Capacitor Connections

Capacitors in Parallel

When capacitors are connected in parallel, all their positive terminals are connected together and all their negative terminals are connected together. Parallel connections increase the total capacitance while the maximum voltage rating remains limited by the lowest-rated capacitor in the network. Parallel capacitor connections are widely used in power supplies, audio amplifiers, motor drives and electronic equipment where greater energy storage or improved filtering is required.

Capacitors Connected in Parallel

What Is a Parallel Connection?

In a parallel connection, each capacitor is connected directly across the same two terminals. As a result, every capacitor experiences the same applied voltage. 


       +------------------+
       |                  |
      ||                 ||
      C1                C2
       |                  |
       +------------------+

Unlike a series connection, the capacitance values simply add together.

Equivalent Capacitance

The total capacitance is the sum of all individual capacitances. 


CT = C1 + C2 + C3 + ...

This makes parallel calculations much simpler than series calculations.

Worked Examples

Capacitors Total Capacitance
10 µF + 10 µF 20 µF
100 µF + 100 µF 200 µF
220 µF + 470 µF 690 µF
4700 µF + 4700 µF 9400 µF
4700 µF + 2200 µF + 1000 µF 7900 µF

Voltage Rating

Each capacitor in a parallel network has the same voltage across it.

The maximum safe operating voltage is limited by the capacitor with the lowest voltage rating.

Capacitors Maximum Safe Voltage
100 µF 25 V + 100 µF 25 V 25 V
100 µF 25 V + 220 µF 35 V 25 V
4700 µF 63 V + 2200 µF 63 V 63 V

Charge Storage

The total electric charge stored by capacitors in parallel is the sum of the charge stored by each capacitor. 


QT = Q1 + Q2 + Q3 + ...

Because the capacitance increases, the capacitor bank can store more energy than any individual capacitor.

Energy Storage

The energy stored in the capacitor bank is: 


E = ½CTV²

Increasing the total capacitance increases the stored energy at the same operating voltage.

Why Connect Capacitors in Parallel?

  • Increase total capacitance.
  • Improve power supply filtering.
  • Reduce ripple voltage.
  • Lower the effective ESR.
  • Increase ripple-current capability.
  • Provide larger energy storage.
  • Improve transient response.

Advantages

  • Higher total capacitance.
  • Greater stored energy.
  • Lower effective ESR.
  • Higher ripple-current capability.
  • Improved reliability when identical capacitors share the load.
  • Better filtering of power supply ripple.

Disadvantages

  • Voltage rating does not increase.
  • Requires more PCB space.
  • Higher cost than a single capacitor.
  • Leakage currents add together.

Effect on ESR and Ripple Current

Connecting identical capacitors in parallel reduces the overall Equivalent Series Resistance (ESR) and increases the ripple-current capability.

Number of Identical Capacitors Approximate ESR Ripple Current Capability
1 100% 100%
2 50% 200%
4 25% 400%

This is one reason why several smaller capacitors are sometimes preferred to one very large capacitor in high-current power supplies.

Typical Applications

  • Power supply smoothing.
  • Audio amplifier filter capacitors.
  • DC-link capacitor banks.
  • Solar inverters.
  • UPS systems.
  • Battery chargers.
  • Motor drives.
  • High-current DC supplies.

Common Mistakes

Mistake Consequence
Assuming the voltage rating increases. The lowest voltage rating still limits the network.
Mixing widely different capacitor types. Unequal current sharing may occur.
Ignoring ripple-current ratings. Possible overheating.
Using poor PCB layout. Higher ESR and ESL reduce performance.

Real-World Examples

Equipment Typical Parallel Capacitor Use
Class AB Audio Amplifier Multiple filter capacitors on the power supply rails.
Computer Power Supply Several low-ESR output capacitors.
Solar Inverter Large DC-link capacitor bank.
Industrial Motor Drive High-current DC bus filtering.
Arduino Power Input 100 nF ceramic in parallel with a 10 µF electrolytic capacitor.

Key Points

  • Connecting capacitors in parallel increases the total capacitance.
  • The total capacitance equals the sum of all individual capacitances.
  • The voltage across every capacitor is the same.
  • The maximum operating voltage is limited by the lowest-rated capacitor.
  • Parallel capacitors reduce effective ESR and improve ripple-current handling.

Next Lesson

Continue by learning about Capacitor Charging and Discharging, including RC time constants, charging curves and discharge behaviour.

Next Lesson → Charging and Discharging