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Extra Fast impres Charger

IP.com Disclosure Number: IPCOM000145663D
Original Publication Date: 2007-Jan-22
Included in the Prior Art Database: 2007-Jan-22
Document File: 2 page(s) / 190K

Publishing Venue

Motorola

Related People

Ooi Thean Song: AUTHOR [+2]

Abstract

When charging a Li Ion battery, there is always voltage drop along charging path and causing cells in the battery not to charge to optimum charging voltage of 4.2V/cell. This paper is to introduce a simple and effective method to improve charging time of Li-Ion battery through improved impresTM charging system, with only charging algorithm change and addition data programmed into the EPROM data in the battery.

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Extra Fast impres Charger

Ooi Thean Song

Chong Kow Chee


Abstract

When charging a Li Ion battery, there is always voltage drop along charging path and causing cells in the battery not to charge to optimum charging voltage of 4.2V/cell. This paper is to introduce a simple and effective method to improve charging time of Li-Ion battery through improved impresTM charging system, with only charging algorithm change and addition data programmed into the EPROM data in the battery.

1.0  Introduction

Due to the volatile nature of lithium, chemistry characteristic of Li Ion cell limits it to be charged at maximum terminal voltage of 4.2V±1%. Typical charging method used is constant current (CC mode) at initial charging phase when the battery terminal voltage is lower than 4.2V times number of cell inside the battery, followed by Constant Voltage (CV mode) when battery terminal voltage reached 4.2V times number of cell inside the battery. During CV mode, charging current tapers and charger terminates charge process once current level drops below certain value.

2.0  Problem with existing charging method

For safety reason, charger terminal voltage is usually set to maximum 4.2V time number of cell in the battery during CV mode, voltage appear at cell terminal is lower than 4.2V due to IR drop caused by resistances along charging path. The higher the resistance and charging current, the higher the voltage will drop. In a Li Ion battery, protection circuitry contributes to the majority of the resistance along the charging path. Figure 1 shows the simplified battery circuitry attached to charger.

Figure 1: Simplified charging system.

The voltage drop across the charging loop will be:

                       (Equation...