In logic control applications requiring high current drive, establishing a reliable interface between low-voltage microcontrollers and high-voltage loads has always been a critical system design task. The ULN2803ADWR, an octal Darlington transistor array driver from Texas Instruments, provides robust switching control for loads such as relays, solenoid valves, stepper motors, and small lighting systems.
With its open-collector output, high voltage tolerance, built-in freewheeling diode, and integrated packaging features, the ULN2803ADWR has become a classic output driver solution widely used in industrial control, home appliances, electrical automation, and other occasions.
Product Overview
The ULN2803ADWR, part of the ULN2803A series, is housed in a SOIC-18 wide-body (DW) package and supplied in tape and reel (with an “R” suffix), making it suitable for automated SMT production lines. The chip integrates eight NPN Darlington pairs, each with high current drive capability and inductive load protection, making it suitable for driving medium-power loads from logic control devices such as microcontrollers, PLCs, and FPGAs.
Each channel has the following key features:
- Up to 500 mA continuous collector output current;
- Can withstand load voltage up to 50 V;
- Input compatible with TTL and CMOS logic levels;
- Each channel has a built-in freewheeling diode to adapt to inductive loads;
- The common COM pin is connected to the freewheeling path, and GND is connected to the logic and power ground.
Core parameter characteristics
Parameter | Specification |
Number of channels | 8 |
Output structure | Open-Collector NPN Darlington Pair |
Maximum output current (single channel) | 500 mA |
Maximum output voltage | 50 V |
Input logic compatibility | TTL/CMOS |
Built-in freewheeling diode | Yes (one per channel) |
Power pin | No dedicated VCC pin required; COM pin connects to the freewheeling diode return path |
Package Type | SOIC-18 DW (Wide Body SMD Package) |
Thermal resistance RθJA | 66.4 °C/W (JEDEC PCB conditions) |
Operating temperature range | –40°C to +85°C (industrial grade) |
Application advantages and engineering value
- Highly integrated multi-channel driving capability
Eight output channels support parallel control of multiple loads, significantly simplifying PCB design and control logic implementation. This makes it particularly suitable for scenarios such as multi-relay control boards, display driver boards, and buzzer/light arrays.
- Strong logical compatibility
The input is compatible with TTL/CMOS levels and can be directly driven by 3.3V/5V microcontrollers, FPGAs, and CNC systems, avoiding the need for additional level conversion devices.
- Inductive load protection capability
The integrated flyback diode in each channel can safely drive inductive loads such as relays, solenoid valves, and DC motors, preventing reverse voltage from damaging control devices.
- No logic power supply required
The device body does not require an additional VCC power supply, the input and output are completely based on GND as the common reference, and the COM pin is connected to the positive voltage of the freewheeling path (such as 12V, 24V), which greatly simplifies the wiring and power supply structure.
Typical application scenarios
Application | Description |
Output stage of PLC or MCU control board | Acting as a driver bridge from low voltage logic to medium power loads |
Multi-channel relay control board | Directly controls 8 12V/24V relay coils without external protection diodes |
Light/Buzzer/Display Control | Suitable for multi-digit digital tube segment selection, buzzer control or LED indicator array |
Solenoid valve group control | Parallel Control of Multi-channel Solenoid Valves in Industrial Pneumatic/Hydraulic Systems |
Stepper Motor/Fan Array | Configure a channel for each winding or motor to achieve independent control and protection |
Comparison of products in the same series
The Darlington driver array product line to which the ULN2803ADWR belongs also includes models with different package types and channel counts. The following is a comparison of the core parameters of several typical products to help engineers select the model based on system I/O resources and package requirements:
Model | Number of Channels | Output Structure | Input Logic | Maximum Output Current | Package | Application Positioning |
ULN2803ADWR | 8 | NPN open collector | TTL/CMOS | 500 mA | SOIC-18 Wide (SMD) | MCU/PLC drive, relay control |
8 | NPN open collector | TTL/CMOS | 500 mA | DIP-18 (through hole) | Educational platform, through-hole replacement design | |
7 | NPN open collector | TTL | 500 mA | SOIC-16 (SMD) | Stepper motor control, relay group drive (saving PCB space) |
Note : The above models are all members of the ULN series, with slight differences in channel number, package size, and input level, suitable for system designs with different cost and space constraints.
PCB Design Recommendations
- Input current limiting resistor: In long-distance transmission or in situations with strong electromagnetic interference, it is recommended to connect a current limiting resistor of about 1 kΩ in series at the input to enhance the signal’s anti-interference ability; this is not necessary in normal short-circuit applications.
- Freewheeling path design: Ensure that the COM pin is connected to the positive terminal of the load power supply to form a freewheeling path to prevent inductive spike voltage from damaging the output;
- Ground design: GND should be the common ground for logic and power. During layout, ensure a clear return path to avoid high-current ground loops.
- Heat dissipation assessment: When the total output current is greater than 300–400 mA, pay attention to the junction temperature rise corresponding to the device RθJA (66.4 °C/W). Appropriate copper foil or GND blocks should be reserved to assist in heat dissipation.
- Mixed-voltage design note: When using ULN2803ADWR to drive high-voltage (such as 24V) loads, ensure sufficient creepage distance between the logic terminals and the output area.
The ULN2803ADWR is a stable, mature, and highly adaptable multi-channel logic driver. It offers a cost-effective and low-complexity bridge between digital control systems and analog power outputs, making it especially well-suited for embedded applications that demand reliable drive capability, simplified wiring, and multi-load control.
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