Fault diagnosis of switching devices is crucial for improving the reliability of power converters. In this paper, a current-slope-based fault diagnosis scheme is proposed for power switches in asymmetric half-bridge converters. First, a new current sensor installation scheme is proposed to obtain more current information for fault diagnosis while using fewer power devices and current sensors. In addition, a simple algebraic expression for the phase current under normal conditions is derived. Second, the principles of the fault diagnosis scheme are presented, enabling effective fault diagnosis of switches by digitizing the current slope. Finally, experiments are carried out on a four-phase switched reluctance motor system to verify the effectiveness of the proposed fault diagnosis scheme.