Application Scenarios
Consider a food and beverage plant where the entire control panel is powered from a centralized 24 V DC distribution system. The plant standard calls for 24 V DC inputs on all power supplies, both to simplify the electrical design and to support the plant’s uninterruptible power supply (UPS) strategy—when the mains fail, the 24 V DC bus is backed up by a battery string, so every control panel rides through the outage without a separate UPS at each cabinet.
The 1756-PB72 fits this architecture precisely. It accepts the 24 V DC from the plant distribution, handles the 18–32 V DC input range comfortably even when the battery bus sags during a prolonged outage, and delivers clean, isolated power to the ControlLogix backplane. When one supply failed after eight years of continuous operation, the maintenance team replaced it hot—without removing the chassis from the panel or disturbing a single I/O wire. The line was back online within the shift, and the plant never lost a batch. For this customer, the 1756-PB72 is not a commodity part; it is the interface between the plant’s power strategy and the control system’s uptime.
Parameter
| Parameter | Value / Description |
|---|---|
| Product Model | Allen-Bradley 1756-PB72 (Series A) |
| Manufacturer | Rockwell Automation / Allen-Bradley (USA) |
| Product Category | ControlLogix Chassis Power Supply |
| Input Voltage | 24 V DC nominal (18–32 V DC range) |
| Input Frequency | 47–63 Hz |
| Output Power | 72 W |
| Backplane Output | 1.5 A @ 5.1 V DC, 19.5 A @ 1.2 V DC, 1 A @ 24 V DC |
| Isolation Voltage | 30 V AC / 5 V DC (input to output) |
| Operating Temperature | 0 °C to +60 °C (32 °F to 140 °F) |
| Storage Temperature | −40 °C to +85 °C (−40 °F to 185 °F) |
| Enclosure / Protection | None (open-style), IP20 when installed in cabinet |
| Mounting | DIN rail or panel mount |
| Slot Requirement | None (mounts on chassis, does not occupy a slot) |
| Hot-Swappable | Yes |
| Dimensions / Weight | 132 × 35 × 120 mm; 0.6 kg (1.32 lb) |
Technical Principles and Innovative Values
Innovation Point 1 – DC Input for Simplified Panel Design: The 1756-PB72 accepts a 24 V DC input, making it ideal for panels that already have a 24 V DC distribution system or for applications where a DC input is preferred for safety or redundancy. This eliminates the need for a separate AC-to-DC converter in the panel and allows the ControlLogix system to be powered directly from the plant’s 24 V DC bus.
Innovation Point 2 – Hot-Swappable Design: Unlike many power supplies that require a system shutdown for replacement, the 1756-PB72 is hot-swappable. This means a failed supply can be replaced without powering down the chassis or removing it from the panel, dramatically reducing downtime in critical applications where every minute of outage costs money.
Innovation Point 3 – Wide Input Voltage Range: The 18–32 V DC input range provides substantial headroom for variations in the plant’s 24 V DC supply. This is particularly valuable when the DC bus is battery-backed: during a prolonged outage, the battery voltage sags as it discharges, and a supply with a narrow input range would drop out while the 1756-PB72 continues to deliver stable backplane power.
Innovation Point 4 – High-Current 1.2 V Backplane Rail: The 19.5 A at 1.2 V output is the workhorse rail that powers the logic circuitry of the installed modules. This high-current capability is what allows the 1756-PB72 to support a fully loaded chassis with multiple processors, I/O modules, and communication modules without voltage sag or overheating.
Innovation Point 5 – 30 V AC / 5 V DC Isolation: The isolation between the input and output sides of the 1756-PB72 protects the control system from ground loops, transients, and electrical noise on the plant power bus. This is especially important in industrial environments where the 24 V DC distribution may be shared with contactors, solenoids, and other noisy loads.
