9.2.2.7 Passives

Among the passives included in the design, the gain setting resistors should be chosen to exhibit tight tolerances in order to achieve high accuracy. These resistors -- R4, R5, R6, R9, R11, R10, and R12 -- are primarily responsible for setting the gain of the current loop, along with primary path of the output current flow. Since the biased transistor, Q1, is responsible for sourcing most of the output current, components in the path of this current flow should be chosen with appropriate power ratings. In this case R8 is a 0.25-W resistor.