  We model a tiny heat engine as a Brownian particle that moves in a viscous
medium in a sawtooth potential (with or without load) assisted by $\it
{alternately}$ placed hot and cold heat baths along its path. We find closed
form expression for the steady state current as a function of the model
parameters. This enables us to deal with the energetics of the model and
evaluate either its efficiency or its coefficient of performance depending upon
whether the model functions either as a heat engine or as a refrigerator,
respectively. We also study the way current changes with changes in parameters
of interest. When we plot the phase diagrams showing the way the model
operates, we not only find regions where it functions as a heat engine and as a
refrigerator but we also identify a region where the model functions as neither
of the two.
