Product Overview

The Allen Bradley 1769-PB4K CompactLogix DC Power Supply is a conformally coated power supply for CompactLogix 5370 L3x and L3y controller systems. It accepts a nominal 24V DC input and supplies power to the CompactLogix backplane and connected 1769 Compact I/O modules. Its output capacity is rated at 4 A on the 5V DC bus and 2 A on the 24V DC bus, making it suitable for compatible control assemblies that require both backplane voltage levels.

In a CompactLogix installation, the power supply supports the controller and its associated I/O modules by maintaining the electrical power required for processor operation, signal acquisition, and output control. The controller executes the application program, while the I/O modules exchange signals with field devices. The 1769-PB4K provides the power foundation for this arrangement; it does not perform the program execution or communication functions handled by the controller.

The 1769-PB4K is distinguished by its conformal coating. This protective layer adds resistance to certain environmental contaminants that may affect electronic assemblies. It does not make the power supply suitable for unrestricted exposure to moisture, corrosive chemicals, conductive dust, or temperatures outside its specified operating range. Appropriate enclosure design and installation practices remain necessary.

The power supply uses a 24V DC input, with a documented input range of 19.2 to 31.2V DC for the corresponding 1769-PB4 family. Its two output buses serve different electrical requirements within the Compact I/O system. The 5V DC bus supplies the backplane power required by compatible modules, while the 24V DC bus provides power for other supported module functions. The available current on each bus must be evaluated separately when planning the complete assembly.

The 1769-PB4K provides up to 4 A at 5V DC and 2 A at 24V DC according to the product family’s published specifications. These values are important when calculating the power demand of the controller and connected modules. The total system arrangement must also respect module distance ratings, placement requirements, and the maximum number of modules supported by the relevant controller configuration.

This model belongs to the 1769 power-supply family used with CompactLogix L3x and L3y platforms. In a compatible configuration, up to eight I/O modules can be placed on either side of the power supply, subject to each module’s distance rating and the system’s overall expansion limits. The exact module arrangement should be established using the applicable controller and I/O installation documentation rather than relying on the current rating alone.

The power supply is designed for installation on a DIN rail or suitable panel mounting arrangement. Correct mounting helps secure the assembly and supports the required electrical connections. The installation must allow access for wiring and maintenance while maintaining the clearances and environmental conditions specified for the Compact I/O system.

The 1769-PB4K is a DC-input device and must not be connected directly to an AC supply. The upstream DC power source must provide the required input range and enough current for the power supply and connected system. Correct polarity, grounding, conductor selection, and protection are essential to prevent damage and ensure stable operation.

The 1769-PB4K is the conformally coated counterpart of the standard 1769-PB4. When choosing between these models, engineers should consider the installation environment as well as electrical compatibility. The K suffix should not be treated as a different output-capacity class; the key electrical ratings remain those of the 4A/2A DC power-supply configuration.

Typical uses include CompactLogix machine controllers, local Compact I/O assemblies, packaging equipment, material-handling systems, and other industrial control panels built around compatible 1769 hardware. The supply should be selected according to the calculated backplane load, required input voltage, mounting arrangement, and environmental conditions.

The Allen Bradley 1769-PB4K provides DC power for compatible CompactLogix and Compact I/O systems, combining 4 A at 5V DC, 2 A at 24V DC, and conformally coated construction in a compact industrial power-supply module.

Technical Specifications

Product Features

• 24V DC input: Operates from a compatible industrial DC power source within the specified input range.
• 4 A at 5V DC: Supplies the 5V backplane bus for compatible CompactLogix and Compact I/O assemblies.
• 2 A at 24V DC: Provides the 24V output capacity specified for the power-supply family.
• Conformal coating: Adds protection against certain environmental contaminants affecting electronic assemblies.
• Compact I/O integration: Supports compatible 1769 modules when system power and distance requirements are met.
• Flexible mounting: Supports DIN rail or panel mounting within the applicable installation arrangement.
• Defined module placement limits: Supports module placement on either side of the supply subject to the system configuration.
• Industrial operating range: Supports operation within the specified temperature and environmental limits.
• Dedicated power-supply function: Provides electrical power to the system without replacing the controller’s logic or communication functions.

Working Principle

The 1769-PB4K converts the incoming 24V DC supply into the DC power required by the CompactLogix and Compact I/O backplane. Its internal power-conversion circuitry regulates the output buses so compatible modules can operate within their specified electrical requirements.

24V DC Input → Internal Power Conversion → 5V DC and 24V DC Outputs → Controller and I/O Modules

The upstream DC source supplies power through the power-supply input terminals. Before energizing the unit, the installer must verify the input voltage, polarity, wiring, and protective arrangements. An input outside the permitted range can cause incorrect operation or damage to the power supply and connected equipment.

After power is applied, the internal conversion circuitry produces the required DC output levels. The 5V DC bus supplies backplane power for compatible modules, while the 24V DC bus supports the additional power requirements defined for the system. The output buses have separate current ratings, so the load calculation must account for the demand on each bus rather than treating the power supply as one undifferentiated current source.

The power supply distributes the available power through the Compact I/O assembly. The connected controller and I/O modules draw current according to their individual requirements. Adding a module increases the load on the relevant bus, so the system designer must confirm that the total current demand remains within the supply’s published limits.

Module placement also affects the installation. Each 1769 module has a power-supply distance rating that limits how far it can be positioned from the supply. The physical arrangement must comply with these ratings and the controller’s expansion requirements. An assembly can have sufficient total current capacity and still be incorrectly configured if a module is placed beyond its permitted distance.

The 1769-PB4K does not execute control instructions or determine output states. Those tasks belong to the CompactLogix controller and the application program. Instead, the power supply maintains the electrical conditions required for the controller and I/O modules to operate. If the supply is overloaded or its input is unstable, the resulting power problems can affect the behavior of the connected control system.

The conformal coating adds a protective layer to the electronic assemblies. Its purpose is to improve resistance to certain contaminants, not to replace electrical isolation, grounding, enclosure protection, or proper wiring. Installation conditions must remain within the limits specified for the complete system.

During commissioning, engineers should check the input voltage, polarity, output loading, module arrangement, and controller status. If a power-related fault occurs, the diagnostic process should include the upstream DC source, wiring connections, load distribution, and the ratings of the connected modules.

Through regulated DC conversion and distribution, the 1769-PB4K supplies the electrical power required by compatible CompactLogix and Compact I/O assemblies.

Role in the Industrial Control Architecture

The 1769-PB4K occupies the power-distribution layer of a CompactLogix control system. It provides the DC output buses required by compatible controllers and local I/O modules, allowing the controller to execute its program and the I/O modules to interface with field devices.

24V DC Power Source → 1769-PB4K → CompactLogix Backplane and 1769 I/O Modules → Field Control System

The power supply supports the operation of the control hardware, while the controller and I/O modules perform the application-specific control and signal-handling functions.

Industrial Applications

Installation and Maintenance

1. Verify the catalog number: Confirm that the installed unit is the conformally coated 1769-PB4K and that the application requires the 4A/2A DC power-supply configuration.
2. Check the input supply: Confirm that the upstream source provides 24V DC nominal voltage within the specified input range.
3. Observe input polarity: Verify the positive and negative connections before energizing the module to prevent wiring errors.
4. Calculate the output load: Check the combined current requirements of the controller and connected modules on both the 5V DC and 24V DC buses.
5. Confirm module placement: Ensure that each connected 1769 module is within its power-supply distance rating and that the assembly follows the system’s expansion requirements.
6. Install the unit securely: Mount the power supply on the permitted DIN rail or panel arrangement and ensure that it is firmly seated.
7. Inspect wiring and terminals: Check conductor size, terminal condition, and connection security in accordance with the applicable installation instructions.
8. Check protective arrangements: Confirm that upstream circuit protection and grounding meet the requirements of the power source and installed control system.
9. Maintain suitable environmental conditions: Keep the module within the specified temperature and humidity limits and use an appropriate enclosure for the installation.
10. Verify startup behavior: After energizing the system, check the controller and I/O module status to confirm that the assembly operates normally.
11. Investigate power-related faults: If modules reset or fail to operate, check the DC input, output loading, wiring, and module arrangement before replacing components.
12. Document system changes: Update the module inventory, power-load calculation, wiring records, and maintenance documentation whenever the Compact I/O assembly is modified.

Related Components

Recommended Related Models

Key Advantages

• Supplies the 5V DC and 24V DC buses required by compatible CompactLogix systems.
• Provides 4 A at 5V DC and 2 A at 24V DC.
• Uses a conformally coated construction for additional protection against certain contaminants.
• Supports compatible 1769 Compact I/O configurations.
• Allows DIN rail or panel mounting within the specified installation arrangement.
• Provides a dedicated power-supply solution for CompactLogix L3x and L3y platforms.

Technical FAQs

How should the 1769-PB4K be sized for a CompactLogix I/O assembly?

Calculate the current demand on the 5V DC and 24V DC buses separately, using the published requirements of the controller and each connected module. Also check module distance ratings and placement restrictions because electrical capacity alone does not determine whether an assembly is valid.

Can the 1769-PB4K be connected directly to an AC power source?

No. The 1769-PB4K is a DC-input power supply designed for a nominal 24V DC source. An appropriate DC power source must be used, with input voltage and polarity verified before energizing the system.

What is the practical difference between the 1769-PB4K and 1769-PB4?

The K suffix identifies the conformally coated version. Both models belong to the 4A/2A DC power-supply class, but the coated version is intended for applications where the additional protection is appropriate. The coating does not remove the need for proper enclosure design and environmental control.

What should be checked if the controller or I/O modules experience intermittent power problems?

Check the stability of the incoming 24V DC supply, input wiring, terminal connections, and total current demand on both output buses. Also verify that module placement complies with the system requirements and that the power supply is operating within its specified environmental limits.