How is three-phase AC from a DC alternator rectified to DC?

• A. Three Diode Rectifier
• B. Two Diode Rectifier
• C. SCR Rectifier
• D. Six Diode Rectifier Circuit

Answer: (D)

Three-phase rectification is done with a six-diode bridge. Each of the three input phases connects to two diodes: one to the positive DC rail and one to the negative DC rail. At any moment, the most positive phase forward-biases its diode to the positive rail and the most negative phase forward-biases its diode to the negative rail, while the other diodes are reverse-biased. This creates a continuous current path from the highest potential phase to the load and back via the lowest potential phase, producing a DC output with six pulses per AC cycle. This arrangement gives smooth, reliable DC from a three-phase source. Using fewer diodes would not capture all three phases, and using SCRs would provide a controllable rectifier rather than the simple uncontrolled conversion shown by the six-diode bridge.