Gate Drive Circuit for Fast Power Transistor Turn-Off
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Solution Overview
Problem
Existing gate drive circuits for power transistors face challenges in quickly turning off power transistors without generating over-voltages or excessive electromagnetic interferences, often requiring external resistors that increase switching losses or complex feedback control loops.
Innovation Solution
A gate drive circuit with a measurement circuit and switch control circuit that monitors and controls the discharge current of the internal gate-emitter capacitance, allowing for a fast and controlled turn-off of power transistors without the need for external resistors or complex feedback loops, by switching on and off a first switch to manage the discharge current and voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an external resistor is used in series with the control terminal to limit discharge current, then over-voltages are limited, but turn-off time increases and switching losses increase
Solution Approach 1:
The patent applies dynamics by making the gate resistance variable rather than fixed. The control circuit dynamically adjusts the gate resistance during the turn-off process: initially providing low resistance to enable fast discharge current for quick turn-off, then increasing resistance to limit over-voltage. This dynamic adjustment resolves the contradiction between fast turn-off and over-voltage limitation.
Solution Approach 2:
The patent changes the parameter of gate resistance from a constant value to a time-varying parameter. By controlling the gate resistance to change during the turn-off transient, the system achieves both fast initial discharge (low resistance) and controlled voltage rise (high resistance), resolving the trade-off between turn-off speed and over-voltage protection.
2Object-affected harmful factors
If an external resistor is used in series with the control terminal to limit discharge current, then over-voltages are limited, but switching losses increase
Solution Approach 1:
The patent uses dynamic gate resistance control to minimize switching losses while still limiting over-voltages. By keeping resistance low during the critical initial discharge phase and only increasing it when the voltage needs to be limited, the system reduces the energy dissipated in the gate resistance compared to using a fixed high resistance throughout the entire turn-off process.
Solution Approach 2:
The patent applies preliminary action by first establishing a low-resistance path for rapid charge removal from the gate, achieving fast turn-off before over-voltage becomes an issue. The resistance is only increased afterward when the voltage reaches levels requiring limitation, thus avoiding unnecessary energy loss in the resistance during the critical turn-off phase.
3Object-affected harmful factors
If a complex feedback control loop is used to generate intermediate gate voltage levels, then over-voltages are reduced, but device complexity increases
Solution Approach 1:
The patent extracts the complex feedback control loop from the system and replaces it with a simpler control mechanism. Instead of continuously monitoring output voltage and adjusting gate voltage through a complex feedback loop, the invention uses a simplified control circuit that directly regulates the gate resistance, achieving over-voltage limitation without the complexity of traditional feedback control.
Solution Approach 2:
The patent introduces an intermediary element (the controllable gate resistance) between the gate voltage source and the transistor gate. This intermediary allows indirect control of the discharge current and over-voltage through resistance modulation, replacing the need for direct complex feedback control of the gate voltage itself.
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 solution enables faster turn-off of power transistors with reduced over-voltages and electromagnetic interferences, eliminating the need for external resistors and simplifying the control loop, thus improving switching efficiency and reducing component complexity.
Implementation Method 1
measuring a voltage at a control terminal of the power transistor when the discharge current has reduced to a predetermined current threshold
Implementation Method 2
switching on and off a first switch to manage the discharge current
Data Source
AI summary
A gate drive circuit drives a control terminal of a power transistor and comprises: a drive terminal for electrically coupling the control terminal, a first reference source, a first switch arranged between the first reference source and the control terminal, a switch control circuit and a measurement circuit. The first switch is switched-on to turn-off the power transistor. The switch control circuit switches-off the first switch during a transition period to a fully off-state. The measurement circuit outputs a control signal to the switch control circuit in response to a value of a voltage at the control terminal measured when a discharge current flowing to the drive terminal has been reduced to a predetermined threshold, for switching-on the first switch if the measured value is smaller than a threshold voltage.