If you connect a switch and a capacitor in a circuit, the behavior of the capacitor depends on the state of the switch. When the switch is closed, the capacitor will start to charge if connected to a voltage source. The current will flow through the circuit, causing the voltage across the capacitor to increase gradually until it matches the supply voltage. When the switch is opened, the capacitor will retain its charge and maintain the voltage across its terminals unless there is a discharge path.
Putting a capacitor across a switch can help suppress voltage spikes and reduce electrical noise. This practice is known as “snubbing.” When a switch opens, especially in inductive circuits, it can generate high-voltage transients due to the collapsing magnetic field. A capacitor across the switch absorbs these transients, protecting the circuit components and ensuring smoother operation. It also helps in reducing electromagnetic interference (EMI) generated by the switching action.
When the switch is open, the capacitor will generally retain its charge if there is no discharge path. The voltage across the capacitor remains constant, and it effectively acts as a temporary storage device for electric charge. Over time, if there is any leakage or a small resistive path in the circuit, the capacitor will slowly discharge. However, in an ideal situation with perfect insulation, the charge on the capacitor would remain indefinitely.
When a capacitor is switched on, meaning when the switch in the circuit is closed, the capacitor will begin to charge if connected to a voltage source. The charging process involves current flowing into the capacitor, causing the voltage across it to rise. Initially, the current is high because the voltage difference is greatest. As the capacitor charges, the current gradually decreases until the capacitor is fully charged and the voltage across it equals the supply voltage.
The purpose of a switched-capacitor is to emulate resistive elements and perform analog signal processing tasks like filtering, amplification, and integration in integrated circuits. Switched-capacitor circuits use capacitors and switches to transfer charge between different parts of the circuit at a controlled rate. This allows precise control of the equivalent resistance and other circuit parameters, making them highly useful in applications like analog-to-digital converters, voltage-controlled oscillators, and various types of filters in signal processing.