Parallel Commutation Paths Reduce Reverse Recovery Loss
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Solution Overview
Problem
Power switching circuits with semiconductor switching elements experience increased switching loss and noise due to reverse recovery currents through intrinsic diodes, particularly in MOSFETs with high breakdown voltage, where conventional solutions complicate circuit structures and introduce additional losses.
Innovation Solution
A power switching circuit design that includes a first commutation path with a diode and a second commutation path with a Schottky diode in parallel, where the second diode has a shorter reverse recovery time and higher inductance, allowing the reverse recovery current to be reduced by distributing the current through both diodes and minimizing minority carrier charging in the first diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a MOSFET with super junction structure is used to achieve high breakdown voltage and low resistance, then power efficiency is improved, but reverse recovery current increases and becomes steeper, resulting in increased loss and noise
Solution Approach 1:
A capacitor is introduced as an intermediary component connected in parallel with the MOSFET. During the reverse recovery period, this capacitor provides an alternative current path that bypasses the intrinsic diode, thereby reducing the reverse recovery current and its associated noise while maintaining the benefits of the super junction MOSFET structure
Solution Approach 2:
The capacitor is pre-charged during the MOSFET on-state and then discharges during the reverse recovery period to counteract the reverse recovery current. This preliminary action prepares the circuit to neutralize the harmful reverse recovery effect before it fully manifests, reducing loss and noise
2Object-generated harmful factors
If a diode with low breakdown voltage is connected in anti-series to the intrinsic diode to reduce reverse recovery current, then loss and noise are reduced, but circuit structure becomes complicated
Solution Approach 1:
Instead of modifying the diode structure or adding complex anti-series connections, the invention extracts the reverse recovery current path from the intrinsic diode by introducing a parallel capacitor. This separates the flywheel current function (handled by the intrinsic diode) from the reverse recovery current path (handled by the capacitor), simplifying the overall circuit structure while achieving the desired reduction in reverse recovery current
Solution Approach 2:
The parallel capacitor serves multiple functions: it provides an alternative path for reverse recovery current, maintains the flywheel current capability through the intrinsic diode, and can be integrated into existing MOSFET packages. This multi-functionality reduces the need for additional specialized components, thereby simplifying the circuit structure
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 configuration simplifies the circuit structure, reduces reverse recovery current, and minimizes noise and loss in the MOSFET, enhancing the availability and efficiency of the power switching circuit.
Implementation Method 1
Normal PN junction diodes have a reverse recovery time between instantaneous switching from a forward bias (conducting state) to a reverse bias (non-conducting state). During the reverse recovery time, a reverse recovery current flows through a PN junction diode
Implementation Method 2
The second commutation path has a second inductance. The second inductance is higher than the first inductance
Implementation Method 3
when a MOSFET is used as a semiconductor switching element to be installed in a power converter, because MOSFETs each have an intrinsic diode intrinsically formed in antiparallel thereto, the intrinsic diode is used to cause a flywheel current to continuously flow therethrough
Data Source
AI summary
In a power switching circuit, a second commutation member has a second commutation path electrically connected in parallel to a first commutation path and a second diode provided in the second commutation path and electrically connected antiparallel to a semiconductor switching element. While the semiconductor switching element is off, the second commutation path allows a second current based on the inductive load to flow therethrough in a forward direction of the second diode within a commutation period. The second diode has a second reverse recovery time shorter than a first reverse recovery time of the first diode. A second inductance of the second commutation path is higher than a first inductance of the first commutation path.