Gate Driver Resonant Circuit for Negative MOSFET Gate Bias
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Solution Overview
Problem
Existing circuit arrangements for driving insulated gate transistors, such as IGBTs and MOSFETs, require complex and costly negative voltage supplies to ensure reliable switching off and blocking, which can lead to undesired switching on due to voltage fluctuations and increased circuit complexity.
Innovation Solution
A circuit arrangement that uses an inductance in parallel with the gate-source path of the transistor to form an oscillating circuit, allowing the capacitance to recharge to a negative gate-source voltage without a negative voltage supply, with a switching element to interrupt the oscillating circuit and maintain the negative voltage, and a freewheeling diode to divert current for charging the capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative voltage supply is used to charge the gate capacitor to ensure reliable switching off, then the transistor blocking reliability is improved, but the circuit complexity and cost increase
Solution Approach 1:
The patent introduces a resonant circuit consisting of an inductor and capacitor as an intermediary mechanism. This resonant circuit generates the negative gate-source voltage through oscillation when triggered by the gate driver, eliminating the need for a dedicated negative voltage supply. The resonant circuit acts as a mediator that transforms the positive driver voltage into the required negative gate voltage, thereby maintaining reliability while reducing circuit complexity.
Solution Approach 2:
The gate driver signal itself is used to trigger the resonant circuit, making the system self-sufficient. The same gate driver that controls the transistor also initiates the resonant oscillation to generate the negative gate voltage. This self-service approach eliminates the need for separate negative voltage generation circuits, reducing overall system complexity while maintaining reliable transistor switching.
2Reliability
If a capacitor is connected in parallel with the gate-source path to maintain negative voltage, then the transistor can be reliably switched off, but the positive driver voltage is reduced and circuit complexity increases
Solution Approach 1:
The resonant circuit operates periodically, oscillating only when needed to generate the negative gate voltage during switching transitions. During the on-state, the transistor gate is driven by the full positive driver voltage without interference from the resonant circuit. The periodic activation of the resonant circuit ensures that the negative voltage is generated only when required for switching off, maintaining full driver voltage availability during the on-phase while ensuring reliable switching off.
3Loss of time
If the capacitor is dimensioned to charge quickly during turn-on phase, then the negative voltage is reached faster, but the turn-on phase duration must be increased which reduces switching frequency
Solution Approach 1:
The resonant circuit provides dynamic voltage generation with inherently fast charging characteristics. The oscillatory nature of the resonant circuit allows the capacitor to charge rapidly to the negative voltage level during the brief turn-off transition, without requiring an extended turn-on phase. This dynamic approach enables fast voltage establishment while maintaining high switching frequencies, as the resonant charging occurs during the natural oscillation period rather than during the transistor on-time.
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
Enables reliable switching off and blocking of transistors without a negative voltage supply, simplifying the circuit design and reducing costs, while maintaining a negative gate-source voltage to prevent unintended switching on, and allowing full positive driver voltage for switching on during the switch-on phase.
Implementation Method 1
an inductor is provided for forming a resonant circuit with the capacitor, which, when the transistor is switched off, is formed by the change of the driver signal to the second driver voltage to charge the capacitor to a negative gate-source voltage below the second driver voltage
Implementation Method 2
a first freewheeling diode is arranged in parallel to the switching element
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a circuit arrangement (1) for controlling a transistor (T1) with an insulated gate (3), a gate driver (2) for generating a driver signal (UTR), and a capacitor (C) parallel to the gate-source path of the transistor (T1), wherein the gate driver (2) is designed for generating a driver signal (UTR) greater than or equal to zero volts, an inductor (L) is provided for forming a resonant circuit (9) with the capacitor (C), and a switching element (S) is provided in the resonant circuit (9), which is designed for interrupting the resonant circuit (9) after recharging the capacitor (C). According to the invention, the part of the circuit arrangement (1) downstream of the gate driver (2) is designed for exclusive voltage supply using the driver signal (UTR) of the gate driver (2), and the switching element (S) is formed by an additional transistor (T2), a first freewheeling diode (D1) is arranged parallel to the switching element (S), and the inductor (L) of the resonant circuit (9) is arranged between the additional transistor (T2) and the gate (3) of the transistor (T1).