Current Sensing IGBT Spike Filtering via Blanking Circuit
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Solution Overview
Problem
Current sense IGBTs face issues with false triggering during short-circuit events due to spikes in sensed current and voltage, leading to potential damage and prolonged exposure to harmful currents, with existing solutions like large capacitors causing slow response times and inductors being sensitive to parasitic capacitance, making them unsuitable for large-scale manufacturing.
Innovation Solution
A circuit configuration incorporating a filter circuit and a blank circuit with a blanking MOSFET, resistor, and capacitor between the IGBT and controller, which removes artificially created spikes and allows quick detection of short-circuit events by creating a blank time and using high-pass filter components to track voltage slopes accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large capacitors are used to filter current sense spikes, then false triggering is reduced, but response time increases
Solution Approach 1:
The filtering function is segmented into two distinct circuits: a blanking circuit that provides rapid initial response by ignoring spikes, and a filtering circuit that processes signals after the blanking period. This segmentation allows the system to achieve both fast response and effective filtering without using large capacitors.
Solution Approach 2:
The blanking circuit performs preliminary action by immediately ignoring voltage spikes when they occur, before the filtering circuit processes the signal. This preliminary blanking action prevents false triggering from spikes while maintaining fast response time, eliminating the need for large filtering capacitors that would slow down the response.
2Reliability
If inductors are used to filter spikes, then false triggering is reduced, but sensitivity to parasitic capacitance increases
Solution Approach 1:
The inductor component is completely extracted from the filtering circuit and replaced with an RC filtering circuit. This extraction eliminates the sensitivity to parasitic capacitance that inductors inherently have, while still achieving effective spike filtering through the combination of blanking and RC filtering.
Solution Approach 2:
The filtering approach is changed from inductive filtering to capacitive-resistive (RC) filtering. By changing the fundamental parameters of the filtering circuit from L-based to RC-based, the system eliminates parasitic capacitance sensitivity while maintaining effective spike filtering capabilities.
3Measurement precision
If complex filtering circuits are used to remove spikes, then measurement precision improves, but device complexity increases
Solution Approach 1:
The blanking function and filtering function are merged into a coordinated two-stage system where the blanking circuit operates first to eliminate spikes, followed by the simple RC filtering circuit. This merging of functions achieves superior spike removal accuracy without requiring a single complex filtering circuit.
Solution Approach 2:
The blanking circuit acts as an intermediary between the voltage spike source and the filtering circuit. It mediates by temporarily ignoring spikes during the blanking period, allowing the subsequent filtering circuit to process only legitimate signals, thereby achieving high measurement precision with simple circuitry.
Data Source
AI summary
A control circuit and method are disclosed for controlling a current sense Insulated-Gate Bipolar Transistor (IGBT). In particular, the current sense IGBT creates voltage spikes in a sense voltage as a result of normal switching operations. The control circuit creates a blank period so that the voltage spikes are ignored and false detections of short-circuit events are avoided.