AC to DC Conversion Calculator

Convert AC voltage to estimated DC voltage (with optional ripple)

This AC to DC conversion calculator estimates what DC voltage you can expect when you take an AC source (like a transformer or wall adapter) and run it through a rectifier, optionally with a smoothing capacitor. The dominant intent here is simple: you want to know whether an AC source can produce a usable DC voltage for a project, and whether the DC will stay high enough under load to avoid brownouts or unstable behaviour.

The calculator assumes a basic, widely used “linear” front end: AC input, then either a full-wave bridge rectifier (most common) or a half-wave rectifier (single diode), and then a reservoir capacitor. That setup is common in basic DC supplies and quick prototypes. If you are using a switching regulator, an active PFC stage, or a regulated bench supply, this tool is not for those systems. It is for estimating the unregulated DC you get immediately after rectification and filtering.

Start with the minimum inputs: your AC RMS voltage and rectifier type. That gives you a no-load DC estimate based on peak voltage minus diode losses. If you also know (or can estimate) your load current and your capacitor value, the calculator estimates ripple (the up-and-down voltage variation) and shows a practical minimum voltage. That minimum voltage is often what matters, because many circuits fail at the dips, not at the average.

Assumptions and how to use this calculator

• The AC input value is RMS voltage at the rectifier input (not “peak” and not a regulated DC label).
• Full-wave bridge rectification is assumed to have two diode drops in the conduction path; half-wave is assumed to have one.
• Diode drop is treated as a fixed value (default 0.7 V per diode). Real diode drop changes with current and temperature.
• Ripple is estimated using the standard capacitor-discharge approximation: ripple (Vpp) ≈ I / (f_ripple × C), where f_ripple is 2× mains frequency for full-wave and 1× for half-wave.
• Transformer regulation, wiring resistance, rectifier heating, and inrush effects are not modelled. Treat results as a planning estimate, not a lab measurement.

Common questions

Why is the DC estimate higher than the AC RMS input?

AC RMS is not the peak voltage. A sine wave’s peak is approximately RMS × 1.414. After rectification and smoothing, the capacitor charges close to that peak (minus diode losses), so the no-load DC can look “higher” than the AC RMS rating.

What does “ripple (V peak-to-peak)” mean in practice?

Ripple is how much the DC voltage rises and falls between charging peaks. For a capacitor-input supply, the voltage climbs near the peak, then decays as the load draws current, then gets topped up again. The peak-to-peak value is the difference between the highest and lowest points of that cycle.

If I leave load current and capacitor blank, is the result still useful?

Yes. You still get a no-load DC estimate, which is a quick sanity check for whether the rectified peak is in the right ballpark. Just remember that real supplies drop under load and will not stay at the no-load value.

How do I pick a capacitor value if I only know the load current?

Use the target ripple input. If you know your load current and you choose an acceptable ripple level (for example 1.0 V peak-to-peak), the calculator estimates the capacitance needed. Larger capacitors reduce ripple but increase inrush current and stress the rectifier and transformer.

When will this calculator not apply?

Do not use this for regulated DC outputs (like a phone charger’s USB output), switch-mode power supplies, or designs where the AC source sags significantly under load. Also avoid using it for precision design limits without a safety margin. It is intended for first-pass planning and quick checks.