More of a basic electronics Q than an 8052 core question, but I've got a device that will run off of either USB power or a external regulated 5v supply. I'm not totally sure how I should "switch" the two possible supplies or how I should default to the external supply if both are plugged in.

I AM aware of the USB requirements for bus powered devices and I've got all that pretty much straightened out so that's not an issue.

I guess the problem is, howwhere do the two +5v "supplies" get connected? The way i've done it in the past is by connecting both through two low-drop diodes and then connecting the dropped voltages together. In this case, I really can't have a supply that is a diode drop less (5.0-0.7 = 4.3 for example).

Any helpadvice is appreciated!
John