I would like to offer an alternate solution to the problem of protecting a high-side solid-state switch from inductive transients (see Walsh's Design Idea #1275 referenced above). An inductive load can generate 1000 or more negative volts, depending on the size of the inductor. I doubt that Walsh's scheme really protects the Darlington. I suggest that paralleling the inductor with a diode limits the transient resulting from the magnetic field's collapse to one diode drop plus some minor amount of overshoot.
Glenn F Hoffstatter
15600 Ocaso Ave
La Mirada, CA 90638
Changing a diode position in a battery circuit can save you some forward-drop voltage (see Walsh's Design Idea #1275 referenced above). However, in some situations, such as with a nonrechargeable lithium battery, this technique may not be advisable. Several safety agencies, such as UL, require two devices in series to prevent a hazard. Hazards can be reverse charging, forced charge, forced discharge or reverse-polarity installation. Two devices are required in the event of a fault in one device. If your circuit may be affected, you must keep this restriction in mind.
James Goedderz
Product Safety Engineer
Zenith Data Systems
211 Hilltop Rd
St Joseph, MI 49085