety isolation between input and output, required for most indoor lighting applications. Non-isolated buck or buck-boost drivers are simpler and lower cost but don't provide isolation, suitable for some outdoor or integrated fixtures. Select based on safety requirements and application.
Power Factor Correction
Commercial LED lighting often requires high power factor (>0.9) and low THD to meet regulations and utility requirements. Active PFC circuits using dedicated PFC controllers (like OB3338) precede the LED driver stage. Two-stage design (PFC + DC-DC) provides best performance but higher cost than single-stage.
Current Regulation Techniques
Primary-side regulation senses current indirectly through auxiliary winding, eliminating optocoupler and reducing cost. Secondary-side regulation uses current sense resistor and feedback loop for highest accuracy. Choose based on accuracy requirements and cost constraints.
💡 FAE Insights
📋 Customer Cases
Challenge
Needed 40W isolated LED driver with high PF and low flicker for commercial lighting
Solution
Designed two-stage driver with OB3338 PFC and OB2263 flyback controller
Results
Achieved PF>0.95, flicker-free operation, passed all commercial lighting standards
Frequently Asked Questions
1. What is the difference between constant voltage and constant current LED drivers?
Constant voltage drivers provide fixed output voltage and rely on external current limiting. Constant current drivers regulate output current directly, which is preferred for LED applications as it ensures consistent LED current regardless of forward voltage variations.
2. How much current ripple is acceptable in LED drivers?
For general lighting, current ripple should be <10% to avoid visible flicker and ensure long LED lifetime. For high-quality or video applications, <5% ripple is recommended. Excessive ripple reduces LED lifetime and may cause visible flicker.
3. What is the typical efficiency of LED drivers?
LED driver efficiency varies by topology and power level. Isolated flyback drivers typically achieve 85-90% efficiency. Adding active PFC reduces efficiency by 1-2%. Non-isolated buck drivers can achieve 90-95% efficiency.
4. How do I achieve high power factor in LED drivers?
High power factor requires active PFC circuit (boost converter) before the LED driver stage. The PFC stage shapes input current to follow voltage waveform. Single-stage PFC+driver ICs are available for lower power applications; two-stage designs provide best performance for higher power.
5. What protection features are needed for LED drivers?
Essential protections include LED open-circuit, LED short-circuit, over-voltage, over-temperature, and input under-voltage. These ensure safe operation under fault conditions and protect both the driver and LEDs.