LM317HVT

LM317HVT: High Voltage Adjustable Positive Voltage Regulator

Overview

The LM317HVT is a high-voltage variant of the popular LM317 adjustable positive voltage regulator. Designed to deliver over 1.5A of output current, this component offers an exceptionally wide output voltage range from 1.2V up to 57V. Its simple two-resistor configuration makes it easy to implement in various circuit designs while providing superior line and load regulation compared to fixed regulators. The device is packaged in industry-standard transistor packages for easy integration into existing designs.

Key Features

• Wide output voltage range: 1.2V to 57V
• Output current capability exceeding 1.5A
• 0.01% typical load regulation
• 0.02% typical line regulation
• Internal thermal overload protection
• Internal short-circuit current limiting
• Output transistor safe-area compensation
• Standard transistor package options
• Requires only two external resistors for voltage setting
• Superior performance to fixed voltage regulators

Applications

The LM317HVT's versatile characteristics make it suitable for a wide range of applications:

• Adjustable power supplies
• High voltage regulator circuits
• Industrial control systems
• Test and measurement equipment
• Battery chargers
• Power supply pre-regulators
• Electronic loads
• Laboratory power supplies
• Motor control circuits
• HVAC control systems

Electrical Characteristics

The following table summarizes the key electrical parameters of the LM317HVT:

Absolute Maximum Ratings

• Input-Output Voltage Differential: 60V
• Power Dissipation: Internally Limited
• Operating Junction Temperature Range: -40°C to +125°C
• Storage Temperature Range: -65°C to +150°C

Operating Characteristics (Tj = 25°C unless otherwise noted)

• Reference Voltage (VREF): 1.25V (typical)
• Line Regulation: 0.02% (typical)
• Load Regulation: 0.01% (typical)
• Adjustment Pin Current: 50μA (typical)
• Minimum Load Current: 3.5mA (typical)
• Ripple Rejection: 80dB (typical)
• Output Noise Voltage: 0.003% of VOUT (typical)
• Thermal Resistance, Junction-to-Air (TO-220): 50°C/W

Package Information

The LM317HVT is available in several industry-standard packages:

TO-220 Package

• Package Type: TO-220-3
• Dimensions: 10.0mm x 15.0mm x 4.5mm
• Lead Pitch: 2.54mm
• Mounting: Through-hole
• Thermal Characteristics: 50°C/W junction-to-air

TO-3 Package

• Package Type: TO-3 metal can
• Dimensions: 22.1mm diameter
• Mounting: Requires hardware for heatsink attachment
• Thermal Characteristics: 35°C/W junction-to-case

Detailed Functional Description

The LM317HVT operates as a floating regulator, with the adjustment terminal functioning as the regulator's reference point. The device develops a nominal 1.25V reference voltage (VREF) between the output and adjustment terminals. This reference voltage is impressed across resistor R1 (see typical application circuit), and since the voltage is constant, a constant current flows through the output set resistor R2, giving an output voltage of:

VOUT = VREF (1 + R2/R1) + IADJ × R2

The device features internal current limiting, thermal overload protection, and safe-area compensation for the output transistor. These protection features make the regulator essentially immune to overload conditions that might otherwise cause damage.

Thermal Considerations

Proper heat sinking is crucial for reliable operation when operating at high input-output differentials or high output currents. The maximum allowable power dissipation is a function of the maximum junction temperature (125°C), the thermal resistance of the package, and the ambient temperature. Designers should calculate power dissipation as:

PD = (VIN - VOUT) × IOUT

And ensure the junction temperature remains within specified limits:

TJ = TA + (PD × θJA)

Typical Application Circuit

The basic LM317HVT configuration requires only two external resistors:

• R1: 240Ω (typical value between output and adjust pins)
• R2: Variable resistor for output voltage adjustment
• Optional output capacitor (1μF tantalum or 25μF aluminum) for improved transient response
• Input capacitor (0.1μF) when regulator is far from power supply filter

Design Considerations

For optimal performance, consider the following design guidelines:

• Place R1 physically close to the regulator to minimize noise pickup
• For fixed output applications, R2 can be replaced with a fixed resistor
• For improved ripple rejection, bypass the adjustment terminal with a capacitor (10μF)
• When operating near the minimum input-output differential, ensure sufficient headroom for line variations
• For high current applications, consider using a heatsink to maintain safe operating temperatures

Reliability and Quality

The LM317HVT is designed for robust operation in demanding environments:

• Manufactured using high-reliability processes
• 100% electrical testing during production
• ESD protection on all pins
• Extended temperature range operation (-40°C to +125°C)

Ordering Information

The device is available in several package and temperature variants:

• LM317HVT/NOPB: TO-220 package, lead-free
• LM317HVT: TO-220 package, standard
• LM317HVTK: TO-3 package