Temperature-Dependent Clamping for Transistor Thermal Stress Reduction

Solution Overview

Problem

Existing power switch arrangements face high power losses and reduced service life when turning off inductive loads due to excessive clamping energy and thermal stresses, particularly as components miniaturize and energy storage increases.

Innovation Solution

A circuit arrangement that dynamically adjusts the clamping voltage based on the temperature difference between the power transistor and the ambient temperature, using a clamping circuit with zener diodes and a temperature sensor to reduce the clamping voltage as temperature rises, thereby managing thermal stresses and extending the service life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a constant clamping voltage is used during turn-off operation, then the switching speed is improved, but the thermal stress and power loss increase

Engineering Contradiction:

Improveswitching speedVSAvoidthermal stress

Core Design Contradiction:

SpeedVSTemperature

Solution Approach 1:

The clamping voltage is changed from a constant value to a dynamically adjustable value that varies with temperature. The circuit includes a voltage divider with thermally sensitive resistors that automatically adjust the clamping voltage level based on the power transistor's temperature, resolving the contradiction between maintaining high switching speed and reducing thermal stress.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The clamping voltage parameter is changed from fixed to variable based on temperature conditions. By using thermally sensitive components in the voltage divider network, the system automatically modifies the clamping voltage parameter in response to temperature changes, allowing optimal performance across different thermal conditions.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If a constant clamping voltage is used during turn-off operation, then the circuit simplicity is maintained, but the service life and reliability decrease

Engineering Contradiction:

Improvecircuit simplicityVSAvoidservice life

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The clamping voltage parameter is changed from fixed to variable based on temperature conditions. By using thermally sensitive components in the voltage divider network, the system automatically modifies the clamping voltage parameter in response to temperature changes, allowing optimal performance across different thermal conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The circuit uses the power transistor's own temperature to automatically control its clamping voltage through thermally sensitive resistors in the voltage divider. This self-regulating mechanism improves reliability without requiring external temperature sensors or complex control circuits, maintaining relative simplicity while enhancing service life.

Inventive Principle:

Principle #25Self-service

3Loss of energy

If the clamping voltage is reduced to lower power loss, then the thermal stress is reduced, but the switching performance deteriorates

Engineering Contradiction:

Improvepower lossVSAvoidswitching performance

Core Design Contradiction:

Loss of energyVSSpeed

Solution Approach 1:

The clamping voltage is changed from a constant value to a dynamically adjustable value that varies with temperature. The circuit includes a voltage divider with thermally sensitive resistors that automatically adjust the clamping voltage level based on the power transistor's temperature, resolving the contradiction between maintaining high switching speed and reducing thermal stress.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The clamping voltage operates in two distinct phases: a high initial voltage during the critical turn-off transition to maintain switching performance, followed by a reduced voltage during the steady-state operation to minimize power loss. This periodic-like voltage profile optimizes both switching performance and energy efficiency.

Inventive Principle:

Principle #19Periodic action

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 dynamic adjustment of clamping voltage reduces thermal stresses and power losses, preventing overheating and extending the service life of the power transistor by allowing heat to dissipate more effectively, thus enhancing the robustness and longevity of the circuit.

Implementation Method 1

measuring a first temperature, measuring a second temperature, and reducing a clamped voltage between a source/drain node of a transistor and a gate of the transistor responsive to a difference between the first and second temperatures increasing

Methodology Applied

Scientific EffectTemperature measurement:

Data Source

PatentUS7528645B2Temperature dependent clamping of a transistor

Publication Date: 2009.05.05 INFINEON TECHNOLOGIES AG

AI summary

An apparatus, comprising a transistor having a source/drain node and a gate, and a circuit coupled between the source/drain node and the gate and configured to limit a voltage between the source/drain node and the gate to a clamping voltage such that the clamping voltage is reduced in response to a rising temperature of the transistor. Also, a method, comprising measuring a first temperature, measuring a second temperature, and reducing a clamped voltage between a source/drain node of a transistor and a gate of the transistor responsive to a difference between the first and second temperatures increasing.