Superjunction MOSFET Power Circuit with Optimized Freewheel Diode
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Solution Overview
Problem
Conventional power conversion circuits with MOSFETs having a superjunction structure experience increased turn-off loss due to irregularities in charge balance, resulting in a hump waveform in the drain current when turned off, which increases surge voltage and loss.
Innovation Solution
A power conversion circuit with a MOSFET having a semiconductor base substrate with n-type and p-type column regions forming a superjunction structure, a freewheel diode with controlled lifetime, and an inductive load, where the switching frequency is 10 kHz or more, and the freewheel diode has a current density within specific ranges to minimize the hump waveform and associated losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching frequency is increased to improve productivity, then power conversion efficiency improves, but hump waveform causes increased turn-off loss
Solution Approach 1:
The patent optimizes the MOSFET's charge balance ratio Qn/Qp to 0.95-1.05 and the freewheel diode's reverse recovery charge Qrr to 20-80 nC, enabling high-frequency switching (100 kHz to 1 MHz) with reduced turn-off loss. This parameter optimization allows the system to achieve high productivity without excessive energy loss.
2Temperature
If the active region area of freewheel diode is increased to reduce current density, then heat dissipation improves, but junction capacitance increases causing larger hump waveform
Solution Approach 1:
The patent optimizes the active region area of the freewheel diode to achieve a balance between heat dissipation and junction capacitance. By controlling the diode's reverse recovery charge Qrr to 20-80 nC and selecting appropriate active region area, the system achieves both adequate heat dissipation and minimal hump waveform.
Solution Approach 2:
The patent uses a freewheel diode with specifically controlled reverse recovery characteristics to compensate for the trade-off between active region area and junction capacitance. The diode's reverse recovery charge acts as a compensating factor that reduces the hump waveform even when the active region area is increased for better heat dissipation.
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 reduces turn-off loss, turn-on loss, and recovery loss, while maintaining efficient heat dissipation and preventing IFSM breakdown, by optimizing the freewheel diode's current density and area to minimize junction capacitance and recovery current.
Implementation Method 1
a MOSFET having a semiconductor base substrate which includes a n-type column region and a p-type column region, the n-type column region and the p-type column region forming a super junction structure
Implementation Method 2
the freewheel diode is a lifetime-controlled Si-FRD or SiC-SBD
Implementation Method 3
an inductive load
Data Source
AI summary
A power conversion circuit includes: a MOSFET having a super junction structure; an inductive load; and a freewheel diode. A switching frequency of the MOSFET is 10 kHz or more. When the MOSFET is turned off, a first period during which a drain current decreases, a second period during which the drain current increases, and a third period during which the drain current decreases again appear in this order. The freewheel diode is an Si-FRD or an SiC-SBD, and current density obtained by dividing a current value of the forward current by an area of an active region of the freewheel diode falls within a range of 200 A/cm2 to 400 A/cm2 when the freewheel diode is the Si-FRD, and the current density falls within a range of 400 A/cm2 to 1500 A/cm2 when the freewheel diode is the SiC-SBD.