Full wave rectifier forwarding state

In a bridge rectifier, the current passes through two rectifying elements in series. It accepts input in either direction, including AC, but outputs (after passing through two elements) in only one direction.

The forward voltage is the voltage lost across the elements. For a silicon rectifier this will be a minimum of 0.65 V for very low currents, but due to internal resistance it will increase as the current increases. By the time the current reaches 8 A, your rectifier is dropping 1.0 V across each element.

That makes 2.0 V in all, whichever direction the input is flowing, so the output voltage will be 2 V less than the input voltage.

All silicon diodes are exponential towards rated current and above this become linear due to bulk resistance, Rs, due to chip size and its Pmax rating @ 85’C. Thus the peak voltage drop is totally dependant on the peak current and chip size. Voltage drop will increase with junction temp. rise.

To reduce Vf, a much larger diode chip size with a much higher current continuous current rating for your load.

Incidentally The series Rs is inversely related to the max current and/or power rating by some constant. Rs=k/Pmax where k~0.2 in good parts.