IGBT Gate Feedback Circuit for Turn-Off Overvoltage Control
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Solution Overview
Problem
Existing power converters using insulated-gate bipolar transistors (IGBTs) face challenges in limiting turn-off voltages, particularly during short circuits, where overvoltages can exceed permissible levels due to stray inductances, leading to potential switch destruction, and existing solutions like increasing gate resistor size or active clamping are ineffective or result in significant switching losses.
Innovation Solution
A control circuit with a first feedback path comprising parallel capacitors and threshold devices, where each threshold device sets a voltage level, and additional capacitors are switched in based on the voltage level, increasing effective capacitance to manage overvoltages without significant switching losses, and an optional second feedback path provides further clamping action.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the size of the resistor at the gate of the semiconductor switch is increased to limit overvoltage, then the overvoltage is reduced, but switching losses become unacceptable
Solution Approach 1:
The feedback path is segmented into multiple parallel branches, each containing a capacitor and threshold device. This segmentation allows the circuit to activate different capacitance levels based on voltage thresholds, providing graduated protection rather than a single fixed resistance value, thereby limiting overvoltage without excessive switching losses.
Solution Approach 2:
The feedback path dynamically adjusts its effective capacitance based on the collector-emitter voltage level. When voltage exceeds thresholds, additional capacitors are switched into the circuit, providing adaptive protection that responds to actual operating conditions rather than using a static resistor value, thus avoiding constant energy loss.
2Object-affected harmful factors
If feedback of collector-emitter voltage to the gate is used to maintain on-state, then voltage control is achieved, but the method is ineffective due to significant delay between gate voltage falling below Miller plateau and rise of collector-emitter voltage
Solution Approach 1:
The feedback path is prepared in advance with multiple capacitors already connected in parallel but isolated by threshold devices. When overvoltage occurs, the protective action is immediately available without delay for capacitor charging or circuit reconfiguration, as the circuit structure is pre-established and ready to respond.
Solution Approach 2:
The circuit implements direct feedback from the collector-emitter voltage to the gate through the feedback path containing capacitors and threshold devices. This creates a negative feedback loop that automatically counteracts voltage rises by injecting charge to the gate, providing rapid response without the delays associated with Miller plateau transitions.
3Measurement precision
If an active clamp is incorporated to determine voltage across emitter-collector path, then overvoltage detection is improved, but collector current slope changes significantly increasing switching losses
Solution Approach 1:
The feedback path is connected locally between the collector and gate, providing targeted voltage control at the critical switching node. This localized feedback approach addresses overvoltage at its source without requiring global circuit modifications or active clamping that would affect the entire current path, thereby minimizing impact on collector current slope.
Solution Approach 2:
The feedback path creates an electrical copy or replica of the collector-emitter voltage at the gate through the capacitor network. This voltage copying mechanism provides overvoltage protection by replicating the voltage information and using it to control the gate, avoiding the need for physical clamping components that would directly alter current flow.
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 solution effectively limits the rate of change in collector current and collector-emitter voltage, reducing the risk of overvoltage damage to the IGBT while minimizing switching losses, as demonstrated by the reduced peak overvoltage and energy losses in the traces provided.
Implementation Method 1
a first feedback path between collector and the input to driver stage 110. This first feedback path comprises transient-voltage-suppression (TVS) diode 130, capacitor 170, resistor 180 and switch 190
Implementation Method 2
said control circuit being operable such that each threshold device causes a corresponding threshold voltage level to be set, and such that when the voltage level at said first electrode exceeds one of said voltage threshold levels, a further capacitor is switched into
Data Source
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AI summary
Disclosed is a control circuit for control of a semiconductor switching device, such as an IGBT. The control circuit comprising a first feedback path between a first electrode and a control electrode of said semiconductor switching device which has a capacitance. The circuit is operable such that the capacitance in the first feedback path is dependent on the voltage level at said first electrode. In another embodiment the control circuit is operable such that a feedback signal begins to flow in the first feedback path immediately as the semiconductor switching device begins switching off, thereby causing a control action on the semiconductor switching device.