When Q1 is switched on, current flows from the input
source through L and Q1, and energy is stored in the inductor.s magnetic field. There is no current through D1, and the load current is supplied by the charge in C1. Then when Q1 is turned off, L opposes any drop in current by immediately reversing its EMF . so that the inductor voltage adds to (i.e., .boosts.) the source voltage, and current due to this boosted voltage now flows from the source through L, D1 and the load, recharging C1 as well.
The output voltage is therefore higher than the input
voltage, and it turns out that the voltage step-up ratio is equal to: