Allen-Bradley 1756 ControlLogix Modules: 1756-PA75/B Power Supply

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

Q: How are RFQ terms confirmed?
A: Quantity, required condition, documentation needs, destination and sourcing route are confirmed during RFQ review before quotation.

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform was introduced by Rockwell Automation / Allen-Bradley in 1997 as a successor to the PLC-5 and SLC 500 families. The architecture is defined by the 1756 backplane, which uses a high-speed serial bus to interconnect controller, I/O, communication, and motion modules within a single chassis. Key architectural milestones include:

Generation 1 (1997–2004): Original 1756-L1 through 1756-L55 controllers with 256KB to 7.5MB user memory. Backplane communication at 100Mbps. Power supplies limited to PA72 and PB72 variants. EtherNet/IP support via 1756-ENBT bridge module.

Generation 2 (2004–2012): Introduction of the 1756-L6x controller family with expanded memory (up to 32MB), integrated USB programming port, and support for Integrated Motion on EtherNet/IP. Power supply line expanded to include the 1756-PA75 (75W AC) and 1756-PB75 (75W DC) for higher-density chassis configurations. Series B revisions introduced across the power supply range.

Generation 3 / ControlLogix 5580 (2016–present): The 1756-L8x series (5580 controllers) introduced dual-port EtherNet/IP, CIP Security, and up to 40MB user memory. Backward-compatible with existing 1756 chassis and I/O modules, including the 1756-PA75/B, ensuring long-term investment protection for installed base systems.

Compatibility note: All 1756 Series B power supplies (PA75/B, PB75/B, PA72/B, PB72/B) are compatible with both legacy L6x controllers and current L8x (5580) controllers within the same 1756 chassis. No firmware changes are required when replacing power supply modules across series revisions.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Power Supply Modules

Controller Modules (CPU)

1756-L71: ControlLogix 5571 controller, 2MB user memory, standard processing speed.
1756-L72: ControlLogix 5572 controller, 4MB user memory, dual EtherNet/IP ports.
1756-L73: ControlLogix 5573 controller, 8MB user memory, high-capacity applications.
1756-L74: ControlLogix 5574 controller, 16MB user memory, large-scale process control.
1756-L75: ControlLogix 5575 controller, 32MB user memory, maximum capacity L7x platform.
1756-L81E: ControlLogix 5580 controller, 3MB user memory, CIP Security, dual-port EtherNet/IP.
1756-L83E: ControlLogix 5580 controller, 10MB user memory, current-generation flagship.

Digital I/O Modules (DI / DO)

1756-IB16: 16-point 24V DC sourcing digital input module.
1756-IB32: 32-point 24V DC sourcing digital input module, high-density.
1756-OB16E: 16-point 24V DC electronically fused digital output module.
1756-OB32: 32-point 24V DC digital output module, high-density.
1756-IA16: 16-point 120V AC digital input module for legacy AC field devices.
1756-OA16: 16-point 120V AC digital output module.

Analog I/O Modules (AI / AO)

1756-IF16: 16-channel analog input module, 4–20mA / 0–10V, 16-bit resolution.
1756-OF8: 8-channel analog output module, 4–20mA / ±10V, 16-bit resolution.
1756-IF8: 8-channel analog input module, differential inputs, high-accuracy process measurement.

Communication & Network Adapter Modules

1756-EN2T: Single-port EtherNet/IP communication module, 100Mbps.
1756-EN2TR: Dual-port EtherNet/IP module with Device Level Ring (DLR) support.
1756-CN2: ControlNet communication module for deterministic network topologies.
1756-DNB: DeviceNet scanner module for legacy field device networks.
1756-DHRIO: Data Highway Plus / Remote I/O communication module for PLC-5 migration.

Sourcing Hard-to-Find & Obsolete 1756 ControlLogix Parts

The 1756 ControlLogix platform spans nearly three decades of production. Modules introduced in the late 1990s and early 2000s — including the 1756-PA72/B, 1756-PB72/B, 1756-L55, 1756-L60M03SE, and first-generation 1756-ENBT — have reached end-of-life (EOL) status with Rockwell Automation. Replacement parts are no longer available through standard distribution channels.

For facilities operating 1756 systems beyond their planned lifecycle — common in nuclear, chemical, and water treatment applications where control system replacement projects span 5–15 years — DriveKNMS provides long-term maintenance supply agreements (LTMSA) that guarantee module availability for defined periods, with optional testing and certification documentation.

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates at 100Mbps with strict timing requirements for module communication. Power supply modules such as the 1756-PA75/B must deliver stable DC output within ±2% tolerance across the full load range to prevent backplane faults and controller diagnostic errors. DriveKNMS applies the following test protocol to all 1756 power supply and I/O modules prior to shipment:

Controller Modules (CPU): Firmware version verification and documentation. Memory read/write cycle test across full user memory range. EtherNet/IP port connectivity and throughput test. Battery voltage check (where applicable). Backplane communication test via 1756 chassis test fixture.

I/O Modules: Point-by-point channel verification for all DI, DO, AI, and AO channels. Isolation resistance test between field-side and backplane-side circuits. Calibration verification for analog modules against NIST-traceable reference standards.

Q: How is condition confirmed before quotation?
A: Available condition, photos, test records and documentation are checked according to the requested model and sourcing channel before a formal RFQ response.