Parallel MOSFET Protection Circuit for Inductive Avalanche Relief
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Solution Overview
Problem
In high power demand applications, such as vehicles with parallel MOSFET switches, the energy stored in cable harness inductance can cause current to continue flowing after the main switch shuts off, leading to potential avalanche events and damage to MOSFETs without additional countermeasures.
Innovation Solution
A protection switch circuit with MOSFETs arranged in parallel to the main switch, controlled by detection and control circuitry to dynamically manage current and energy dissipation, reducing the risk of avalanche events and allowing the use of less expensive MOSFETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the main switch shuts off to protect against faults, then the load is protected from damage, but the stored energy in cable harness inductance causes current to continue flowing through the MOSFETs, leading to avalanche events and potential MOSFET damage
Solution Approach 1:
The patent introduces a protection circuit as an intermediary element between the main switch and the load. This protection circuit includes a protection MOSFET and associated components that act as a mediator to handle the inductive kickback energy, preventing it from causing avalanche events in the main switch MOSFETs while allowing the main switch to perform its fault protection function.
Solution Approach 2:
The protection circuit is designed to be in place before fault conditions occur, providing a pre-established pathway for dissipating inductive energy. The circuit includes energy dissipation components that are ready to absorb and dissipate the stored energy from cable harness inductance before it can cause damage to the main switch MOSFETs.
2Reliability
If robust MOSFETs with high avalanche capability are used, then MOSFET damage is prevented, but the cost of the power switch circuit increases significantly
Solution Approach 1:
The patent employs cheaper MOSFETs for the main switch that do not require high avalanche capability, since the protection circuit will handle the energy dissipation. The protection circuit itself acts as a sacrificial element that absorbs the stress, allowing the use of more cost-effective main switch components.
Solution Approach 2:
By introducing the protection circuit as an intermediary, the patent decouples the requirement for high avalanche capability from the main switch MOSFETs. The protection circuit absorbs the avalanche stress, allowing the main switch to use less expensive, lower-rated MOSFETs.
3Reliability
If costly countermeasures like TVS diodes and snubber circuits are added, then avalanche events are prevented, but the device complexity and cost increase
Solution Approach 1:
The patent merges the protection function into a integrated protection circuit that combines a protection MOSFET with energy dissipation components. This unified approach provides avalanche protection without requiring separate TVS diodes, snubber circuits, or other discrete protection components, thereby reducing overall circuit complexity.
Solution Approach 2:
The protection circuit is designed to perform multiple functions: it provides avalanche protection, dissipates inductive energy, and enables the use of cheaper main switch MOSFETs. This multi-functional design eliminates the need for multiple separate protection components.
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 dissipates stored energy, preventing MOSFET damage and reducing costs by using less robust MOSFETs, while minimizing the need for costly countermeasures like TVS diodes and snubber circuits.
Implementation Method 1
The protection switch circuit is configured to relieve the main switch MOSFETs while current and energy dissipates after the main switch circuit detects a fault and shuts off power to a load
Implementation Method 2
energy stored in the cable harness as inductance may cause current to continue to flow through the main switch MOSFETs after the main switch shuts off
Data Source
AI summary
Circuitry and techniques for detecting a circuit malfunction and disconnecting a main switch when the main switch comprises two or more smaller MOSFET switches connected in parallel. The circuitry of this disclosure includes a protection circuit switch using a protection switch arranged in parallel to the main switch. The protection switch circuit is configured to relieve the main switch MOSFETs as energy dissipates after the main switch circuit detects a fault and shuts off power to a load, but energy stored in the cable harness as inductance may cause current to continue to flow through the main switch MOSFETS. Dissipating this stored energy may result in an avalanche event in MOSFETs of the main switch. The protection circuit of this disclosure take more current shortly after the main switch turns OFF when the break-down voltages of the main switch MOSFETs may not be aligned.