The LM7805 is based on the series voltage regulator design.
Here's how it works:
LM7805 Overview:
The LM7805 is a linear voltage regulator, which means it maintains a constant output voltage (5V in this case) by dissipating excess input voltage as heat. Internally, the LM7805 uses a series pass transistor to drop the excess voltage between the input and output.
Internal Working of LM7805:
Series Pass Transistor: The LM7805 uses a pass transistor (typically a BJT or MOSFET) connected in series with the load. The transistor is controlled by an internal feedback loop, which regulates the output voltage. The pass transistor allows current to flow from the input to the output, but the amount of current is regulated to ensure the output stays at a constant voltage.
Feedback Loop (Error Amplifier): Inside the LM7805, there is an internal error amplifier (typically an op-amp) that compares the output voltage with a reference voltage (around 1.25V). This feedback is used to control the base of the pass transistor, adjusting its resistance to keep the output voltage stable.
Voltage Reference: The LM7805 has an internal voltage reference (typically 1.25V) that sets the threshold for the feedback loop. This reference voltage is compared with the output voltage, and the pass transistor adjusts the output accordingly.
Current Limiting and Thermal Protection: The LM7805 also includes features such as overcurrent protection and thermal shutdown to prevent damage to the regulator when the load current is too high or the temperature rises too much.
Summary:
The LM7805 operates as a series voltage regulator because it regulates the output voltage by adjusting the series pass transistor's resistance. It is a linear regulator, meaning it does not switch on and off like a switching regulator, and instead, it uses continuous adjustment of the pass transistor to maintain a steady 5V output, dropping the excess input voltage as heat.
This is similar to other linear regulators, like the LM317, which also uses a series pass transistor but is adjustable and can regulate a wider range of output voltages. See LM7805 vs LM317: Which Voltage Regulator to Use for Your Project.
See next how to make your own +5V Regulated Power Supply for Breadboard.
