7805 Voltage Regulator Overview

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Below is a detailed explanation for U3, which is used in this design as U3:
Purpose and Key Functions
  • The 7805 is a three-terminal linear voltage regulator designed to output a fixed 5 V supply from a higher, unregulated input (typically 8–18 V).
  • It functions as a simple, low-noise supply that maintains a constant output voltage even when the input voltage or load current varies.
  • Key functions include built-in thermal overload protection and short-circuit limiting, which protect both the regulator and the load.
Operating Characteristics and Circuit Operation
  • Operating Principle: The 7805 works by dissipating excess voltage as heat. It uses an internal error amplifier, reference voltage, and pass transistor to maintain regulation.
  • Required Supporting Components:
    • An input capacitor (commonly around 0.33 µF) placed between the input and ground helps to filter transients.
    • An output capacitor (around 0.1 µF) at the output improves transient response and stability.
  • Notable Characteristics:
    • It can supply up to 1.5 A (depending on package thermal limits) and exhibits a typical dropout voltage of about 2.0 V at higher load currents.
    • Its quiescent current is relatively low, and load regulation is typically within a few tens of millivolts.
    • It is usually housed in a TO-220 package, making it suitable for applications requiring effective heat dissipation.
Common Applications
  • The 7805 is widely used in power supply circuits for electronics, such as microcontroller systems, sensors, and other digital circuits that require a reliable 5 V rail.
  • Its reliability and ease of use make it a popular choice for prototyping and low-cost consumer electronics.
Family or Series – The 78xx Series
  • The 7805 is part of the 78xx family of fixed linear voltage regulators, where the “xx” indicates the output voltage. For example:
    • 7805: Provides 5 V
    • 7809: Provides 9 V
    • 7812: Provides 12 V
  • Key Differences and Variations:
    • Output Voltage: While the 7805 is fixed at 5 V, other members deliver different output voltages using a similar internal design.
    • Load Current and Dropout: Although many 78xx regulators share similar characteristics, variations exist in maximum current ratings and dropout voltage levels. Some modern versions may have slightly improved thermal performance or lower dropout voltages.
    • Packaging Options: They are available in different packages (e.g., TO-220, TO-3) depending on the application and heat-sinking requirements.
  • Typical Use Cases Comparison:
    • Designers choose the 7805 when a 5 V supply is needed, especially when simplicity and low noise are more critical than efficiency.
    • In contrast, for battery-powered or high-efficiency applications where power dissipation is a concern, switching regulators might be preferred despite the higher complexity.
This comprehensive overview illustrates how U3 serves as a robust and straightforward voltage regulator within circuits, and how its characteristics fit within the broader 78xx family of regulators.
Capacitor Recommendations
Heatsink Size Inquiry
Comparison with Switching Regs
78xx Series Distinctions
PCB Layout Guidelines
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Schematic

Layout

3D View

MotorA_IN1
MotorA_IN1
MotorB_IN1
Encoder2_ChA
Encoder2_ChA
I2C_SCL
Encoder2_ChB
MotorA_IN2
Button3
QTR1
S4
QTR1
I2C_SDA
I2C_SCL
MotorB_IN1
S1
Button2
MotorB_IN2
Encoder1_ChA
QTR2
S4
Button3
S5
MotorB_IN2
Button2
IBUS_TX
Button1
IBUS_RX
S3
IBUS_RX
S5
MotorA_IN2
Button1
QTR2
S2
S3
Encoder2_ChB
Encoder1_ChA
IBUS_TX
Encoder1_ChB
S1
Encoder1_ChB
S2
I2C_SCL
J5
+3.3V
J4
+VBAT
+3.3V
+5V
+3.3V
+5V
+5V
+5V
+5V
+3.3V
+VBAT
+3.3V
+3.3V
+5V
+5V
+VBAT
+5V
+3.3V
+3.3V
+5V
+5V
+3.3V
J14
J11
R6
Resistance
10KΩ
R19
Resistance
10KΩ
J9
R17
Resistance
20KΩ
R11
Resistance
20KΩ
R14
Resistance
10KΩ
R2
Resistance
10KΩ
R7
Resistance
20KΩ
R16
Resistance
10KΩ
R10
Resistance
10KΩ
R5
Resistance
20KΩ
R13
Resistance
20KΩ
J6
J7
R18
Resistance
20KΩ
R3
Resistance
10KΩ
R9
Resistance
2 Ω
J12
R8
Resistance
10KΩ
R15
Resistance
20KΩ
R1
Resistance
10KΩ
R4
Resistance
10KΩ
J8
J10
R12
Resistance
10KΩ
C2
Capacitance
Capacitance
Capacitance
100uF
U2
J3
C3
Capacitance
Capacitance
U3
Manufacturer Part Number
7805
J1
C1
Capacitance
Capacitance
Capacitance
100uF
J2
C4
Capacitance
Capacitance
U1
Manufacturer Part Number
ESP32-DEVKIT-V1
SW3
SW1
D1
SW8
SW2
J13
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