By Dimitrij Martins and Achim M. Kruck, Vishay
INTRODUCTION
The number of electric vehicles on the roads is steadily growing, increasing the need for safe and reliable battery systems and high efficiency battery chargers.
Modern electric vehicles use battery systems with voltages up to 1000 V and charge times down to a few hours. This application note uses two examples to illustrate how optocouplers play a major role in on-board chargers battery monitoring systems, and explores the benefits they provide to designers and drivers.
SAFETY ISOLATION
Safety is a key element in electric vehicles. Designers need to ensure that drivers and passengers will not come in contact with high voltage or high current parts or wires. Well known from common switchmode power supplies, optocouplers are safety elements that deliver proven long term, reliable optical isolation.
Vishay offers a wide selection of optocouplers in a variety of packages to address a broad range of applications. In accordance with national requirements, Vishay optocouplers are certified by the most demanding safety houses. Key parameters of each certificate are isolation voltage, creepage, and clearance distance, and on some certificates also the distance through isolation (DTI). In battery chargers, the devices protect humans from the high battery system voltage and the high voltage grid.
NOISE ISOLATION
In addition to safety isolation, optocouplers are the first choice for protecting sensitive low power devices such as microcontrollers and user interfaces from high voltage devices like the AC/DC converter stage. They provide low driving currents of 1 mA for microcontroller usage at various output configurations to drive individual loads.
Due to very high noise immunity ratios up to 50 000 V/μs, transient spikes and high voltage switching effects will not negatively impact the sensitive low voltage microcontroller controller part of the circuit.
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