Ripple Voltage Calculator: Power Supply Filter & Smoothing Capacitor

Calculate peak-to-peak ripple voltage, RMS ripple, DC output voltage, ripple factor percentage, and load voltage regulation for AC-to-DC power supplies. Modeled for full-wave bridge, center-tapped, and half-wave rectifiers with capacitor-input, inductor choke, and pi (π) filter topologies in accordance with IEEE power electronics standards.

When an alternating current (AC) sinusoidal voltage is rectified, the resulting pulsating DC waveform contains periodic voltage fluctuations termed 'ripple'. A smoothing reservoir capacitor charges during conduction peaks and discharges into the load during inter-peak valleys.

• Peak Rectified Voltage: V_peak = √(2) × V_in,rms - N_diode × V_D. Unfiltered peak voltage. Full-wave bridge rectifiers drop 2 diode drops (2 × 0.7V = 1.4V for silicon), while half-wave and center-tapped drop 1 diode drop.
• Peak-to-Peak Ripple Voltage (Capacitor Filter): V_r(p-p) = fracI_loadf_ripple × C. Ripple voltage sag where f_ripple = 2 × f_mains for full-wave (120 Hz on 60 Hz mains) and f_ripple = f_mains for half-wave (60 Hz).
• RMS Ripple Voltage (Sawtooth Approximation): V_r(rms) = fracV_r(p-p)2√(3) ≈ fracV_r(p-p)3.4641. Root-mean-square AC ripple component under linear capacitor discharge approximation.
• Average DC Output Voltage: V_dc = V_peak - fracV_r(p-p)2. Effective usable DC rail voltage delivered to the downstream regulator or load.
• Ripple Factor (γ): gamma = fracV_r(rms)V_dc × 100\%. Figure of merit quantifying the purity of DC power. Linear supplies target < 1% to 2%.
• Voltage Regulation Percentage: VR (\%) = (fracV_no-load - V_full-loadV_full-load) × 100. Percentage drop in output voltage from open-circuit zero-load (V_peak) to full rated load current.

• Transformer Secondary: 12.0 V RMS, 60 Hz Mains
• Rectifier Topology: Full-Wave Bridge (2 Diode Drops @ 0.7V = 1.4V drop)
• Filter Capacitor: 2,200 μF (0.0022 F) Electrolytic
• DC Load Current: 1.5 Amperes

1. AC Peak Voltage = 12.0 × sqrt(2) = 16.97 V
2. No-Load Peak DC = 16.97 - 1.40 = 15.57 V
3. Full-Wave Ripple Frequency = 2 × 60 Hz = 120 Hz
4. Peak-to-Peak Ripple Voltage = 1.5 A ÷ (120 Hz × 0.0022 F) = 1.5 ÷ 0.264 = 5.682 V (p-p)
5. RMS Ripple Voltage = 5.682 V ÷ (2 × sqrt(3)) = 5.682 ÷ 3.4641 = 1.640 V (rms)
6. Average DC Output Voltage = 15.57 V - (5.682 ÷ 2) = 15.57 - 2.841 = 12.729 V
7. Ripple Factor = (1.640 V ÷ 12.729 V) × 100% = 12.88%
8. Minimum Valley Voltage = 15.57 - 5.682 = 9.888 V
9. Voltage Regulation = ((15.57 - 12.73) ÷ 12.73) × 100% = 22.31%

A 5.68V ripple (12.88% ripple factor) is too high for precision electronics. Upgrading the capacitor to 4,700 μF or 6,800 μF will suppress peak-to-peak ripple below 1.8V, safely supporting a 9V or 5V linear regulator.

• Application: Precision Audio & Instrumentation Pre-amps | Max Ripple Factor: < 0.05% (V_r < 5 mV) | Recommendation: Requires dual-stage π-filter or ultra-low-dropout (LDO) linear regulator with >80 dB PSRR.
• Application: Linear Regulated DC Supplies (LM317, 7805) | Max Ripple Factor: 1.0% to 3.0% | Recommendation: Ensures minimum ripple valley voltage remains at least 2.5V above regulator output (dropout headroom).
• Application: Relay Coils, Solenoids & DC Motor Drives | Max Ripple Factor: 5.0% to 10.0% | Recommendation: High ripple tolerance; modest reservoir capacitance is sufficient without thermal penalty.
• Application: Lead-Acid & Li-Ion Battery Float Chargers | Max Ripple Factor: 3.0% to 5.0% | Recommendation: Low ripple prevents unnecessary battery internal heating and extends cell cycle lifespan.