Input capacitor and damped EMI filter
Loaded LC transfer and source-impedance screening against a constant-power converter input.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Assumptions
- Converter is approximated as a negative incremental resistance −VIN²/PIN across the entire plotted range. This is generally valid only within its control bandwidth.
- Damping branch is a resistor in series with a capacitor, in parallel with the main input capacitor. Main-capacitor heat assumes all entered ripple current flows there, a conservative screen.
- Capacitance screen uses ΔQ≈Irms/fs; enter the real topology pulse waveform for accurate ripple sizing.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Converter input voltage
- 24 V
- Converter input power
- 50 W
- Input-filter inductance
- 0.000022 H
- Inductor plus source resistance
- 0.05 Ω
- Main filter capacitance
- 0.000047 F
- Main capacitor ESR
- 0.05 Ω
- Series-RC damping capacitance
- 0.0001 F
- Series damping resistor
- 1 Ω
- Converter pulsed-input RMS current
- 2 A
- Target input-ripple amplitude
- 0.1 V
- Converter switching frequency
- 200000 Hz
Results
- Filter attenuation at switching frequency
- 54.7668 dB
- Peak |Zsource| / |Zinput|
- 0.0785271
- Undamped LC resonance
- 4949.48 Hz
- Magnitude of constant-power input resistance
- 11.52 Ω
- Maximum swept filter output impedance
- 0.904632 Ω
- Main-capacitor ESR heat bound
- 0.2 W
- Charge-ripple capacitor screen
- 0.0001 F