SLUSD37E October 2017 – November 2019 UCC28056
The power switch carries the Boost inductor current during its ON period (TON). It carries no current during its OFF period (TDCH). Equation 28 describes the switch RMS current, over a single switching cycle, at angle θ in the Line half-cycle.
Equation 29 describes the duty cycle of switch conduction for ideal transition mode (CrM) operation.
The switch ON time is constant across the Line cycle but the OFF time varies according to the position in the Line cycle. Volt-second balance across the Boost inductor, within each switching cycle, requires that.
Equation 31 calculates the duty cycle of switch conduction.
Equation 32 describes the RMS switch current across a complete Line half-cycle.
Maximum RMS current in the switch occurs at maximum load and minimum Line.
Use the following guidelines for MOSFET selection for the Boost switch.