The LM2578AN Switchmode Voltage Regulator

LM2578AN is a switchmode voltage regulator capable of both buck and boost performance,
with a maximum output current of 750 milliampers. Although it uses more components in a
typical application than a linear regulator, it has far-increased efficiency, and not prone to
safe-operating constraints that are found in linear counterparts.

LM2578AN Application Schematics

However, the disadvantage of any switchmode parts is that they are relatively noisy in comparison
to their linear regulator counterpars, and may affect associated circuitry in sensative applications.

While time-proven and seemingly easy to apply, there are some common unpleasant surprises that
users may encounter; despite the relatively simplistic appearance in the manufacturwers' data sheet,
they earn some considerations that need to be mastered in order to make their application

One element of these constraints include the choice of the feedback network resistor (R1, RV1,
and R2 shown in the figures.) Another is size of the inductor (L1), which, if too small, will saturate,
and thus cause the circuits to draw excessive curren and attendant heating of the ICs.

It is quite surprising to  learn that the values of the voltage divider resistors and potentiometers
desrve critical analysis viz a viz simple formulae provided by the manufacturer. Yet, often, the
values of these reistors must be quite exact, and demand parts that are one-percent tolerance types
from the EIA E96 series of values. Forunately, the values of capacitors in these circuits are far-more
forgiving, with +/-20 per=cent being quite suffcient.

The diode, D1, should always be selected to have a working voltage minimally twice that of the
output voltage; this is not intuitively obvious, since the instinctive selection of this parameter is to
use a part that has a reverse working voltage just a bit above the output voltage.

So, if you are having trouble with applying this circuit, feel free to drop me an email, and I'll do
my best to help.

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Art Harrison
December 2, 2023

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