Enter your AC voltage, rectifier type, and diode drop to estimate the DC output after rectification and check whether it meets a required voltage.
Advanced options
Increase above the entered AC voltage, including any supply variation or transformer no-load rise you need to model. 0% uses the entered value.
Your chosen margin above the modeled reverse voltage. 2 means twice that voltage; it is not a universal component-selection rule.
Reduction below the entered capacitor value. For example, 20% uses 80% of its nominal capacitance.
The main result and target check still use the entered nominal values. These optional estimates assume a sine wave and do not include unentered transformer regulation, switching spikes, surge or ripple-current limits.
Table of contents
How to use our AC to DC Rectifier Voltage Calculator
- Choose a value in "DC output model." Use "Rectified peak" for the unloaded maximum, "Unfiltered average" for rectified AC without a smoothing capacitor, or "Capacitor-filtered average" for a capacitor feeding a load.
- Enter "AC input voltage (V)" from the source label or measurement. Then choose "RMS" or "Peak" in "Entered AC voltage is." Transformer secondary ratings are normally RMS.
- Select "Rectifier type." For "Center-tapped full-wave," enter the voltage from the center tap to one end of the transformer secondary, not the end-to-end voltage.
- Enter "Forward drop per diode (V)" from the diode or bridge datasheet at a current close to the planned load.
- If you chose "Capacitor-filtered average," enter "Load current (A)," "Filter capacitor (uF)," and "AC frequency (Hz)."
- Optionally enter "Minimum required DC voltage (V, optional)" from the downstream circuit or regulator datasheet.
- Select "Calculate." Read "Estimated DC output" with its selected model, then check ripple and any voltage headroom before choosing components.
Definitions
RMS voltage: The usual AC rating on a transformer or AC adapter. For a sine wave, peak voltage equals RMS voltage times the square root of 2.
Rectified peak: The highest modeled voltage after the conducting diode-path loss. It is not the same as loaded DC voltage.
Unfiltered average: The average of the rectified waveform when no smoothing capacitor is included.
Capacitor-filtered average: An estimated average DC voltage after a reservoir capacitor charges near the peak and discharges into the load between charging pulses.
Forward drop: Voltage lost across one conducting diode. A full-wave bridge has two conducting diodes in its current path, while half-wave and center-tapped full-wave paths have one. [1]
Ripple voltage: The estimated peak-to-peak voltage swing while the filter capacitor discharges between charging pulses.
Voltage headroom: Selected modeled DC output minus the entered minimum required DC voltage. A negative value means the modeled output falls short.
Common mistakes and quick fixes
Mistake: Entering a transformer RMS rating while "Entered AC voltage is" is set to Peak.
Fix: Select RMS for a typical transformer or AC adapter rating. Select Peak only when the source value is already the sine-wave peak.
Mistake: Using the full end-to-end secondary voltage for a center-tapped rectifier.
Fix: Enter the voltage from the center tap to one end because one rectifier path uses that half of the secondary.
Mistake: Expecting one diode drop in a full-wave bridge.
Fix: Enter the drop for one diode. The bridge model subtracts two conducting diode drops.
Mistake: Treating rectified peak as the voltage available to a loaded circuit.
Fix: Choose "Capacitor-filtered average" and enter the actual load current, capacitor value, and source frequency.
Mistake: Entering capacitance in farads when the field uses uF.
Fix: Enter microfarads. A 1,000 uF capacitor is entered as 1000, not 0.001.
Limitations & Key Assumptions / Boundary Conditions
- The RMS-to-peak conversion assumes a sine-wave AC source. It does not model square waves, distorted waveforms, or arbitrary signals.
- The diode forward drop is treated as constant, although it changes with current, temperature, diode type, and pulsed conduction.
- The capacitor model assumes constant load current and uses a simplified ripple estimate. It does not include transformer regulation, winding resistance, source impedance, capacitor ESR, wiring loss, or changing diode conduction angle.
- The capacitor-filtered calculation stops when estimated ripple is at least the rectified peak because the simplified model no longer describes the supply well.
- A passing target check compares only the selected voltage model with the entered minimum. It does not verify current capacity, heat, regulator behavior, component ratings, isolation, or electrical safety.
Methodology
Optional tolerance and reverse-voltage estimates
In “Advanced options”, “Tolerance and reverse-voltage estimates” adds separate scenarios without changing the main nominal answer. “AC voltage increase (%)” multiplies the entered peak by 1 + percentage/100. Include any transformer no-load rise in that percentage when it is not already included in your entered voltage; do not count it twice. For “Center-tapped full-wave”, the AC input remains center tap to one end, not the entire secondary.
The ideal reverse-stress estimate is one increased input peak for a bridge, twice the half-winding peak for center-tapped full-wave, and one peak for half-wave without a reservoir capacitor or two with one. Ignoring diode drops makes these estimates conservative within the stated circuit model, not protection against unmodeled spikes. “Reverse-voltage multiplier” must be at least 1 and applies to that increased-voltage estimate. No particular multiplier guarantees component suitability.
“Capacitance reduction (%)” applies only to “Capacitor-filtered average”: effective C = entered C × (1 − percentage/100), and ripple = load current / (ripple frequency × effective C). The separate nominal-AC average is withheld when that ripple reaches the nominal rectified peak, outside this simple model. The existing target check remains nominal, not a worst-case minimum-voltage check.
Reference: Hammond’s rectifier design guide discusses source regulation and capacitor ripple-current requirements. ANU’s full-wave rectifier notes distinguish bridge and center-tapped diode reverse voltage. These simplified estimates do not replace component datasheets or an electrical design review.
Voltage model
The calculator converts an RMS input to sine-wave peak voltage when needed, then subtracts the conducting diode-path loss. A bridge path has two conducting diode drops; the supported half-wave and center-tapped paths have one. [1]
V_peak,input = V_RMS × √2, or the entered value when Peak is selected
V_diode,path = diode count × forward drop per diode
V_rectified,peak = max(0, V_peak,input - V_diode,path)
Unfiltered and capacitor-filtered output
For "Unfiltered average," the calculator integrates the part of each sine-wave lobe above the diode-path loss. This avoids using an ideal-diode average when a nonzero forward drop is entered. Half-wave rectification has one lobe per cycle, while full-wave circuits use both half cycles.
For "Capacitor-filtered average," ripple frequency equals AC frequency for half-wave rectification and twice AC frequency for bridge and center-tapped full-wave rectification. The capacitor entry is converted from uF to F.
f_ripple = f_AC for half-wave; otherwise 2 × f_AC
V_ripple,p-p = I_load / (f_ripple × C)
V_filtered,average = V_rectified,peak - V_ripple,p-p / 2
Target check and example
"Estimated DC output" uses the selected model. If a minimum required voltage is entered, voltage headroom equals modeled output minus that target. A zero or positive value passes this voltage-only comparison; a negative value is a shortfall.
Example: a 12 V RMS source, full-wave bridge, and 0.7 V drop per diode produce a 16.971 V input peak and a 15.571 V rectified peak. At 0.1 A with a 1,000 uF capacitor and 60 Hz source, estimated ripple is 0.833 V p-p, so the capacitor-filtered average is about 15.154 V.