7.1 Overview

A basic functional diagram for the LM1086-ADJ (excluding protection circuitry) is shown in Figure 13. The topology is basically that of the LM317 except for the pass transistor. Instead of a Darlingtion NPN with its two diode voltage drop, the LM1086 uses a single NPN. This results in a lower dropout voltage. The structure of the pass transistor is also known as a quasi LDO. The advantage of a quasi LDO over a PNP LDO is its inherently lower quiescent current. The LM1086 is specified to provide a minimum dropout voltage of 1.5V over temperature, at full load.

Figure 13. Basic Functional Block Diagram