Constant voltage systems are commonly used in electronic devices, battery charging systems, and DC power supplies where maintaining a specific voltage is crucial for proper operation. For example, in battery chargers, the voltage is kept constant to ensure safe and efficient charging. Constant Frequency refers to an AC power system where the frequency of the electrical signal is kept stable, typically at 50 Hz or 60 Hz, depending on the region. In such systems, while the voltage and current may vary, the frequency remains constant.