What Does a Capacitor Do in a Power Supply Circuit

 A capacitor is used in power supply circuits to smooth or filter the voltage. After converting AC to DC using a rectifier, the output is not steady. Instead, it has ripples because the voltage rises and falls with the AC waveform. A capacitor is placed after the rectifier to reduce this ripple and make the output closer to a stable DC voltage.

To understand why, we need to look at what a capacitor does. A capacitor stores energy in the form of electric charge. When a voltage is applied to a capacitor, it stores charge on its plates. The amount of charge stored depends on the voltage and the capacitance value. This relationship is defined by the equation:

Q = C * V

Q is the charge in coulombs, C is the capacitance in farads, and V is the voltage across the capacitor. The energy stored in a capacitor can be calculated as:

E = 1/2 * C * V^2

Once charged, the capacitor acts like a small energy reservoir. In a power supply, when the output voltage from the rectifier rises, the capacitor charges up and stores energy. When the voltage drops, the capacitor discharges and releases the stored energy into the circuit. This fills in the missing parts of the waveform and reduces voltage variation.

In simple terms, the capacitor charges when the supply voltage is higher than its stored level and discharges when the voltage tries to drop. This charging and discharging action smooths the output and produces a more consistent DC voltage. Because of this behavior, capacitors are also called smoothing capacitors or filter capacitors in power supply designs.

The key idea is that the capacitor does not create energy or push voltage by itself. It only stores energy temporarily and releases it when the circuit needs it. The circuit decides when the capacitor charges or discharges based on voltage differences across the capacitor.

To summarize in one sentence: In a power supply, a capacitor stores energy when the voltage is high and releases energy when the voltage drops, resulting in a smoother and more stable DC output.