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Diode Bridge Rectifier Calculator (Smoothing Capacitor)

Calculate DC output, ripple voltage, and required smoothing capacitor for AC-to-DC supplies. Visualizes Silicon vs Germanium drops.

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About

Designing a linear power supply requires converting AC to DC using a bridge rectifier and a smoothing capacitor. The challenge lies in selecting a capacitor large enough to reduce the "ripple" (voltage fluctuation) to acceptable levels without stressing the transformer with excessive inrush current. This tool models the full-wave rectification process. It accounts for the forward voltage drop of the diodes (typically 1.4V total for Silicon bridges) to provide the true DC load voltage.

rectifier power supply capacitor ripple voltage ac to dc

Formulas

The smoothing capacitor C is calculated based on the allowable ripple voltage Vr.

C ≈ Iload2 × f × Vr

The Peak DC voltage accounts for the bridge drop (2 diodes):

Vpeak = (VAC × p2) − 2Vf

Reference Data

ComponentMaterialVoltage Drop (Vf)
Standard DiodeSilicon (Si)0.7 V
Schottky DiodeSilicon0.3 - 0.5 V
Vintage DiodeGermanium (Ge)0.3 V

Frequently Asked Questions

A bridge rectifier is a "Full Wave" rectifier. It flips the negative half of the AC sine wave to positive. This doubles the frequency of the pulses reaching the capacitor. For 50Hz mains, the ripple is 100Hz; for 60Hz, it is 120Hz.
While a larger capacitor reduces ripple, it draws current in very short, high-energy pulses. This increases stress on the transformer and diodes (inrush current), potentially blowing fuses or overheating components.
Always choose a voltage rating at least 20% higher than the Peak DC voltage. For example, if your Vpeak is 15V, use a 25V capacitor, not a 16V one, to ensure longevity and safety.