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Choosing a DC Solid State Relay transistor technology

What are the different DC Solid-State Relay transistor technologies and how to choose the correct one?

Circuit Board - Transistor Technology

DC (Direct Current) Solid-State Relays allow to switch DC loads (solenoid valves, brakes, LEDs, motors, …).

DC solid-state relays can be composed of different types of transistors (MOSFET, IGBT, Bipolar). However, it can be difficult to choose the correct technology depending on the application.

This article will introduce the different technologies available on the market, and how to choose the correct one.


AC Solid state relays vs. DC solid state relays

AC (Alternative Current) solid-state relays

AC solid-state relays are composed of thyristors or triacs.

A thyristor, also called SCR (Silicon Controlled Rectifiers) is an electronic semiconductor switch composed of two main terminals called Anode and Cathode, and a control terminal called the Gate. A thyristor conducts current in one direction only.

thyristor - showing Anode, Cathode and Gate

A triac (Triode for Alternating Current), is an electronic semiconductor, equivalent to two back-to-back thyristors. It is composed of three electrodes (anode 1, anode 2, gate) and conducts current bilaterally.



DC (Direct Current) solid-state relays

DC solid-state relays are equipped with transistors.

A transistor is used to rectify, modulate, or amplify electric currents. It can be a Bipolar, IGBT (Insulated Gate Bipolar Transistor) or MOSFET (Metal Oxide Semiconductor Field Effect Transistor) type.


Choose between the technologies

Introducing the technologies

DC Solid-State Relay with MOSFET transistor

MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistors are composed of three terminals: the drain, the gate and the source. A MOSFET transistor generates voltage through the gate. It is a unipolar component.


DC MOSFET Solid-State Relays are used for applications requiring transient overcurrent withstand (motors).

The advantage of MOSFET technology is that it generates a very low voltage drop when the load voltage is low. Nevertheless, the control current is high. The voltage drop can be high when the load voltage is also high.

DC MOSFET Solid-State Relays from celduc® relais :


SLD Range 

SLD Range  (445-5224)

STD Range 

STD Range  (917-4832)

SPD Range

SPD Range 

SKLD Range

SKLD Range  (270-0051)

SCM Range

SCM Range  (702-6813)

SOM Range

SOM Range  (917-4838)


DC Solid-State Relay with Bipolar transistor

Bipolar transistors are composed of 3 terminals (Base (B), Collector (C), Emitter (E)), and of three semiconductor layers: NPN or PNP. Each one has different directions. A Bipolar transistor is controlled through current.

Bipolar transistors Bipolar transistors - NPN and PNP Symbols

DC Bipolar solid-state relays fit applications with low control current and are recommended for resistive and inductive loads. They work the same way as a current amplifier.

The advantage is that a DC Bipolar solid-state relay can be controlled by a very low current. Nevertheless, the voltage drop is high when the load voltage is low, even if the load current is also low.

DC Bipolar Solid-State Relays from celduc® relais :


SKD Range

SKD Range  (231-0949)

SCC Range

SCC Range  (917-2696)

XKD Range

XKD Range  (231-0977)


DC Solid-State Relay with IGBT transistor

DC IGBT (Insulated Gate Bipolar Transistor) solid-state relays are used for power electronics (>600VDC). An IGBT transistor generates voltage through the gate. It is a hybrid transistor, regrouping a MOSFET transistor on the input and a Bipolar transistor on the output. It is composed of three terminals: the collector, the gate, and the emitter.

IGBT (Insulated Gate Bipolar Transistor)

The advantage of a DC IGBT solid-state relay is that it combines the advantages of both Bipolar and MOSFET transistors. Nevertheless, the control current is relatively high.

DC IGBT Solid-State Relays from celduc® relais :

Gamme SCI

SCI Range  (702-6804)

Gamme SDI

SDI Range


Choose the correct technology

This graph allows you to easily define the necessary technology depending on the nominal current and nominal voltage of the application.

Technology Graph Showing Current vs Voltage

Applications examples for DC Solid-State Relays

  • DC power supplies converters like choppers or inverters
  • Signal switching like testing or monitoring equipment
  • Electro-magnets like induction motor braking systems
  • Heating elements like air conditioning in trains or tramways and de-icing of railways
  • Batteries like boat batteries or solar energy storage systems
  • DC Motors like travelling cranes, cranes, or construction machines


celduc® relais is a solid-state relay expert, manufacturing all of its products in France. The SSR manufacturing at celduc® guarantees quality and reliability for each product.

With nearly 200 full-time employees in 4 countries on 3 continents, celduc® relais is a leading player in the global market for industrial automation and magnetic proximity sensors. Founded and located in Sorbiers, France, celduc® relais, is known as the expert in solid state relays and magnetic sensors. Every year, we are proud to manufacture more than 1 million relays sold worldwide, helping to promote French industrial expertise and “100% made in France” quality.
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