Calculate DC link voltage from AC input RMS voltage, or find the AC voltage needed for a DC link, using the √2 relationship for V, mV, and kV units.

DC Link Voltage Calculator

Enter one value to calculate the other.

Note: This uses VDC ≈ √2 · VAC,rms (peak of the AC). In real circuits, diode drops and load/ripple reduce the DC link voltage.

DC Link Voltage Formula

The calculator uses the ideal peak-voltage relationship between an AC RMS input voltage and the approximate DC link voltage after rectification and capacitor filtering.

V₍DC) ≈ √(2) × V₍AC,rms)
V₍AC,rms) ≈ (V₍DC)) / (√(2))
  • VDC = approximate DC link voltage
  • VAC,rms = AC input voltage in RMS volts, line-to-line for a 3-phase input
  • √2 = 1.41421356, the factor used to convert RMS voltage to peak voltage for a sine wave

If you enter the AC input voltage, the calculator multiplies it by √2 to estimate the DC link voltage. If you enter the DC link voltage, the calculator divides it by √2 to estimate the equivalent AC RMS input voltage. Unit selections such as mV, V, and kV are converted to volts before the formula is applied, then converted back to the selected output unit.

This is an ideal approximation. Real DC link voltage can be lower because of diode drops, rectifier losses, capacitor ripple, source impedance, and load current.

Typical AC Input to DC Link Voltage Values

The table below shows common RMS AC input voltages and their ideal approximate DC link voltages using VDC ≈ 1.414 × VAC,rms.

AC Input Voltage RMS Approx. DC Link Voltage Common Use
120 V 169.7 V DC Single-phase mains input
230 V 325.3 V DC Single-phase or line-to-line input
400 V 565.7 V DC 3-phase line-to-line input
480 V 678.8 V DC 3-phase industrial input
690 V 975.8 V DC Higher-voltage drive systems

Voltage Unit Reference

Unit Equivalent in Volts Example
mV 0.001 V 1000 mV = 1 V
V 1 V 230 V = 230 V
kV 1000 V 0.4 kV = 400 V

Example Calculations

Example 1: Calculate DC link voltage from AC input

You have a 230 V RMS AC input and want the approximate DC link voltage.

V₍DC) ≈ √(2) × 230
V₍DC) ≈ 1.41421356 × 230 = 325.27 V

The approximate DC link voltage is 325.27 V DC.

Example 2: Calculate AC RMS input from DC link voltage

You have a 650 V DC link and want the approximate AC RMS input voltage.

V₍AC,rms) ≈ (650) / (√(2))
V₍AC,rms) ≈ (650) / (1.41421356) = 459.62 V

The approximate AC input voltage is 459.62 V RMS.

FAQ

Why is the DC link voltage higher than the AC RMS voltage?

AC RMS voltage is not the same as peak voltage. For a sine wave, the peak voltage is √2 times the RMS voltage. A rectifier with a capacitor-input DC link tends to charge the capacitor near the peak of the AC waveform, so the ideal DC link voltage is approximately 1.414 times the RMS input voltage.

Does this formula apply to 3-phase input?

Yes, for this calculator, use the 3-phase line-to-line RMS voltage as the AC input. For example, a 400 V 3-phase system means 400 V line-to-line RMS, giving an ideal DC link estimate of about 566 V DC.

Why might the measured DC link voltage be lower than the calculated value?

The calculated value is ideal. A real circuit can have lower DC link voltage due to rectifier diode voltage drops, capacitor ripple, wiring resistance, source impedance, transformer regulation, and load current. The difference becomes more noticeable under heavier load.