SEMIKRON SKD31F/16

The brand is SEMIKRON, now part of Danfoss, not “semilron”. It is a 3-phase uncontrolled full-bridge rectifier module with fast recovery diodes, belonging to the SEMIPONT®1 series. It converts 3-phase AC into DC power and is widely applied in DC drives, power supplies and excitation circuits.

1. Model Decoding

SKD31F16

SKD: 3-phase rectifier bridge series of SEMIKRON

31: Rated DC output current \(I_D=31\mathrm{A}\) (at \(T_C=100^\circ\mathrm{C}\))

F: Fast Recovery Diode. It features short reverse recovery time (\(t_{rr}\approx2.5\mu\mathrm{s}\)), ideal for high-frequency and low-loss applications.

16: Repetitive peak reverse voltage \(V_{RRM}=1600\mathrm{V}\) (1.6kV)

2. Core Technical Parameters

3. Package & Pin Definition (G26 Package)

Pin 1: L1 (U-phase of 3-phase AC input)

Pin 2: L2 (V-phase of 3-phase AC input)

Pin 3: L3 (W-phase of 3-phase AC input)

Pin 4: DC+ (DC output positive terminal)

Pin 5: DC− (DC output negative terminal)

4. Typical Applications
5. Excitation power rectification and front-end rectification for main circuit of ABB DCS500 DC drives
6. Industrial DC power supplies, battery chargers and front-end circuits of UPS
7. Motor excitation power supply, welding machines and front-end rectification for frequency converters
8. Compatible Replacement Models (Same Package & Specifications)

Direct Replacements of the Same Brand

SKD31/16: Standard version with slow recovery diodes. The F-version adopts fast recovery diodes and is preferred for high-frequency and low-loss scenarios.

SKD53F16: Higher current rating (53A/1600V) with identical G26 package, available for performance upgrade.

Cross-brand Equivalents (Same Package & Specifications)

Infineon: DD31S16

Fuji Electric: 6RI30G-160

6. Installation & Selection Guidelines
7. Adequate heat dissipation is mandatory: The 31A rating is guaranteed at \(T_C=100^\circ\mathrm{C}\). Equip with a qualified heat sink, apply thermal grease and set the mounting torque to 2Nm.
8. Isolation requirement: The baseplate provides 3600V isolation. Maintain proper clearance between the baseplate and cabinet/heat sink during installation.
9. Surge protection: Install RC snubber circuit (0.1μF + 50Ω) on the AC side and a 25A fast fuse on the DC side to suppress surges.
10. On-site Fault Diagnosis Methods
11. Visual inspection: The module is defective if signs such as cracking, burning, corroded pins or bulging baseplate are observed.
12. Static test (power off, resistance mode):

Each 3-phase input terminal (L1/L2/L3) conducts in one direction and blocks in reverse towards DC+ and DC−. Bidirectional conduction or short circuit indicates bridge arm breakdown.

Direct short circuit between any two phase terminals means module failure.

3. Power-on test: If 3-phase input is normal but there is no DC output, low output voltage or unbalanced voltage across phases, one internal diode arm is damaged.

Pin Definition of SEMIKRON SKD31F16 (G26 Package / SEMIPONT®1)

Overview

It is a 5-pin 3-phase full-wave uncontrolled rectifier bridge consisting of 6 fast recovery diodes. When viewing the top printed side facing you, the pins are numbered 1, 2, 3, 4 and 5 from left to right.

1. Pin Numbering, Markings & Functions (Standard Definition)

2. Physical Layout (Top View)

(Model SKD31F/16 facing upward)

Pin arrangement (Left → Right):

1(L1)   2(L2)   3(L3)   4(+)   5(−)

Package: G26 (SEMIPONT®1) with isolated metal baseplate and 5 quick-connect / solder pins.

Positioning: A notch or indentation on one corner marks Pin 1.

3. Internal Topology (6-diode 3-phase Full Bridge)

Upper bridge arms (D1/D3/D5): Anodes connected to L1/L2/L3; cathodes commonly connected to Pin 4 (DC+).

Lower bridge arms (D2/D4/D6): Cathodes connected to L1/L2/L3; anodes commonly connected to Pin 5 (DC−).

4. Wiring & Measurement Guidelines (On-site Reference)
5. AC side: There is no strict sequence requirement for L1/L2/L3 (Pin 1/2/3). Swapping any phases will not affect rectification performance.
6. DC side: Pin 4 = DC+, Pin 5 = DC−. Reverse connection is strictly prohibited.
7. Power-off test (multimeter in diode mode):

L1/L2/L3 (Pin 1/2/3) conduct unidirectionally (approx. 0.8~1.7V) towards Pin 4 (+).

L1/L2/L3 (Pin 1/2/3) conduct unidirectionally (approx. 0.8~1.7V) towards Pin 5 (−).

Reverse blocking (infinite resistance) between Pin 4 and Pin 5. Bidirectional conduction means the module is broken down.

5. Supplementary Key Parameters

Rated Current: 31A (@ \(T_C=100^\circ\mathrm{C}\)), 44A (@ \(T_C=85^\circ\mathrm{C}\))

Repetitive Peak Reverse Voltage: 1600V (\(V_{RRM}\))

Isolation Voltage: 3600V AC / 1s (isolation between baseplate and internal circuit)

Common Applications of SEMIKRON SKD31F16

This 3-phase fast recovery rectifier bridge features 1600V withstand voltage, 31A rated current, G26 package, low switching loss, strong surge resistance and isolated metal baseplate. Combined with its wide use in ABB DC drives, the mainstream applications, detailed equipment and operating conditions are listed below, along with its application advantages.

1. Industrial DC Drive Systems (Most Common Application, Optimized for ABB DCS Series)

This module is a standard rectifier component for excitation circuits and low-power main circuits of domestic and overseas DC drives, and a frequently replaced spare part on site.

1.1 ABB DC Drives (Core Application)

Compatible models: Full range of DCS400 and DCS500 DC drives

Function 1: Rectification for motor excitation power supply

The internal 3-phase AC of the drive is rectified by this module to provide stable DC excitation current for DC motor excitation windings. This is the most common application position in DCS500 with high failure and replacement frequency.

Function 2: Front-end rectification for main power circuit of low-power models

It converts industrial-frequency AC into DC bus voltage for the main circuit of low-current DCS500 units.

Application advantages: The 1600V high withstand voltage resists thyristor commutation surges and grid voltage spikes inside drives. Fast recovery diodes reduce temperature rise under pulsating current conditions.

1.2 Siemens DC Drives

Compatible models: 6RA24, 6RA28, 6RA70, 6RA80 series

Function: Rectification for excitation units and auxiliary DC power supplies inside cabinets. It can directly replace original rectifier modules of the same power rating.

1.3 DC Drives of Other Brands

Widely used in medium-power excitation circuits of imported DC drive equipment such as Eurotherm, Parker and Lenze.

Typical industries: Metallurgical rolling mills, papermaking lines, cranes, wire drawing machines and extruders.

2. Independent Motor Excitation Power Systems

Applied to external independent excitation cabinets for large synchronous motors, wound rotor induction motors and large DC motors:

1. Excitation power supply for main motors of cranes, portal cranes and overhead travelling cranes in ports;
2. Excitation rectification for blast furnace fans and main sintering motors in metallurgy industry;
3. Excitation devices for large and medium-sized water pumps and fan synchronous motors.

Operating features: 24-hour continuous operation, stable load and severe grid fluctuation. The 1600V high withstand voltage and wide industrial temperature range (\(-40^\circ\mathrm{C}\) ~ \(125^\circ\mathrm{C}\)) enable long-term reliable operation.

3. Industrial Welders & Plasma Cutting Equipment

These devices work under severe impact and large surge current conditions, which match the module’s excellent surge resistance (\(I_{FSM}=370\mathrm{A}/10\mathrm{ms}\)):

1. AC/DC arc welders: Front-end rectification for 3-phase input to provide basic DC voltage for welding arc circuits;
2. Air plasma cutters: Industrial-frequency front-end rectifier units;
3. Auxiliary power rectification for resistance welders and spot welders.

Operating features: Frequent start-stop and large instantaneous surge current. The module’s surge resistance prevents instantaneous breakdown, while fast recovery diodes cut down switching loss at the front end of high-frequency inverters.

4. Industrial Switch Power Supplies, Chargers & Energy Storage Equipment

Benefiting from low reverse recovery loss of fast recovery diodes (suffix F), it is suitable for medium and high-frequency rectification:

1. High-power industrial DC power supplies

Special DC power supplies for control cabinets and centralized power supply units, converting 3-phase AC into stable DC output.

2. Battery chargers

Front-end rectification for 3-phase intelligent chargers of forklift batteries, energy storage batteries and industrial standby battery packs.

3. UPS & industrial inverters

Front-end rectifier bridges of online UPS and industrial-frequency inverters. The 1600V withstand voltage adapts to industrial high-voltage grid environments.

Advantage: Lower heat generation and higher efficiency during high-frequency operation compared with conventional slow recovery rectifier bridges.

5. Auxiliary Circuits of Frequency Converters & Soft Starters

Note: Not for high-current main circuit rectification of frequency converters (Main circuits adopt higher-current rectifier modules or IGBT modules). Only for auxiliary circuits.

1. Rectification for power supplies of internal fans, oil pumps and control boards inside frequency converters;
2. Power rectification for signal circuits and cooling systems of motor soft starters and solid-state voltage regulator cabinets;
3. Pre-processing rectification for medium-frequency power supplies and induction heating equipment.
4. General Industrial Control Complete Equipment (General Supporting Applications)
5. Hydraulic stations and servo hydraulic systems: Convert 3-phase AC to DC for hydraulic solenoid valves and DC motors;
6. Elevators and escalators: Rectification for auxiliary DC power supplies and brake power supplies inside control cabinets;
7. Air compressors, textile machinery and printing machines: Rectification for auxiliary power circuits of complete equipment;
8. High-voltage control cabinets and relay protection devices: Low-voltage DC working power supplies inside cabinets.

Core Selection Advantages

1. 1600V high reverse withstand voltage

Industrial sites commonly suffer from grid harmonics, lightning surges and commutation voltage spikes. The high withstand voltage provides sufficient safety margin to avoid breakdown, ideal for old factories and harsh grid environments such as metallurgy and mines.

2. Fast recovery diodes (F version)

Compared with standard SKD31/16 (slow recovery type), it features lower switching loss and less heat generation, especially suitable for pulsating current and medium/high-frequency circuits such as excitation systems, switch power supplies and welders.

3. 31A rated current

Perfectly matched with the current rating of excitation circuits, auxiliary power supplies and low-power main circuits, covering most small and medium-sized industrial control equipment.

4. Universal G26 standard package

Industry-standard pin layout and mounting dimensions ensure high interchangeability of spare parts. No wiring or heat sink modification is required for on-site replacement.

5. Isolated metal baseplate

Complete isolation between baseplate and internal circuit eliminates the need for extra insulation treatment on heat sinks, simplifying installation and cabinet wiring.

Operation Notes for Different Applications

1. Excitation circuits of DC drives (e.g. DCS500)

A fast fuse must be connected in series for short-circuit protection. Conventional air cooling for heat sinks is acceptable; perform regular dust removal.

2. Welders & cutting equipment

Install an RC snubber circuit (0.1μF + 50Ω) on the AC side to absorb surges and extend module service life.

3. High-frequency switch power supplies & chargers

Ensure sufficient heat dissipation, apply thermal grease strictly and keep case temperature \(T_C\leq100^\circ\mathrm{C}\).

4. Factories with severe voltage fluctuation

Do not select rectifier bridges with lower voltage rating; keep the 1600V version for safety.