Stacked MOSFET Switching Circuit for High-Voltage Low-Loss Operation
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Solution Overview
Problem
Existing circuit technologies face challenges in achieving efficient and cost-effective switching at high frequencies using low-voltage switches, as series connections of high-voltage switches introduce losses and reliability issues due to voltage balancing requirements, limiting their application to low-frequency operations.
Innovation Solution
The use of stacked low-voltage MOSFETs to form an equivalent switch with increased voltage blocking capability, combined with parallel high-voltage MOSFETs or IGBTs, and optimized timing of switching to reduce losses and risk of breakdown, along with the inclusion of diodes for efficient reverse recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If series connection of high-voltage switches is used to increase voltage blocking capability, then voltage blocking capability is improved, but switching losses and conduction losses increase
Solution Approach 1:
The patent divides the high-voltage switching function into multiple low-voltage MOSFETs connected in series, where each device operates at a lower voltage stress level. This segmentation allows each transistor to maintain low conduction resistance while collectively providing high voltage blocking capability, thereby reducing overall power losses compared to using a single high-voltage switch.
Solution Approach 2:
The patent combines multiple low-voltage MOSFETs in series to achieve the voltage blocking capability of a single high-voltage device. By merging these lower-voltage devices, the circuit achieves both high voltage tolerance and low conduction losses, as each MOSFET operates in its optimal low-loss region.
2Stress or pressure
If series connection of high-voltage switches is used to increase voltage blocking capability, then voltage blocking capability is improved, but reliability deteriorates due to voltage balancing requirements
Solution Approach 1:
The patent introduces voltage balancing circuits as intermediary components between the series-connected MOSFETs. These balancing circuits actively monitor and equalize the voltage distribution across each device, eliminating the reliability issues associated with passive voltage sharing. This intermediary mechanism ensures stable operation without compromising the high voltage blocking capability.
Solution Approach 2:
The patent implements active voltage balancing with feedback control that continuously monitors the voltage across each MOSFET and adjusts the gating signals accordingly. This feedback mechanism dynamically compensates for voltage imbalances, ensuring reliable operation of the series-connected low-voltage switches under varying operating conditions.
3Loss of energy
If low-voltage switches are used to reduce losses, then switching efficiency is improved, but voltage blocking capability deteriorates
Solution Approach 1:
The patent segments the high-voltage blocking function across multiple low-voltage MOSFETs connected in series. Each MOSFET handles a portion of the total voltage, allowing them to operate at low voltage stress with minimal conduction resistance, while the series combination provides the required high voltage blocking capability.
Solution Approach 2:
The patent transitions from a single-device vertical voltage blocking approach to a multi-device series configuration, adding the dimension of device quantity to achieve voltage multiplication. This dimensional change allows low-voltage devices to collectively provide high-voltage capability while maintaining individual low-loss characteristics.
4Productivity
If high-frequency switching is enabled using low-voltage switches, then productivity is improved, but risk of switch breakdown increases due to reverse voltage
Solution Approach 1:
The patent employs clamping circuits and voltage balancing mechanisms that act beforehand to limit reverse voltage exposure on each MOSFET during high-frequency switching. By preemptively controlling voltage distribution and providing alternative current paths, the circuit prevents breakdown conditions before they can occur, enabling safe high-frequency operation.
Solution Approach 2:
The patent introduces protective circuits that cushion each MOSFET against reverse voltage stress during high-frequency switching transitions. These circuits absorb transient voltage spikes and provide voltage clamping, creating a protective buffer that prevents breakdown while allowing high-speed switching operation.
Data Source
AI summary
An apparatus includes a first leg having a plurality of transistors connected in series between a first node and a second node. Each of the plurality of transistors includes a respective body diode. The apparatus further includes a second leg connected between the first node and the second node and in parallel to the series connection of the plurality of transistors of the first leg. The second leg includes a first transistor. The second leg has lower reverse recovery losses relative to the first leg.