Stacked MOSFET Voltage Sharing Circuit
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Solution Overview
Problem
Stacked MOSFET configurations face challenges in efficient gate drive signal distribution and voltage sharing, leading to suboptimal performance and breakdown voltage capacity when capacitive coupling is used, especially when body diode conduction occurs at zero drain-source voltage.
Innovation Solution
A MOSFET circuit design featuring a controller that supplies a single control signal to both MOSFETs in a series configuration, coupled with a voltage sharing circuit using series-connected resistors and capacitors to balance voltages, enabling zero-voltage-switching (ZVS) and increased breakdown voltage capacity by ensuring equal voltage distribution across each MOSFET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If capacitive coupling is used to drive stacked MOSFETs, then gate drive signal distribution is achieved, but voltage sharing becomes suboptimal and breakdown voltage capacity decreases
Solution Approach 1:
The patent divides the gate drive signal distribution into two independent paths: one path uses capacitive coupling for signal transmission, while the other path uses resistive voltage sharing for voltage balancing. This segmentation allows each path to perform its specialized function optimally without interfering with the other, resolving the contradiction between ease of operation and reliability.
Solution Approach 2:
The patent introduces an intermediary resistive voltage sharing circuit between the stacked MOSFETs to mediate the voltage distribution. This intermediary component ensures equal voltage sharing across the MOSFETs during off-state, compensating for the voltage imbalance that would otherwise occur with capacitive coupling alone, thereby improving reliability without sacrificing operational ease.
2Device complexity
If capacitive coupling is used in stacked MOSFET configuration, then device operation is simplified, but leading edge voltage spikes increase during turn-off
Solution Approach 1:
The resistive voltage sharing circuit acts as an intermediary damping element that suppresses leading edge voltage spikes during MOSFET turn-off. The resistors provide a discharge path for parasitic inductances and capacitances, reducing voltage overshoot and spikes while maintaining the simplicity of the capacitive coupling gate drive configuration.
Solution Approach 2:
The patent changes the electrical parameters of the gate drive system by adding resistive elements with specific resistance values that optimize the damping effect. By carefully selecting the resistance values in the voltage sharing circuit, the leading edge voltage spikes are reduced without significantly increasing the overall device complexity or affecting the normal switching operation.
3Productivity
If body diode conduction occurs at zero drain-source voltage, then MOSFET switching is enabled, but voltage sharing balance deteriorates
Solution Approach 1:
The resistive voltage sharing circuit provides continuous feedback on the voltage distribution across the stacked MOSFETs. When body diode conduction occurs and disrupts voltage balance, the resistive path ensures that voltage redistributes evenly across all MOSFETs, stabilizing the voltage sharing balance while allowing switching operation to proceed.
Solution Approach 2:
The resistive voltage sharing circuit provides beforehand cushioning against voltage imbalance that may occur during body diode conduction. By having the resistive path in place before switching events, the circuit preemptively prevents severe voltage imbalance rather than reacting to it after the fact, maintaining stability during dynamic switching operations.
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 enables precise timing control, reduced parts count, and enhanced voltage sharing, resulting in improved reliability and efficiency by maintaining balanced voltages across MOSFETs, thereby increasing breakdown voltage capacity and reducing leading edge voltage spikes during turn-off.
Implementation Method 1
The voltage sharing circuit includes at least two series-connected resistors or at least two series-connected capacitors
Implementation Method 2
These stacked MOSFET configurations typically use capacitive coupling to drive different MOSFETs in the stacked configuration. Specifically, charge variations on capacitors are used to obtain gate drive signals for the MOSFETs.
Data Source
AI summary
Example MOSFET circuits include a first metal-oxide-semiconductor field-effect transistor (MOSFET) having a gate, a source and a drain, and a second MOSFET coupled in series with the first MOSFET. The second MOSFET has a gate, a source and a drain. The MOSFET circuit also includes a controller configured to supply a same control signal to the gate of the first MOSFET and the gate of the second MOSFET to turn on or turn off the first MOSFET and the second MOSFET when a drain-source voltage of the first MOSFET and a drain-source voltage of the second MOSFET are substantially zero. Other MOSFET circuits and methods of operating MOSFET circuits are also disclosed.