  In this letter we propose a holistic analysis merging the techniques of
passivity-based control (PBC) and control barrier functions (CBF). We
constructively find conditions under which passivity of the closed-loop system
is preserved under CBF-based safety-critical control. The results provide an
energetic interpretation of safety-critical control schemes, and induce novel
passive designs which are less conservative than standard methods based on
damping injection. The results are specialised to port-Hamiltonian systems and
simulations are performed on a cart-pole system.
