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STMicroelectronics ULN2801A
- Part No.:
- ULN2801A
- Manufacturer:
- STMicroelectronics
- Category:
- Bipolar Transistor Arrays
- Package:
- 18-DIP (0.300", 7.62mm)
- Datasheet:
-
ULN2801A.pdf
- Description:
- TRANS 8NPN DARL 50V 500MA 18DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,825
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Product details
Overview
ULN2801A from STMicroelectronics is an eight-channel Darlington transistor array with common-emitter outputs, 500 mA continuous output current per channel, 50 V output voltage rating, and integrated clamp diodes for inductive load driving. It features input-current-limiting resistors for general-purpose logic interfacing and is used in relay drivers, stepper motor controllers, and LED matrix displays.
For engineers reviewing the ULN2801A datasheet, ULN2801A pinout, ULN2801A application, or ULN2801A equivalent, key selection criteria include per-channel saturation voltage at 350 mA, input current requirements for TTL/CMOS compatibility, thermal resistance (55 °C/W), clamp diode forward voltage, and DIP-18 layout-optimized pin arrangement.
Technical Context
The ULN2801A integrates eight independent NPN Darlington pairs, each with a built-in base resistor and cathode-connected clamp diode to suppress inductive kickback. Its input structure is optimized for direct connection to 5 V logic without external biasing.
It operates across –20 °C to +85 °C ambient, supports paralleling of outputs for higher current, and delivers guaranteed 1000 minimum DC current gain at 350 mA collector current and 2 V VCE.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output current | 500 mA continuous per channel - supports driving relays, solenoids, and small motors without external heatsinking |
| Output voltage rating | 50 V - enables safe switching of 24 V industrial loads and 36 V automotive auxiliary circuits |
| VCE(SAT) | 1.1 V max at IC = 350 mA - minimizes power loss and self-heating during sustained conduction |
| Clamp diode VF | 1.7–2.0 V at 350 mA - provides effective flyback energy dissipation for inductive loads |
| Input current (II(ON)) | Typ. 1.1 mA at VI = 5 V - compatible with standard 5 V TTL/CMOS outputs without loading |
| RthJA | 55 °C/W - defines thermal derating curve for multi-channel operation in plastic DIP-18 package |
| Operating temperature | –20 °C to +85 °C - validated for industrial control and embedded equipment environments |
Pinout & Package
ULN2801A is housed in an 18-lead plastic dual in-line package (DIP-18) with copper lead frame and input pins opposite corresponding outputs to minimize PCB trace crossovers.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 7, 8 | Inputs (IN1–IN8) | Logic-level inputs with internal current-limiting resistors; accept 5 V TTL/CMOS directly |
| 9 | Common emitter | Shared emitter connection for all eight Darlington outputs; tied to system ground |
| 10, 11, 12, 13, 14, 15, 16, 17 | Outputs (OUT1–OUT8) | Open-collector Darlington outputs with integrated cathode-down clamp diodes |
| 18 | Common cathode | Shared anode connection for all eight clamp diodes; connects to positive supply rail of inductive load |
Key Features
| Feature | Design Value |
|---|---|
| Eight Darlington channels | Enables compact control of multiple high-current loads from a single IC footprint |
| Integrated clamp diodes | Eliminates need for external flyback diodes when driving relays, solenoids, or stepper windings |
| Input-opposite-output pinout | Reduces PCB routing complexity and layer count in dense control boards |
| 500 mA per channel (continuous) | Supports direct drive of industrial-grade electromechanical components without external buffers |
| 50 V off-state voltage rating | Ensures robustness against voltage transients in 24 V and 36 V systems |
Applications
| Relay Driver Module | Stepper Motor Controller |
|---|---|
Use Scenario: Driving eight 24 VDC SPDT relays in PLC I/O expansion modules. IC Role / Device Role / Timing Role: High-side switch interface between microcontroller GPIO and relay coils. Use Value: Single ULN2801A replaces eight discrete transistors and eight flyback diodes, reducing BOM count and board area by >60%. | Use Scenario: Unipolar stepper motor phase sequencing in CNC positioning stages. IC Role / Device Role / Timing Role: Current-sinking driver for four-phase, six-wire unipolar stepper windings. Use Value: Clamp diodes protect against back-EMF during rapid direction reversal, enabling reliable 10 kHz step rates. |
| LED Matrix Display | Industrial Sensor Interface |
Use Scenario: Row/column scanning of 8×8 red LED matrices in factory HMI panels. IC Role / Device Role / Timing Role: Column sink driver with 500 mA peak capability for multiplexed brightness control. Use Value: Low VCE(SAT) ensures minimal voltage drop across rows, preserving LED forward voltage margin at full brightness. | Use Scenario: Interfacing 4–20 mA current-loop sensors to isolated microcontroller inputs. IC Role / Device Role / Timing Role: Active pull-down stage converting sensor loop current into digital logic-level signals. Use Value: Input resistor network allows direct connection to 5 V logic while maintaining loop compliance voltage down to 12 V. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar Darlington array applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| ULN2803A | 2.7 kΩ input resistor; optimized for 5 V TTL/CMOS; lower input threshold voltage | Better noise immunity and faster switching in mixed-signal 5 V systems | Select ULN2803A when interfacing with legacy 5 V microcontrollers or FPGAs without level-shifting |
| TPIC6B595 | Serial-input, 8-bit shift-register + Darlington output; 500 mA per channel; SPI interface | Reduces GPIO count from 8 to 3; adds daisy-chain capability and latch control | Choose TPIC6B595 when system GPIO is constrained and sequential load control is acceptable |
Compared with ULN2803A, ULN2801A offers identical output specs but different input biasing-making it suitable for general-purpose 5 V logic where no strict TTL threshold is required; TPIC6B595 trades parallel interface simplicity for serial configurability and reduced pin count.
Availability
ULN2801A is available at Aetrix Electronics and suitable for relay driver modules, stepper motor controllers, LED matrix displays, and industrial sensor interfaces requiring stable component supply across extended production lifecycles.
Supply support for ULN2801A includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, MCU, power, and sensing solutions for industrial, automotive, and consumer markets.
The ULN2801A belongs to ST's high-voltage Darlington array product line, engineered specifically for robust, low-complexity interfacing between digital logic and medium-power inductive or resistive loads.
FAQ
Is ULN2801A pin-compatible with ULN2803A?
No. While both are 18-pin DIP Darlington arrays with identical output pinouts (pins 10–17) and common connections (pin 9 and 18), ULN2801A has no internal input resistors, whereas ULN2803A integrates 2.7 kΩ resistors on each input. Direct substitution requires verifying external biasing and logic voltage levels.
Can ULN2801A outputs be paralleled for higher current?
Yes. The datasheet explicitly permits paralleling outputs to increase total current capacity. When two channels are paralleled, continuous current rises to 1 A with appropriate thermal management; derating must follow the 2.25 W total package power limit and RthJA = 55 °C/W.
What is the purpose of Pin 18 (common cathode)?
Pin 18 connects the anodes of all eight internal clamp diodes. It must be tied to the positive supply rail of the inductive load (e.g., +24 V) so that flyback current flows safely through the diode into the supply, preventing voltage spikes at the output pins.
Does ULN2801A require external pull-up resistors on inputs?
No. ULN2801A inputs are designed for direct connection to active-high logic sources. Unlike open-collector inputs, they do not require pull-ups; however, unused inputs should be grounded to prevent floating states and unintended channel activation.
ULN2801A Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 18-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Transistor Type:
- 8 NPN Darlington
- Current - Collector (Ic) (Max):
- 500mA
- Voltage - Collector Emitter Breakdown (Max):
- 50V
- Vce Saturation (Max) @ Ib, Ic:
- 1.6V @ 500µA, 350mA
- Current - Collector Cutoff (Max):
- -
- DC Current Gain (hFE) (Min) @ Ic, Vce:
- 1000 @ 350mA, 2V
- Power - Max:
- 2.25W
- Frequency - Transition:
- -
- Operating Temperature:
- -20°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 18-DIP
ULN2801A FAQ
1.How can I place an order for ULN2801A through Aetrix?
Please submit a Request for Quotation (RFQ) for ULN2801A on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for ULN2801A reliable?
The price and inventory of ULN2801A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for ULN2801A is usually 5 days.
3.What payment methods are accepted for ULN2801A?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for ULN2801A transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for ULN2801A?
ULN2801A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your ULN2801A order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for ULN2801A?
For technical support, including ULN2801A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your ULN2801A requirements.
6.How does Aetrix verify that ULN2801A is sourced from the original manufacturer or authorized distributors?
All ULN2801A products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that ULN2801A meets industry standards.
7.What is the process for return or replacement of ULN2801A?
All ULN2801A units undergo pre-shipment inspection (PSI). If there is an issue with ULN2801A, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The ULN2801A part is unused and in its original packaging.
Return procedure for ULN2801A:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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