LM117-Series, Adjustable, Three-Pin Positive Voltage Regulators

Texas Instruments' LM117-series of adjustable three-pin positive voltage regulators are capable of supplying, in excess of, 1.5 A over a 1.25 V to 37 V output range and a wide temperature range. They are exceptionally easy to use and require only two external resistors to set the output voltage. Furthermore, both line and load regulation are better than standard fixed regulators.

The LM117-series offers full overload protection such as current limit, thermal overload protection, and safe area 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 six 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 that are difficult to achieve with standard, three-terminal regulators.

Because the 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. That is, avoid short-circuiting the output.

By connecting a fixed resistor between the adjustment pin and output, the LM117-series can also 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 1.25 V where most loads draw little current.