The LM317 and LM338 are popular adjustable linear regulator ICs that are easy to use – the output is adjustable using a potentiometer decoupling and other external components are minimum. Despite their outward appearance, there are differences between the two ICs, which we will take a look at in this article.

LM317 and LM338 Specifications

From the specifications, we can see that the LM338 is basically a higher current version of the LM317. There is a small 10mV difference in the stated reference voltages in the datasheets. Care should be taken to ensure a minimum of 3V between the input and output voltage for both parts to ensure proper output voltage regulation. Power dissipation for both parts must also be taken into account. Both chips are internally dissipation limited, so overtemperature might cause undesired operation.

Note: More technical details can be found in the LM317 datasheet and LM338 datasheet linked at the bottom of this page.

Taking A Look at Inside Circuitry of LM317 and LM338

FIG.3 LM317 AND LM338 INTERNAL CIRCUIT

The only major differences to be observed in the internal circuits of the LM317 and LM338 are the values of the resistors, and although not show, the size of the output transistors. The different resistor values in the reference and feedback section might have to do with manufacturing differences, but the lower value resistors on the output stage of the LM338 show that it has been designed to output a higher current than the LM317.

Major Difference Between LM317 And LM338

Conclusion

The LM317 and LM338 are almost identical adjustable linear voltage regulators, but the LM338 has a higher current capability of 5A, whereas the LM317 is limited to 1.5A output max. Care must be taken to ensure that the power dissipation and temperature limits are taken into account to ensure reliability and max. output current.