U2 Component Overview

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Overview of U2: ULN2803ADWR
[U2] is a ULN2803A-series 8-channel Darlington transistor array from Texas Instruments. It serves as a high-current, high-voltage driver interface between low-power logic and inductive or resistive loads.

Key Functions and Characteristics
  • Darlington Pairs
    • Eight NPN Darlington pairs, each with a built-in 2.7 kΩ series base resistor for direct TTL/5 V CMOS interfacing.
    • Collector-emitter voltage rating up to 50 V and collector current up to 500 mA per channel.
  • Built-in Clamp Diodes
    • Integrated common-cathode diodes for inductive-load suppression (relays, solenoids, motors).
  • Parallel Operation
    • Individual outputs can be paralleled for higher current capability.
  • Package
    • Available in 18-pin SOIC (as used in your design) and through-hole DIP variants.

How It Operates in a Circuit
  1. Input Stage
    • A logic‐level signal (e.g., from an MCU GPIO) is applied to one of the eight inputs.
    • The series base resistor limits input current, allowing direct interfacing without extra resistors.
  2. Darlington Amplification
    • The input drives two cascaded NPN transistors, yielding high current gain.
  3. Output Stage & Protection
    • When activated, the Darlington pair pulls the output low, sinking up to 500 mA.
    • Clamp diodes divert inductive kickback to the common cathode (VCC), protecting the transistors.

Common Applications
  • Relay and solenoid drivers
  • Lamp and LED display drivers
  • Hammer drivers in printing and impact-dot applications
  • Stepper-motor control
  • Line-driver and logic-buffer interfaces

ULN280xA Device Family


VariantInput ResistorLogic-Level CompatibilityUse Case Highlights
ULN2801A2.7 kΩGeneral-purposeStandard industrial loads
ULN2802A10.5 kΩ14–25 V PMOS logicHigher-voltage logic interfaces
ULN2803A2.7 kΩ5 V TTL and CMOSMost common relay/LED driving
ULN2804A10.5 kΩ6–15 V CMOSMid-range CMOS logic loads
  • Key Differences
    • Input-resistor value tailors each variant to different logic-level voltages.
    • All variants share 8 Darlington channels, clamp-diode protection, and 50 V/500 mA output capabilities.
  • Typical Use-Case Selection
    • Choose ULN2803A (as in [U2]) for standard 5 V logic control of relays, lamps, and solenoids.
    • Opt for ULN2802A or ULN2804A when interfacing with higher-voltage CMOS or PMOS logic domains.
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please explain what U2 does.

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is the relay suited for switching 400V

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2
LED3
J8
RS16
LED2
LED8
+5V
RS9
LED7
J3
RS14
RS7
+5V
RS3
J4
RS12
RS7
+5V
RS5
+5V
+5V
RS4
J7
+5V
+5V
LED1
RSS7
RSS5
RSS8
LED5
LED4
RSS6
RSS3
RSS1
RS6
RSS2
RS5
VCC
LED9
RS13
RSS5
+5V
RS4
RS6
RS1
RS2
RS15
RS8
+5V
RSS7
RSS1
RSS2
RSS6
RS10
RSS4
RS3
RS1
RSS4
J2
RSS8
RSS3
+5V
J9
RS8
+5V
LED6
RS2
RS11
C1
Capacitance
Capacitance
R1
Resistance
120 Ω
R7
Resistance
120 Ω
RLY8
R2
Resistance
120 Ω
R8
Resistance
120 Ω
R3
Resistance
120 Ω
RLY5
R5
Resistance
120 Ω
RLY3
R9
Resistance
120 Ω
RLY1
U2
U1
RLY2
RLY4
R6
Resistance
120 Ω
U3
RLY6
R4
Resistance
120 Ω
RLY7


  • Ground
    A common return path for electric current. Commonly known as ground.
  • Net Portal
    Wirelessly connects nets on schematic. Used to organize schematics and separate functional blocks. To wirelessly connect net portals, give them same designator. #portal
  • Power Net Portal
    Wirelessly connects power nets on schematic. Identical to the net portal, but with a power symbol. Used to organize schematics and separate functional blocks. To wirelessly connect power net portals, give them the same designator. #portal #power
  • Generic Resistor
    A generic fixed resistor for rapid developing circuit topology. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard resistor values: 1.0Ω 10Ω 100Ω 1.0kΩ 10kΩ 100kΩ 1.0MΩ 1.1Ω 11Ω 110Ω 1.1kΩ 11kΩ 110kΩ 1.1MΩ 1.2Ω 12Ω 120Ω 1.2kΩ 12kΩ 120kΩ 1.2MΩ 1.3Ω 13Ω 130Ω 1.3kΩ 13kΩ 130kΩ 1.3MΩ 1.5Ω 15Ω 150Ω 1.5kΩ 15kΩ 150kΩ 1.5MΩ 1.6Ω 16Ω 160Ω 1.6kΩ 16kΩ 160kΩ 1.6MΩ 1.8Ω 18Ω 180Ω 1.8KΩ 18kΩ 180kΩ 1.8MΩ 2.0Ω 20Ω 200Ω 2.0kΩ 20kΩ 200kΩ 2.0MΩ 2.2Ω 22Ω 220Ω 2.2kΩ 22kΩ 220kΩ 2.2MΩ 2.4Ω 24Ω 240Ω 2.4kΩ 24kΩ 240kΩ 2.4MΩ 2.7Ω 27Ω 270Ω 2.7kΩ 27kΩ 270kΩ 2.7MΩ 3.0Ω 30Ω 300Ω 3.0KΩ 30KΩ 300KΩ 3.0MΩ 3.3Ω 33Ω 330Ω 3.3kΩ 33kΩ 330kΩ 3.3MΩ 3.6Ω 36Ω 360Ω 3.6kΩ 36kΩ 360kΩ 3.6MΩ 3.9Ω 39Ω 390Ω 3.9kΩ 39kΩ 390kΩ 3.9MΩ 4.3Ω 43Ω 430Ω 4.3kΩ 43KΩ 430KΩ 4.3MΩ 4.7Ω 47Ω 470Ω 4.7kΩ 47kΩ 470kΩ 4.7MΩ 5.1Ω 51Ω 510Ω 5.1kΩ 51kΩ 510kΩ 5.1MΩ 5.6Ω 56Ω 560Ω 5.6kΩ 56kΩ 560kΩ 5.6MΩ 6.2Ω 62Ω 620Ω 6.2kΩ 62KΩ 620KΩ 6.2MΩ 6.8Ω 68Ω 680Ω 6.8kΩ 68kΩ 680kΩ 6.8MΩ 7.5Ω 75Ω 750Ω 7.5kΩ 75kΩ 750kΩ 7.5MΩ 8.2Ω 82Ω 820Ω 8.2kΩ 82kΩ 820kΩ 8.2MΩ 9.1Ω 91Ω 910Ω 9.1kΩ 91kΩ 910kΩ 9.1MΩ #generics #CommonPartsLibrary
  • Generic Capacitor
    A generic fixed capacitor ideal for rapid circuit topology development. You can choose between polarized and non-polarized types, its symbol and the footprint will automatically adapt based on your selection. Supported options include standard SMD sizes for ceramic capacitors (e.g., 0402, 0603, 0805), SMD sizes for aluminum electrolytic capacitors, and through-hole footprints for polarized capacitors. Save precious design time by seamlessly add more information to this part (value, footprint, etc.) as it becomes available. Standard capacitor values: 1.0pF 10pF 100pF 1000pF 0.01uF 0.1uF 1.0uF 10uF 100uF 1000uF 10,000uF 1.1pF 11pF 110pF 1100pF 1.2pF 12pF 120pF 1200pF 1.3pF 13pF 130pF 1300pF 1.5pF 15pF 150pF 1500pF 0.015uF 0.15uF 1.5uF 15uF 150uF 1500uF 1.6pF 16pF 160pF 1600pF 1.8pF 18pF 180pF 1800pF 2.0pF 20pF 200pF 2000pF 2.2pF 22pF 20pF 2200pF 0.022uF 0.22uF 2.2uF 22uF 220uF 2200uF 2.4pF 24pF 240pF 2400pF 2.7pF 27pF 270pF 2700pF 3.0pF 30pF 300pF 3000pF 3.3pF 33pF 330pF 3300pF 0.033uF 0.33uF 3.3uF 33uF 330uF 3300uF 3.6pF 36pF 360pF 3600pF 3.9pF 39pF 390pF 3900pF 4.3pF 43pF 430pF 4300pF 4.7pF 47pF 470pF 4700pF 0.047uF 0.47uF 4.7uF 47uF 470uF 4700uF 5.1pF 51pF 510pF 5100pF 5.6pF 56pF 560pF 5600pF 6.2pF 62pF 620pF 6200pF 6.8pF 68pF 680pF 6800pF 0.068uF 0.68uF 6.8uF 68uF 680uF 6800uF 7.5pF 75pF 750pF 7500pF 8.2pF 82pF 820pF 8200pF 9.1pF 91pF 910pF 9100pF #generics #CommonPartsLibrary
  • Generic Inductor
    A generic fixed inductor for rapid developing circuit topology. *You can now change the footprint and 3D model at the top level anytime you want. This is the power of #generics
  • Terminal
    Terminal
    An electrical connector acting as reusable interface to a conductor and creating a point where external circuits can be connected.
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  • 875105359001
    10uF Capacitor Aluminum Polymer 20% 16V SMD 5x5.3mm #forLedBlink #commonpartslibrary #capacitor #aluminumpolymer #radialcan
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ESP32 8 Relay Board

ESP32 8 Relay Board
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