Regulators are used to create a stable, clean DC voltage to power other electronic systems. The regulator voltage should not change as its load changes. A linear regulator may be based on a series-parallel feedback loop, using an op amp as a controller. The op amp compares a scaled version of the load voltage to a reference voltage. By changing either the reference or the scaling factor, a range of load voltages may be obtained. Because op amps typically produce insufficient current to drive many loads, a current pass transistor is used to boost output current capability.