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.