IGBT Gate Capacitor Disconnection to Prevent LC Oscillation
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Solution Overview
Problem
Existing semiconductor devices with gate capacitors connected to switching elements are prone to parasitic oscillation, which can lead to damage of the switching elements, especially during short circuits, as they do not effectively address the issue of LC oscillation in the loop circuit formed by the capacitor and the switching element.
Innovation Solution
A semiconductor device with a disconnection unit that disconnects the gate capacitor from the control signal input terminal when a detection current exceeds a predetermined threshold, preventing the formation of a loop circuit that causes oscillation and protecting the switching element from overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a gate capacitor is connected to the gate of the IGBT to suppress radiated noise, then radiated noise is reduced, but LC oscillation occurs in the loop circuit causing the IGBT to be damaged
Solution Approach 1:
The patent applies preliminary action by detecting the current flowing through the IGBT before LC oscillation can occur, and preemptively disconnecting the gate capacitor from the gate terminal. The current detection unit monitors the current in advance, and when it exceeds the threshold value, the disconnection unit activates to remove the capacitor from the circuit before oscillation can damage the IGBT.
Solution Approach 2:
The patent introduces a disconnection unit as an intermediary component between the gate capacitor and the IGBT gate terminal. This intermediary switch (implemented as a MOSFET or similar switching device) acts as a mediator that can selectively connect or disconnect the capacitor based on current conditions, allowing the system to have both the noise suppression benefit and the protection against oscillation.
2Ease of operation
If a gate capacitor is mounted on the control board to adjust recovery dv/dt, then switching performance is improved, but a loop circuit is formed causing parasitic oscillation during short circuit
Solution Approach 1:
The patent applies dynamics by making the connection between the gate capacitor and the IGBT gate terminal dynamic rather than static. The disconnection unit changes the circuit configuration based on operating conditions: the capacitor is connected during normal operation to improve switching performance, but disconnected during short-circuit conditions to prevent parasitic oscillation. This dynamic reconfiguration allows the system to adapt to different operational states.
Solution Approach 2:
The patent changes the circuit parameter (connection state of the gate capacitor) based on the detected current parameter. When the current exceeds the threshold value, the system changes the connection parameter from connected to disconnected, thereby preventing parasitic oscillation while maintaining switching performance during normal operation.
3Ease of operation
If the gate capacitor remains connected during high current operation, then switching control is maintained, but the switching element may be broken by oscillation
Solution Approach 1:
The patent applies the taking out principle by extracting the gate capacitor from the loop circuit when high current is detected. The disconnection unit removes the capacitor connection to the gate terminal, separating the potentially harmful capacitive element from the high-current path, thereby preventing oscillation while maintaining switching control through the detection and protection circuitry.
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 prevents damage to the switching element by disconnecting the gate capacitor during high detection currents, reducing radiated noise and loss in the semiconductor device, while maintaining the benefits of the gate capacitor during normal operation.
Implementation Method 1
a capacitor arranged between the control signal input terminal and a reference potential terminal
Implementation Method 2
a disconnection unit configured to disconnect a connection between the capacitor and the control signal input terminal when a detection current being a current output from the current detection terminal is equal to or larger than a first current
Data Source
AI summary
The present invention is directed to provide a semiconductor device capable of protecting a switching element even though having a capacitor connected to a control signal input terminal of the switching element. Semiconductor device includes an IGBT including a gate configured to be input a gate signal and a current detection terminal used to detect at least one of overcurrent or short-circuit current, a gate capacitor arranged between the gate and a reference potential terminal, the gate capacitor being disconnected from the gate as needed, and a disconnection unit configured to disconnect a connection between the gate capacitor and the gate when a detection current being a current output from the current detection terminal is equal to or larger than a first current set on a basis of a minimum current causing oscillation in a loop circuit formed by including the IGBT and the gate capacitor.