Capacitor Size Calculator
Calculate the required filter capacitor size for power supplies
Milliamperes (mA)
Volts (V)
Volts (V) - acceptable ripple voltage
Hertz (Hz) - typically 50 Hz or 60 Hz
How to Use This Calculator
Enter Load Current
Enter the maximum load current in milliamperes (mA). This is the current your circuit will draw from the power supply.
Enter Supply Voltage
Enter the DC supply voltage in volts. This is the nominal output voltage of your power supply.
Enter Maximum Ripple Voltage
Enter the maximum acceptable ripple voltage in volts. This is how much the voltage can drop during the discharge cycle. Typical values: 0.1V to 1V for most applications.
Set AC Frequency
Enter the AC line frequency (50 Hz for most countries, 60 Hz for USA). This affects how often the capacitor needs to supply current.
Get Capacitor Size
Click calculate to see the required capacitor value. The result is shown in microfarads (µF), millifarads (mF), or nanofarads (nF) as appropriate.
Formula
C = I / (2 × f × Vripple)
(for full-wave rectification)
Where:
- C = Capacitance (F)
- I = Load current (A)
- f = AC frequency (Hz)
- Vripple = Maximum acceptable ripple voltage (V)
For Half-Wave Rectification:
C = I / (f × Vripple)
(Double the capacitance compared to full-wave)
Example 1:
Load Current = 100 mA, Supply = 12 V, Ripple = 0.5 V, Frequency = 60 Hz
C = 0.1 / (2 × 60 × 0.5) = 0.1 / 60 = 0.00167 F = 1667 µF
Example 2:
Load Current = 500 mA, Supply = 5 V, Ripple = 0.1 V, Frequency = 50 Hz
C = 0.5 / (2 × 50 × 0.1) = 0.5 / 10 = 0.05 F = 50,000 µF
About Capacitor Size Calculator
The Capacitor Size Calculator is a free online tool that helps you determine the required filter capacitor size for power supply circuits. After rectifying AC to DC, a filter capacitor is needed to smooth out the pulsating DC and reduce ripple voltage. This calculator uses the relationship between load current, ripple voltage, and frequency to determine the minimum capacitor size needed.
When to Use This Calculator
- Power Supply Design: Size filter capacitors for AC-DC power supplies
- Ripple Reduction: Determine capacitor size to achieve acceptable ripple levels
- Load Current Analysis: Calculate capacitor requirements for different load currents
- Component Selection: Choose appropriate capacitor values for power supply circuits
- Educational Purposes: Learn about power supply filtering and ripple reduction
Why Use Our Calculator?
- ✅ Accurate Calculations: Uses the correct filter capacitor sizing formula
- ✅ Easy to Use: Simple interface requiring load current, voltage, ripple, and frequency
- ✅ Multiple Units: Displays results in appropriate units (mF, µF, or nF)
- ✅ Full-Wave Assumption: Assumes full-wave rectification (more efficient)
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Includes formulas and examples for learning
Common Applications
Linear Power Supplies: Traditional linear power supplies use large filter capacitors to smooth the rectified AC. A 12V, 1A supply might need 2000-4700 µF capacitor to achieve less than 0.5V ripple.
Switching Power Supplies: Even switching supplies need output capacitors to filter switching ripple. The requirements are typically lower than linear supplies but still important for clean output.
Battery Chargers: Battery chargers use filter capacitors to provide smooth charging current. The capacitor size depends on the charging current and acceptable ripple.
Audio Amplifiers: Audio power supplies require very low ripple to prevent hum. Larger capacitors (10,000+ µF) are often used to achieve ripple levels below 0.1V.
Tips for Accurate Results
- Enter load current in milliamperes (mA) - the calculator converts to amperes
- Ripple voltage should be a small fraction of supply voltage (typically 1-10%)
- For full-wave rectification, ripple frequency is 2× AC frequency
- For half-wave rectification, double the calculated capacitance
- Consider capacitor tolerance - add 20-30% margin for actual capacitance
- Ensure capacitor voltage rating exceeds supply voltage (typically 1.5-2×)
- Higher load currents require larger capacitors for the same ripple
Frequently Asked Questions
Why does ripple voltage matter?
Ripple voltage is the AC component on the DC output. Too much ripple can cause problems: audio circuits get hum, digital circuits may reset, and sensitive circuits may malfunction. Lower ripple requires larger capacitors.
What's the difference between full-wave and half-wave?
Full-wave rectification uses both halves of the AC waveform, giving ripple frequency of 2× AC frequency. Half-wave uses only one half, giving ripple frequency equal to AC frequency. Full-wave requires smaller capacitors for the same ripple.
Can I use a smaller capacitor than calculated?
You can, but ripple voltage will be higher. The formula calculates the minimum size for your specified ripple. Using a smaller capacitor increases ripple, which may be acceptable for some applications but not others.
What if my load current varies?
Use the maximum expected load current for calculation. This ensures the capacitor can handle peak loads without excessive ripple. For variable loads, size for the worst case.
Do I need to consider ESR (Equivalent Series Resistance)?
For high-frequency applications or very low ripple requirements, ESR becomes important. This calculator assumes ideal capacitors. For critical applications, consider low-ESR capacitors and may need larger values than calculated.