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#20
January 12th 04, 12:19 AM
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This sounds like a good solution
Thanks Richard Dave Platt wrote: 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. |
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