Subthreshold Gate Biasing for Buck Converter Dead-Time Losses
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Buck converters experience conduction power losses during dead-time periods due to forward biasing of the body diode in n-type MOSFETs, which can lead to parasitic NPN power losses, and reducing dead-time may result in power supply shorting issues.
Innovation Solution
A conduction-loss reduction circuit comprising a transistor, pullup resistor, and level shifter is used to bias the gate of the n-type MOSFET with a voltage less than its threshold voltage during dead-time, creating a weak-inversion current that parallels the body diode current, reducing conduction losses without risking power supply shorting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead-time is extended to prevent power supply shorting, then reliability is improved, but conduction power losses increase due to body diode forward biasing
Solution Approach 1:
The patent changes the electrical parameter (gate voltage) of the MOSFET during dead-time from a standard off-state (0V) to a subthreshold bias state (voltage less than threshold voltage). This parameter change creates a weak-inversion conductive channel that provides a low-impedance path for inductor current, preventing body diode forward biasing and reducing conduction power losses while maintaining reliable operation during dead-time periods
2Loss of energy
If dead-time is reduced to minimize conduction power losses, then energy efficiency is improved, but power supply shorting issues occur
Solution Approach 1:
The patent applies preliminary action by pre-biasing the MOSFET gate with a subthreshold voltage during dead-time periods. This preliminary biasing creates a weak-inversion channel before the switching transition completes, ensuring a safe current path exists immediately when dead-time begins, thus preventing power supply shorting while enabling shorter dead-time periods for reduced conduction losses
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 effectively reduces conduction power losses by lowering the voltage across the body diode and maintaining the power supply's safety from shorting, thereby enhancing the efficiency of the buck converter during dead-time periods.
Implementation Method 1
creating a weak-inversion current that parallels the body diode current
Implementation Method 2
conduction power losses during dead-time periods due to forward biasing of the body diode
Data Source
AI summary
Various embodiments of the present application are directed towards an integrated circuit (IC) including a first switching device, a second switching device, an inductor, and a controller. The inductor is electrically coupled to a first source/drain region of the first switching device and a first source/drain region of the second switching device at a node. The controller is configured to alternatingly change the first and second switching devices between a first state and a second state, respectively. The first switching device is in a third state before or after the second switching device transitions between the first and second states. A subthreshold voltage is applied to a first gate of the first switching device during the third state, such that the third state is between a cutoff mode and a triode mode of the first switching device.