Regulating Element Placement in Op-Amp Voltage Regulators

In an Op-Amp voltage regulator circuit, the primary goal is to maintain a stable output voltage delivered to the load, regardless of changes in input voltage or load current. The Op-Amp compares a fraction of the output voltage with a stable reference voltage (often a Zener diode) and adjusts a control element accordingly.

Series Connection for Voltage Control

The 'regulating element' is typically a transistor (like a BJT or MOSFET) that acts as a variable resistor or voltage source. To effectively control the voltage reaching the load, this element must be placed directly in the path of the current flowing to the load.

• Placing the regulating element in series with the load allows it to adjust its resistance or voltage drop to compensate for fluctuations, thereby ensuring the voltage across the load remains constant.
• Connecting it across the Zener diode or across the load would not allow it to regulate the voltage delivered to the load effectively.
• Connecting it in series with the Zener diode would affect the reference voltage, not the output voltage regulation.

Therefore, the regulating element is fundamentally connected in series with the load it is intended to regulate.