stores energy in the form of a magnetic field. If the switch is opened while the current is still changing, then there will always be a voltage drop across the inductor, so the net voltage at the load will always be less than the input voltage source. When the switch is opened again (off-state), the voltage source will be removed from the circuit, and the current will decrease. The decreasing current will produce a voltage drop across the inductor (opposite to the drop at on-state), and now the inductor becomes a current source. The stored energy in the inductor's magnetic field supports the current flow through the load. This current, flowing while the input voltage source is disconnected, when appended to the current flowing during on-state, totals to current greater than the average input current (being zero during off-state). The "increase" in average current makes up for the reduction in voltage, and ideally preserves the power provided to the load. During the off-state, the inductor is discharging its stored energy into the rest of the circuit. If the switch is closed again before the inductor fully discharges (on-state), the voltage at the load will always be greater than zero. Continuous mode Buck converters operate in continuous mode if the current through the inductor () never falls to zero during the commutation cycle. In this mode, the operating principle is described by the plots in figure 4: When the switch pictured above is closed (top of figure 2), the voltage across the inductor is . The current through the inductor rises linearly (in approximation, so long as the voltage drop is almost constant). As the diode is reverse-biased by the voltage source V, no current flows through it; When the switch is opened (bottom of figure 2), the diode is forward biased. The voltage across the inductor is (neglecting diode drop). Current decreases. The energy stored in inductor L is Therefore, it can be seen that the energy stored in L increases during on-time as increases and then decreases during the off-state. L is used to transfer energy from the input to the output of the converter. The rate of change of can be calculated from: With equal to during the on-state and to during the off-state. Therefore, the increase in current during the on-state is given by: where is a scalar called the duty cycle with a value between 0