Pre-Heater Relay Circuit With Parallel MOSFET Current Sharing
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Solution Overview
Problem
Existing pre-heater relays in vehicles face challenges in efficiently managing high currents and heat dissipation, as well as ensuring safety against reverse polarity and short-circuits, particularly with the obsolescence of high current Smart MOSFETs.
Innovation Solution
A relay design incorporating multiple parallel N-channel MOSFETs in high, low, and intermediate stages, with charge pumps to control gate voltages and body diodes for reverse polarity protection, and current measurement through MOSFETs instead of shunt resistances to monitor and prevent short-circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single high current MOSFET is used, then the device complexity is reduced, but the current handling capability and heat dissipation performance deteriorate
Solution Approach 1:
The patent divides the high current path into multiple parallel MOSFETs (at least two) to share the current load. Each MOSFET handles a portion of the total current, reducing individual device stress and improving overall current handling capability while maintaining manageable device complexity through systematic arrangement.
Solution Approach 2:
The patent combines multiple MOSFETs in parallel configuration within the same circuit topology, merging their current handling capabilities to achieve higher total power capacity. The body diodes of multiple MOSFETs are also merged to provide collective reverse polarity protection.
2Loss of energy
If multiple parallel MOSFETs are used, then the current handling capability and heat dissipation performance are improved, but the device complexity increases
Solution Approach 1:
The patent segments the power handling function across multiple parallel MOSFETs, distributing heat generation across multiple devices rather than concentrating it in a single component. This segmentation enables better thermal management while achieving the required power handling capability.
Solution Approach 2:
The patent introduces an intermediate stage with MOSFETs and body diodes that acts as a mediator between the high voltage side and the load. This intermediate configuration provides both current sharing and reverse polarity protection, managing the complexity through functional decomposition.
3Reliability
If body diodes of MOSFETs are utilized for reverse polarity protection, then the safety is improved, but the device complexity is reduced (no separate protection circuit needed)
Solution Approach 1:
The patent employs the inherent body diodes of the MOSFETs to provide reverse polarity protection without requiring separate protection circuits or components. The body diodes naturally conduct during reverse polarity conditions, diverting harmful currents and protecting the circuit through the MOSFETs' own structural features.
Solution Approach 2:
The MOSFETs in the patent serve multiple functions: current switching, current sharing, and reverse polarity protection through their body diodes. This multi-functionality eliminates the need for dedicated protection circuits, reducing overall device complexity while improving reliability.
4Measurement precision
If shunt resistances are used for current measurement, then the measurement precision is improved, but the heat generation and device complexity increase
Solution Approach 1:
The patent extracts the current measurement function from separate shunt resistance components and integrates it into the existing MOSFET structure. By measuring current through the MOSFETs themselves (using their on-resistance), the design eliminates dedicated shunt resistors, reducing heat generation and device complexity while maintaining measurement capability.
Solution Approach 2:
The patent merges the current measurement function with the power handling MOSFETs. The same MOSFETs that handle power also serve as the sensing elements for current measurement, eliminating the need for separate measurement components and reducing overall system heat generation.
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 design reduces current per MOSFET, minimizes heat generation, provides effective reverse polarity protection, and quickly detects and blocks short-circuits, enhancing the relay's efficiency and safety without adding heating components.
Implementation Method 1
the body diodes of the MOSFETs to protect the circuit during reverse polarity conditions
Implementation Method 2
a channel between a drain electrode and a source electrode
Implementation Method 3
The charge pumps are configured to increase the voltage applied to the gate electrodes of the MOSFETs
Data Source
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AI summary
There is disclosed a relay (100) comprising a high stage (HS), a low stage (LS), an intermediate stage (IS), and a microcontroller (U4). The relay is configured to be connected between a voltage source (110) and a pre-heater (120) to be driven.