1 Features

1• For a newer drop-in alternative, see the LM317

• Typical 0.005%/V line regulation

• 1% output voltage tolerance

• 1.5-A output current

• Adjustable output down to 1.25 V

• Input-output differential up to 40 V

• Current limit constant with temperature

• No output capacitor required

• Short-circuit protected output

• −40°C to 125°C operating temperature range

2 Applications

• Automotive LED lighting

• Battery chargers

• Post regulation for switching supplies

• Constant-current regulator

• Microprocessor supplies

3 Description

The LM317A adjustable 3-terminal, positive-voltage

regulators are capable of supplying current in excess

of 1.5 A over a 1.25-V to 37-V output range and

provide 1% output-voltage accuracy. Both line

regulation and load regulation are better achieved

with the LM317A device than with standard fixed

regulators.

The LM317A offers full overload protection such as

over current, thermal-overload protection, and safearea

protection. All overload protection circuitry

remains fully functional even if the adjustment

terminal is disconnected.

Typically, no capacitors are needed unless the device

is situated more than 6 inches from the input filter

capacitors, in which case an input bypass is needed.

An optional output capacitor can be added to improve

transient response and can be replaced with a

ceramic and appropriate ESR. The adjustment

terminal can be bypassed to achieve very high ripplerejection

ratios that are difficult to achieve with

standard 3-terminal regulators.

Because the LM317A regulator is floating and detects

only the input-to-output differential voltage, supplies

of several hundred volts can be regulated as long as

the maximum input-to-output differential is not

exceeded. Exceeding the maximum input-to-output

deferential will result in short-circuiting the output. By

connecting a fixed resistor between the adjustment

pin and output, the LM317A can be also used as a

precision current regulator.

For applications requiring greater output current, see

the LM150 series (3A) and LM138 series (5A) data

sheets. For the negative complement, see the LM137

series data sheet.