Short Circuit and Reverse Polarity Protection

Can anyone help me? I have been designing some battery powered circuits and want to add Short Circuit and Reverse Polarity Protection to the boards in case my users put the batteries in wrong and was wondering what were the accepted methods (schematics) to go about adding this level of protection. I would like it all to be passive components but if someone knows of an ic that does it, please tell me. My circuits run off of a 9V-12V battery and as low as 3.6V. Current draw measured at 120mA under normal load but rated to hit as much as 7A under maximum load.

Any help/suggestions would be greatly appreciated.

-Jeremy

0 jvdberg@ieee.org over 14 years ago

A series diode will protect against reverse polarity, however this will lower the battery Voltage by 0.6 Volt. A fuse and parallel (zener)diode will protect against reverse polarity but will blow a fuse if the batteries are inserted the wrong way. If a PPTC resettable fuse is used in combination with a parallel zenerdiode, the circuit is protected against reverse polarity, overvoltage and short circuits. The PPTC resettable fuse will disconnect the circuit if the batteries are inserted the wrong way. If the batteries are removed, the fuse will reset. See http://www.farnell.com/datasheets/612670.pdf or the farnell catalog for data about PPTC resettable fuses. Johan
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0 Former Member over 13 years ago in reply to jvdberg@ieee.org

You could also use a Schottky diode as a series diode, that will only eat up 0.4V or less (depending on the size of the diode, and the current). Consider the MBR0520L from Fairchild, in a very small package (SOD123) and it has 250mV of voltage drop at room temp and 100mA. A resettable fuse certainly sounds like a good idea
hope that helps
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