The LM317 adjustable 3-terminal positive voltage regulator is capable of supplying in excess of 1.5A over a 1.2V to 37V output range. It is exceptionally easy to use, and requires only two external resistors to set the output voltage. Further, both line and load regulation are better than standard fixed regulators. Also, the LM317 is packaged in a standard transistor package which is easily mounted and handled.
In addition to higher performance than fixed regulators, the LM317 offers full overload protection available only in ICs. Included on the chip are current limit, thermal overload protection and safe area protection. All overload protection circuitry remains fully functional even if the adjustment terminal is disconnected.
Normally, 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. The adjustment terminal can be bypassed to achieve very high ripple rejection ratios which are difficult to achieve with standard 3-terminal regulators.
Besides replacing fixed regulators, the LM317 is useful in a wide variety of other applications. Since the regulator is "floating" and sees 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, i.e., you avoid short-circuiting the output.
Also, it makes an especially simple adjustable switching regulator, a programmable output regulator or, by connecting a fixed resistor between the adjustment pin and output, the LM317 can be used as a precision current regulator. Supplies with electronic shutdown can be achieved by clamping the adjustment terminal to ground which programs the output to 1.2V where most loads draw little current.
LM317 Adjustable Voltage Regulator Features
- Guaranteed 1.5% output voltage tolerance
- Guaranteed max. 0.07%/V line regulation
- Guaranteed max. 1.5% load regulation
LM317 Adjustable Voltage Regulator Typical Application
Full output current not available at high input-output voltages
* Needed if device is more than 6 inches from filter capacitors.
† Optional — improves transient response. Output capacitors in the range of 1µF to 1000µF of aluminum or tantalum electrolytic are commonly used to provide improved output impedance and rejection of transients.
Download LM317 Adjustable Voltage Regulator Datasheet.