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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Bipolar Transistor Arrays

STMicroelectronics ULQ2801A

Name: ULQ2801A
Brand: STMicroelectronics
SKU: ULQ2801A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: ULQ2801A

Manufacturer:: STMicroelectronics

Category:: Bipolar Transistor Arrays

Package:: 18-DIP (0.300", 7.62mm)

Datasheet:: ULQ2801A.pdf

Description:: TRANS 8NPN DARL 50V 500MA 18DIP

Quantity:: RFQ Add To RFQ list

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Inventory:1,995

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Product details

Overview

ULQ2801A from STMicroelectronics is an eight-channel Darlington transistor array with common-emitter outputs and integrated clamp diodes for inductive load driving. It delivers 500 mA continuous output current per channel, withstands 50 V off-state voltage, operates from −40 °C to +105 °C, and features input-resistor-limited logic interface for general-purpose switching in industrial control systems.

For engineers reviewing the ULQ2801A datasheet, ULQ2801A pinout, ULQ2801A application, or ULQ2801A equivalent, key selection criteria include per-channel current capability, integrated flyback diode functionality, DIP-18 input-opposite-output layout compatibility, thermal derating above 85 °C, and discrete logic-level interfacing without external base resistors.

Technical Context

The ULQ2801A integrates eight independent NPN Darlington pairs, each with a built-in 2.7 kΩ series input resistor and reverse-biased clamp diode across collector–emitter. It is optimized for direct TTL/CMOS-compatible drive without external current-limiting components.

Each channel provides DC current gain (h_FE) ≥1000 at I_C = 350 mA and V_CE = 2 V, with V_CE(SAT) ≤1.6 V at I_C = 350 mA and I_B = 500 µA, enabling efficient low-side switching of solenoids, relays, and LED banks.

Key Specifications

Parameter	Value and Actual Design Meaning
Output channels	8 independent Darlington drivers with common emitter
Continuous output current	500 mA per channel - supports medium-power relay/solenoid loads
Off-state voltage rating	50 V - enables safe switching of 24 V industrial control rails
Operating temperature	−40 °C to +105 °C - qualified for extended ambient industrial environments
Input interface	Internal 2.7 kΩ resistor - accepts 5 V TTL/CMOS directly, no external bias needed
V_CE(SAT)	≤1.6 V at 350 mA - minimizes power loss and heat generation per channel
Clamp diode	Integrated reverse-biased diode - suppresses inductive kickback without external components

Pinout & Package

ULQ2801A is housed in a standard 18-lead plastic dual in-line package (DIP-18) with copper leads and input pins physically opposite corresponding output pins to minimize PCB trace crossovers and simplify routing.

Pin/Terminal	Circuit Role	Design Meaning
1, 2, 3, 4, 5, 6, 7, 8	Input (IN1–IN8)	Logic-level inputs with internal 2.7 kΩ pull-up resistor to V_CC; compatible with 5 V TTL/CMOS
9	Common Emitter (COM)	Shared emitter connection for all eight Darlington outputs; must be tied to system ground
10, 11, 12, 13, 14, 15, 16, 17	Output (OUT1–OUT8)	Open-collector Darlington outputs with integrated clamp diodes; sink current to COM
18	V_CC	Positive supply for internal input resistors; typically connected to 5 V logic rail

Key Features

Feature	Design Value
Input-opposite-output pinout	Reduces PCB layer count and routing congestion in high-density industrial control boards
Integrated clamp diodes	Eliminates need for 8 discrete external flyback diodes in relay/solenoid driver designs
Parallel output capability	Allows combining two or more channels to deliver up to 1 A continuous load current
Extended temperature range	Validated operation up to +105 °C ambient - suitable for enclosed cabinet deployments
Logic-family optimized version	ULQ2801A variant specifically tuned for 5 V TTL/CMOS with 2.7 kΩ input resistor

Applications

Industrial Relay Driver

PLC Output Module

Use Scenario: Driving 24 VDC electromechanical relays in factory automation panels.

IC Role / Device Role / Timing Role: Low-side switch array providing isolated, current-sinking control of relay coils.

Use Value: Integrated clamp diodes prevent voltage spikes that could damage upstream logic or cause EMC issues.

Use Scenario: Modular digital output stage in programmable logic controller backplanes.

IC Role / Device Role / Timing Role: Eight-channel buffered output driver translating microcontroller GPIO to field-side loads.

Use Value: Input-resistor integration eliminates 8 external components per module, reducing BOM cost and assembly steps.

Solenoid Control Board

LED Signage Driver

Use Scenario: Controlling pneumatic valve solenoids in HVAC control units.

IC Role / Device Role / Timing Role: High-current Darlington sink driver handling intermittent 350 mA coil loads.

Use Value: V_CE(SAT) ≤1.6 V at 350 mA limits power dissipation to <0.6 W per channel under full load.

Use Scenario: Segment-level current sinking for monochrome LED displays in transit signage.

IC Role / Device Role / Timing Role: Constant-current sink for multiplexed LED rows requiring robust transient suppression.

Use Value: 50 V off-state rating accommodates LED string forward voltages up to 48 V with margin.

Equivalent & Alternatives

The following parts are listed as comparable options for similar Darlington array applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
ULN2803A	Same DIP-18 package, identical pinout, but uses 2.7 kΩ input resistor and rated for 500 mA per channel at T_A ≤ 70 °C	Rated only to +70 °C ambient; lacks extended temperature qualification to +105 °C	Select ULN2803A only for commercial-temperature applications where cost is prioritized over thermal margin
TB6549FNG	8-channel DMOS H-bridge driver with higher voltage (80 V), higher current (1.2 A peak), but requires external logic-level translation and flyback diodes	Supports bidirectional motor control; not a drop-in replacement due to different architecture and pinout	Choose TB6549FNG when bidirectional drive or higher voltage/current is required, accepting added design complexity

Compared with ULN2803A, ULQ2801A offers guaranteed operation up to +105 °C and tighter V_CE(SAT) spec at high current; versus TB6549FNG, it provides simpler unidirectional sinking with integrated protection but lower voltage headroom and no H-bridge capability.

Availability

ULQ2801A is available at Aetrix Electronics and suitable for industrial relay drivers, PLC output modules, solenoid control boards, and LED signage drivers requiring stable component supply across extended temperature ranges.

Supply support for ULQ2801A 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, Switzerland, designing and manufacturing analog, MCU, power, and sensor solutions for industrial, automotive, and consumer markets.

The ULQ2801A belongs to ST's high-reliability Darlington array product line, engineered specifically for ruggedized industrial interface applications demanding integrated protection, wide temperature operation, and simplified logic-level drive.

FAQ

Is ULQ2801A pin-compatible with ULN2803A?

Yes - ULQ2801A shares identical DIP-18 pinout, terminal numbering, and functional assignment with ULN2803A, including input-opposite-output layout and common emitter pin (Pin 9). This allows direct PCB footprint reuse in existing designs where extended temperature operation is needed.

Can ULQ2801A outputs be paralleled for higher current?

Yes - the datasheet explicitly permits paralleling multiple outputs (e.g., OUT1 + OUT2) to increase total sink current capacity up to 1 A continuous, provided thermal limits of the package (2.25 W total) are observed and current sharing is verified under worst-case V_CE(SAT) mismatch.

What is the purpose of Pin 18 (V_CC) on ULQ2801A?

Pin 18 supplies the positive reference for the internal 2.7 kΩ input resistors. It must be connected to the same 5 V logic rail used by the driving microcontroller or gate driver. Leaving it unconnected disables all inputs, while connecting it to a higher voltage risks exceeding VI absolute maximum ratings.

Does ULQ2801A require external flyback diodes when driving relays?

No - each channel includes a monolithically integrated clamp diode connected cathode-to-collector and anode-to-emitter (common emitter). This provides complete inductive kickback suppression for standard 24 V relay coils without any external components.

ULQ2801A 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:: -40°C ~ 105°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 18-DIP

ULQ2801A FAQ

1.How can I place an order for ULQ2801A through Aetrix?

Please submit a Request for Quotation (RFQ) for ULQ2801A 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 ULQ2801A reliable?

The price and inventory of ULQ2801A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for ULQ2801A is usually 5 days.

3.What payment methods are accepted for ULQ2801A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for ULQ2801A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for ULQ2801A?

ULQ2801A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your ULQ2801A 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 ULQ2801A?

For technical support, including ULQ2801A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your ULQ2801A requirements.

6.How does Aetrix verify that ULQ2801A is sourced from the original manufacturer or authorized distributors?

All ULQ2801A 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 ULQ2801A meets industry standards.

7.What is the process for return or replacement of ULQ2801A?

All ULQ2801A units undergo pre-shipment inspection (PSI). If there is an issue with ULQ2801A, 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 ULQ2801A part is unused and in its original packaging.

Return procedure for ULQ2801A:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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