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AUTOMATIC BATTERY POLARITY REVERSING CIRCUIT

IP.com Disclosure Number: IPCOM000005981D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-21
Document File: 1 page(s) / 55K

Publishing Venue

Motorola

Related People

Jim Wiggenhorn: AUTHOR [+3]

Abstract

DC voltage operated electronic circuits are often polarity sensitive and require their battery source to be placed correctly or else possible damage may occur. A full-wave bridge diode circuit would allow battery placement regardless of polarity but would drop 1.4V if Silicon diodes are used and would result in significant power loss.

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MOlVROLA Technical Developments Volume 11 October 1990

AUTOMATIC BATTERY POLARITY REVERSING CIRCUIT

by Jim Wiggenhorn, Dave Goodman and Junious Wilson

   DC voltage operated electronic circuits are often polarity sensitive and require their battery source to be placed correctly or else possible damage may occur. A full-wave bridge diode circuit would allow battery placement regardless of polarity but would drop 1.4V if Silicon diodes are used and would result in significant power loss.

   This circuit similarly enables battery placement regardless of polarity but provides a low voltage drop from battery to load (about 0.3V) and is therefore more efficient than a full wave bridge using diodes. Two possible circuits using transistors biased in saturation may accomplish this and are shown below. Each circuit has advantages and disadvan- tages to consider.

   Circuit I: For the polarity with plus on the top and minus on the bottom, transistors B and C will be biased ON (in saturation) and transistors A and D will be biased OFF. The reverse is true if minus is on the top and plus is on the bottom. Either way, the load RL will see the correct polarity. The resistor Rb provides the biasing of both transistors B & C or A & D depending on the polarity of the battery. This circuit has the advantage of lower base currents since the gain of the transistors are utilized. Its disadvantage is that the reverse emitter-base junction breakdown voltage of the transistors must not be exceede...