Line regulation describes a power supply's ability to maintain a stable output voltage (Vout) regardless of fluctuations in the line voltage (input voltage, Vin). Ideally, the output voltage remains constant regardless of input changes. These regulation specifications in product catalogs often list the maximum deviation as a percentage (%) or voltage (mV) over the allowable input range, it can also be expressed as a sensitivity ratio in percent per volt (%/V), calculated as follows:
Here, ΔVout is the change in output voltage, Vout is the nominal output voltage, and ΔVin is the change in input voltage. For example, if the input voltage changes from 100 V to 110 V (a ΔVin of 10 V) and the 5.00 V nominal output shifts to 5.05 V (a ΔVout of 0.05 V), the line regulation is calculated as: ((0.05 V / 5.00 V) / 10 V) × 100 = 0.1 %/V
Line regulation is typically measured by varying the input voltage across its specified operating range (e.g., ±10% of nominal) while maintaining a constant full load at an ambient temperature of 25°C. A lower value indicates superior output stability against input fluctuations.
High-performance line regulation is critical in applications with unstable input power sources or significant electrical noise, such as industrial and automotive environments. In these settings, the voltage regulator must effectively isolate the output from input disturbances. Since stability can vary depending on the current draw, it is essential to verify these specifications under various load conditions to ensure the system operates reliably.
To verify and improve line regulation, engineers utilize feedback control loops, high-gain error amplifiers, and stable voltage references. These circuit designs significantly enhance the ability to maintain a constant output voltage, ensuring precision and reliability even when the input voltage varies.
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