Browse Prior Art Database

Reversed Battery Polarity Protection

IP.com Disclosure Number: IPCOM000117974D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Kangas, PD: AUTHOR [+3]

Abstract

This disclosure describes a method for preventing circuit damage by restricting reverse current flow in the event that the battery is installed with the polarity reversed. This method provides a low cost means of restricting reverse current flow without the added voltage drop of a simple diode, significant leakage current (important for high lifetime batteries such as for time of day clocks), or the added expense of a special battery receptacle.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 79% of the total text.

Reversed Battery Polarity Protection

      This disclosure describes a method for preventing circuit
damage by restricting reverse current flow in the event that the
battery is installed with the polarity reversed.  This method
provides a low cost  means of restricting reverse current flow
without the added voltage drop  of a simple diode, significant
leakage current (important for high lifetime batteries such as for
time of day clocks), or the added expense  of a special battery
receptacle.

      A MOSFET is used to interrupt the current from the battery in
the case where the battery is inserted backwards.  Using an insulated
gate FET will allow control of the device resistance without wasting
current.  Using a N channel, enhancement mode FET, the source should
be connected to circuit ground, gate to the positive battery terminal
and drain to the negative battery terminal.

      The FET must have a low Vgs threshold to insure low Rds (low
voltage drop) when the battery is correctly inserted and near it's
minimum voltage.  In this case the voltage of the battery will
approach 2 V when it is near depletion.  The current required by the
battery power circuit is 30 to 60 uA.  If the battery polarity is
reversed, the  gate of the FET will become very positive with respect
to the source, and the FET will be switched into a high impedance
state, preventing current flow which would damage the circuits.

      Note that this configuration applies opposit...