What are Opto-MOSFET Relays? How do Opto-MOSFET Relays Work? - FAQs | Toward Technologies, Inc.

Manufacturer of Opto-MOSFET Solid State Relays, Reed Relays, and RF MEMS Switches. We mainly serve the Semiconductor Testing, ATE, BMS (Battery Management Systems), industrial machinery and Electric Vehicle industries.

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What are Opto-MOSFET Relays? How do Opto-MOSFET Relays Work?

How Toward's OPTO-MOSFET Solid-State Relays Work

How Toward's OPTO-MOSFET Solid-State Relays Work
How Toward's OPTO-MOSFET Solid-State Relays Work

What are Opto-MOSFET Relays? How do Opto-MOSFET Relays Work?

Toward's Resilient, Powerful, and Reliable Switching Technology

What Is an OPTO-MOSFET Relay?

An OPTO-MOSFET relay—also known as an opto-isolated solid-state relay—uses light to control its output state. When an LED on the input side emits light, a photovoltaic generator (PVG) produces a voltage between the gate and source terminals of the MOSFET chip, effectively "turning on" the relay. This light-driven, contactless switching architecture provides optical isolation between the LED and MOSFETs, maximizing the breakdown voltage between inputs (LED) and outputs (MOSFET) of the relay. For example, Toward Technologies' 3,300V load voltage (53 Series) achieves 5,000 VRMS isolation, a critical specification for users incorporating relays into protective circuits.

How OPTO-MOSFET Relays Work

OPTO-MOSFET relays utilize a proprietary Photovoltaic Generator (PVG) structure to achieve stable and precise switching. The operating process is as follows:

  1. Input Current
    2. A current is supplied to the input side, powering the internal LED. This current activates the LED, emitting light. This is why OPTO-MOSFET relay datasheets specify "Operational LED Current" rather than a "Nominal Voltage"—LEDs are current-driven devices.

  2. Photovoltaic Generator (PVG) Activation
    3. The emitted light strikes the PVG, where it is converted into voltage through the photovoltaic effect, similar to how a solar panel operates.

  3. MOSFET Gate Drive
    4. The voltage generated by the PVG is applied to the MOSFET's gate terminal, creating a positive gate-to-source voltage. This voltage opens a conductive channel within the MOSFET.

  4. Current Flow
    5. Once the MOSFET's threshold voltage is reached, the MOSFET turns on, allowing current to flow from drain to source.
    • For DC relays, a single MOSFET is used.
    • For AC switching, two MOSFETs are typically connected in an anti-series configuration (source terminals connected) to conduct in both polarities.
  5. Turn-Off Process
    6. When input current is removed, the LED turns off, stopping PVG voltage generation. The MOSFET gate voltage drops, and the relay returns to its non-conductive (off) state.

Process Summary:Input Current → LED Emission → PVG Voltage Generation → MOSFET Gate Drive → Current Flow

Key Advantages of OPTO-MOSFET Relays

As a solid-state switching device, the OPTO-MOSFET relay offers key benefits thanks to its non-mechanical structure and optical isolation. These advantages include:

  • Extremely Long Lifespan
    With no mechanical parts, OPTO-MOSFET relays have near unlimited operational lifetimes. Limited by only the degradation of the LEDs, these relays can often reach more than1 billion cycles, compared to traditional electromechanical relays (EMRs), which typically reach only 10 million cycles. The lifetime of OPTO-MOSFET relays is primarily limited by the degradation of the LED. Alternative designs, such as capacitor-driven MOSFET relays, can bypass the limitation of LEDs and reach near unlimited lifetime.
  • Silent Operation
    No audible switching noise, making them ideal for medical equipment and telecom applications.
  • Fast Switching Speed
    Enables precise control for applications requiring rapid response times.
  • Strong Electrical Isolation
    Complete separation between input and output provides system protection and safety.
  • Compact Size
    Supports high-density modular designs and integration into space-constrained systems.
  • Low Input Current
    The LED drive requires minimal current, contributing to low power consumption and efficient operation.

Why Choose Toward's OPTO-MOSFET Relays?

While many OPTO-MOSFET relays share general benefits like contactless switching, high speed, and isolation, Toward's unique designs and vertically integrated manufacturing deliver unmatched performance advantages:

  • Ultra-High Voltage Capability (Up to 3300V on a single mosfet)
    One of the few brands capable of producing high-voltage OPTO-MOSFET relays for demanding applications in EVs, energy storage systems, and industrial testers.
  • Proprietary PVG Architecture
    In-house developed PVG structure offers superior light-to-voltage conversion, driving higher-capacity MOSFETs with faster response time.
  • Ultra-Low On-Resistance (Rds(on))
    Efficient design reduces power loss and thermal output—ideal for high-switching frequency or high-current loads.
  • Exceptional Leakage Control
    Delivers stable, ultra-low leakage current performance even at elevated temperatures—perfect for precision test systems. Toward's newest chip design can achieve nanoamps level of leakage.
  • Light-Driven Switching with Zero Contact Bounce
    Optical control eliminates mechanical contacts entirely, avoiding arc flashes, contact bounce, or EMI issues—especially critical in high-voltage or signal-sensitive environments.
  • Certified for Automotive and Global Safety Standards
    Compliant with UL, VDE, and RoHS; manufactured under AEC-Q101 automotive-grade quality to ensure reliability in BMS, OBCs, chargers, and other EV systems.
  • High levels of In-House Manufacturing
    From wafer sawing to packaging and final testing, all production is managed internally to ensure consistent quality and dependable lead times.
  • Flexible Customization Options
    Custom packages, pin layouts, and voltage/current ratings available for application-specific needs.

Applications of Toward's OPTO-MOSFET Relays

Toward's OPTO-MOSFET relays are widely used across the following sectors:

  • Electric Vehicles (EV) and Charging Systems
    • BMS, battery modules, and OBCs requiring high-speed and safe isolation—AEC-Q101 certified

  • High-Voltage Testing & Electrical Insulation
    • Dielectric testers, capacitor insulation analyzers, and power module validation—ensuring safe, arc-free switching

  • Semiconductor Test & Measurement Equipment
    • Supports high-density, high-speed signal switching with minimal leakage and low Rds(on)

  • Medical Devices
    • Silent operation and electrical isolation enhance safety in diagnostic and monitoring equipment

  • Communication & Network Modules
    • Signal routing and module switching with high signal integrity and noise immunity

Conclusion

Toward Technologies' OPTO-MOSFET relays combine optical isolation with high-voltage switching up to 3,300V, making them ideal for EVs, energy storage, and precision testing. Using a proprietary photovoltaic generator (PVG) and high-power LEDs, these relays offer ultra-fast, silent, and efficient performance with lifetimes reaching 1 billion cycles. Designed for automotive-grade reliability and in-house manufactured for consistent quality, Toward's relays eliminate mechanical contact issues, ensuring stable, low-leakage, and zero-contact bounce switching for demanding industrial and high-voltage applications.

Ready to optimize your next design? Get in touch with Toward to find the ideal OPTO-MOSFET relay for your application.

Mos Relays
SiC MOSFET Relays (1500V to 6600V)
SiC MOSFET Relays (1500V to 6600V)

By applying Silicon Carbide MOSFETs into our optically coupled relays, load voltages are boosted up to 3300V, with 6600V in development. Input/Output breakdown voltage is in choices of 3750V and 5000V. These high load voltage Opto SiC-MOSFET Relays are AEC-Q101 certified, manufactured in Toward's factory's 1K grade clean rooms.

Opto-MOSFET Relays (60V to 600V)
Opto-MOSFET Relays (60V to 600V)

Our General Purpose Opto-MOSFET Relays product line includes Opto-MOSFET Relays that can load voltage from 60V to 400V. With Form A, Form B and Form C contact arrangements that are applicable in both AC and DC applications.

Opto-MOSFET Relays (600V to 1500V)
Opto-MOSFET Relays (600V to 1500V)

Our High Load Voltage Opto-Si MOSFET Relays product line includes Opto-MOSFET Relays that can load voltage from 600V to 1500V. We also offer load voltage options beyond 1500V up to 3300V, please see sub-category "SiC Chip" for Opto-MOSFET Relays loading voltage from 1800V to 3300V.

AEC-Q101 Certified Opto-MOSFET Relays
AEC-Q101 Certified Opto-MOSFET Relays

A series of our Opto-MOSFET Relays are AEC-Q101 certified to satisfy customers in the automotive industry. They include 45-Q Series (60V / 200mA), 47-Q Series (80V / 1.25A), 30-Q Series (400V / 100mA), 38-Q Series (400V / 70mA) and 58 Series (1800V / 30mA SiC MOSFET). All of our Opto-MOSFET Relays are manufactured in our Hsinchu factory with IATF16949 automotive certification.

Opto-MOSFET Relays ( > 1Amp)
Opto-MOSFET Relays ( > 1Amp)

Our High Load Current Opto-Si MOSFET Relays product line can load current from 1Amp to 7Amps. These optically coupled miniature Opto-MOSFET Relays are applicable in both AC and DC applications with Form A and Form B contact options.


Toward Technologies, Inc - A manufacturer of Solid State Relays, Reed Relays and MEMS Switches.

Located in Taiwan since 1988, Toward Technologies, Inc. is a relay supplier and manufacturer. Main products, including Opto-MOSFET Relays, Opto-SiC MOSFET Relays, Solid State Relays, Reed Relays, And RF MEMS Switches, etc.

Toward supplies relays to the world's semiconductor and automotive industries for over three decades and has long term long-term partnerships with OKITA Works based in Japan; Menlo Microsystems based in California; JEL Systems based in Japan and Teledyne Relays and Coax Switches based in California. Mainly serve the Semiconductor Testing, ATE, BMS (Battery Management Systems), industrial machinery and Electric Vehicle industries.

Toward has been offering customers high-quality Opto-MOSFET and Opto-SiC MOSFET relays since 1988, both with advanced technology and 37 years of experience, Toward ensures each customer's demands are met.