BMS Protection Circuit Using Diode Array Against MOSFET Avalanche

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Solution Overview

Problem

Existing battery management systems (BMS) face challenges in protecting MOSFETs from voltage spikes and degradation during short-circuit events, as energy accumulated in inductive elements can cause the MOSFET to conduct and enter avalanche mode even when switched OFF.

Innovation Solution

A vehicle battery system is provided with a BMS that includes a cutoff circuit electrically coupled to a short-circuit protection circuit. The short-circuit protection circuit features a diode array that redirects and dissipates current resulting from undesirable voltage conditions, while a reverse bias protection circuit maintains the MOSFET in an OFF state by directing current to a low-current leakage transistor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a current detection circuit is implemented to detect higher current during short-circuit events, then the MOSFET can be switched OFF in time, but energy accumulated in inductive elements can still cause the MOSFET to conduct and enter avalanche mode

Engineering Contradiction:

ImproveMOSFET protection from short-circuit degradationVSAvoidEnergy accumulation in inductive elements causing avalanche mode

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A diode array is introduced as an intermediary component between the inductive elements and the MOSFET. The diode array provides a dedicated current path that allows accumulated energy to dissipate through the diodes rather than forcing the MOSFET into avalanche mode. The diodes act as a mediator that safely channels the harmful energy away from the vulnerable MOSFET device.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The diode array is pre-configured to provide a protective current path before the MOSFET can be damaged by avalanche mode. When voltage conditions indicate potential short-circuit events, the diode array is already in place to redirect current away from the MOSFET, preventing the harmful avalanche effect from occurring in the first place.

Inventive Principle:

Principle #9Preliminary anti-action

2Reliability

If the MOSFET is switched OFF to protect from higher current, then short-circuit protection is achieved, but voltage spikes can still cause degradation to electronic components

Engineering Contradiction:

ImproveProtection from short-circuit currentVSAvoidVoltage spikes degrading electronic components

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The diode array serves as an intermediary that absorbs and redirects voltage spikes away from sensitive electronic components. When voltage spikes occur during or after MOSFET switching, the diodes provide a clamping effect and alternative current path, preventing the spikes from reaching and degrading other electronic components in the system.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The diode array is pre-positioned in the circuit to cushion against upcoming voltage spikes. Before the spikes can damage components, the diodes are already configured to absorb and redirect the excess voltage energy, providing a protective buffer that cushions the system against electrical shocks and transients.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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

The solution effectively protects the MOSFET and the BMS from degradation by maintaining the MOSFET in an OFF state during reverse bias voltage or short-circuit events, preventing energy accumulation and subsequent avalanche mode, thus extending the lifespan of the BMS and battery pack.

Implementation Method 1

the short-circuit protection circuit includes a diode array, where cathodes of the diode array are directly electrically coupled to a positive terminal post of the battery pack and anodes of the diode array are directly electrically coupled to a negative terminal post of the battery pack

Methodology Applied

Scientific EffectDiode rectification: Diode

Implementation Method 2

a reverse bias protection circuit maintains the MOSFET in an OFF state by directing current to a low-current leakage transistor

Methodology Applied

Scientific EffectReverse bias protection:

Implementation Method 3

the BMS to timely switch OFF a given MOSFET at risk of receiving the higher current

Methodology Applied

Scientific EffectMOSFET switching:

Data Source

PatentUS12266923B2Protection circuit for battery management system

Publication Date: 2025.04.01 A123 SYSTEMS LLC

AI summary

Systems and methods are provided for a battery management system (BMS) having a protection circuit. In one example, a vehicle battery system may include the BMS, the BMS including a cutoff circuit coupled to a short-circuit protection circuit, and a battery pack, wherein the short-circuit protection circuit may include a diode array, cathodes of the diode array being coupled to a positive terminal post of the battery pack and anodes of the diode array being coupled to a negative terminal post of the battery pack. In some examples, the cutoff circuit may further be coupled to a reverse bias protection circuit including a switchable current path arranged between a control input of the cutoff circuit and an output of the cutoff circuit. In this way, the vehicle battery system may be protected from unexpected voltage conditions via the BMS redirecting and dissipating excess current away from the cutoff circuit.