Output impedance (Zout) refers to the internal impedance as viewed from the output terminals of power supplies or signal generators, serving as a critical parameter that determines how output voltage responds to external load variations. Output impedance is generally expressed by the following relationship:
where Δ V represents the change in output voltage due to load current variations and Δ I represents the change in load current. Lower output impedance results in minimal output voltage changes despite load fluctuations, enabling stable voltage delivery.
High-quality regulated power supplies typically maintain Zout values of just a few milliohms, ensuring output voltage remains virtually constant even under significant load variations. This stability proves essential for high-precision electronic circuits and experimental equipment. Devices featuring low Zout generally offer superior accuracy but command higher prices due to their advanced design requirements.
Output impedance maintains a close relationship with load regulation-the measure of output voltage stability against load changes. Generally, lower Zout values yield better load regulation percentages, maintaining constant output voltage regardless of load variations. Conversely, high Zout causes significant output voltage fluctuations with load changes, compromising system stability.
When selecting high-quality power supplies or signal sources, thorough examination of both output impedance and load regulation specifications is essential. Additionally, high-frequency circuit applications require careful impedance matching between the output impedance and connected device impedance to ensure optimal performance.