To achieve reliable power amplifier designs you must consider the stress on the amplifier compared to its power handling limitations. Power handling limits are specified by the Safe Operating Area (SOA) curves of the power amp. Stress on the amplifier depends on amplifier load and signal conditions which can be evaluated with straightforward techniques. Consider the simplified power op amp shown in Figure 1. Output transistors Q1 and Q2 provide positive and negative output current to the load. IOUT is shown flowing out of the amplifier, so Q1 is supplying the output current. For positive output current, Q2 is “off” and can be ignored.