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Method for accurate measurement of Battery voltage

IP.com Disclosure Number: IPCOM000009244D
Original Publication Date: 2002-Aug-13
Included in the Prior Art Database: 2002-Aug-13
Document File: 3 page(s) / 30K

Publishing Venue

Motorola

Related People

TANEKA FRAZIER: AUTHOR

Abstract

It is not uncommon for a battery pack to have a thermistor and/or code resistor contact(s) to allow battery detection by a charger. Although these contacts can be changed based on the battery's environment, the battery pack will always have a B+ and B- contact for charge/discharge purposes. This invention will discuss how a battery can be detected by relying on battery voltage and a charger's discharge circuit.

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Method for accurate measurement of Battery voltage

AUTHOR

TANEKA FRAZIER

Problem

It is not uncommon for a battery pack to have a thermistor and/or code resistor contact(s) to allow battery detection by a charger.� Although these contacts can be changed based on the battery’s environment, the battery pack will always have a B+ and B- contact for charge/discharge purposes.� This invention will discuss how a battery can be detected by relying on battery voltage and a charger’s discharge circuit.

Solution

For most chargers, it is a must that a discharge circuit is in place to allow discharging of over-voltage lithium batteries or for providing a means for battery calibration.� Another common element of these chargers is the presence of one or more capacitors at the charger output.� These caps are required for filtering, stability, or even ESD protection of the charger output.

Depending on the environment, when a battery is removed while charge current is applied, the charger will read a high battery voltage, V1.� If the termination voltage of the battery is relatively close to V1, then it becomes difficult for the charger to distinguish a fully charged battery from a battery that has been removed.� The charger must then disable the charge current and measure battery voltage.� When no battery is present, the battery voltage will drop to roughly 0V.� If a battery is present, then the battery voltage will be maintained.� However, a problem arises, when the charger attempts to measure the battery voltage just after the charge current has been disabled.� The un-discharged energy storage elements, i.e. capacitors, on the charger output will maintain a voltage on the charger output for some time, T1, even after the charge current has been turned off.� Consequently, any attempt to read the battery voltage in this time frame will result in an erroneous measurement.

This invention solves this problem by using the charger’s discharge feature to explicitly discharge the charger’s output caps to enable an accurate measurement of the battery voltage.� When the battery voltage reaches the voltage where battery presence becomes unknown, the charger must then instantly disable charging, take a voltage reading, V2, instantly enable the discharge circuit, take another voltage reading, V3, instantly disable discharging, and finally compare the two voltages.� If no battery is present, then the voltage...