Fig 1a's conventional common-drain MOSFET-based power op amp, with a simple and stable configuration, has a dynamic response identical to that of IC₁. However, as a power amplifier, it exhibits a limited-output voltage swing that is typically less than either supply by 6V. This limitation results from the combination of the turn-on voltage of the MOSFET transistors and the limited voltage swing of the monolithic op amp. Usually this deficiency is overcome by an auxiliary pair of higher voltage power supplies for the monolithic op amp. Alternatively, other suggested configurations combine an op amp with a complementary common-source power stage. However, these configurations are inherently unstable and difficult to compensate because of the added wideband gain of the output stage.

In reality, a large voltage swing is necessary only in transient situations and not in the steady state. This is typical of loudspeaker drivers as well as servo-motor drivers. The modified power op amp in Fig 1b attains transient rail-to-rail voltage swing by adding just a few passive components to Fig 1a's design. The bootstrapping mechanism implemented by clamping network R₁, C₁, D₁, and D₂ for the positive power supply and by R₁, C₂, D₃, and D₄ for the negative power supply automatically increases the op amp's supply voltage when necessary. R₁ limits the boost amount and protects the output voltage from destroying D₁ and D₄. Along with the supply current of the op amp, C₁ and C₂ determine the cut-on frequency above which the output-voltage-swing range starts to increase. The range is typically 300 Hz for the values in the figure.