Output impedance (Zout) represents the internal impedance of a power supply or signal generator as viewed from its output terminals. It is a critical parameter determining how the output voltage responds to changes in load current. The relationship is generally expressed as:
Where Δ V represents the fluctuation in output voltage and Δ I is the change in load current. A lower output impedance ensures that voltage fluctuations remain minimal even when the load current varies, resulting in stable power delivery.
High-performance regulated DC power supplies typically feature an output impedance of just a few milliohms (mΩ) or less. This allows the power supply to behave as an ideal voltage source, maintaining a constant output level regardless of load variations. While achieving such low impedance requires sophisticated circuit design, it is essential for driving high-precision electronic circuits and sensitive experimental equipment.
Output impedance is directly linked to Load Regulation. A lower Zout corresponds to superior load regulation (minimal voltage drop). Conversely, a high output impedance leads to significant voltage fluctuations as the load changes, potentially compromising system stability.
Selection Guide: DC vs. High-Frequency
When selecting a power source, the requirements for output impedance depend on the application:
- For DC Power Supplies: Prioritize models with low output impedance and tight load regulation specifications to ensure voltage stability against variable loads.
- For High-Frequency or Pulse Applications: In RF generators or fast-switching circuits, impedance matching is critical. Matching the source's output impedance to the load's impedance prevents signal reflection and ensures maximum power transfer, thereby optimizing performance.