Capacitors in Series and Parallel Explained

A capacitor is a passive two-terminal electronic component that can store electrical charge. But did you know that you can connect multiple capacitors in either parallel or series to meet specific design requirements in electronic circuits?

Before delving into this topic, let’s first understand the fundamental parameters that characterize the behavior of capacitors.

What is Capacitance?

When a voltage is applied across the terminals of a capacitor, it stores electric charge (Q). Now, capacitance (C) on the other hand, is how you can measure the capacitor’s ability to store this electric charge.

Many capacitors have their capacitance values marked directly on their casings. In most circuits, a capacitance of one farad is relatively large, so, you can often see capacitors in smaller units like microfarads, nanofarads, or even picofarads.

However, sometimes, it also depends on the capacitor’s size, type, or physical characteristics.

For example, some capacitors are influenced by factors such as the surface area of their conducting plates, the distance between the plates, and the properties of the dielectric material positioned between the plates.

Relationships Between Charge and Capacitance

In the context of capacitors, charge and capacitance are closely related concepts; however, they represent different aspects of the capacitor’s behavior.

The relationship between charge and capacitance is defined by the following formula:

\[ Q=C\cdot V\]

where:

• Q is the charge stored on the capacitor (measured in coulombs)
• C is the capacitance of the capacitor (measured in farads)
• V is the potential difference across the capacitor (measured in volts).

As we can see, this formula expresses that the charge stored on a capacitor is directly proportional to the capacitance and the voltage applied across its terminals.

If you rearrange the formula, you can express capacitance as:

\[ C=\frac{Q}{V}​\]

This equation highlights that capacitance is the ratio of the stored charge to the applied voltage. A higher capacitance means that the capacitor can store more charge for a given voltage.

Now, what happens if you connect capacitors in series or parallel? Will the total capacitance change? What will happen to the overall voltage? Let’s find out.

Capacitors Connected in Parallel

When capacitors are connected in parallel, the total capacitance of the circuit increases. Think of it as you’re increasing the effective surface area of a single capacitor, which means having a higher total capacitance.

Capacitance is also directly proportional to the surface area of the conducting plates. So, the larger the surface area, the higher the capacitance.

So, this makes the total capacitance as the sum of the individual capacitors. Mathematically, it is expressed as:

\[C_{total}​=C_1​+C_2​+C_3​+…\]

Why Connect Capacitors in Parallel?

This configuration is advantageous when a larger capacitance is needed in a circuit, especially when you don’t have the right part or a capacitor with the exact rating on hand.

It’s also more common in applications where smooth and stable power is required, such as in power supply filtering.

In electronic circuits, especially those with integrated circuits (ICs) or other sensitive components, decoupling capacitors are used to provide a stable and noise-free power supply. This helps prevent voltage fluctuations from affecting the operation of the component.

These decoupling capacitors (typically ceramic capacitors) are connected in parallel between the positive and negative power supply.

In the circuit above, the parallel combination of capacitors (C1, C2, C3) helps filter out high-frequency noise introduced from the power supply. This ensures a stable voltage supply to the IC.

Does the total voltage of the circuit increase?

No, the total voltage of the circuit does not increase or change when capacitors are connected in parallel.

Capacitors in parallel share the same potential difference because they are all connected to common points. This connectivity ensures that all capacitors have equal voltage levels across their terminals.

Although this configuration allows capacitors to accumulate charge independently, each capacitor still maintains a uniform voltage across its terminals.

So, the purpose of connecting capacitors in parallel is to increase the total capacitance and enhance the energy storage capacity, not to alter the voltage.

Capacitors Connected in Series

The equivalent capacitance in series is given by the reciprocal of the sum of the reciprocals of individual capacitors, just like resistors in parallel.

\[C_{total}=\frac{1}{\frac{1}{C_1}+\frac{1}{C_2}+\frac{1}{C_3}+…}\]​

Note that the total capacitance is always less than the value of the smallest individual capacitor.

Let’s say when you add more capacitors in series, you’re also decreasing the total capacitance of the circuit. This reduction is due to the charge on capacitors being shared, and the effective electric field across the combination being weakened.

The overall effect is akin to increasing the spacing between the plates of a single capacitor, which, in turn, decreases its capacitance.

Is dropping the overall capacitance a bad thing?

No. The depletion in overall capacitance is not inherently a “bad” thing; rather, it is a deliberate design choice with specific purposes.

For example, when you connect capacitors in series, you can control how long it takes for the capacitor to charge or discharge to about 62.7% of its full capacity. We call this “time constant.”

Despite the decrease in capacitance, it’s also important to note that capacitors in series can withstand a higher potential difference. This is because the potential difference across the combination is distributed among individual capacitors.

In the end, combining capacitors, whether in series or parallel, allows you to tweak the overall capacitance. You can do this to provide the right capacitance that your circuit requires.