# Powering up an OpAmp and thermal analysis

#### engr_david_ee

Joined Mar 10, 2023
176
I have a general question regarding thermal analysis of an OpAmp.

If we power up an OpAmp by +/- 12 V. The input to the OpAmp is 1 V and I need for example 5 V output that means the OpAmp need to provide the gain of 5. The output current is 50 mA through the load connected at the output of the OpAmp which is well within the limits of the OpAmp maximum output current. How do we perform the thermal analysis ?

In linear regulators, we just find the power dissipation Pd = (Vin - Vout) x Iout. Then we find the Tj which is junction temperature using thermal-resistance but that is true for linear regulators.

How do we perform the thermal analysis for OpAmp ? I saw in the datasheets of OpAmp there are parameters like thermal-resistance and is given in the unit of degC/Watt. The thermal-resistance is the parameter that actually used to calculate the junction temperature Tj. How do we perform the thermal analysis ? How do we calculate how much the OpAmp will be hot during the run ?

#### crutschow

Joined Mar 14, 2008
34,679
How do we perform the thermal analysis ?
You do it similar for the op amp as the linear regulator.
It's the power supply voltage minus the output voltage times the load current, plus the op amp quiescent current times the sum of both the supply voltages.
The quiescent power may be low enough to ignore.

In your example the load power would be (12V-5V) * 50mA = 350mW.