Hi Jonathan,
JDBP> JDBP>> The FIC PA 2012 uses a switching voltage regulator.  I'm told 
that
JDBP> JDBP>> that is good, although I have yet to find an explanation as to
JDBP> JDBP>> why.
JDBP> GW> Because they generate a lot less heat than a linear one and so need
JDBP> GW> much smaller heatsinks. Which is why the main power supply uses
JDBP> GW> switching regulators.
JDBP>What's the difference, electrically speaking, between the two ?
I see you've asked several of us basically the same question :-(
Here's my version of the details.
In a linear regulator the controlling element (a transistor or FET) can
be considered as a controllable variable resistor. The current in is
essentially the same as the current out (+ a litle for the control
circuit), and so the power in is Vin * I, the power out is Vout * I, and
the difference, (Vin - Vout) * I, is dissapated in the controlling
element.
In a switching regulator the controlling element is a compound of two
devices, a transistor, FET or thyristor used as a switch and an
inductor. The variation of the on/off ratio of the switch, in
conjunction with the inductor is used to control the amount of charge
(== power) transferred from the supply to the load. The power loss is
the resistive loss of the inductor, plus the on resistive loss of the
switching device plus the switching loss of the controlling device plus
the power for the control circuitry. With careful design these can be
made very small, >90% efficiency is possible. Even where the regulator
is designed to handle a wide range of load current and supply voltage
variations they can be >80% efficient. The lowest efficiency quoted for
a module in the Farnell catalogue is 60% typical for a range of units
generating 1.5 Watts of power at rated outputs ranging from 200V to
1500V from a 12 volt input.
The higher the switching frequency, the smaller the inductances needed,
and switching regulators usually run anywhere from 20 kHz up to the low
100s of kHz. As part of the control element is an inductor it can be
used as a transformer so that if required a switching power supply can
be designed provide output voltages above the input voltage.
I have some old Cromemco "boat anchor" system boxes here using linear
supplies. The transformer alone is about the same size as a standard PC
power supply (and they are mostly empty space these days). The smoothing
capacitors are enormous, they take up even more space than the
transformer. The requlation was done on the S100 cards, so for an output
capability around that of a current PC it uses several times as much
space and dissapates many times the amount of power.
George
 * SLMR 2.1a * Wastebasket: Something to throw things near.
--- Maximus/2 3.01
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