Driver-on-Board (DOB) and Linear Driver solutions are the two predominant driver technologies in modern LED lighting. They exhibit significant distinctions in working principles, performance characteristics, and suitable applications. This article provides a detailed comparison:
Quick Reference: Core Differences
Detailed Analysis:
Operating Principle:
DOB: Functions as a high-frequency switched-mode power converter. A controller IC drives Power MOSFET(s) switching at high frequencies (tens to hundreds of kHz). A high-frequency transformer performs AC-DC conversion, voltage transformation, and isolation (optional). Output is rectified and filtered to provide smooth DC for the LEDs. This complex conversion process achieves high efficiency.
Linear: A passive drive method without high-frequency switching or magnetic components. It relies on the inherent voltage drop (or resistance) of semiconductor devices (like linear constant current ICs, JFETs, BJTs + resistors) to limit current. Simple versions use RC (Resistor-Capacitor) droppers. It inherently "wastes" a portion of the input voltage as heat across the driver device(s) to deliver the required current to the LEDs. This results in a highly pulsating DC output current at 100/120Hz (the double frequency of mains input).
Efficiency & Thermal Performance:
DOB: Achieves high efficiency (85-95%+) due to efficient energy conversion through switching. Losses are relatively small and occur during switching transitions and in semiconductors. While the controller IC and MOSFET generate localized heat, overall heat generation is manageable if properly heatsinked. The high efficiency means less input power is wasted as heat.
Linear: Suffers from inherently low efficiency (often <60-70%). The voltage difference between the input supply and the required LED voltage is dissipated as heat directly in the driver components. For example, driving a 3V LED string from 230V AC results in ~227V dropping across the driver device! This creates extremely high temperatures on the power device(s), demanding robust thermal management and high temperature-rated components. Efficiency is poor and decreases as the input voltage increases relative to the LED voltage.
Power Factor (PF) & Total Harmonic Distortion (THD):
DOB: Can easily achieve high PF (>0.9, often >0.95) and low THD (<20%, <10% for quality designs) using techniques like Critical Conduction Mode (CrM), Discontinuous Conduction Mode (DCM), or Active Power Factor Correction (Active PFC). This is essential for compliance with global energy efficiency and electrical standards (ErP, ENERGY STAR).
Linear: Naturally has very poor PF (typically <0.6) because the input current waveform is a series of narrow peaks, misaligned with the voltage sine wave. Even "improved" IC designs (using valley-fill circuits) usually only reach PF ~0.7-0.8 and THD remains high (>30%). Linear drivers act as a "polluting load" on the AC mains.
Output Ripple & Flicker:
DOB: Delivers smooth, well-filtered DC output with minimal ripple. This enables flicker-free or very low-flicker performance, which is critical for visual comfort, health, and high-quality lighting applications.
Linear: Output is fundamentally a pulsating DC current at 100/120Hz. While constant current ICs regulate the peak current, they cannot eliminate the deep valley between peaks. This results in significant current ripple and inherent light output flicker. Using large output capacitors to reduce ripple is impractical due to cost and size constraints.
Complexity & Cost:
DOB: Requires more components (Controller IC, MOSFET, transformer, capacitors, inductors). Integration onto the LED board (or a closely coupled small board) adds design complexity and manufacturing steps. This results in a higher unit cost.
Linear: Utilizes very few components (IC, bridge rectifier, handful of resistors/capacitors). The circuit is exceptionally simple, making design, assembly, and board integration straightforward. This translates into the lowest possible unit cost, its primary advantage.
Reliability:
DOB: Mature and generally reliable. The main potential weak point is the electrolytic capacitor lifetime, especially at high temperatures. Using long-life electrolytic capacitors or replacing them with ceramic/solid-state capacitors significantly boosts reliability. Adequate thermal design for the IC/MOSFET is also critical.
Linear: Reliability is primarily threatened by excessive heat. Power devices operate near their maximum temperature limits. This creates significant thermal stress and makes the driver highly vulnerable to voltage surges or spikes. Reliability is lower, especially at high input voltages, in hot ambient temperatures, or within enclosed fixtures.
Summary & Recommendations:
Choose DOB when you need:
High Efficiency (Key for energy savings).
High PF & Low THD (Mandatory for regulatory compliance: ErP, ENERGY STAR).
Flicker-free / Low Ripple Output (Essential for high visual comfort - homes, offices, task lighting).
Wide Input Voltage Compatibility (Global market requirements).
Medium to High Power Applications (>10W).
High Reliability and Long Lifetime (with appropriate component selection/cooling).
Higher cost is acceptable for superior performance.
Consider Linear when:
Absolute Lowest Cost is the #1 Priority (Ultra low-cost products).
Application Power is Very Low (Typically <10W, Max <20W).
Light Quality Requirements are Minimal (Tolerance for low PF, high THD, ripple/flicker acceptable - e.g., basic decorative lights, functional nightlights).
Thermal Conditions are Excellent (Or ambient temperature is low).
Electrical Standards Compliance is not strictly required.
Extremely Simple and Rapid Design is needed.
Market Trend: As global energy regulations tighten and consumer demand for high-quality (flicker-free) light grows, DOB solutions are increasingly dominating the mid-to-low power segment (e.g., standard light bulbs) due to their improving cost-effectiveness. Meanwhile, Linear drivers maintain a foothold in the ultra-low-cost, very-low-power market segment where performance demands are minimal.