Passive Protection Circuit for Floating-Gate Power Switching
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Solution Overview
Problem
Dual control switching devices face challenges in safely transitioning between active and inactive modes, leading to potential damage from transient voltages and currents, especially when the high voltage transistor's gate voltage becomes floating and uncontrolled, risking overvoltage across low voltage transistors.
Innovation Solution
Incorporating a protection circuit with a bipolar transistor and resistors to maintain the high voltage transistor in a blocked state by setting its gate voltage when the device is in inactive mode, and using a control circuit to manage transitions between operating modes, ensuring safe operation and preventing uncontrolled switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the drive circuit is not electrically powered in inactive mode, then energy consumption is reduced, but the gate voltage becomes floating and uncontrolled causing high voltage transistor to turn on unintentionally
Solution Approach 1:
The protection circuit automatically activates when the drive circuit is powered down, using the floating gate voltage itself to trigger the bipolar transistor through the resistor network, which then clamps the gate voltage to prevent unintended conduction without requiring external control signals
Solution Approach 2:
The bipolar transistor and resistor network act as an intermediary mechanism between the floating gate and ground, providing automatic voltage clamping that protects the low voltage transistor from overvoltage damage while maintaining energy efficiency
2Reliability
If a diode is placed between the gate of the high voltage transistor and ground to limit gate voltage, then the high voltage transistor can be blocked in inactive mode, but the drain-source resistance increases significantly reducing energy efficiency
Solution Approach 1:
The protection circuit dynamically changes the gate voltage parameter based on operating mode: in inactive mode it clamps the gate to prevent conduction, while in active mode it allows the drive circuit to establish proper gate-source voltage for low resistance conduction, thus resolving the contradiction between blocking reliability and energy efficiency
Data Source
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AI summary
The invention relates to a power circuit switching device comprising two switching terminals, a high voltage depletion mode transistor and a low voltage enhancement mode transistor arranged in series between the two switching terminals, a first terminal for receiving a switching signal and electrically connected via a driver circuit to the gate of the high voltage transistor, and a second terminal for receiving a control signal and electrically connected to the gate of the low voltage transistor. The device comprises a normally-on protection circuit electrically connected between the second terminal and the gate of the high voltage transistor to keep the high voltage transistor in an off-state when the driver circuit is not electrically powered.