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LOW BATTERY ALERT FOR A VOLTAGE REGULATED INTRINSICALLY SAFE BATTERY

IP.com Disclosure Number: IPCOM000007376D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-20
Document File: 2 page(s) / 97K

Publishing Venue

Motorola

Related People

Scott M. Garrett: AUTHOR

Abstract

Certain intrinsically safe radio systems require that the voltage available to the radio be limited by regulation to preclude the possibility of an unsafe energy storage level. However, when the regulated voltage is significantly below the nominal raw cell pack voltage, charge level information is masked from the radio and it can no longer make any end of life determinations. For example, Jedi CENELEC has a 6.2V regulator inside the battery. The standard radio software would consider this a low battery Sim- ply changing the voltage at which the radio alerts the user is not sufficient since that assumes the reg- ulator falls out of range at the appropriate point.

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MOTOROLA Technical Developments Volume 24 March 1995

LOW BATTERY ALERT FOR A VOLTAGE REGULATED INTRINSICALLY SAFE BATTERY

by Scott M. Garrett

  Certain intrinsically safe radio systems require that the voltage available to the radio be limited by regulation to preclude the possibility of an unsafe energy storage level. However, when the regulated voltage is significantly below the nominal raw cell pack voltage, charge level information is masked from the radio and it can no longer make any end of life determinations. For example, Jedi CENELEC has a 6.2V regulator inside the battery. The standard radio software would consider this a low battery Sim- ply changing the voltage at which the radio alerts the user is not sufficient since that assumes the reg- ulator falls out of range at the appropriate point.

  Regulator fallout would be a solution were it only necessary to indicate a low battery under one condition, i.e. standby or transmit, however, that solu- tion is not acceptable. If the regulator is set to fall out in standby, and the user transmits just before the standby input voltage is low enough to cause regulator fall out, the regulator voltage will fall out so much that the radio will reset witthout ever warn- ing the user. This was the case with prototype cir- cuits where it was found that at a 5/S/90 duty cycle the user would have only one minute of warning before the battery voltage dropped low enough to reset the radio. On the other hand, if the regulator is set to fall out during transmit, and the user only transmits occasionally, or never, the low battery alert will come on very early. To enable the radio to alert the user at the appropriate time, something had to be done in the battery.

  To help aid the radio to alert the user of a low battery condition, the battery regulator circuit has a sub-circuit that samples the input (cell pack) volt- age and adjusts the output voltage to a value significantly lower than the regulated nominal volt-

age. For example, the...