The negative complement of LM317 is the LM337 which regulates voltages below the reference voltage, rather than above.
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The LM317 can output a voltage from 1.25 to 37. As can be seen from the schematic diagram, the output voltage is determined by the values of the two resistors connected between the Vout and ADJ pins, i.e. RH and RL.
Specifications of LM317
| Symbol | Parameter | Value |
|---|---|---|
| Vout | 1.25 - 37 V | |
| Vin - Vout | difference | 30 - 40 V |
| Tj | operating junction temperature | 0 - 125 degree Celsius |
| Io (max) | maximum output current | 1.5 Amperes |
| IL (min) | minimum load current | typically, 3.5mA with a maximum of 12mA |
| PD | power dissipation | internally limited |
| R⬲JA | thermal resistance of junction to ambient | 80 degree Celsius/W |
| R⬲JC | thermal resistance of junction to case | 5 degree Celsius/W |
If the device is not mounted on a heat sink and there is a surrounding temperature of about 50 ⁰C, for example, on a hot summer day inside a container, a most extreme power dissipation of (TJ-TA)/RθJA = ((125-50)/80) = 0.98 W can be allowed. (A bit of gleaming sheet metal of Aluminum with the measurements 6 x 6 cm and 1.5 mm thick, brings about a thermal resistance that grants 4.7 W of heat dissipation.
When operating in a constant voltage mode with an input voltage source, VIN at 34 V with a desired output voltage of 5 V, the highest output current will be PMAX/(VI-VO) = 0.98/(34-5) = 32 mA.
For a constant current mode with an input voltage source, VIN at 12 V and a forward voltage drop of VF=3.6 V, the highest output current will be PMAX/(VI - VF) = 0.98/(12-3.6) = 112 mA.
All linear regulators normally waste power, the power wasted is the product of the current and the voltage difference between input and output. When in use LM317 ordinarily requires a heat sink to prevent the working temperature going too high. For large voltage differnces, the wasted energy in the form of heat can be more than that supplied to the circuit. This is what you'll sacrifice for using linear regulators which are a basic approach to supply a steady voltage with couple of extra parts. A better way is to use a switching voltage regulator which usually performs better, however has a bigger impression and requires many other related components.
For LM317 with heat dissipating mounting tab, for example, TO-220, the tab is hooked up inside to the output pin which is the reason why it may be necessary to isolate the tab or the heat sink from different parts of the application circuit. Inability to do this may make the circuit short.
LM317 Operation
As direct controllers, the LM317 and LM337 are utilized as a part of DC to DC converter applications.All linear regulators normally waste power, the power wasted is the product of the current and the voltage difference between input and output. When in use LM317 ordinarily requires a heat sink to prevent the working temperature going too high. For large voltage differnces, the wasted energy in the form of heat can be more than that supplied to the circuit. This is what you'll sacrifice for using linear regulators which are a basic approach to supply a steady voltage with couple of extra parts. A better way is to use a switching voltage regulator which usually performs better, however has a bigger impression and requires many other related components.
For LM317 with heat dissipating mounting tab, for example, TO-220, the tab is hooked up inside to the output pin which is the reason why it may be necessary to isolate the tab or the heat sink from different parts of the application circuit. Inability to do this may make the circuit short.
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