Allen-Bradley 1771-OBN​ PLC-5 32-Point 24V DC Sourcing (PNP) Transistor Output Module – 1771 Series Digital DC Output Card

Product Overview

The Allen-Bradley 1771-OBN​ is a 32-point, 10–30 V DC sourcing (PNP) transistor digital output module that belongs to Rockwell Automation’s classic 1771 I/O family, designed for use in PLC-5, PLC-3 (with adapter), and SLC 500 1771 rack configurations when interfaced through the appropriate processor or remote I/O adapter. The Allen-Bradley 1771-OBN​ provides thirty-two individually controlled NPN/PNP-style sourcing outputs organized into four electrically isolated groups of eight points each (Groups 0–3), with each group requiring a separate external DC common connection to the positive rail of the 24 V DC field supply. When an output is energized, the Allen-Bradley 1771-OBN​ sources current from the group’s +V terminal through the load to 0 V DC, making it the natural complement to sinking (NPN) input devices and a standard choice for driving 24 V DC relay coils, solenoid valves, indicator beacons, and interposing contacts in North American legacy automation installations.Each output point on the Allen-Bradley 1771-OBN​ is rated for 0.5 A continuous at 60 °C with a 2.0 A surge rating for 10 ms, and the module incorporates a 4.0 A slow-blow fuse per output group (user-replaceable) to protect against short-circuit conditions. Optical isolation of 1500 V AC (1 min) is provided between the output circuits and the 5 V DC logic backplane, safeguarding the PLC-5 processor from field-side transients. The module draws approximately 330 mA from the 1771 backplane 5 V DC supply and communicates output state via the rack’s serial I/O bus scanned by the processor. Front-panel LEDs display both individual point activity and group fuse integrity, allowing maintenance staff to identify open fuses or active outputs without test equipment. With its high point density, group isolation, and proven robustness in continuous-process and heavy-discrete environments, the Allen-Bradley 1771-OBN​ remains a widely specified spare and replacement module for plants maintaining PLC-5-based control systems where modernization has not yet been completed.

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Description

 

Technical Specifications

Product Model | 1771-OBN (also 1771-OBN/B, 1771-OBN/C)Manufacturer | Allen-Bradley / Rockwell AutomationProduct Type | 1771 Series 24 V DC Sourcing (PNP) Transistor Digital Output ModuleNumber of Outputs | 32 points (4 isolated groups × 8 points)Output Type | Sourcing (PNP) Solid-State Transistor (high-side switch to +V DC)Operating Output Voltage Range | 10 … 30 V DC (24 V DC nominal)Current per Output Point (max continuous) | 0.5 A @ 60 °C (1.0 A de-rated at lower temps per group limit)Current per Output Group (max) | 4.0 A (protected by 4 A slow-blow fuse per group)Surge Current per Point | 2.0 A for 10 ms, repeatable every 2 sON-State Voltage Drop (max) | 1.5 V DC @ 0.5 AOFF-State Leakage Current (max) | 1.0 mA @ 30 V DCTurn-ON Delay (typ / max) | 0.25 ms / 1.0 msTurn-OFF Delay (typ / max) | 0.25 ms / 1.0 msBackplane Current Draw | 330 mA @ 5 V DC; 0 mA @ 24 V DC (field supply not drawn from backplane)Isolation (Field to Backplane Logic) | 1500 V AC for 60 s; 750 V working (reinforced optical isolation)Fusing | One 4 A, 250 V, Time-Delay (Slow-Blow) fuse per output group; user-replaceableIndicators | 32 individual Output Point LEDs (green); 4 Group Fuse Status LEDs (amber); Module Active LEDTermination Style | 1771-series pivoting wiring arm with screw terminals (e.g., 1771-WN or 1771-WH)Slot Width | 1 standard 1771 slot (approx. 2.75 in / 69.9 mm)Operating Temperature | 0 … +60 °C (+32 … +140 °F)Storage Temperature | -40 … +85 °CHumidity (non-condensing) | 5 % – 95 % RHEnclosure Rating | IP20 (install inside control cabinet / 1771 enclosure)Certifications | UL Listed, cUL, CE Marked, RoHS compliant (later revisions)

Main Features and Advantages

High-density four-group sourcing architecture: The Allen-Bradley 1771-OBN​ packs 32 sourcing DC outputs into a single 1771 slot—among the highest-density DC output options in the 1771 family—while separating them into four independently fused, electrically isolated commons. This lets you power different machine zones, safety-rated sections, or segregated process areas from distinct 24 V DC supply feeds within one module, containing ground faults and simplifying troubleshooting. Each group’s +V DC terminal is wired to the positive of an external 24 V DC supply; the module sinks the return through the load to 0 V externally.Per-group fusing with front-panel indication: Unlike many generic I/O cards, the Allen-Bradley 1771-OBN​ includes a user-replaceable 4 A slow-blow fuse on each of the four output groups. If a short circuit occurs on one group, only that group’s fuse opens while the remaining three groups continue operating. An amber LED per group illuminates when the associated fuse is blown, so technicians can instantly see which group needs attention without probing with a multimeter. Spare fuses are standard 4 × 250 mm, 4 A, time-delay glass cartridge types.Optical isolation and transient protection: Reinforced isolation (1500 V AC tested) between the 1771 backplane 5 V logic and the 10–30 V DC field side protects the PLC-5 processor from voltage spikes, inductive kickback, or accidental cross-wiring on the output side. Although the Allen-Bradley 1771-OBN​ has internal transient suppression, best practice still dictates the use of flyback diodes across DC inductive loads (solenoids, relay coils) to prolong output transistor life.Legacy system compatibility & diagnostics: The Allen-Bradley 1771-OBN​ is fully recognized by PLC-5 processors (1771-PLC5/, 1785-Lxx), 1771-ASB remote I/O adapters, and compatible 1771 I/O scanners. Configuration is handled entirely through the PLC-5 programming software (RSLogix 5) by assigning the module’s slot position and word address—no DIP switches are required on the module itself. Thirty-two green point LEDs mirror the logic state of each output word bit, giving immediate visual confirmation of commanded output status at the rack.Sourcing (PNP) output suitability: The Allen-Bradley 1771-OBN​ sources current—i.e., when ON, the output terminal is switched to the group’s +V DC common. This is the conventional wiring method in North American 24 V DC control panels where NPN (sinking) inputs are common on the input side. Ensure your field devices are compatible with a sourcing output; if sinking (NPN) outputs are required, the 1771-ODD or 1771-OBS series should be considered instead of the Allen-Bradley 1771-OBN.

Application Field

The Allen-Bradley 1771-OBN​ is principally deployed in legacy PLC-5-based control systems that continue to operate in refineries, power generation auxiliaries, pulp & paper mills, metal rolling mills, water/wastewater treatment plants, and large-scale batch process facilities. In these environments, the Allen-Bradley 1771-OBN​ drives 24 V DC interposing relay coils that in turn energize AC motor starter contactors for pumps, compressors, agitators, and conveyors. It also directly switches 24 V DC solenoid-operated valves used in process skids—such as boiler fuel-gas shutoff, cooling-water diverter valves, and chemical-additive injection solenoids—where the high point count and grouped commons simplify distribution panel wiring.Discrete-manufacturing lines originally commissioned with PLC-5 controllers—automotive body shops, stamping presses, large assembly lines—use the Allen-Bradley 1771-OBN​ to activate pneumatic clamp solenoids, part-eject cylinders, stack lights (beacons & audible alarms), and guard-door release magnets across multiple machine stations, with each of the four groups mapped to a different cell or safety zone. In bulk-material handling and mining conveyor systems, the Allen-Bradley 1771-OBN​ operates local start/stop pushbutton indicator lamps, belt-alignment alarm beacons, and chute-jam annunciators fed from distributed 24 V DC power supplies. Because the module is backward-compatible with the extensive installed base of 1771 I/O racks (1771-A1B, A2B, A3B, A4B), the Allen-Bradley 1771-OBN​ is equally valuable as a direct replacement spare during life-extension programs, keeping mature assets running while longer-term migration to ControlLogix / Studio 5000 is planned. Care should be taken to confirm the PLC-5 program’s I/O image table mapping matches the physical slot position of the Allen-Bradley 1771-OBN, as 1771 I/O addressing is slot-dependent in PLC-5 architecture.

Contact Us WhatsApp / Wechat：+86 18150087953
Phone：+86 18150087953
Email：sales@cxplcmro.com

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