In article ,
Dr. A.T. Squeegee wrote:

I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Power Schottky diodes are available that have a forward voltage
drop of 0.3 or less. More expensive, yes, but they really do work.

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

When a power supply of the correct polarity is hooked up, the MOSFET's
intrinsic substrate diode is biased forward (conducting normally) and
the MOSFET is turned on "hard" (giving a low Rds, and thus a very low
forward voltage drop). If the supply is hooked up backwards, the
MOSFET is turned off (the gate is pulled down towards hard depletion)
and the substrate diode is reverse-biased, switching it off.

--
Dave Platt AE6EO
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