This design example demonstrates electro-thermal trade-off analysis for power dissipating circuits. The design includes a 3.3V linear regulator that drives up to 1A of load current. To reduce the input voltage to the regulator and thereby reduce its power dissipation, a series NPN transistor with a zener diode controlling its base voltage is used.
To explore the design trade-offs, the user can change the zener voltage and re-run the simulation. This will result in not only a change to the electrical voltage split across the transistor and regulator, but also a corresponding change to their observed junction temperatures. The user can also change the values of the thermal resistances (from case to ambient*) for those components, to identify the heat-sink or other thermal mitigation required to meet all the design constraints of this circuit.
The user can also change the circuit's operating environment, including the battery voltage, the ambient temperature and the load resistance (initial and pulse values).
*Note: The junction to case thermal resistances are specified by the manufacturer for these parts, so they cannot be changed by the circuit's thermal designer.