Specifications

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running directly from the power output of the alternator, rather than from the
stable output of a healthy car battery being charged from the alternator.
In addition, some simple voltage regulation will be used on the portable unit, in
order to protect against any unexpected voltage transients. The battery in the
portable unit will also serve as a sort of voltage stabilizer, as it should output a
constant voltage within a certain, acceptable range as long as the battery is an
acceptable level of charge. However, wide variances in input voltage could be
dangerous as it could allow the battery to discharge acid, explode, or catch on
fire. Since this device will be used by the general public, as well as likely an
intoxicated individual, basic safety is an important concern.
Since one of the objectives of the overall project is to reduce cost, this concern
also extends to the voltage regulation portion of the circuits. This will be separate
from the charging circuit. The charging circuits will be designed with the
assumption of a regulated voltage input. The basic function of the voltage
regulator for this implementation is summarized in Figure 2.3.1-1.
2.3.1 Requirements
These regulators should be able to reliably function without failing or operating
below a desirable range, since the voltage regulators are essential for the basic
operation of the entire unit (both the control/base unit and the portable unit). They
should be able to accept an input from 5V all the way up to 20V, in order to
account for any possible temporary over voltages on the line. This is a realistic
possibility both in the vehicle and in the portable unit.
They should be able to output usable voltages. Since most logic operates at
3.3Vdc, this must be able to be output by a voltage regulator. In addition, there
will be additional voltage requirements. Namely, a 5Vdc output capability must be
present in order to account for devices that require the higher voltage. Despite
this, it must also be as compact as possible, since space it as at a premium in
both units, but especially in the portable unit.
Related to the size restraints, the regulators should not be taking up a significant
amount of room, since there are many other devices and circuits present in both
units. As such, they should be as compact as possible, as mentioned. In order to
accomplish this, they should be as simple as possible. In general, the more
complex the solution, the more space it will take up, as well as introduce points of
failure which would disable the rest of the devices. As such, the regulators should
ideally have the minimum number of components.
They also need to be low in cost. Since there will be other components that will
cost more, these regulators cannot take up a large portion of the budget. As
such, an ideal price would be below $5 for each regulator, bought in individual
quantity. In addition, given the overall requirement of reducing cost as much as