a) Linear voltage regulators
Linear voltage regulators control the output voltage, continuously adjusting the voltage drop in a power transistor that is connected in series between the unregulated input and the load.
Since an electric current must flow through the transistor all the time, the transistor have to operate in its linear region.
Although they are simpler to use than the switching regulators, they tend to be very inefficient due to the power consumed by the element in series. (the transistor)
Its efficiency is about 20% and are effective only for low power (<5 W).
b) Switching Regulators
Switching regulators use a power transistor as a high frequency switch, so that the energy is transferred from the input to the load in discrete packages.
Pulses of electric current are then converted into a direct current through an inductive and capacitive filter.
The transistor, operating as a switch, consumes less power than operating in its linear region.
These regulators are more efficient (up to 80%) than linear regulators; moreover, are smaller and lighter. These regulators can be designed to operate directly on the network voltage that is rectified and filtered, eliminating the need for a bulky transformer.
The disadvantage of switching regulators is that they have a more complex circuit and a higher ripple noise. Switching regulators are used especially in digital systems, where it is often more important a high efficiency and a low weight than a small output ripple.
The actual trend in designing multiple outputs power supplies, is to use switching regulators to leverage their strengths and then use regulators in series to achieve cleaner and better regulated voltages.
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