IGBT Emitter Current Sensing for Early Desaturation Detection
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Solution Overview
Problem
Existing IGBT desaturation detection methods are delayed due to blanking times, leading to increased power dissipation and reduced reliability during short circuit events, as they rely on diodes and voltage proxies rather than direct current sensing.
Innovation Solution
A gate driver system with a current reconstruction circuit and comparator that directly senses the IGBT emitter current across an inductance, eliminating the need for diodes and blanking times, allowing for early detection of desaturation and short circuit conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a blanking time is inserted to avoid false detection during IGBT turn-on transition, then false desaturation detection is prevented, but detection delay occurs leading to increased power dissipation during short circuit events
Solution Approach 1:
The patent extracts the current sensing function from the voltage-based desaturation detection circuit by adding a separate current sensing path through an operational amplifier that directly monitors emitter current. This extracted current information is fed to the desaturation detection comparator independently of the blanking time mechanism, allowing current-based detection to occur immediately without waiting for the voltage-based detection to complete its blanking period.
Solution Approach 2:
The patent introduces an operational amplifier as an intermediary component that directly senses the emitter current and provides this current information to the desaturation detection circuit. This intermediary current sensing path acts as a mediator between the IGBT emitter and the detection circuit, enabling direct current measurement that bypasses the voltage-based detection delay and blanking time requirements.
2Reliability
If RC filter or charged capacitor is added to filter noise pickup, then noise immunity is improved, but detection response time increases
Solution Approach 1:
The patent changes the detection parameter from voltage-based desaturation detection to direct current sensing. By using an operational amplifier to directly measure emitter current, the system achieves noise immunity through current-based detection rather than relying on RC time constants or capacitor charging methods. This parameter change enables fast response because current measurement does not require integration over time like voltage-based methods with filters.
3Ease of manufacture
If diodes are used for desaturation detection, then circuit implementation is simplified, but detection accuracy is reduced due to voltage proxy rather than direct current sensing
Solution Approach 1:
The patent substitutes the mechanical/diode-based voltage detection method with an electronic operational amplifier-based current sensing system. Instead of using diodes to detect voltage drops that indirectly indicate current flow, the system uses an operational amplifier to directly sense and measure the emitter current electronically. This substitution provides precise current measurement while maintaining ease of implementation through standard operational amplifier circuits.
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 approach significantly reduces power dissipation and extends the operating life of IGBTs by enabling earlier detection of desaturation and short circuit events, thereby minimizing stress and improving reliability.
Implementation Method 1
measuring a voltage across an inductance associated with the power device
Data Source
AI summary
A gate driver system includes a gate driver having a first input for receiving a digital input signal, a second input for receiving a short circuit protection signal, and output for driving a power device; a current reconstruction circuit having a first input for receiving a voltage across an inductance associated with the power device, a second input for receiving a current associated with the power device, a third input for receiving the digital input signal, and an output for providing a sensed power device current; and a comparator having a first input coupled to the output of the current reconstruction circuit, a second input coupled to a reference, and an output coupled to the second input of the gate driver.