Walking back through the link that Rob provided (albeit updated a bit) --

http://www.8052.com/forumchat/read/151766

One can track through an original link provided by Richard to:

http://electronicdesign.com/article/p...tecti.aspx

There the design concept for this type of circuit is shown in both the P-Channel configuration for high side switching and in the N-Channel configuration for low side switching.

In reviewing this I have to comment that it is important to carefully select the MOSFET so that its V_GS threshold is low enough that the device can be turned on as hard as possible to gain the best advantage of using the FET in lieu of a diode.

Another comment to be made is that in Stefan's original posting he showed using a voltage divider at the Gate connection to his N-FET. This circuit topology actually has the disadvantage of raising the voltage needed to fully enhance the N-FET and should probably be avoided in low voltage applications. In his case with the 6V battery and the 2SK2503 N-FET things are probably just fine as long as the battery is not expected to still be delivering power at very low voltages. The V_GS spec for the 2SK2503 reads as 1.0V-min to 2.5V-max at V_DS=10V and I_D=1mA.

Note that it took some doing to find a data sheet for the 2SK2503. Rohm has apparently discontinued this part and has a recommendation for another part number (RSD050N06). I ended up finding a datasheet to view at alldatasheet.com that was marked with a Rev.A but no published date.

Michael Karas