Vehicle Rectifier Circuit Using MOSFET and Schottky Diode

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Solution Overview

Problem

The use of Schottky barrier diodes in vehicle AC generators leads to increased leakage current, especially at high temperatures, requiring costly thermal design measures to prevent thermal runaway, while MOSFETs offer lower voltage drop and smaller leakage current but are expensive, posing a trade-off between cost, rectification loss, and leakage current.

Innovation Solution

A rectifier configuration that uses a MOSFET at one of the positive or negative electrode sides and a Schottky barrier diode at the other, reducing rectification loss and leakage current, while minimizing cost by avoiding the use of MOSFETs at both sides.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a Schottky barrier diode is utilized for each of a positive electrode side semiconductor device and a negative electrode side semiconductor device, then the forward drop voltage is reduced and rectification loss is decreased, but the leakage current becomes large especially at high temperature

Engineering Contradiction:

Improverectification lossVSAvoidleakage current

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The rectifier circuit is segmented into positive electrode side and negative electrode side semiconductor devices. By dividing the rectification function across different device types (MOSFETs on one side, Schottky barrier diodes on the other), the patent achieves low forward drop voltage through the Schottky barrier diodes while the MOSFETs suppress leakage current, thus resolving the contradiction between reduced rectification loss and controlled leakage current

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different semiconductor devices with complementary characteristics are assigned to different positions in the rectifier circuit. Schottky barrier diodes are placed where low forward drop voltage is critical for reducing rectification loss, while MOSFETs are placed where leakage current suppression is paramount. This local optimization of device selection resolves the contradiction by allowing each position to contribute its strength

Inventive Principle:

Principle #3Local quality

2Loss of energy

If a MOSFET is utilized for each of positive and negative polarities, then the voltage drop is reduced and leakage current is small, but the cost increases

Engineering Contradiction:

Improvevoltage dropVSAvoidcost

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The patent changes the device configuration parameter from using identical MOSFETs at both polarities to using MOSFETs at one polarity and Schottky barrier diodes at the other. This parameter change maintains the low voltage drop benefit (through Schottky barrier diodes) while reducing cost (by using fewer expensive MOSFETs), thus resolving the contradiction between reduced voltage drop and cost reduction

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If a Schottky barrier diode is utilized, then the forward drop voltage is lower, but the leakage current increases requiring thermal design measures

Engineering Contradiction:

Improveforward drop voltageVSAvoidthermal runaway risk

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

MOSFETs are introduced as intermediary devices on one side of the rectifier circuit to mediate between the Schottky barrier diodes and the power system. The MOSFETs act as leakage current suppressors that protect the system from thermal runaway while allowing the Schottky barrier diodes to provide low forward drop voltage, thus resolving the contradiction between reduced forward drop voltage and reduced thermal runaway risk

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 rectification loss by 35%, suppresses leakage current, and lowers the risk of thermal runaway, enhancing the reliability and efficiency of the vehicle AC generator while reducing costs.

Implementation Method 1

a rectifier configuration that uses a MOSFET at one of the positive or negative electrode sides and a Schottky barrier diode at the other, reducing rectification loss

Methodology Applied

Scientific EffectRectification: Diode

Implementation Method 2

a Schottky barrier diode, with which more forward drop voltage can be reduced than that with a PN-junction diode

Methodology Applied

Scientific EffectSchottky barrier effect: Diode

Implementation Method 3

the MOSFET provided at one of the positive electrode side and the negative electrode side can reduce the leakage current

Methodology Applied

Scientific EffectField effect transistor conduction:

Data Source

PatentEP3832875B1Rectification device and vehicle ac power generating apparatus provided with same

Publication Date: 2024.06.05 MITSUBISHI ELECTRIC CORP

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AI summary

A rectifier and a vehicle AC generator that can suppress the cost, the rectification loss, and the leakage current from increasing are provided. A rectifier (1) is configured in such a way that in each of n sets, one of a positive electrode side semiconductor device (2) and a negative electrode side semiconductor device (3) is a MOSFET, in such a way that in at least one of the n sets, the other one of the positive electrode side semiconductor device (2) and the negative electrode side semiconductor device (3) is a specific diode, and in such a way that the specific diode is a Schottky barrier diode or a MOS diode, which is a MOSFET whose drain terminal and gate terminal are short-circuited.