Starting voltage pulse
The start voltage pulse has two completely different meanings:
- On the one hand, it is a model replica of the collapse of the on-board voltage in an automobile when the starter is operated.
- On the other hand, it is a name for the high-voltage ignition pulse for xenon light in automobiles or for other gas discharge lamps .
On-board voltage when starting the car engine
The voltage curve typically shows an extreme voltage dip at the beginning due to the starter motor, then a phase of moderate dip while the starter motor is running and then the return to normal level when the internal combustion engine has started and the starter is disengaged again. The (relative) voltage levels and timing are defined by the car manufacturer (and changed from time to time or from model to model). The whole curve extends over a time of more than a second.
In extreme cases, this voltage curve can also be run through several times at specified time intervals.
The voltage curves are based on a fully functional and charged starter battery . Another extreme case would be a dead or deeply discharged battery, which would further exacerbate the situation. However, this case is classified under the topic of "undervoltage behavior", for which there are specific specifications.
In the car, the control units have to withstand these voltage supply curves without getting mixed up. In order to test this in the development phase, the curves shown are used precisely as specified by the car manufacturers. Programmable voltage sources are used, which are configured for such curves. The reactions of the control unit are then examined and checked with a vehicle diagnostic system.
The function of the control unit
Various approaches are used in the control units to cope with this situation:
- In some of them, their own voltage stabilization is then equipped with hardware. Typically, the 12 V of the on-board voltage is reduced to 5 V for the electronics of the control unit. The voltage is stabilized at the same time. If the charging capacities are dimensioned so large that they can bridge voltage drops of whole seconds, that is already a solution. However, such large capacitors are very voluminous and possibly a cost factor that cannot be neglected for mass production, so that this simple approach is not always optimal.
- The alternative is to design the voltage stabilization of the control unit only for a shorter period of time, but also to ensure by programming the control unit that there is still no data loss. To this end, the control unit recognizes the special case of undervoltage and reacts to it with, if necessary, multi-stage measures, in particular to temporarily lower its power consumption so that the reserve in the charging capacitor lasts longer. For this purpose, load is shed , for example by switching off light emitting diodes and / or other consumers. In extreme cases, the control unit can go into a kind of hibernation with a reduced clock rate and greatly reduced consumption, only to wake up again immediately after recognizing that full voltage has been reached again.
Ignition of the xenon light or another gas discharge lamp
The xenon light is based on the gas discharge of xenon gas, which is under very high pressure .
Cars have their own control unit for the complex processes, especially when switching on. Other gas discharge lamps are called ballasts or operating devices.
When switching on, an impulse with a very high voltage is primarily necessary to get the gas discharge going , the ignition or starting voltage impulse . Then, when the gas discharge is stable, the control unit can regulate it down to normal operating voltage. For further details see under gas discharge lamp and in the main article mentioned.