Bidirectional FET Gate Drive Without Shunting Diode Losses
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Solution Overview
Problem
Bidirectional switching elements in power conversion circuits suffer from significant power loss due to the forward diode voltage drop when conducting high currents, which is not effectively addressed by existing technologies.
Innovation Solution
A single gate architecture for bidirectional FET switches that eliminates the need for shunting diodes by employing a special gate drive circuit capable of actively sinking and sourcing gate currents, along with dynamic biasing of field plates, allowing for high-speed switching and efficient operation in both polarities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If bidirectional switching elements are fabricated using two FET devices with shunting diodes, then current conduction in both polarities is achieved, but significant power loss occurs due to forward diode voltage drop at high currents
Solution Approach 1:
The invention extracts and removes the shunting diodes from the bidirectional FET structure. By eliminating the diodes that cause forward voltage drop, the patent achieves bidirectional current conduction through the FET channel itself, controlled by a specialized gate drive circuit that can source and sink gate current, thereby removing the source of power loss while maintaining bidirectional functionality
Solution Approach 2:
Instead of using diodes to steer current to proper FET polarity (conventional approach), the invention inverts the approach by using a gate drive circuit that actively controls the FET channel to conduct current in either polarity. The gate drive circuit sources current to turn on the FET for one polarity and sinks current to turn it off or reverse for the other polarity, eliminating the need for passive diode steering
2Loss of energy
If a single gate architecture bidirectional FET is used, then power loss from diodes is eliminated, but high-speed switching capability requires complex gate drive circuits with active current sinking and sourcing
Solution Approach 1:
The invention merges the functions of current sourcing and sinking into a single integrated gate drive circuit architecture. Rather than using separate circuits for each function, the gate drive circuit combines both capabilities to control the bidirectional FET, reducing overall system complexity while enabling high-speed switching and eliminating diode-related power losses
3Device complexity
If conventional bidirectional switching elements are used, then circuit simplicity is maintained, but switching speed is insufficient for high power conversion circuits
Solution Approach 1:
The invention introduces dynamic gate drive capabilities with active current sinking and sourcing that adapt to the switching requirements. The gate drive circuit dynamically adjusts its operation based on the desired switching state, enabling rapid transitions between on and off states. This dynamic control mechanism achieves high switching speeds necessary for power conversion applications while maintaining a relatively simple overall circuit architecture
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 solution reduces power loss by eliminating diode voltage drops, enabling high-speed and efficient switching in both polarities, thus enhancing the performance of power conversion circuits.
Implementation Method 1
a gate electrode positioned along the channel between the channel electrodes, where current flowing in a first polarity from the first channel electrode to the second channel electrode and current flowing in a second polarity from the second channel electrode to the first channel electrode are both controlled by a gate voltage applied to the gate electrode
Implementation Method 2
A gate drive circuit provides a gate drive signal to the gates of each of the set of bidirectional FET semiconductor switches dynamically referenced to a different one of the first channel electrode and second channel electrode depending on a voltage polarity between the first and second channel electrodes, the gate drive circuit including semiconductor switches sourcing and sinking current to and from the gate
Data Source
AI summary
A drive system suitable for motors and the like employs bidirectional FETs with active gate current sourcing and sinking to eliminate series diode losses. In one embodiment, the bidirectional FETs have floating field plates that can be dynamically biased according to device polarity.