High-Voltage LED Driver Design Using the Microchip HV9803BLG-G Controller

The demand for efficient, compact, and reliable high-voltage LED drivers is rapidly increasing across industrial, automotive, and consumer lighting applications. Designing such drivers requires a careful balance between performance, size, and cost. The Microchip HV9803BLG-G controller emerges as a pivotal solution, enabling the development of highly efficient non-isolated buck converters optimized for driving long series strings of high-brightness LEDs directly from rectified AC line voltages or high-voltage DC rails.

Core Architecture and Operating Principle

The HV9803BLG-G is a high-voltage monolithic buck converter controller specifically engineered for LED driving. Its architecture is designed to operate with input voltages from 9V up to 450V, making it exceptionally versatile. The device integrates a high-side switch driver and control logic on a single chip, significantly reducing external component count and board space.

At the heart of its operation is a fixed off-time (FOT) control method. Unlike traditional PWM controllers that use a constant switching frequency, the FOT scheme regulates the LED current by maintaining a constant off-time for the internal power MOSFET. The on-time is then modulated to maintain regulation. This approach offers several key advantages:

Inherent stability without complex compensation networks.

Fast transient response to input voltage variations.

Simple dimming through either a linear (DC) voltage or a low-frequency PWM signal applied to the `CTRL` pin.

Key Design Considerations

A robust driver design hinges on several critical factors centered around the HV9803 controller:

1. Sensing and Regulating LED Current: The average current through the LED string is sensed via a low-value external sense resistor (R_SENSE) connected between the source of the external N-channel MOSFET and ground. The voltage across this resistor is compared to an internal 250 mV reference. The controller adjusts the switching duty cycle to maintain this reference, ensuring a constant, flicker-free LED current.

2. External Component Selection: The performance and efficiency of the driver are heavily dependent on the choice of external components.

Power MOSFET: Selection is based on voltage rating (must exceed maximum VIN), on-resistance (RDS(ON)), and gate charge to optimize switching losses.

Freewheeling Diode: A fast-recovery Schottky diode is crucial for minimizing reverse recovery losses and improving overall efficiency.

Inductor: The inductor value is calculated based on the desired LED current ripple, the input/output voltages, and the controller's off-time. Its saturation current must be rated above the system's peak current.

3. Thermal Management: Despite its high efficiency, power dissipation in the MOSFET and diode must be managed. Proper PCB layout with adequate copper pour for heat sinking is essential for long-term reliability, especially in high-ambient-temperature environments.

4. Dimming Implementation: The HV9803 provides exceptional dimming capabilities. Applying a DC voltage (0.5V to 2.5V) to the `CTRL` pin provides linear dimming control. For a wider dimming range and better colour consistency (no chromaticity shift), a low-frequency PWM signal (typically 100 Hz - 1 kHz) can be applied, effectively turning the LED current on and off.

Advantages of the HV9803BLG-G Based Design

Utilizing this controller offers distinct benefits:

Simplified Circuitry: The monolithic design and FOT control eliminate the need for a compensation network and reduce the total bill of materials (BOM).

High Efficiency: By minimizing switching losses and using a low-side current sense resistor, efficiencies exceeding 90% are readily achievable.

Wide Input Voltage Range: Capable of operating from a universal AC input (85 VAC to 265 VAC) or high-voltage DC sources with minimal design changes.

Excellent Dimming Performance: Supports both analog and wide-range PWM dimming with a high dimming ratio.

ICGOODFIND: The Microchip HV9803BLG-G controller stands as an exceptional integrated solution for high-voltage LED driver designs. Its innovative fixed off-time architecture simplifies the development process while delivering high efficiency, robust performance, and superior dimming control. It effectively addresses the core challenges of driving LED strings from high-voltage sources, making it an ideal choice for designers seeking to create compact, reliable, and high-performance lighting systems.

Keywords:

HV9803BLG-G

High-Voltage LED Driver

Fixed Off-Time Control

Buck Converter

PWM Dimming