RE:""danyk:.... that duty cycle is very low. The upper diode is opened for very short times only (and carries almost no average current) and thus almost the entire 40A flows through the lower diode.""
Sure right, yet upper comes in with large voltage, whilst load has small Voltage, therefore even at short period the carried energy by D1 is sufficient for load current sustain. Thus D1 has equal I(Peak to Peak) with D2 but smaller I(AVR), except the 50/50% duty cycle.
Have a nice weekend, guys!

