I was studying about 3-phase power supplies. After going through several searches, i found this formula of three phase bridge rectifier's output voltage:

Vdc = ( 3 x sqrt(2)/pi ) x Vrms

Vdc = 1.35 x Vrms

So, in the figure given below, should I take 200 Vac as a phase voltage or line voltage. Is it Rms or peak voltage. what should i put in the equation.

three phase bridge rectifier

  • 2
    \$\begingroup\$ Since no Neutral is used. It seems to be delta wiring, thus delta voltage \$\endgroup\$ Mar 8, 2018 at 15:31

1 Answer 1


AC voltages that are stated simply as "nnn VAC" are assumed to be RMS voltages unless otherwise specified. Three-phase voltages that are stated that way are assumed to be line-to-line voltages unless otherwise specified. The circuit shown shows no neutral connection, so that also indicates the line-to-line voltage is the voltage of interest. The source could be delta or wye with no neutral connection to the circuit. Either way, the line-to-line voltage is what the circuit uses.

  • \$\begingroup\$ @ Charles Coewie. Thank you for answering me sir, but could you tell me the output voltage of this circuit and the correct formula for the calculation \$\endgroup\$
    – Z. Miller
    Mar 10, 2018 at 2:53
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    \$\begingroup\$ I believe the formula you presented in the question is correct for the unfiltered output of a three phase rectifier neglecting the forward drops of the diodes. Each phase contributes to the output voltage the peak of the waveform and the portion of the waveform +/- 30 degrees from the peak. In other words the portion of the waveform that starts at 60 degrees and ends at 120 degrees. The minimum voltage is sin(60) X sqrt(2) X input and the maximum is sqrt(2) X input. The average is given by the formula that you have. I am too tired to derive that or find the derivation tonight. Can you do it? \$\endgroup\$
    – user80875
    Mar 10, 2018 at 4:22

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