An implantable pulse generator (IPG) for an implantable medical device is disclosed herein. The IPG is capable of sensing the presence of an external magnetic field, such as a magnetic field associated with magnetic resonance imaging (MRI). The IPG includes a circuit that contains a magnetic core inductor and that is configured to boost a first voltage to a second voltage and use the second voltage to drive a current through a load. In a strong magnetic field, the magnetic core of the inductor becomes magnetically saturated, causing the inductance of the inductor to sharply drop. The inductance drop can be detected, for example, by detecting an increase in the second voltage. The circuit may be a boost converter circuit used to provide a compliance voltage for operation of the IPG.
