Abstract: An undershoot eliminator circuit that avoids the occurrence of a negative undershoot that typically occurs when the secondary side synchronous driver of an isolated DC-DC converter is turned off. An energy storage element in an auxiliary supply on the secondary side of the converter is discharged to avoid a negative undershoot. The circuit includes a transistor having a gate terminal, a drain terminal connected to the storage element, a source terminal connected to the output of the converter; means for trapping charge on the gate terminal while the converter is on; and means for coupling the voltage on the output of the converter to the gate terminal, such that, when the converter goes off and its output voltage begins to drop, the trapped charge causes the gate-to-source voltage of the transistor to increase until the gate terminal is sufficiently saturated to cause it to turn on for a sufficient time to discharge the storage element.