  We present the closed loop approach to linear nonequilibrium thermodynamics
considering a generic heat engine dissipatively connected to two temperature
baths. The system is usually quite generally characterized by two parameters:
the output power $P$ and the conversion efficiency $\eta$, to which we add a
third one, the working frequency $\omega$. We establish that a detailed
understanding of the effects of the dissipative coupling on the energy
conversion process, necessitates the knowledge of only two quantities: the
system's feedback factor $\beta$ and its open-loop gain $A_{0}$, the product of
which, $A_{0}\beta$, characterizes the interplay between the efficiency, the
output power and the operating rate of the system. By placing thermodynamics
analysis on a higher level of abstraction, the feedback loop approach provides
a versatile and economical, hence a very efficient, tool for the study of
\emph{any} conversion engine operation for which a feedback factor may be
defined.
