An electronic actuator assembly (130, 200) configured for use with a pushbar assembly having a drive assembly operable to retract a latchbolt, the electronic actuator (135, 250) assembly (130, 200) comprising: a link (132, 220) mounted for reciprocal movement along a longitudinal axis in a proximal direction and an opposite distal direction between an extended position and a retracted position, wherein the link (132,220) is configured for connection to the drive assembly such that movement of the link (132, 220) in the distal direction is operable to cause retraction of the latchbolt; an input shaft (133, 230) connected to the link (132, 220) via a lost motion connection (134, 240), wherein the input shaft (133, 230) is mounted for reciprocal movement in the proximal direction and the distal direction, the input shaft (133, 230) having a proximal position, a distal position, and an intermediate position between the proximal position and the distal position; an electronic actuator (135, 250) operable to drive the input shaft (132, 220) between the proximal position and the distal position; and an overtravel spring connected between the link (132, 220) and the input shaft (133, 230), wherein the overtravel spring is configured to drive the link (132, 220) from the extended position to the retracted position in response to movement of the input shaft (133, 230) from the proximal position to the intermediate position, and to deform in response to movement of the input shaft (133, 230) from the intermediate position to the distal position such that the link (132, 220) remains in the retracted position during movement of the input shaft (133, 230) from the intermediate position to the distal position, thereby altering a relative position of the link (132,220) and the input shaft (133, 230); characterized in that the electronic actuator assembly (130, 200) comprises a boost spring exerting a boost force urging the input shaft (133, 230) in the proximal direction, wherein the boost force is independent of the relative position of the link (132, 220) and the input shaft (133, 230). a link (132, 220) mounted for reciprocal movement along a longitudinal axis in a proximal direction and an opposite distal direction between an extended position and a retracted position, wherein the link (132,220) is configured for connection to the drive assembly such that movement of the link (132, 220) in the distal direction is operable to cause retraction of the latchbolt; an input shaft (133, 230) connected to the link (132, 220) via a lost motion connection (134, 240), wherein the input shaft (133, 230) is mounted for reciprocal movement in the proximal direction and the distal direction, the input shaft (133, 230) having a proximal position, a distal position, and an intermediate position between the proximal position and the distal position; an electronic actuator (135, 250) operable to drive the input shaft (132, 220) between the proximal position and the distal position; and an overtravel spring connected between the link (132, 220) and the input shaft (133, 230), wherein the overtravel spring is configured to drive the link (132, 220) from the extended position to the retracted position in response to movement of the input shaft (133, 230) from the proximal position to the intermediate position, and to deform in response to movement of the input shaft (133, 230) from the intermediate position to the distal position such that the link (132, 220) remains in the retracted position during movement of the input shaft (133, 230) from the intermediate position to the distal position, thereby altering a relative position of the link (132,220) and the input shaft (133, 230); characterized in that the electronic actuator assembly (130, 200) comprises a boost spring exerting a boost force urging the input shaft (133, 230) in the proximal direction, wherein the boost force is independent of the relative position of the link (132, 220) and the input shaft (133, 230).