Power dissipation depends on power supply, signal, and load conditions. For dc signals, power dissipation is equal to the product of the output current times the voltage across the conducting output transistor, P_D = I_L (V_S – V_O). Power dissipation can be minimized by using the lowest possible power-supply voltage necessary to provide the required output voltage swing.

For resistive loads, the maximum power dissipation occurs at a dc output voltage of one-half the power-supply voltage. Dissipation with ac signals is lower because the root-mean square (RMS) value determines heating. The Instruments, Power Amplifier Stress and Power Handling Limitations application bulletin explains how to calculate or measure dissipation with unusual loads or signals.

The OPA455 can supply output currents of up to 45 mA. Supplying this level of current is common for op amps operating from ±15-V supplies. However, with high supply voltages, internal power dissipation of the op amp can be quite high. Relative to the package size, operation from a single power supply (or unbalanced power supplies) can produce even greater power dissipation because a large voltage is impressed across the conducting output transistor. Applications with high power dissipation may require a heat sink or a heat spreader.