Load regulation is a measure of a power supply's ability to maintain a constant output voltage (Vout) despite changes in the output current (Iload). Ideally, the output voltage should remain stable as the load changes; therefore, a smaller voltage variation indicates better performance. Load regulation is often expressed as a percentage change per ampere (%/A) and is calculated with the following formula:
Where Vfl is the voltage at full load and Vnl is the voltage at no load. For example, if the output voltage is 5.00 V at no load (0 A) and changes to 4.95 V at full load (2 A), the load regulation is: ((4.95 V − 5.00 V) / 5.00 V) × 100% = −1% In some cases, it may be expressed in %/A. Using the same example, the calculation would be: ((4.95 V − 5.00 V) / 5.00 V) × 100% / 2 A = −0.5 %/A
Standard measurement conditions involve fixing input voltage at its nominal value (e.g., 100 V), varying load current from 0 % to 100 % of rated capacity, and maintaining ambient temperature at 25 °C.
In an equivalent circuit model, load regulation is directly related to the power supply's output impedance (Rout). The change in output voltage (ΔVout) is a product of the change in output current (ΔIload) and the output impedance (Rout), as described by Ohm's Law (ΔVout = ΔIload × Rout). Therefore, a lower output impedance results in a smaller voltage drop and, consequently, better load regulation.
It is important to distinguish between static and dynamic load regulation.
- Static load regulation, as described above, refers to the output voltage variation under steady-state or slow-changing load conditions.
- Dynamic load regulation, often called transient response, measures the power supply's ability to respond to sudden, step-like changes in load current. This includes parameters like voltage overshoot, undershoot, and recovery time.
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