Semiconductor Switch Layout for Freewheeling Diode Heat Loss
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Solution Overview
Problem
Conventional power conversion circuits with high-speed freewheeling diodes experience increased heat loss and require stringent cooling designs due to continuous current flow during abnormal conditions, which is costly and inefficient, especially with high-voltage SiC diodes.
Innovation Solution
The semiconductor switch configuration includes a main element with a high-withstanding voltage and an auxiliary element with lower voltage, connected in a specific parallel configuration with a freewheeling diode, allowing independent control of both elements to minimize current flow through the high-speed freewheeling diode during abnormal conditions, thereby reducing heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high-speed freewheeling diode is connected anti-parallel to the main element in conventional power conversion circuits, then the switching speed and power conversion efficiency are improved, but during abnormal conditions (device gate-off state), the diode experiences continuous current flow causing significant heat generation and loss, requiring stricter cooling design
Solution Approach 1:
The invention divides the single high-speed freewheeling diode function into two separate diodes: a first freewheeling diode connected anti-parallel to the main element, and a second freewheeling diode connected anti-parallel to the auxiliary element. This segmentation allows independent control of current paths - during normal operation the first diode handles freewheeling current, while during abnormal conditions the second diode provides an alternative path through the auxiliary element, preventing continuous current flow and heat generation in the first diode.
2Loss of energy
If SiC diodes are used as high-speed freewheeling diodes to reduce loss and improve switching speed, then the power conversion efficiency is improved, but the cost increases significantly
Solution Approach 1:
The invention changes the operational parameters of the freewheeling diodes by introducing conditional control through the auxiliary element. By monitoring abnormal conditions (overcurrent, overtemperature) and activating the auxiliary element with its associated second freewheeling diode, the system dynamically alters the current path parameters. This allows the use of more economical diode specifications since the first high-speed diode no longer needs to handle continuous abnormal condition currents, reducing the required current rating and associated cost while maintaining power loss performance.
3Reliability
If the auxiliary element is continuously supplied with off-signal in synchronism with the main element during abnormal conditions, then the main current is forced to flow through the high-speed freewheeling diode, but this causes a sharp increase in average current value and heat generation in the diode
Solution Approach 1:
The invention introduces the second freewheeling diode and auxiliary element as an intermediary current path during abnormal conditions. Instead of forcing all current through the first high-speed freewheeling diode, the auxiliary element acts as a mediator that provides an alternative route. The control unit activates the auxiliary element and its associated second diode during abnormal conditions, creating a parallel current path that bypasses the first diode and redirects current through the auxiliary element, thereby reducing the current burden and heat generation on the first diode while maintaining system protection.
Data Source
AI summary
According to one embodiment, a semiconductor switch includes a first element that includes a switching element and an anti-parallel diode. The switching element has a breakdown voltage and is coupled to a control terminal and second and third terminals. The semiconductor switch further includes a second element having a breakdown voltage lower than that of the first element. The second element is coupled to a control terminal and second and third terminals. The semiconductor switch also includes a flyback diode having a breakdown voltage substantially similar to that of the first element. A negative electrode of the first element is connected to a negative electrode of the second element and the flyback diode is connected in parallel between a positive terminal of the first element and a positive terminal of the second element. The control terminal for the first element and the control terminal for the second element are coupled to one or more control circuits independently of each other.