Vertical MOSFET Gate Voltage Control for Diode Power Loss Reduction
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Solution Overview
Problem
Conventional methods for controlling vertical type MOSFETs in bridge circuits face challenges such as increased on-state resistance, circuit complexity, and self turn-on phenomena due to reverse recovery currents, which are not effectively addressed by existing solutions like reverse blocking diodes or additional control terminals.
Innovation Solution
A method that controls the gate voltage of vertical type MOSFETs to manage the forward voltage of built-in diodes, switching them into specific modes where the current through the external diode is greater or lesser than the built-in diode, thereby reducing power loss and improving reverse recovery characteristics without requiring additional diodes or control terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a reverse blocking diode is connected in parallel with the MOSFET to reduce reverse recovery current, then the switching loss is reduced and switching speed is increased, but the on-state resistance of the MOSFET increases and the circuit becomes more complicated
Solution Approach 1:
The invention extracts the reverse blocking function from a separate external diode component and integrates it into the MOSFET's body diode by controlling its forward voltage through gate voltage. This eliminates the need for an additional reverse blocking diode, reducing circuit complexity while maintaining the switching loss reduction benefit
Solution Approach 2:
The gate voltage of the MOSFET is made to serve a dual function: controlling the MOSFET channel conduction and simultaneously controlling the forward voltage of the built-in diode. This multi-functionality allows the single gate terminal to achieve both switching control and reverse recovery suppression without adding extra control terminals
2Reliability
If an additional reverse blocking diode is connected to suppress reverse recovery phenomenon, then the reverse recovery current is reduced, but the circuit is enlarged and becomes more complicated
Solution Approach 1:
The invention merges the reverse blocking diode function with the MOSFET's built-in body diode by controlling the forward voltage of the built-in diode through gate voltage. This combination eliminates the need for a separate reverse blocking diode, achieving reverse recovery suppression while simplifying the circuit structure
Solution Approach 2:
The MOSFET's own built-in diode is made to perform the reverse blocking function that would otherwise require an external diode. By controlling the forward voltage of the built-in diode through the gate voltage, the MOSFET serves itself to suppress reverse recovery current without requiring additional external components
3Reliability
If a lateral type MOSFET with separate back gate is used to suppress reverse recovery, then reverse recovery phenomenon is suppressed, but additional control terminal and reverse bias power supply are required leading to circuit complication
Solution Approach 1:
The gate voltage is made to simultaneously control both the MOSFET channel and the built-in diode forward voltage. This multi-functionality allows the single gate terminal to replace the need for separate back gate control terminals and reverse bias power supplies, achieving reverse recovery suppression without additional control circuitry
Solution Approach 2:
The invention changes the operating parameters of the built-in diode by controlling its forward voltage through gate voltage. By adjusting the gate voltage to specific ranges, the diode is controlled to operate in different modes (first off mode or second off mode), achieving reverse recovery suppression through parameter control rather than additional hardware
4Loss of energy
If the forward voltage of built-in diode is controlled to be low to reduce power loss, then diode power loss is reduced, but reverse recovery characteristic may deteriorate
Solution Approach 1:
The invention dynamically switches between different gate voltage ranges depending on the operating condition. During normal conduction, the gate voltage maintains the built-in diode in the first off mode with lower forward voltage for reduced power loss. During switching events where reverse recovery is a concern, the gate voltage is adjusted to put the diode in the second off mode with higher forward voltage for improved reverse recovery characteristic
Solution Approach 2:
The gate voltage is periodically adjusted between two distinct ranges corresponding to the first off mode and second off mode. This periodic switching allows the system to optimize for diode power loss during steady-state operation and optimize for reverse recovery characteristic during switching transitions, achieving both goals through time-varying control
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 approach reduces diode power loss, enhances reverse recovery characteristics, and suppresses self turn-on phenomena, simplifying the circuit and avoiding the need for additional diodes or control terminals.
Implementation Method 1
a gate voltage of the vertical type MOSFET controls a forward voltage of a built-in diode of the vertical type MOSFET
Implementation Method 2
controlling the forward voltage of the built-in diode to be a first forward voltage by setting the gate voltage of the vertical MOSFET to a first gate voltage
Data Source
AI summary
A method for controlling a vertical type MOSFET in a bridge circuit is provided to reduce diode power loss and improve a reverse recovery characteristic. The method includes controlling a forward voltage of a built-in diode of the vertical type MOSFET to be a first forward voltage by setting a gate voltage of the vertical MOSFET to a first gate voltage, so that the vertical type MOSFET is switched into a first off mode; and controlling the forward voltage of the built-in diode of the vertical type MOSFET to be a second forward voltage by setting the gate voltage of the vertical MOSFET to a second gate voltage, so that the vertical type MOSFET is switched into a second off mode.