Siemens 6ES5950-3AA51 | SIMATIC S5 PS951

The Siemens 6ES5950-3AA51 delivers stable DC power to your SIMATIC S5 backplane. This rack-mounted power supply replaces older PS951 units with higher efficiency. It converts 120/230V AC input into 5V and 24V DC outputs. Consequently, you can power both logic circuits and I/O modules from a single device.

Technical Specifications Overview

Parameter	Detailed Specification
Model	Siemens 6ES5950-3AA51
Category	SIMATIC S5 Power Supply Unit (PS951 series)
Input Voltage	120/230V AC (selectable, ±15%)
Input Frequency	50/60 Hz
Output Voltage 1	5V DC (nominal, 4.75V to 5.25V)
Output Current 1	20 A (maximum)
Output Voltage 2	24V DC (nominal for I/O)
Output Current 2	0.5 A (sensor supply)
Internal 24V Output	For backplane communication bus
Power Rating	120 W (total combined output)
Efficiency	Approximately 85% at full load
Hold-up Time	20 ms (at nominal input)
Dimensions	250 mm x 25 mm x 130 mm (single-width)
Weight	0.85 kg (850 grams)
Energy Storage	Internal electrolytic capacitors (no battery)
Protection Features	Short-circuit, overvoltage, overtemperature
Operating Temperature	0°C to 60°C

Functional Features and Power Delivery

The Siemens 6ES5950-3AA51 provides clean, regulated power for all rack components. You can select the input voltage using a recessed switch on the front panel. The 5V output supplies the CPU, memory, and communication modules reliably. Meanwhile, the 24V output powers sensors and input devices directly.

The unit includes a green LED for output status indication. A red LED lights up during overload or short-circuit conditions. Furthermore, the internal capacitors store enough energy for a 20 ms hold-up time. This feature allows the CPU to perform controlled shutdowns during brief power dips.

Installation and Connection Guidelines

First, set the voltage selector to match your local mains supply. Next, slide the Siemens 6ES5950-3AA51 into the leftmost slot of the S5 rack. Then, secure it using the top and bottom retaining screws. Finally, connect the AC mains wiring to the rear terminal block.

You must use a protective earth connection for safe operation. The unit requires adequate ventilation around its heatsink for cooling. Do not operate this power supply without a proper rack enclosure.

This power supply works with all SIMATIC S5 racks including 6ES5950-3AA51 compatible models. It replaces both PS951 and older PS950 units without modification. You can mix this unit with other power supplies for larger systems. The fanless design ensures silent operation in office environments.