Linear Voltage Regulator with Thermal Effects

This example shows a low-cost voltage regulator circuit whose performance depends on both load current and temperature. Bias resistor R1 ensures that the voltage at the transistor base is close to the rated zener voltage. The regulator output voltage is also approximately at this voltage, the base-emitter voltage being a few tenths of a volt. The precise base-emitter voltage depends on the transistor working point (which in turn depends on the load) and also the temperature. Resistor R2 only serves to provide some protection in the event of a transient output short circuit.

You can use this model to validate that selected circuit components result in an adequate level of voltage regulation. You can also use it to size the heatsink that keeps the transistor junction temperature within the permitted operating range. By modeling both electrical and thermal properties, you understand the trade-offs between the electrical and thermal parameter choices.

You can achieve better regulation by using feedback. For more information, see Linear Voltage Regulator with Feedback.