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RC Фильтр Калькулятор | Electrical Мощность Калькулятор

Low-pass & high-pass filter calculator

Ω
Результат
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Формулы

ττ = R × C
fcfc = 1 / (2πRC)
XCXC = 1 / (2πfC)

Время Constant Response

ВремяChargeDischarge
1τ63.2%36.8%
2τ86.5%13.5%
3τ95.0%5.0%
5τ99.3%0.7%

Связанные

RL FilterOhm's LawНапряжение Divider

Understanding RC Filters

RC filters are fundamental electronic circuits that use a resistor and capacitor to selectively pass or block certain frequencies. They're used in audio systems, power supplies, signal processing, and countless other applications.

Low-Pass Фильтр

In a low-pass configuration, the output is taken across the capacitor. At low frequencies, the capacitor's high impedance allows signals to pass. At high frequencies, the capacitor's low impedance shunts signals to ground. Used for: noise filtering, smoothing DC supplies, audio bass filters.

Высшая-Pass Фильтр

In a high-pass configuration, the output is taken across the resistor. The capacitor blocks DC and low frequencies while passing high frequencies. Used for: DC blocking, audio treble filters, coupling stages in amplifiers.

Cutoff Частота

The cutoff frequency (fc) is where output power is half the input power (-3dB point). At fc, the capacitive reactance equals the resistance (Xc = R). The filter's roll-off is -20dB/decade (first-order filter).

Время Constant

The time constant τ = RC determines how fast the circuit responds to changes. After one time constant, a charging capacitor reaches 63.2% of final напряжение. After 5τ, it reaches 99.3% - essentially complete.

Часто задаваемые вопросы

The cutoff frequency fc = 1/(2πRC) is the -3dB point where output is 70.7% of input напряжение (50% power). At this frequency, capacitive reactance equals resistance. It marks the boundary between the passband and stopband of the filter.

Время constant τ = R × C (in seconds when R is омы and C is farads). It's the time for capacitor напряжение to reach 63.2% of final value during charging or 36.8% during discharging. Five time constants (5τ) gives 99.3% completion.

The capacitor is in parallel with the output. At low frequencies, capacitor impedance is high (Xc = 1/2πfC), so signal passes through. At high frequencies, impedance drops, shunting signal to ground. The resistor limits current flow.

Low-pass: Output across capacitor, passes DC and low frequencies, attenuates high frequencies. High-pass: Output across resistor, blocks DC and low frequencies, passes high frequencies. Same R and C values give same fc for both configurations.

A single RC filter (first-order) has a roll-off of -20 dB/decade or -6 dB/octave. This means for every 10× increase in frequency beyond fc, the output drops by 20 dB. For steeper roll-off, cascade multiple filter stages or use active filters.

After 5 time constants, the capacitor reaches 99.3% of final напряжение - close enough to 100% for most practical purposes. The charging curve is exponential and technically never reaches 100%, but 5τ is the engineering convention for "complete" charging/discharging.

Rearrange the formula: RC = 1/(2πfc). Choose a practical capacitor value first (they have limited standard values), then calculate R = 1/(2πfcC). Keep R between 1kΩ and 100kΩ for best results. Use standard component values closest to calculated values.

Low-pass: Мощность supply ripple filtering, anti-aliasing before ADC, audio tone controls, noise reduction. High-pass: DC blocking in audio, coupling between amplifier stages, removing DC offset, bass cut filters.