High-Voltage Regulator Design Using the Microchip LR8N8-G

Designing a reliable high-voltage (HV) power supply presents unique challenges, particularly when input voltages can exceed standard IC tolerances. The Microchip LR8N8-G high-voltage, adjustable linear regulator offers a robust and flexible solution for such demanding applications. This article explores the key design considerations and advantages of utilizing this specialized component.

The LR8N8-G distinguishes itself with an impressively wide input voltage range of up to 450V. This capability allows it to operate directly from rectified high-voltage AC lines or other DC sources that would instantly destroy conventional low-voltage regulators. Its adjustable output, which can be set from 1.20V to 440V using an external resistor divider, provides exceptional versatility for biasing, sensor systems, or as a stable reference in HV circuits.

A primary advantage of the LR8N8-G is its inherent simplicity and minimal external component count. The basic configuration requires only two external resistors to set the output voltage and two capacitors for stability. The output voltage is determined by the formula Vout = Vref (1 + R1/R2) + Iadj R1, where Vref is a stable 1.20V. This simplicity translates into a highly reliable and compact circuit footprint. Furthermore, the device incorporates critical internal protection features, including current limiting and thermal shutdown, which safeguard both the regulator and the load under fault conditions.

Despite its advantages, designers must carefully manage its limitations. As a linear regulator, its efficiency is governed by the voltage drop across it multiplied by the output current. Power dissipation is the most critical design constraint. For example, with an input of 300V and an output of 250V at 10mA, the device must dissipate (300V - 250V) 0.01A = 0.5W. Adequate heatsinking is absolutely essential to prevent the internal thermal protection from engaging. Consequently, the LR8N8-G is ideally suited for applications where output currents are low, typically in the range of a few milliamps.

Typical applications include:

Biasing for avalanche photodiodes (APDs) and photomultiplier tubes (PMTs).

Start-up power for offline switch-mode power supplies (SMPS).

Reference voltage sources for industrial and test equipment.

Low-current, high-voltage supplies for vacuum tubes and displays.

In conclusion, the Microchip LR8N8-G provides an elegant and highly effective solution for generating stable, low-noise, and adjustable high voltages. Its design simplicity and integrated protections make it an excellent choice for niche applications where high voltage and low current are the primary requirements, though thermal management remains a paramount consideration.

ICGOODFIND: The LR8N8-G is an exceptional component for niche high-voltage, low-current design challenges, offering unparalleled input voltage tolerance and design simplicity where other regulators cannot operate.

Keywords: High-Voltage Regulator, Linear Regulator, Power Dissipation, Thermal Management, Adjustable Output.