Vishay Offers Industry-First for Optocoupler MOSFET Drivers

Electrical isolation is one of the most important considerations in electrical power system design. While there are many different ways of achieving electrical isolation, one particularly popular method is optocouplers.

VOMDA1271 automotive-qualified optocoupler. Image used courtesy of Vishay

 

Vishay has announced a new optocoupler device that offers industry-first features and competition-beating specifications. This article examines electrical isolation, optocouplers, and Vishay’s latest product announcement. 

 

Electrical Isolation

Electrical isolation is a means of physically and electrically separating two different circuits so they cannot interfere. In electrical system design, there may be many situations that necessitate the use of electrical isolation.

One situation that could call for electrical isolation is controlling high-voltage circuits using lower-voltage electronics. Control circuitry for large power switches and transistors operates at low-voltage rails in power electronic systems. In contrast, the power system itself is a much higher voltage. 

In an instance like this, electrical isolation helps protect the sensitive lower-voltage circuits, which could be easily damaged by transients on the high-voltage side, such as surges and or voltage spikes. Electrical isolation is often required in circuits where one desires to use DC  electronics to control AC waveforms. 

 

Electrical isolation is often required in medical devices for patient safety. Image used courtesy of Avnet

 

Electrical isolation is often also needed to ensure safety and meet compliance standards for a product. For example, a medical device may require electrical isolation for patient protection. In an instance like this, electrically isolating the applied part of a medical device from the rest of the electrical system ensures that leakage currents cannot harm the medical patient.

 

Optocouplers

While there are many different means of achieving electrical isolation in a system design, one of the most common methods is by using optocouplers.

Optocouplers are electronic components that work to provide electrical isolation to a circuit through the use of optical signaling. A standard optocoupler generally consists of two parts: an infrared-emitting LED on the primary side and a phototransistor on the secondary side, both of which are electrically isolated. 

 

An optocoupler block diagram. Image used courtesy of Texas Instruments

 

In this architecture, the LED takes an electrical control signal as an input and converts that electrical signal into infrared light. The phototransistor then senses the incident light from the LED and uses that light to bias itself into a conductive state, hence creating an electrical signal at the output that is proportional to the electrical input signal at the LED.

Because of their simplicity and ease of use, optocouplers have become a popular way to achieve electrical isolation.

 

Vishay’s Product Launch

This week, Vishay announced the launch of a new optocoupler product for automotive applications.

The VOMDA1271 product is an automotive-qualified optocoupler designed specifically for MOSFET driving use cases. Unlike standard optocouplers with a phototransistor on the secondary side, the VOMDA1271 features a “photovoltaic gate array,” which Vishay claims help simplify design and lower costs by removing the need for an external power supply.

 

VODMA1271 MOSFET driving application circuit. Image used courtesy of Vishay

 

The VOMDA1271 is notable as Vishay claims it's the industry’s first optocoupler that features an integrated turn-off circuit. Some interesting specs include voltage isolation of 3750 Vrms, a turn-off time of 0.7 ms, and a turn-on time of 0.05 ms. Vishay claims that the turn-on time is twice as fast as competing devices, while the turn-off time is the fastest for a MOSFET driver in an SOP-4 package.