Allen-Bradley 1769-PB2 PLC Power Supply Module – CompactLogix 1769 Series

Allen-Bradley 1769-PB2: 24VDC Bus Power Supply for CompactLogix 1769 I/O Systems

The Allen-Bradley 1769-PB2 is a dedicated 24VDC-input bus power supply engineered for the CompactLogix 1769 distributed I/O platform. Its primary function within a control loop is to convert an unregulated 24VDC field supply into a stable, regulated 5VDC backplane bus rail that powers all downstream 1769 I/O modules in the local bank. Without a correctly rated bus power supply, the deterministic scan cycle of the CompactLogix controller cannot be maintained — voltage droop on the 5VDC rail directly causes module health faults and forces the CPU into a faulted program state. The 1769-PB2 therefore occupies a structurally critical position: it is the sole energy source for every digital and analog I/O module mounted to its right, up to the bank terminator or the next power supply in a multi-bank configuration.

Unlike generic DIN-rail switching power supplies, the 1769-PB2 integrates directly into the 1769 bus connector system. Its right-side bus connector carries both the 5VDC regulated output and the 24VDC pass-through rail, allowing downstream modules to draw field-side power without additional wiring. This architecture eliminates the need for separate field-power distribution terminals for each module, reducing panel wiring density and the associated risk of loose terminations in high-vibration environments.

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Technical Parameters

Hardware Logical Analysis

The 1769-PB2 employs a non-isolated DC-DC conversion topology internally, accepting the 18–32VDC input range and regulating it to a tight 5.0VDC ±2% output. The wide input tolerance is deliberate: in field environments where 24VDC supply rails experience transient sag during motor starts or solenoid switching, the 1769-PB2 maintains regulation without nuisance trips. The 6VDC of headroom below nominal (18V minimum) accommodates worst-case cable voltage drop across long panel runs.

EMC Design: The module’s PCB layout incorporates a common-mode choke on the 24VDC input lines, suppressing conducted emissions in the 150kHz–30MHz band per EN 55011 Class A limits. The metal housing acts as a Faraday shield for radiated emissions, and the bus connector ground pin provides a low-impedance chassis bond that ties the 1769 bank ground plane to the panel earth. In environments with variable-frequency drives (VFDs) or high-current contactors, this ground architecture prevents common-mode noise from coupling into the 5VDC logic rail — a failure mode that manifests as intermittent I/O module communication errors rather than hard faults, making it particularly difficult to diagnose without proper grounding.

Overcurrent and Short-Circuit Protection: The 5VDC output is electronically current-limited. On a sustained overload (bus current demand exceeding 2.0A), the module enters a hiccup-mode protection cycle: it shuts down the output, waits approximately 100ms, then attempts restart. If the overload persists, it cycles continuously. This behavior is logged as a module health fault in the CompactLogix controller’s I/O tree, allowing the PLC program to detect the condition via the module’s fault status bits without requiring external current monitoring hardware.

24VDC Pass-through Architecture: The right-side bus connector carries the 24VDC input rail directly to downstream modules that require field-side power (e.g., 1769-OB16 sourcing output modules). This pass-through is not regulated — it mirrors the input voltage. Modules that draw field power from the bus therefore see the same voltage variations as the input supply. Engineers specifying the 1769-PB2 must account for this when calculating worst-case module input voltage for analog modules with tight reference accuracy requirements.

Thermal Management: The module is rated for 0–60°C ambient without derating. At maximum 2.0A bus load, internal dissipation is approximately 4.5W. In sealed enclosures without forced airflow, the thermal rise from ambient to module case temperature must be calculated using the enclosure’s thermal resistance. Rockwell’s panel thermal design guidelines recommend a minimum 25mm clearance above and below the 1769 bank for natural convection.

System Integration Benefits

• Deterministic bus voltage stability: The regulated 5VDC output maintains ±2% tolerance across the full load range (0–2.0A), ensuring that all connected 1769 modules operate within their specified logic supply window and do not introduce scan-cycle jitter caused by brownout conditions.
• Fault transparency via controller I/O tree: Overcurrent and under-voltage conditions on the bus are surfaced as module health faults in the CompactLogix I/O configuration tree, enabling ladder logic or structured text routines to respond programmatically — for example, triggering a safe-state output sequence before a full controller fault.
• Reduced panel wiring complexity: The integrated 24VDC pass-through eliminates the need for a separate field-power terminal block row for each I/O module, reducing the number of field wiring terminations by up to 30% in a typical 16-module bank.
• Multi-bank scalability: A single CompactLogix controller can support multiple 1769 banks, each with its own 1769-PB2. The power supply’s right-side bus connector allows banks to be extended without rewiring the controller backplane, supporting modular machine designs where I/O count grows incrementally.
• Wide input voltage tolerance for field reliability: The 18–32VDC input range accommodates 24VDC supply sag during high-inrush events (motor starts, solenoid banks), preventing nuisance power supply faults that would otherwise halt production.
• EMC-hardened design for noisy industrial environments: Common-mode input filtering and chassis-bonded housing suppress conducted and radiated interference from VFDs, servo drives, and high-current switching loads, maintaining signal integrity on the 5VDC logic bus.
• Hot-swap compatible within CompactLogix platform: The 1769-PB2 supports the CompactLogix platform’s module replacement procedures, allowing maintenance teams to follow documented swap protocols without full system shutdown in appropriate configurations.
• Standardized certification footprint: UL 508, CE (EN 61131-2), cUL, and C-Tick certifications cover North American, European, and Australian regulatory requirements, allowing a single SKU to be deployed across global machine variants without re-certification of the control panel.
• Predictable lifecycle and spare parts availability: As a current Rockwell Automation catalog item, the 1769-PB2 has a defined product lifecycle with published migration paths, enabling maintenance planners to stock spares with confidence in long-term availability.
• Compact form factor preserves panel space: The 1769 module-width form factor integrates flush with the I/O bank, avoiding the additional panel depth and width required by external DIN-rail power supplies with separate bus wiring.

Quality Assurance & Global Logistics

Every 1769-PB2 unit supplied by siemensplc.com is sourced from verified supply channels with full traceability. Pre-shipment inspection covers visual examination, label and date-code verification, and functional power-on testing. Units are packed in anti-static bags with humidity indicator cards and shipped in double-wall corrugated cartons with foam cushioning rated for the module’s 15g shock specification.

Our logistics hub is located in Xiamen, China, with direct access to international express carriers (DHL, FedEx, UPS) and sea freight consolidators. Standard express delivery to Europe and North America is 3–5 business days. South and Southeast Asia destinations typically receive shipments within 2–3 business days. All shipments include tracking numbers issued within 24 hours of dispatch. For project orders requiring multiple line items, consolidated shipment with a single commercial invoice and packing list is available on request.

A 12-month warranty from shipment date covers manufacturing defects. Certificate of Conformance (COC) and inspection reports are provided at no additional charge. For projects requiring third-party inspection or specific export documentation, contact our team in advance to arrange.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
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Location: Xiamen, China
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