Siemens 6ES5955-3LF11 Power Supply

Physical Dimensions and Mounting Details

The Siemens 6ES5955-3LF11 provides stable DC power for SIMATIC S5 systems. This unit measures 250mm in height, 30mm in width, and 150mm in depth. You can mount this unit on a standard 35mm DIN rail inside any S5 cabinet. The power supply weighs 0.72 kilograms , requiring secure mounting for reliable operation.

Internal Architecture and Component Density

The Siemens 6ES5955-3LF11 contains 162 individual components on its two-layer PCB. A 50 kHz switching controller manages power conversion with high efficiency. Four fast-recovery diodes handle rectification in the secondary circuit. Additionally, eight current-sense resistors monitor output loads for overload protection.

Energy Storage and Hold-Up Performance

This power unit stores 32.6 joules across seven electrolytic capacitors. This energy reserve maintains full output regulation for 45 milliseconds after input power drops. The storage also supports controlled shutdown signaling to the connected CPU. Consequently, the S5 system remains stable through brief mains interruptions.

Parameter	Value	Unit
Dimensions (H x W x D)	250 x 30 x 150	mm
Weight	0.72	kg
PCB layer count	2	layers
Total components	162	pieces
Switching controller frequency	50	kHz
Fast-recovery diodes	4	units
Current-sense resistors	8	units
Electrolytic capacitors	7	units
Total energy storage	32.6	J
Hold-up time (full load)	45	ms
Input voltage range (AC)	85–264	V AC
Input frequency	47–63	Hz
Output voltage (5V)	5	V DC
Output current (5V)	20	A
Output voltage (24V)	24	V DC
Output current (24V)	1.5	A
Total output power	136	W
Efficiency (typical)	86	%
Output ripple (5V max)	30	mV pp
Output ripple (24V max)	100	mV pp
MTBF (mean time)	50,000	hours
LED indicators	2	units

Interface and Connectivity Features

The Siemens 6ES5955-3LF11 provides one 6-pin screw terminal block for AC input. A single 20-pin IDC header links the unit to the S5 backplane. You will also find one 4-pin connector for external 24V loads. Each terminal accepts AWG 20 to AWG 12 copper wire for high-current connections.

Output Specifications and Regulation

This power unit delivers 20 amperes at 5V DC for logic circuits and backplane. A separate 24V DC output provides 1.5 amperes for field devices and relays. The 5V output maintains ±2% regulation from no load to full load. The 24V output holds ±3% regulation under all operating conditions.

Protection Features and Safety Circuits

The Siemens 6ES5955-3LF11 includes input overvoltage protection that shuts down at 280V AC. A thermal overload sensor reduces output current when internal temperature reaches 85°C. Output short-circuit protection limits current on both outputs and auto-recovers after fault removal. Reverse polarity protection prevents damage from accidental output wiring errors.

Diagnostic and Status Indication

Two LED indicators provide immediate feedback for power and fault conditions. Green 5V confirms the presence of valid 5V DC output to the backplane. Amber 24V glows steadily when the auxiliary 24V output remains active. The absence of either LED alerts you to an internal power supply failure.

Compatibility and System Integration

This power unit works exclusively with Siemens SIMATIC S5 programmable controllers. You must install this unit in the first slot of any S5 rack configuration. The power supply provides backplane power to all other modules in the same rack. The unit supports redundant configurations with two power supplies in parallel.

Environmental Specifications and Compliance

You can operate this power unit from 0°C to 60°C ambient temperature without derating. Derate output current by 3% per degree between 50°C and 60°C for reliability. Storage temperature ranges from -20°C to 70°C for long-term preservation. Non-condensing humidity tolerance spans 10% to 95% for industrial environments. This unit meets UL 508 and CE safety standards.