Battery Pack Discharge Control for Limiting Inrush Current

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Solution Overview

Problem

Traditional battery packs face issues with excessive discharge current when a capacitor is fully discharged, leading to potential damage and requiring additional off-chip components like current limiting switches and resistors, which increase cost and prolong turn-on time.

Innovation Solution

A battery management system (BMS) that generates a normal drive voltage and a ramp drive voltage to control the discharging switch, selecting between the two based on the voltage difference between the battery and pack voltages to prevent excessive current and adjust turn-on time, eliminating the need for additional off-chip components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an external pre-bias circuit with current limiting switch and resistor is used, then excessive current flowing into the capacitor is prevented, but additional cost and PCB area are incurred

Engineering Contradiction:

Improveprotection against excessive currentVSAvoidnumber of off-chip components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent integrates the current limiting function directly into the BMS chip by incorporating a current limiting circuit within the discharge control circuitry. This merging of functions eliminates the need for external current limiting components (switch and resistor), thereby reducing component count, PCB area, and cost while maintaining protection against excessive current when the capacitor is fully discharged

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The BMS chip is designed to perform multiple functions: battery management, discharge control, and current limiting protection. By making the BMS chip universal and capable of handling current limiting internally, the system eliminates dedicated external protection components, simplifying the overall circuit architecture while maintaining reliability

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If an external pre-bias circuit with current limiting resistor is used, then excessive current is limited, but battery pack turn-ON time is prolonged due to RC profile

Engineering Contradiction:

Improveprotection against excessive currentVSAvoidbattery pack turn-ON time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent extracts the current limiting function from external passive components (resistor) and implements it actively within the BMS chip's discharge control circuitry. This allows for dynamic current limiting that is not constrained by RC time constants, enabling fast turn-ON time while maintaining protection against excessive current

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the passive RC-based current limiting mechanism with an active electronic control system within the BMS chip. This substitution enables precise control of the discharge switch timing and current limiting without being bound by the inherent delays of RC circuits, thus reducing turn-ON time while maintaining protection

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If additional off-chip components are added for current limiting, then excessive current protection is improved, but manufacturing cost increases

Engineering Contradiction:

Improveprotection against excessive currentVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent combines the current limiting function with the BMS chip's existing discharge control circuitry, eliminating the need for separate external current limiting components. This integration reduces the bill of materials, assembly steps, and overall manufacturing cost while maintaining reliable protection against excessive current

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The BMS chip is designed as a multi-functional integrated solution that handles battery management, discharge control, and current limiting protection internally. This universal approach eliminates the need for multiple separate components, reducing both component count and manufacturing complexity, thereby lowering production costs while maintaining protection reliability

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10658856B1Battery pack and discharge method for limiting an excessive discharge current

Publication Date: 2020.05.19 MONOLITHIC POWER SYSTEMS INC

AI summary

A battery management system (BMS) used in a battery pack, the battery pack has a discharging switch coupled between a battery and a load, and the load has a capacitor charged by the battery pack. The BMS has a driver circuit having a power supply terminal to receive a drive voltage, a ground reference terminal coupled to receive the battery pack voltage and an output terminal coupled to a control terminal of the discharging switch. The BMS generates a normal drive voltage and a ramp drive voltage, and the normal drive voltage is selected as the drive voltage when the voltage difference between the battery voltage and the battery pack voltage is less than a threshold voltage, and the ramp drive voltage is selected as the drive voltage when the voltage difference between the battery voltage and the battery pack voltage is higher than the threshold voltage.