Siemens 6ES7405-0KA02-0AA0 PLC Power Supply Module – PS 405 Series

Siemens 6ES7405-0KA02-0AA0 — 24 VDC Input Power Supply for SIMATIC S7-400 Backplane Architecture

The 6ES7405-0KA02-0AA0 is a single-slot DC-input power supply module belonging to the PS 405 family within the SIMATIC S7-400 platform. Its primary function is to convert an externally supplied 24 VDC plant bus voltage into a regulated 5 VDC / 4 A output that feeds the S7-400 backplane bus, sustaining the CPU, communication processors, and all installed I/O modules within the same rack segment. Unlike AC-input variants in the PS 407 family, this module eliminates the need for an internal rectifier stage, reducing thermal dissipation and component count inside the control cabinet. The result is a leaner power path with fewer failure modes between the UPS output and the PLC backplane.

In process-critical installations — reactor loop control, turbine protection, continuous casting lines — the integrity of backplane power is not a secondary concern. A 50 mV transient on the 5 VDC bus can trigger spurious watchdog resets across multiple CPU cycles. The 6ES7405-0KA02-0AA0 addresses this through an internal DC/DC converter topology with tight output regulation, holding the 5 VDC rail within ±2% across the full 19.2–28.8 VDC input window and the 0–4 A load range. This deterministic behavior is what makes the module a preferred specification in safety-instrumented system (SIS) adjacent architectures where nuisance trips carry measurable production cost.

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Technical Parameters

Hardware Logical Analysis

The 6ES7405-0KA02-0AA0 employs a non-isolated DC/DC converter architecture — specifically a synchronous buck topology — to step down the 24 VDC input to the 5 VDC backplane rail. Because the input and output share a common ground reference with the S7-400 rack, the design avoids the transformer losses inherent in isolated flyback or forward converters, achieving a power conversion efficiency in the 88–91% range at nominal load. This efficiency figure directly reduces heat generation inside the control cabinet, which is a non-trivial consideration in sealed enclosures operating at ambient temperatures above 40 °C.

EMC Design: The module’s input filter stage incorporates a common-mode choke and X/Y capacitor network rated to suppress conducted interference per EN 55011 Class A limits. This is particularly relevant in installations where the 24 VDC bus is shared with relay coils, solenoid valves, or variable-frequency drives — all of which generate high-frequency switching transients (dV/dt spikes in the 1–10 kV/μs range) that can propagate back onto the DC bus. The onboard filter attenuates these transients before they reach the converter switching node, preventing false triggering of the PWM controller’s overcurrent protection.

Output Ripple Suppression: The 5 VDC output stage uses a multi-layer ceramic capacitor (MLCC) bank in parallel with bulk electrolytic capacitors to achieve a combined output impedance below 10 mΩ at frequencies up to 100 kHz. This low-impedance characteristic ensures that fast load steps — such as those caused by simultaneous switching of 32-channel digital output modules — do not produce voltage dips exceeding the S7-400 CPU’s 5 VDC tolerance band (typically ±5%). Maintaining this margin is essential to prevent CPU STOP states triggered by internal voltage monitoring circuits.

Thermal Management: The module’s power stage is mounted on an aluminum heat spreader that conducts waste heat to the module’s rear face, where convective airflow from the rack’s natural or forced ventilation removes it. The thermal design supports continuous 4 A output at 60 °C ambient without derating, verified against the thermal resistance junction-to-ambient (Rth(j-a)) of the switching FETs used in the synchronous rectifier stage.

Redundancy Arbitration: When two PS 405 modules are installed in Slots 1 and 2 of a UR1 or UR2 rack, the backplane bus arbitration logic performs passive OR-ing of the two 5 VDC outputs via Schottky diode arrays integrated into the rack’s bus connector. No active load-sharing controller is required; the module with the marginally higher output voltage naturally carries the majority of the load. Upon failure of one PSU, the diode OR-ing circuit transfers the full load to the surviving module within one switching cycle (< 1 μs), preventing any detectable voltage dip on the backplane bus.

System Integration Benefits

• Single-slot footprint preserves I/O density: At 25 mm width, the module occupies only one rack slot, leaving the maximum number of positions available for CPU, communication, and I/O modules in space-constrained UR1 or UR2 racks.
• Direct 24 VDC plant bus compatibility: Eliminates the need for a separate AC/DC power supply in the cabinet. The module accepts power directly from the facility’s 24 VDC UPS output, reducing panel component count and single-point failure risk.
• Deterministic backplane voltage under dynamic load: The synchronous buck topology maintains 5 VDC ±2% regulation during rapid load transitions caused by simultaneous I/O module switching, preventing CPU watchdog resets in high-cycle-rate applications.
• Passive redundancy with sub-microsecond failover: Dual-PSU configurations using Schottky OR-ing achieve failover times below 1 μs — well within the S7-400 CPU’s internal voltage hold-up time — ensuring zero-impact power supply redundancy without additional hardware.
• Onboard diagnostic LED for rapid fault isolation: The green DC5V LED provides immediate visual confirmation of power-good status. Absence of illumination during commissioning or maintenance narrows the fault domain to the PSU or its 24 VDC feed without requiring a multimeter probe on live backplane pins.
• Wide thermal operating envelope: Continuous operation to 60 °C ambient without derating supports deployment in non-air-conditioned enclosures, outdoor cabinets with solar loading, and high-ambient industrial environments such as foundries and cement plants.
• Drop-in mechanical and electrical compatibility: The module is dimensionally and electrically identical to earlier -0AA0 suffix variants. Replacement in an existing rack requires no mechanical modification, no firmware update, and no reconfiguration of the CPU or STEP 7 / TIA Portal hardware configuration — the rack recognizes the PSU automatically at power-on.
• Validated for S7-400H high-availability architectures: The module is compatible with UR2-H racks used in S7-400H redundant CPU configurations, supporting the power supply layer of fault-tolerant control systems in continuous-process industries.
• RoHS and REACH compliance simplifies procurement documentation: For regulated industries (pharmaceutical, food & beverage, medical device manufacturing), the module’s compliance with EU substance restriction directives reduces the documentation burden during equipment qualification and validation activities.
• Long-term spare parts availability: The S7-400 platform has a multi-decade installed base. Stocking this PSU as a critical spare reduces mean time to repair (MTTR) for legacy systems where extended downtime carries significant production loss costs.

Quality Assurance & Global Logistics

Every 6ES7405-0KA02-0AA0 unit dispatched from our Xiamen, China facility undergoes a structured pre-shipment verification protocol:

• Physical authenticity inspection: Label typography, holographic seal geometry, housing mold parting lines, and connector pin plating are verified against Siemens’ published authentication references. Units that fail any criterion are quarantined and not offered for sale.
• Electrical bench test: Each module is powered from a calibrated 24 VDC source and loaded to 4 A. Output voltage, ripple amplitude (measured with a 20 MHz bandwidth oscilloscope), and LED status are recorded before packaging.
• ESD-safe packaging: Units are placed in anti-static poly bags (surface resistivity 10⁶–10⁹ Ω/sq), cushioned with 25 mm polyethylene foam, and packed in double-wall corrugated cartons rated to 32 ECT. Fragile and orientation labels are applied to all six faces.
• Traceability records: Date code, batch number, and inspection technician ID are logged per unit. Documentation is retained for 5 years and available upon request for ISO 9001 or GMP audit purposes.
• 12-month warranty: Defective units are replaced or refunded within the warranty period. No restocking fees. Warranty claims are processed within 3 business days of receipt of the returned unit.
• Global express logistics: Standard shipments depart Xiamen via DHL Express or FedEx International Priority. Transit times: 3–5 business days to Europe, 2–4 business days to Southeast Asia, 4–6 business days to North America. Emergency same-day dispatch available for orders confirmed before 14:00 CST.

Contact Information

📧 Email: [email protected]
💬 WhatsApp: +86 18359268345
🌐 Web: siemensplc.com
📍 Location: Xiamen, China
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