A therapy system for applying an electrical signal to an internal anatomical feature of a patient includes an implantable component and an external component. The medical device can be checked for safety issues by periodically initiating a sequence of tests of an H-bridge circuit, and, during each test, monitoring a current flow through a sensing resistor electrically connected between a sensing connection of the H-bridge circuit and a ground. Current flow through the sensing resistor indicates that both series electrical switches within at least one of the two pairs of series electrical switches are active during that test.
