The MB8S and MB6S are members of the same onsemi / Fairchild MB bridge rectifier family. They share an identical SOIC-4 footprint and all electrical parameters except voltage rating.
Side-by-Side Specifications
VRRM: MB8S = 800 V | MB6S = 600 V
VRMS: MB8S = 560 V | MB6S = 420 V
IF(AV): Both 0.5 A at TA = 50 °C
IFSM: Both 35 A (8.3 ms half-sine)
Package: Both SOIC-4 / TO-269AA
TJ range: Both −55 °C to +150 °C
When to Use MB8S Instead of MB6S
Choose the MB8S when the design operates from AC mains with higher peak transient voltages, or when an additional voltage margin is needed for reliability. For standard 230 V AC mains applications the MB6S is sufficient, but many engineers prefer the MB8S for extra headroom against voltage spikes and lightning transients.
Both the MB8S and MB6S are drop-in substitutes for each other from a PCB footprint perspective. The MB8S is sometimes used as a universal replacement across the full MB series in high-volume procurement to simplify BOM management.