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A rectifier converts AC into DC. The quality of that DC is described by two numbers: the average value Vdc (what a DC voltmeter reads and what drives the load) and the RMS value Vrms (which sets the heating and the ripple content). Both are fixed fractions of the peak voltage Vm = √2×Vs(rms), and the fraction depends only on the topology.
| Topology | Vdc (average) | Vrms |
|---|---|---|
| 1φ Half-wave | Vm/π = 0.318 Vm | Vm/2 = 0.500 Vm |
| 1φ Full-wave | 2Vm/π = 0.637 Vm | Vm/√2 = 0.707 Vm |
| 3φ Half-wave | 3√3·Vm/(2π) = 0.827 Vm | 0.841 Vm |
| 3φ Full-wave bridge | 3√3·Vm/π = 1.654 Vm | 1.655 Vm |
Here Vm is the peak of the phase voltage. For the three-phase bridge the DC output is above Vm because it stacks two phases (line voltage). The DC load current is simply Idc = Vdc/RL, and the DC power delivered is Pdc = Vdc×Idc.
It is the DC component of the rectified waveform — what a DC voltmeter reads. For a half-wave rectifier Vdc=Vm/π, and for a full-wave rectifier Vdc=2Vm/π, where Vm is the peak voltage.
The average (Vdc) is the mean value that powers the DC load. The RMS (Vrms) is the heating-equivalent value and is always larger; the gap between them represents the AC ripple riding on the DC.
Multiply by the square root of two: Vm=√2×Vs(rms)=1.414×Vs. A 230 V RMS supply has a peak of about 325 V.
Full-wave rectification uses both halves of the AC cycle, so the average DC output is double (0.637Vm vs 0.318Vm), the ripple frequency is twice the line frequency, and the ripple is far smaller and easier to filter.
For a 6-pulse bridge Vdc=3√3·Vm/π=1.654×Vm (peak phase voltage), or about 1.35 times the line-to-line RMS voltage. A 400 V line gives roughly a 540 V DC bus.
For an ideal rectifier with a resistive load, no — Vdc depends only on the input and topology. The load resistance only sets the current (Idc=Vdc/R) and power. Real diodes add a small forward-voltage drop.
Vm is the peak (maximum) value of the sinusoidal voltage applied to the rectifier. For single-phase it is the peak of the secondary voltage; for three-phase formulas here it is the peak of the phase voltage.
A filter capacitor raises the average output toward the peak voltage and reduces ripple. The formulas here give the raw (unsmoothed) rectified values; add a capacitor and use a filter-capacitor calculator to find the smoothed DC and remaining ripple.
Vrms=Vm/√2=0.707Vm, which equals the RMS of the original sine wave because full-wave rectification only flips the negative half — it does not change the RMS.
Yes, for low-voltage supplies. Each conducting silicon diode drops about 0.7 V (Schottky ~0.3 V). A full-wave bridge has two diodes in the path, so subtract ~1.4 V from the output for an accurate low-voltage result.
Half-wave: same as the line (50/60 Hz). Single-phase full-wave: twice the line (100/120 Hz). Three-phase half-wave: 3× line; three-phase bridge: 6× line — higher ripple frequency means smaller filters.
Yes. Use the full-wave option and set Vs to the RMS of one half of the secondary (from centre-tap to one end), since only half the winding conducts at a time.
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