Load regulation measures 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 perfectly stable regardless of load changes. In practice, however, a slight voltage drop may occur as current increases. A smaller variation indicates higher stability and better performance.
Load regulation is typically expressed as a percentage (%) of the rated output voltage or as a specific voltage value (mV). It is calculated using the following concept:
Where Vfl is the output voltage at full load and Vnl is the output voltage at no load.
Example Calculation:
If a power supply is set to 5.00 V at no load (0 A) and the voltage drops to 4.95 V at full load (rated current):
( | 4.95 V - 5.00 V | / 5.00 V ) × 100 = 1.0%
In this example, the load regulation is 1.0%.
Standard measurement conditions involve fixing the input voltage at its nominal value, varying the load current from 0% to 100% of the rated capacity, and maintaining an ambient temperature of 25°C (unless otherwise specified).
Relationship to Output Impedance
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 the product of the change in output current (ΔIload) and the output impedance, as described by Ohm's Law (ΔVout = ΔIload × Rout). Therefore, lower output impedance results in a smaller voltage drop and superior load regulation.
Static vs. Dynamic Load Regulation
It is important to distinguish between two types of load regulation:
- Static Load Regulation: As described above, this refers to the output voltage stability under steady-state or slowly changing load conditions. This is the value typically listed in standard product specifications.
- Dynamic Load Regulation (Transient Response): This measures the power supply's ability to respond to sudden, step-like changes in load current. Key parameters include voltage overshoot, undershoot, and recovery time.
Excellent static and dynamic load regulation are critical for powering voltage-sensitive devices such as microcontrollers, sensors, and communication equipment, ensuring high system stability and reliability.
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