Make green energy go further with stronger, faster optical isolators
Electrification, powered by energy from renewable sources, is central to the world’s strategy for sustainability. Success depends on maximizing the efficiency of the power converters and controllers throughout the electrical distribution infrastructure, as well as in end-user equipment like intelligent motor drivers. This constant quest to increase efficiency is driving system designs into new territories.
Major developments of the moment include the adoption of silicon carbide (SiC) and gallium nitride (GaN) wide-bandgap semiconductor technologies to reduce energy losses. These devices can operate at high voltage and temperature, while internal on-resistance and gate charge are an order of magnitude lower than comparable silicon technology can achieve. At high switching frequencies, power conversion efficiency can exceed 99%.
Another trend is the move to higher DC bus voltages to reduce copper losses. The latest solar generators, for instance, are moving from the typical operating voltage of 1000V up to 1500V. This also allows for longer strings of PV panels, resulting in fewer junction boxes and reduced cabling, hence making solar easier to install and more affordable.
These changes challenge designers to select higher-performing components for critical circuit functions:
Increasing the bus voltage requires stronger mandatory safety isolation between exposed parts of the equipment and the high-voltage circuitry connected to DC buses and incoming supply lines. This calls for a higher isolation voltage in optical components such as the gate drivers that control the power switches, isolation amplifiers used for phase current and bus-voltage measurements, and optocouplers used for data transmission and communication. In addition, component clearance and creepage must be increased although there is precious little space on the circuit board to allow for this.
The higher bus voltage also requires gate drivers to have greater common-mode transient immunity (CMTI) to prevent unwanted random turn-on of power transistors.
On the other hand, the gate drivers must provide a stronger control signal for wide-bandgap semiconductors such as SiC power MOSFETs to ensure fast turn-on and turn-off times. This is critical for efficient operation at high switching frequency.
Also critical for sustainable living is widespread EV adoption, which depends on safe and reliable EV-charging infrastructure. In an EV-charging station, especially DC fast-charging, complex power supply systems deliver huge amounts of energy to the battery in the vehicle within a short period of time. It can be very challenging to design an efficient DC fast charger while complying with safety-isolation requirements. Gate driver optocouplers deliver both safety isolation and respective electrical functions in a single package, helping realize highly efficient systems.
In addition, residential energy storage systems based on renewable sources such as solar and wind power are becoming more popular among consumers and gaining increasing support from governmental bodies. Such systems, however, need fault protection in order to achieve the product lifetime that consumers demand as well as isolation to ensure consumer safety. Gate driver optocouplers by integrating these two features help simplify system design as well as lower cost.
To meet the requirements of this emerging world, powered by electricity from renewable sources, EBV provides the latest optical isolation technology from Broadcom. Among the devices available, the ACPL-355JC isolated gate drive optocouplers have common-mode transient immunity (CMTI) of 100kV/μs, specified up to 1500V. The output can source and sink up to 10A of gate-drive current to ensure fast turn-off when driving SiC MOSFETs.
The ACFL-3161 single-output and ACFL-3262 dual-output 10A drivers combine CMTI of 100 kV/μs at 1000V with extremely fast propagation delay of 95ns, and tight dead-time control for switching SiC MOSFETs at high frequencies.
The devices are housed in compact, surface-mountable SO-12, SO-16 and SO-24 packages featuring high comparative tracking index (CTI) greater than 600V. The high CTI reduces creepage requirement and allows smaller packages to be used in high voltage applications. With 5000VRMS insulation voltage between input and output channels, they help designers create cutting-edge power conversion systems that meet all safety and performance requirements for the latest green-energy applications.
