The LM317Tis a adjustable 3 terminal positive or LM337 negative, voltage regulator capable of supplying in excess of 1.5 amps over an output range of 1.25 to 37 volts for LM317 or -1.25 to -37 volts for LM337. The device also has built in current limiting and thermal shutdown which makes it essentially blow-out proof. Output voltage is set by two resistors R1 and R2 connected as shown below. The voltage across R1 is a constant 1.25 volts and the adjustment terminal current is less than 100μA. The output voltage can be closely approximated from Vout=1.25 / [1+(R2/R1)] , for R1=120Ω the type is R2=120[(Vout/1.25)-1] ,which ignores the adjustment terminal current but will be close if the current through R1 and R2 is many times greater. A minimum load of about 10mA is required, so the value for R1 can be selected to drop 1.25 volts at 10mA or 120ohms. Something less than 120 ohms can be used to insure the minimum current is greater than 10mA.. When power is shut off to the regulator the output voltage should fall faster than the input. In case it doesn't, a diode can be connected across the input/output terminals to protect the regulator from possible reverse voltages. A 1uF tantalum or 25uF electrolytic capacitor across the output improves transient response and a small 0.1uF ΜΚΤ capacitor is recommended across the input if the regulator is located an appreciable distance from the power supply filter. The power transformer should be large enough so that the regulator input voltage remains 3 volts above the output at full load. In case of LM317, the difference with voltage of the input and the output is a maximum of 40 V. Because the most low voltage of the output is 1.25 V, the upper limit with the input voltage becomes 41.25 V correctly. Generally, it makes the maximum input voltage 40 V. Because it is, the voltage adjustment range by LM317 becomes 1.25V - 37V. In LM337, the polarity with the voltage is opposite but the adjustment range is same.

Features · Guaranteed 1% output voltage tolerance ·Guaranteed max. 0.01%/V line regulation · Guaranteed max. 0.3% load regulation · Guaranteed 1.5A output current ·Adjustable output down to 1.2V ·Current limit constant with temperature · 80 dB ripple rejection ·Output is short-circuit protected