Abstract: A protection circuit for a DC power supply which protects the power supply nd its load against transient over voltages which may exist at the input to the power supply. The device also includes circuitry for protection of the power supply elements against short circuiting due to load failure. The circuit provides rapid and positive disconnect at the power supply input when a transient overvoltage is impressed, and an effective shut down of the entire power supply in the event of a short-circuit load. The device includes a transient voltage sensor network connected to a temperature stabilized powerload disconnect switch utilizing semi-conductive elements capable of extremely high switching speeds. The circuit switching is sufficiently fast such that the load operation and performance is not noticeably affected in the presence of fast transients impressed at the input to the power supply. Power dissipation in the device is confined to extremely fast turn on and turn off switching losses and saturation losses.