MOSFET relays: Key components in the densification and efficiency of electronics

Traditional electromagnetic relays, (EMRs), are still popular choices for certain applications, particularly where high-power switching is required. But the characteristics of solid-state relays (SSRs), particularly MOSFET types, mean they are being employed in a growing range of applications. With the exponential growth of the IoT and the arrival of 5G networks driving a trend towards more powerful devices with shrinking form factors, engineers must fit more functionality into less space and find ways of improving switching speeds and power efficiencies. Certain key components in the modern IT infrastructure such as DC-DC converters and switching power supplies present specific design challenges which the characteristics of MOSFET relays can help to address. We look more closely at the MOSFET relay to understand how its characteristics are well suited to a number of key applications.
 

The MOSFET relay: A circuit rather than a switch

MOSFETs are actually electronic circuits, rather than relays, comprising an LED on the input side and a photodiode dome array (PDA), control circuit and FET block on the output side (Figure 1).

Figure 1: MOSFET block diagram

Within the MOSFET relay, the input driver circuit (1) causes current to flow through the LED, turning it on, and the light from the LED (2) is then converted to voltage by the PDA. (3) The PDA output voltage drives the MOSFET output block via a control circuit and the output block, which contains a double MOSFET, allows both AC and DC loads to pass in either direction.

With no moving parts, (unlike EMRs), MOSFET relays can withstand physical shock and vibration and will perform indefinitely when properly used, operating silently with very little electrical interference. The devices can handle a wide range of input voltages, consuming little power and there is no arcing during operation, making them suitable for hazardous environments. The inherent design of the MOSFET relay minimises surge currents and enables switching of both AC and DC signals. As well as their low power consumption, MOSFET relays are considerably smaller than their EMR counterparts, using less space on the PCB.
 

Table 1: Summary of MOSFET relay characteristics
 

Typical applications for MOSFET relays

MOSFET relays are ideal for a wide range of applications, including automated test equipment, (ATE), medical equipment, security equipment, amusement equipment, factory automation, telecommunications, energy-related equipment and many more. The tables below provide an illustrative overview of how the characteristics of Omron’s MOSFET relay family benefit the design of a selection of applications, and the rest of this section examines a subset of these applications in more detail.

Automatic test equipment (ATE)

Semiconductor devices continue to become more complex and ever faster, challenging the designers of automatic test and measurement technology, who must incorporate higher numbers of test channels into their equipment in order to meet market demands for reduced testing time and improved efficiency. The low capacitance of MOSFET relays improves switching times and isolation characteristics for high frequency load signals. Their low on-resistance reduces power dissipation when switching high currents and increases switching speeds to improve measurement precision. Offering physical separation of input and output with minimal leakage, MOSFET relays also enhance measurement precision by reducing noise and their high linearity also contributes to measurement accuracy.

Factory/industrial equipment

The Industry 4.0 smart factory leverages IoT technology and increased levels of automation to achieve cost-effective, flexible production capabilities. The factory environment is typically hostile to electronic equipment, however, and the high tolerance to physical shock and EMI of MOSFET relays make them ideal for the switching and protection of small motors, power supplies and control devices, with load currents up to 10 amps.

Energy-related equipment

Efficiency and densification are two important mega-trends within electronics, not least within the design of switching power supplies. The small form factors of MOSFET relays enable designers to reduce space on the PCB, their reduced output capacitance supports the high-speed switching requirements of modern power supply designs and their lower on-resistance contributes to cost savings through simpler heat management. Also, along with their low-power consumption, the improved noise performance of MOSFET relays contributes to the reduction of electromagnetic noise emission in high-end power supplies for equipment such as LCD TVs, LED lighting, medical power supplies and notebook power adapters.
 

Omron MOSFET relay product line

A global leader in the fields of industrial automation, electronic component industries and healthcare, Omron Corporation provides a variety of products and services, including a range of MOSFETs that set the benchmark for Solid State Relays. Manufactured using the latest advances in automated production and including a variety of improved construction technologies within the areas of LED, PDA and FET chips, Omron’s G3VM MOSFET relay family includes up to 200 devices that handle a wide range of voltages and currents (Figure 3). Options include current limiting, high-dielectric-voltage withstand, normally open and normally closed contact forms, and high-speed switching.

The key features of Omron’s G3VM MOSFET relay family include:

• A wide range of packages: DIP, SOP, SSOP, USOP, VSON, and S-VSON
• S-VSON package is the smallest in the industry: 2 x 1.45 x 1.65 mm
• Single- and dual-contact models available with both NO and NC contacts
• ON-resistance as low as 5 mΩ (typical)
• OFF-state capacitance as low as 0.3 pF (typical)
• Trigger LED forward currents as low as 0.2 mA
• Switching times down to 0.2 ms
• Models including current limiting functions also available
• 100,000 hours of continuous operation
• Dielectric strength up to 5,000 Vac for 1 second
• Models switching up to 10 A* in such a small package
   

Figure 3: Omron's MOSFET relay product range

Conclusion

In a world where densification and efficiency are driving the design of electronic devices and systems, the characteristics of MOSFET relays are responsible for their incorporation in a growing range of applications. As a global leader in electronic components, Omron’s G3VM MOSFET relay range sets the standard. To find out more about the range, download datasheets, and purchase pilot samples click below. Alternatively, if you have specific requirements and would like to discuss your design in detail, click the Ask an Expert button to get in touch with one of our technical specialists in your local language.

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