Power Module Separate Terminals MOSFET Body Diode Testing
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Solution Overview
Problem
The degradation of MOSFET body diodes due to continuous forward current application is a significant issue, especially when using Schottky barrier diodes as freewheeling diodes, as most of the current flows through the Schottky barrier diode, making it difficult to conduct effective energization tests and screen out low-quality chips.
Innovation Solution
A power module configuration that allows for separate paths for current flow through the body diodes of MOSFETs and Schottky barrier diodes, enabling efficient energization testing by ensuring forward current flows primarily through the MOSFET body diodes, thereby facilitating the identification and removal of low-quality chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky barrier diode is used as the freewheeling diode to reduce forward voltage drop, then the forward voltage drop is reduced and switching speed is improved, but most of the freewheeling current flows through the Schottky barrier diode making it difficult to conduct effective energization tests on the MOSFET body diode
Solution Approach 1:
The patent segments the current path by introducing a separate test terminal that connects to the MOSFET body diode through a dedicated path, independent of the Schottky barrier diode's freewheeling current path. This allows the energization test current to be applied specifically to the body diode without being shunted through the Schottky barrier diode, thereby enabling effective screening of MOSFET quality while maintaining the Schottky barrier diode's low voltage drop advantage in normal operation.
2Reliability
If forward current is continuously applied to the body diode for energization testing to screen out low-quality chips, then low-quality chips are screened out, but when a Schottky barrier diode is used as the freewheeling diode, the energization time has to be made considerably long because most current flows through the freewheeling diode
Solution Approach 1:
The patent extracts the testing function from the normal operational current path by providing a dedicated test terminal and separate current path. This extraction allows the energization test current to be applied directly to the MOSFET body diode without competing with the Schottky barrier diode's freewheeling current, significantly reducing the test time required to screen out low-quality chips while maintaining effective screening capability.
3Loss of energy
If a Schottky barrier diode with low forward voltage drop is used, then current flowing through the body diode is reduced during normal operation, but counter-electromotive force in parasitic inductance causes instantaneous current to flow through the body diode during switching operations
Solution Approach 1:
The patent applies preliminary action by carefully controlling the timing and magnitude of the energization test current applied to the body diode. The test current is applied in advance of normal operation to screen out chips that would be susceptible to degradation from instantaneous switching currents. This preliminary screening ensures that only chips with sufficient robustness against instantaneous current stress are deployed, preventing future degradation while maintaining the low forward voltage drop advantage of Schottky barrier diodes during normal operation.
Data Source
AI summary
A power module includes a first MOS transistor and a first Schottky barrier diode for a lower arm, and a second MOS transistor and a second Schottky barrier diode for an upper arm. In one embodiment, one positive-side power supply terminal and one negative-side power supply terminal are provided, while an output terminal to which the first and second MOS transistors are connected and an output terminal to which the first and second Schottky barrier diodes are connected are provided as separate output terminals.