When the power switch in the LM2676 turns OFF, the current through the inductor continues to flow. The path for this current is through the diode connected between the switch output and ground. This forward-biased diode clamps the switch output to a voltage less than ground. This negative voltage must be greater than –1 V so TI recommends a low voltage drop (particularly at high current levels) Schottky diode. Total efficiency of the entire power supply is significantly impacted by the power lost in the output catch diode. The average current through the catch diode is dependent on the switch duty cycle (D) and is equal to the load current times (1-D). Use of a diode rated for much higher current than is required by the actual application helps minimize the voltage drop and power loss in the diode.

During the switch ON time, the diode is reversed biased by the input voltage. The reverse voltage rating of the diode must be at least 1.3 times greater than the maximum input voltage.