The LM117 and LM317-N series of adjustable 3-pin positive voltage regulators are capableof 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 outputvoltage. Further, both line and load regulation are better than standard fixedregulators.
The LM117 and LM317-N offer full overload protection such as current limit, thermaloverload protection and safe area protection. All overload protection circuitry remains fullyfunctional even if the adjustment terminal is disconnected.
Typically, no capacitors are needed unless the device is situated more than 6 inches fromthe input filter capacitors, in which case an input bypass is needed. An optional output capacitorcan be added to improve transient response. The adjustment terminal can be bypassed to achieve veryhigh ripple rejection ratios that are difficult to achieve with standard 3-terminalregulators.
Because the regulator is floating and detects only theinput-to-output differential voltage, supplies of several hundred volts can be regulated as long asthe maximum input-to-output differential is not exceeded. That is, avoid short-circuiting theoutput.
By connecting a fixed resistor between the adjustment pin and output, the LM117 andLM317-N can be also used as a precision current regulator. Supplies with electronic shutdown can beachieved by clamping the adjustment terminal to ground, which programs the output to 1.25 V wheremost loads draw little current.
For applications requiring greater output current, see theLM150 series (3 A) andLM138 series (5 A) data sheets. For thenegative complement, see the LM137 seriesdata sheet.