  Currently, the superconducting diode effect (SDE) is actively discussed due
to large application potential in superconducting electronics. In particular,
the superconducting hybrid structures based on three-dimensional (3D)
topological insulators are among the best candidates due to the strongest
spin-orbit coupling (SOC). Most of the theoretical studies of the SDE focus
either on full numerical calculation, which is often rather complicated or on
the phenomenological approach. In the present paper we perform a comparison of
the linearized and nonlinear microscopic approaches in the superconductor/
ferromagnet/ 3D topological insulator (S/F/TI) hybrid structure. Employing the
quasiclassical Green's function formalism we solve the problem
self-consistently. We show that the results obtained by the linearized
approximation are not qualitatively different from the nonlinear solution. Main
distinction in the results between the two methods is quantitative, i. e. they
yield different supercurrent amplitudes. However, when calculating the
so-called diode quality factor the quantitative difference is eliminated and
both approaches can result in a good agreement.
