Power supplies are generally categorized into two main types: voltage sources and current sources. A voltage source is a power supply that maintains a constant output voltage regardless of the load connected to it. On the other hand, a current source provides a steady and consistent current, regardless of the voltage across its terminals.
A current source typically has a high internal resistance, which allows it to maintain a stable current even when the connected load changes. This means that a current source continuously delivers current, whether or not there is an electrical device connected. However, due to this characteristic, the circuit using a current source may consume more power compared to a voltage source.
In contrast, a voltage source has a low internal resistance, making it ideal for applications where a stable voltage is required, such as in household electronics. The voltage from a voltage source is only available when the circuit is closed, such as when a switch is turned on.
Power sources can also be classified based on their type: alternating current (AC) and direct current (DC). In hardware circuits, DC power sources are most commonly used. These DC sources can be further converted into different voltage levels through DC-DC converters, which are either switching or linear power modules. Common DC voltage values include +3.3V, +5V, +12V, and +15V. Choosing the appropriate voltage source is crucial, as the current capacity of the circuit is limited, and improper selection can lead to performance issues or damage.
One popular linear voltage regulator is the LM7805. The "78" in its name denotes the series, while "05" indicates the output voltage of 5V. It can normally handle up to 1A of current. If the power dissipation exceeds 2W, the LM7805 may overheat, so a heat sink is recommended in such cases. The power dissipated by the regulator is calculated by multiplying the voltage difference between the input (Vin) and output (Vout) by the current flowing through it. If the voltage drop is too large, a higher-voltage regulator like the LM7815 can be used first to reduce the input voltage before feeding it into the LM7805.
Another similar part is the LM78L05, which operates at a lower current rating of 0.5A. It is suitable for applications where power consumption needs to be minimized.
The LM7805 has three pins. The voltage between pin 1 and pin 3 should be greater than 5V, while the voltage between pin 1 and pin 2 is exactly 5V. Pin 3 is grounded. As long as the input voltage (Vin) is above 5V, the output voltage (Vout) will remain at 5V. Typically, the LM7805 is powered by an AC source of around 16V after being rectified by a bridge rectifier.
In engineering applications, common AC voltage sources include 24V, 14V, and 16V. These voltages can be obtained by stepping down the standard mains voltage—such as 220V in China, 110V in Japan, and 120V in Taiwan—using a transformer. This makes AC sources versatile for various power supply designs.
100W Power Bank
Multi-function, multi-device charging solution - With a large 20,000 mAh built-in battery, the mophie Powerstation XXL High Capacity mobile Power supply charges your phone super fast and can fully charge your phone up to 4.6 times. Charge three devices simultaneously
Charge Your Devices Fast - With 18W USB-C power output, charge your phone the fastest and get up to 50% battery power in just 30 minutes. The USB-C port can be used to charge the power station itself during recording hours.
Compatible with various gadgets - In addition to the USB-CpD port, the Portable Portable Power Supply also comes with 2 USB-A ports for charging smartphones, tablets, and other USB devices. The package includes a charging cable (USB-A to USB-C).Functional and stylish - With a classic fabric finish that prevents scuffs and scratches, this mobile power supply is your perfect travel companion. Easily fit in your bag, so you can carry it to work or on adventures without a separate charger
Its main components include: a battery for electrical energy storage, a circuit (DC-DC converter) to stabilize the output voltage, and most mobile power supplies come with a charger for charging as a built-in battery.
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