In this paper, smooth output feedback stabilization (OFS) problem of planar output-constrained switched nonlinear systems (SNS) is investigated. Adding a power integrator technique (APIT) is employed to design state feedback controllers in a systematic manner combining with a constructed common logarithm-type barrier Lyapunov function (BLF). Then, by incorporating the variable-gain reduced-order observers designed constructively, switched systems can be stabilized via smooth output feedback and the output constraint is guaranteed simultaneously. Finally, simulations results are shown to exemplify the validity of the method proposed in this paper. (c) 2021 ISA. Published by Elsevier Ltd. All rights reserved.