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The In-Vehicle computer power subsystem challenges
Date: 2011/05/10

The challenging electrical and environment conditions found in modern automobile have a strong impact on the design of automotive power electronic equipment. Important factors affecting the design of electronics for this application include static and transient voltage ranges, electromagnetic interference and compatibility requirements (EMI/EMC).
The transients on the automobile power supply range form the severe, high energy, transients generated by the alternator/regulator system to the low-level ’’noise’’ generated by the ignition system and various accessories. A standard automotive electrical system has all of these elements necessary to generate undesirable transients.

Typical Automotive Transients

Typical Automotive Transients

The Society of Automotive Engineers (SAE) has defined the automotive power supply transients which are present in the system. Table 1 shows some sources, amplitudes, polarity, and energy levels of the generated transients found in the automotive electrical system(1).












Steady State

Failed voltage regulator





5 Minutes

Jump Start with 24V battery Infrequent




200ms to 400ms

Load dump; disconnection of battery while at high charging




<320 us

Inductive-load switching transient



300V to +80V


Alternator field decay


Each Turn-Off

-100V to -40V


Ignition pulse, battery disconnected


<500Hz Several Times in Vehicle Life



Mutual coupling in harness





Ignition pulse, normal


<500Hz Continuous



Accessory noise


50Hz to 10kHz


Transceiver feedback

~ 20mV





Infrequent/ Random



With the extensive use of computer in today’s vehicles, protection from transient over voltages is essential to ensure reliable operation.

Acrosser Solution

All Acrosser’s In Vehicle Computer power subsystem is designed with protections to prevent damage from most of the transient over voltage in vehicles.
1. Automotive Transient Voltage Suppression
2. Over Voltage and Under Voltage Protection
3. Over Current Protection
4. Reverse Voltage Protection
5. Automotive Fuse

Acrosser ensure its In Vehicle Computers perform as designed during and after exposure to disturbance by certified with the E-Mark.
E/e-Mark is the Economic Commission of Europe (ECE) that grants certificates to ensure all automobiles equipments sold by manufacturers meet traffic safety and environmental protection requirements.
The E-Mark certification includes a series of vehicle transient voltage test according to the ISO 7637-2. ISO 7637-2 was prepared by Technical Committee ISO/TC 22, Road vehicles. It defined specifies bench tests for testing the compatibility to conducted electrical transients of equipment installed on passenger cars and light commercial vehicles fitted with a 12 V electrical system or commercial vehicles fitted with a 24 V electrical system — for both injection and the measurement of transients. There are 8 types of test pulse defined to simulate different transient voltage in real vehicle environments. Table 2 shows the test pulses defined in ISO 7637-2.

 Test Pulse




This test is a simulation of transients due to supply disconnection from inductive loads. It is applicable to DUTs which, as used in the vehicle, remain connected directly in parallel with an inductive load.                              



Pulse 2a simulates transients due to sudden interruption of currents in a device connected in parallel with the DUT due to the inductance of the wiring harness.



Pulse 2b simulates transients from d.c. motors acting as generators after the ignition is switched off.


    3a & 3b

These test pulses are a simulation of transients which occur as a result of the switching processes. The characteristics of these transients are influenced by distributed capacitance and inductance of the wiring harness.



This pulse simulates supply voltage reduction caused by energizing the starter-motor circuits of internal combustion engines, excluding spikes associated with starting



      5a, 5b

This test is a simulation of load dump transient, occurring in the event of a discharged battery being disconnected while the alternator is generating charging current and with other loads remaining on the alternator circuit at this moment. Load dump may occur on account of a battery being disconnected as a result of cable corrosion, poor connection or of intentional disconnection with the engine running.


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