Siemens 6ES5955-3NA12 Power Supply

The 6ES5955-3NA12 supplies regulated DC power to SIMATIC S5 racks. This unit converts 24V DC input into a stable 5V DC output. It provides 4A of continuous current for backplane and module operation.

Key Technical Specifications

Parameter	Value
Input Voltage	24V DC ±20%
Output Voltage	5V DC ±2%
Output Current	4 A continuous
Output Power	20 W maximum
Efficiency	91% at full load
Ripple & Noise	< 50 mV peak-to-peak
Hold-Up Time	100 ms (from nominal input)
Overload Protection	Current limiting at 5.5A
Short-Circuit Protection	Automatic recovery
Board Dimensions	25.0 cm x 8.0 cm x 3.5 cm
Weight	1.2 kg (2.65 lbs)
Component Count	68 discrete components
Energy Storage	2200 µF output capacitance
Operating Temperature	0°C to 60°C

Physical Dimensions and Component Layout

This supply measures 25.0 cm in length and 8.0 cm in width. Its total height reaches 3.5 cm including all components. 6ES5955-3NA12 weighs 1.2 kg for secure rack mounting. You will find 68 discrete components on a two-layer PCB.

Moreover, the unit integrates a 2200 µF output capacitor bank. This bank stores energy for a 100 ms hold-up time. It also filters switching noise from the DC-DC converter.

Power Conversion Topology

A step-down switching regulator performs the DC-DC conversion efficiently. This topology achieves 91% efficiency across most load ranges. The design uses a high-frequency transformer for isolation. Consequently, the unit generates minimal heat during normal operation.

Protection Features and Diagnostics

Current limiting activates when output current exceeds 5.5A. Short-circuit protection automatically resets after fault removal. Over-temperature protection shuts down the unit at 85°C case temperature. A green LED indicator shows output voltage present and stable.

Connector Interface and Installation

A 4-pin screw terminal block accepts 24V DC input wiring. A separate 6-pin header delivers 5V output to the S5 backplane. An additional 2-pin connector provides remote voltage sensing. The unit slides directly into a dedicated power supply slot.

Typical Application Scenarios

You can deploy 6ES5955-3NA12 in SIMATIC S5-115U, 135U, and 155U racks. It also works well for powering expansion units and remote I/O stations. This supply powers CPU modules, I/O cards, and communication processors. Its 4A capacity suits systems with up to 8 modules.