A buck-type step-down converter incurs losses
in the on-resistances of the switches, the series resistance in the inductor, the ESR of
the output capacitor, and the switching transitions.
Approximations of the power dissipation in a
linear (a) and switching (b) regulator ignore the regulators' quiescent current, which is
negligible for high-current supplies.
In a tandem switcher/linear configuration, the
power does not vary with input voltage, except insofar as the input level affects the
efficiency of the switcher.
This tandem switcher/linear design seems
capacitor-heavy, but it uses thousands of microfarads less capacitance than does a pure
switching design (courtesy Linear Technology).
The use of a p-channel pass
element in National Semiconductor's LP2975 LDO regulator eliminates the need for a second
voltage supply or a charge pump to generate gate drive.
An LDO regulator is often the power supply of
choice because of its fast transient response. Fast response keeps transient glitches
smaller than 15 mV in response to a 3A current step in Unitrode's UC182 regulators.
Silence is golden in Linear Technology's
LT1533 switching-regulator controller. Soft switching of the internal power switches keeps
the noise lower than that of many linear regulators.
