The standard, junction-isolated power process has been modified by the addition of polycrystalline-film resistors to solve the topological problems encountered in making 90W, 80V, 10A power transistors and connecting them together for a push-pull output. An all-NPN output stage has been developed that holds cross-over distortion to 0.01-percent while driving a 4Ω load, even with the quiescent current below 20 mA. It is stable with all reactive loads and does not have the spurious-oscillation problems observed with the familiar quasi-complementary amplifier. These innovations are described along with the design of a complete power op amp. The all-important safe-area protection is covered in a companion article [1]. Preventing failures from substrate currents arising when the output is driven outside the supply by inductive loads is discussed here.
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