Charging Apparatus Bypasses Current Sense Resistor

Solution Overview

Problem

Conventional charging apparatuses for lithium-ion batteries face issues with heat production due to power loss in control transistors, especially under heavy load conditions, leading to increased costs and space requirements in mobile devices.

Innovation Solution

A charging apparatus is designed with P-channel MOS transistors and a switch section that bypasses the current detecting resistance, allowing power to be supplied directly from the battery to the load after charging is complete, reducing heat loss and using general-purpose transistors with lower heat resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conventional charging control transistors are used to supply power from AC adapter to battery and load, then charging control function is achieved, but heat production increases under heavy load conditions

Engineering Contradiction:

Improvepower loss in control transistorVSAvoidheat production

Core Design Contradiction:

Loss of energyVSTemperature

Solution Approach 1:

The power supply path is segmented into two separate paths: one path through the control transistor for charging control, and another path through the switch section for direct power supply. This segmentation allows the control transistor to only handle charging current while load current bypasses it, reducing power loss and heat production in the control transistor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The switch section acts as an intermediary component that provides an alternative power supply path. It is controlled based on the difference between output current and battery charging current, enabling direct power supply from AC adapter to load when appropriate, thereby reducing the burden on the control transistor.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Temperature

If high heat resistance transistors are used to reduce heat production, then heat dissipation is improved, but device cost and space requirements increase

Engineering Contradiction:

Improveheat resistanceVSAvoidimplementation cost

Core Design Contradiction:

TemperatureVSEase of manufacture

Solution Approach 1:

The invention uses general-purpose transistors with lower cost instead of expensive high heat resistance transistors. By reducing power loss through circuit configuration rather than relying on expensive specialized components, the system achieves heat management with more economical parts.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Temperature

If high heat resistance transistors are used to minimize power loss, then heat production is reduced, but device area increases

Engineering Contradiction:

Improveheat productionVSAvoiddevice area

Core Design Contradiction:

TemperatureVSArea of stationary object

Solution Approach 1:

The power supply path is segmented into two separate paths: one path through the control transistor for charging control, and another path through the switch section for direct power supply. This segmentation allows the control transistor to only handle charging current while load current bypasses it, reducing power loss and heat production in the control transistor.

Inventive Principle:

Principle #1Segmentation

4Device complexity

If conventional charging control is used without bypass path, then charging control is simplified, but power loss and heat production increase

Engineering Contradiction:

Improvecontrol circuit complexityVSAvoidpower loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The switch section acts as an intermediary component that provides an alternative power supply path. It is controlled based on the difference between output current and battery charging current, enabling direct power supply from AC adapter to load when appropriate, thereby reducing the burden on the control transistor.

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration reduces heat production, lowers implementation costs and space requirements, and enhances safety by minimizing power loss in control transistors, even during heavy loads.

Implementation Method 1

heat production due to power loss of control transistor

Methodology Applied

Scientific EffectJoule Heating: Joule Heating

Implementation Method 2

current detecting resistance Rs that detects current flowing into the secondary battery

Methodology Applied

Scientific EffectOhm's Law: Ohm's Law

Data Source

PatentUS7839122B2Charging apparatus

Publication Date: 2010.11.23 PANASONIC SEMICON SOLUTIONS CO LTD

AI summary

There is provided a charging apparatus that, even when an AC adapter is connected and there is heavy load, makes it possible to reduce heat produced due to the power loss of a control transistor, reduce cost and area for implementation, and improve safety. Charging apparatus 100 has: P-channel MOS transistors M1 and M2 that control charging current; current detecting resistance Rs that is connected to current output terminals of P-channel MOS transistors M1 and M2 and detects the charging current; switch 130 that is arranged on a path that bypasses current detecting resistance Rs; and load 300 that receives power supply from battery 200 without involving current detecting resistance Rs when switch 130 is closed. Current difference amplifier 120 amplifies the detected voltage of current detecting resistance Rs, comparator 160 compares the output voltage of current difference amplifier 129 with the reference voltage, and thereby, when current flowing into battery 200 is equal to or less than a predetermined value, switch 130 is closed and current detecting resistance Rs is short-circuited.