Smooth start-up to limit the inrush current is an important requirement in development of actively controlled power factor correction (PFC) rectifiers. In this paper, a thorough mathematical analysis is conducted to exploit the transient behavior during the start-up and thus, the expression for maximum inrush current is determined. Based on the analyses, a specifically designed start-up technique by controlling the time instant of engaging the PFC control loop is proposed, which achieves smooth start-up with zero current over/undershoot. As a proof-of-concept, experimental measurements are conducted at 1.5kW to validate the theoretical predictions. It is observed that there is no occurrence of inrush during the PFC start-up and also, unity power factor is maintained along with an efficiency of 98 % and input current THD below 5%.