If the adjustment pin is connected to ground the output pin delivers a regulated voltage of 1.25 V at currents up to the maximum. How the adjustment pin is connected determines the output voltage as follows. Internally the device has a bandgap voltage reference which produces a stable reference voltage of V ref= 1.25 V followed by a feedback-stabilized amplifier with a relatively high output current capacity. The LM317 has three pins: INput, OUTput, and ADJustment. Schematic of LM317 in a typical voltage regulator configuration, including decoupling capacitors to address input noise and output transients. Failure to do this may cause the circuit to short. In packages with a heat-dissipating mounting tab, such as TO-220, the tab is connected internally to the output pin which may make it necessary to electrically isolate the tab or the heat sink from other parts of the application circuit. The alternative is to use a switching voltage regulator, which is usually more efficient, but has a larger footprint and requires a larger number of associated components. This is the tradeoff for using linear regulators, which are a simple way to provide a stable voltage with few additional components. For large voltage differences, the power lost as heat can ultimately be greater than that provided to the circuit. A LM317 commonly requires a heat sink to prevent the operating temperature from rising too high. Linear regulators inherently waste power the power dissipated is the current passed multiplied by the voltage difference between input and output. In a constant voltage mode with an input voltage source at V IN at 34 V and a desired output voltage of 5 V, the maximum output current will be P MAX / (V I-V O) = 0.98 / (34-5) = 32 mA.įor a constant current mode with an input voltage source at V IN at 12 V and a forward voltage drop of V F=3.6 V, the maximum output current will be P MAX / (V I - V F) = 0.98 / (12-3.6) = 117 mA.Īs linear regulators, the LM317 and LM337 are used in DC to DC converter applications. (A piece of shiny sheet metal of aluminium with the dimensions 6 x 6 cm and 1.5 mm thick, results in a thermal resistance that permits 4.7 W of heat dissipation ). Without a heat sink with an ambient temperature at 50 ☌ such as on a hot summer day inside a box, a maximum power dissipation of (T J-T A)/R θJA = ((125-50)/80) = 0.98 W can be permitted. LM317 pinout showing its constant voltage reference.

Lm317t opisanie na russkom