Series Regulator Output Voltage Temperature Effect

In a typical series regulator circuit, the output voltage regulation often relies on a reference voltage element, commonly a Zener diode or a bandgap reference. The behavior of these components under temperature changes directly influences the output voltage.

Component Behavior with Temperature

Many semiconductor components exhibit changes in their electrical characteristics as temperature varies. Specifically:

• Zener Diodes: Most Zener diodes have a positive temperature coefficient. This means that as the temperature increases, the Zener breakdown voltage also tends to increase slightly.
• Transistors: The V_BE (base-emitter voltage) of transistors used in the regulator's pass element also decreases with increasing temperature, but the primary factor affecting output voltage stability in many simple designs is the reference voltage.

Impact on Output Voltage

Since the series regulator aims to maintain a constant output voltage (V_out) based on a reference voltage (V_ref) and usually some feedback network, an increase in V_ref due to higher temperature will directly lead to an increase in V_out.

For example, in a simple Zener reference circuit followed by a pass transistor, if the Zener voltage increases with temperature, the base voltage of the pass transistor increases, causing the collector voltage (output voltage) to increase.

Conclusion

Therefore, when the temperature increases in a series regulator, the output voltage tends to increase due to the temperature dependency of the reference voltage element.