Provision of circuit protection, fast data transfer and current conversion for electromobility platforms

The need for reliable circuit protection solutions, high-speed communication and compact current conversion in electromobility and transport systems is growing in many areas.

The need for reliable circuit protection solutions, high-speed communication and compact current conversion in electromobility and transport systems is growing in many areas, including hybrid and electric cars, buses, trucks and vans on and off-road, and offshore platforms. These trends are driven by the growing emphasis on sustainability and safety accompanying the transport industry's shift to more autonomous steerable and electric (EV) or hybrid EV (HEV) vehicles. As a result, new vehicle systems are emerging which are gradually becoming more and more dependent on safe and sustainable operation.

To ensure safety and reliability, designers of internet-connected electric and automated vehicles need a wide range of circuit protection devices as well as communication and current conversion solutions that are designed to operate reliably in harsh environments and are AEC-Q200 certified. , SAE, USCAR and others.

This article briefly reviews some of the circuit protection device specifications that designers need to consider.

Components and protection standards in electric vehicles

To meet the challenges posed by electric vehicles, designers can use a range of certified and approved solutions for automotive circuit protection, high-speed communication and current conversion, such as:

• Automotive cartridge, PCB mounted fuses (through hole and surface mount) and offset screw configurations optimized for power systems and subsystems, as well as fuses for auxiliary applications and accessories such as radar systems, driver assistance systems, brake pump motors, portable chargers, battery systems, infotainment systems, cameras, programmable lighting and power steering. In addition, some applications will require high inrush, fast-blow, slow-blow, and positive temperature coefficient resettable polymer (PPTC) fuses.
• AEC-Q200 compliant electromagnetic interference (EMI) suppression chokes to filter noise and protect high-speed data signals in numerous sensor subsystems that are part of ADAS and navigation systems, multimedia systems, vehicle-to-other receiver (V2X) clusters and antennas, and provide differential noise suppression in Ethernet, CAN, FlexRay and USB networks in automotive applications
• Fully shielded RJ45 connectors complying with the Society of Automotive Engineers (SAE) USCAR2-6 "Specification for Automotive Electrical Connector System - Revision 6", enable designers to replace CAN buses with a faster and lighter Ethernet network for automotive applications to support the growing computing needs in vehicles in a range of ADAS systems, such as driver assistance cameras and radar-based driver assistance systems, as well as telematics, media converters and gates.
• Power converters with IP67 certification, including chargers for electric and hybrid vehicles, qualified for use in the automotive industry and offered in convection or liquid-cooled versions with galvanic isolation.
  
  

Selection of circuit protection devices

When selecting the appropriate circuit protection device in electromobility systems, it is important to clearly understand its performance characteristics. Some basic specifications include:

• Rated voltage: the maximum allowable voltage for safe operation
• Rated current: the amperage (A) that the fuse can carry under normal operating conditions
• Breaking capacity (also called rated breaking capacity or rated short-circuit current): the maximum current that a fuse can break at its rated voltage without damaging it. The breaking capacity must be at least equal to the maximum short-circuit current for the circuit
• Time / Current Curves: Determines whether the fuse is fast or slow-blow. High-speed fuses are used where the speed of protection is critical. Time-delay fuses are used in places with short-term surges or overloads

I2t: specification without test standard

The parameter that deserves special attention is the nominal Joule fusion integral I2t (pronounced "I square T"). It is a measure of the energy required to melt the fuse element, which is an important feature of a fuse in any application. I2t is expressed as "ampere squared times second" (A2s). Unfortunately for designers, neither the UL / CSA 248 nor IEC127 standards for miniature fuses and microfuses contain the test procedure, nor the I2t test criteria. Definition of I2t according to the industry standard:

FELT JOULE FULL I2t measured at 10In, using steady DC current, where In is the fuse rated current.

Using 10In current can be problematic and does not always result in exact opening times. Time-delay fuses, in particular, may require a current higher than 10 times the rated current to achieve the true I2t value. Since different manufacturers deal with this dilemma differently, it is important that designers have a good understanding of the method used to determine the I2t value for specific fuses. A more detailed discussion of these challenges is available here: Joule's integral I2t explained.

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