Most constant voltage power sources operate from what type of primary power?

• A. Three-phase primary power
• B. Single-phase primary power
• C. Direct current supply
• D. Battery power

Answer: (A)

Constant voltage supplies need a stable, low-impedance source so the output stays steady even as load changes. A three-phase primary provides a smoother, more constant voltage and current than single-phase. Because the three waveforms are offset by 120 degrees, the sum of the instantaneous voltages stays much flatter over time, which means less ripple when the power is processed inside the source and easier regulation of the DC or stabilized output. That helps deliver higher power with better efficiency and smaller filtering requirements.

Single-phase can work for smaller or less demanding cases, but it introduces more ripple and limits power capability for the same equipment size. Direct current or battery power aren’t typical primary feeds for these sources in a standard utility setup.