Force Commutating FET Body Diode Current
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Solution Overview
Problem
High voltage applications using Field Effect Transistors (FETs) face significant switching losses due to the substantial reverse recovery time of the FET body diode, which limits switching frequency and efficiency.
Innovation Solution
The solution involves forcing current through the switch from cathode to anode just before turning the switch off, eliminating reverse recovery time by ensuring no current flows in the body diode, thereby reducing recovery time to zero.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a FET switch is used in high voltage applications, then power dissipation is reduced compared to traditional rectifiers, but reverse recovery time of the body diode becomes substantial causing high switching losses
Solution Approach 1:
A commutation circuit is used to force current through the FET from cathode to anode just before turning the FET off, preliminarily reversing the current direction to ensure the body diode has no forward current when the FET switches off, thereby eliminating reverse recovery time
Solution Approach 2:
A commutation diode is introduced as an intermediary component to facilitate the forcing of reverse current through the FET, enabling the body diode to be reverse-biased before FET turn-off and eliminating reverse recovery losses
2Loss of energy
If a Schottky diode is packaged in parallel with the FET switch, then switching losses are reduced, but this solution is not effective for 100V to 200V applications since the forward drop of the FET body diode is comparable to the forward drop of the Schottky diode
Solution Approach 1:
The invention changes the operating parameters by forcing reverse current through the FET to reverse-bias the body diode, making the solution effective for high voltage applications (100V to 200V) where Schottky diodes would otherwise be ineffective due to comparable forward voltage drops
3Ease of operation
If the FET is switched off with current flowing through the body diode, then the switching operation is simple, but the reverse recovery time causes intolerable switching losses
Solution Approach 1:
The commutation circuit performs preliminary action by forcing reverse current through the FET before turn-off, ensuring the body diode is reverse-biased and eliminating reverse recovery time, thereby reducing switching losses while maintaining operational simplicity
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 effectively eliminates reverse recovery losses in high voltage applications, allowing for higher switching frequencies and reduced power dissipation.
Implementation Method 1
a commutation diode electrically coupled in parallel to the FET such that a cathode of the commutation diode is electrically coupled to the cathode terminal of the body diode
Data Source
AI summary
Technologies are described herein for force commutating a current from a cathode terminal of a diode to an anode terminal of the diode. In one aspect, a method for eliminating diode reverse recovery time is presented herein. The method includes force commutating a current from a cathode terminal of a diode to an anode terminal of the diode. According to embodiments, the diode may be an intrinsic part of a component, such as a field effect transistor (FET). In such embodiments, the FET is switched from being on to off while force commutating a current through the body diode of the FET.