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BATTERY CHARGER WITH LOAD DETECTION AND COMPENSATION

IP.com Disclosure Number: IPCOM000007391D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-21
Document File: 2 page(s) / 116K

Publishing Venue

Motorola

Related People

Bob Stengel: AUTHOR [+2]

Abstract

Battery chargers are designed to recharge bat- teries with a rapid rate of current (1 times battery capacity) followed by much lower trickle charging rate (l/20 times battery capacity-NiH)). When the trickle charging rate of the battery charger is lower than the standby current drain ("on" condition) of the portable radio the battery is discharged by a radio left "on" in the battery charger. If the portable is in the charger over a long enough period such as a weekend, this could result in a completely discharged battery coming out of the battery charger on Mon- day morning. This is a condition that exists in the held today for Jedi products and has been a cus- tomer complaint.

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MO7VROLA Technical Developments Volume 24 March 1995

BATTERY CHARGER WITH LOAD DETECTION AND COMPENSATION

by Bob Stengel and Curtis Griffin

  Battery chargers are designed to recharge bat- teries with a rapid rate of current (1 times battery capacity) followed by much lower trickle charging rate (l/20 times battery capacity-NiH)). When the trickle charging rate of the battery charger is lower than the standby current drain ("on" condition) of the portable radio the battery is discharged by a radio left "on" in the battery charger. If the portable is in the charger over a long enough period such as a weekend, this could result in a completely discharged battery coming out of the battery charger on Mon- day morning. This is a condition that exists in the held today for Jedi products and has been a cus- tomer complaint.

  There are several good methods that can be con- sidered to solve this battery discharging condition. However, the solution ideally would be backward compatible with the equipment that exist in the field with no rework required. This means the radios and battery chargers in stock and in the field must work with any new batteries designed to overcome this discharging condition. The new battery must work with equal or better performance to the existing equipment, and establish a condition where the charger will supply sufficient trickle current. The trickle current must be able to maintain the battery charging function and if the transceiver is "on" increase to accommodate the standby current as well.

  To achieve this the battery circuitry was modi- fied with a TMOS n-channel SenseFet"' in series with the transceiver ground terminal to the battery, This provides a means of measuring the transceiver current drain by a current mirror method instead of an in-line series resistor voltage drop measurement. Using a current mirror eliminates the power loss in the series resistance during transmitter very high current conditions. In addition the SenseFetTM can be used to control the transceiver connection to the battery supply limiting current or disabling the trans- ceiver. Another important use would be short cir- cuit protection that would eliminate the fixed safety

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resistors used in battery packs.

  When the transceiver current is measured by the SenseFet" above a predetermined level the bat- tery internal capacity resistance value is modified. T...