PTC-Coupled Thyristor Assembly for Thermal Runaway Protection
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Solution Overview
Problem
Thyristors in AC power control applications often experience thermal runaway due to lack of effective temperature control, leading to catastrophic failure, and in cost-sensitive applications, large heat sinks or cooling fans are not feasible, forcing operation below maximum ratings to prevent failure.
Innovation Solution
A hybrid device integrating a thyristor with a positive temperature coefficient (PTC) device and a thermal coupler, where the PTC device is electrically coupled to the thyristor's gate, acting as a thermal switch to regulate current flow and prevent overheating by changing resistance significantly at a specific temperature, thereby controlling the thyristor's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large heat sinks or cooling fans are used to manage thyristor heat generation, then thermal runaway is prevented, but device size and cost increase significantly
Solution Approach 1:
A PTC device is introduced as an intermediary thermal protection mechanism between the thyristor and the external circuit. The PTC device senses thyristor temperature through thermal coupling and automatically limits current by increasing its resistance when temperature exceeds a threshold, preventing thermal runaway without requiring large heat sinks or cooling fans.
Solution Approach 2:
The PTC device provides self-regulating thermal protection for the thyristor. When the thyristor temperature rises, the thermally coupled PTC device automatically increases its resistance to limit current flow, and when temperature decreases, it automatically reduces resistance to restore normal operation, eliminating the need for external control systems.
2Productivity
If thyristor operates at maximum rating to improve efficiency, then power control performance improves, but risk of thermal runaway increases
Solution Approach 1:
The PTC device provides automatic feedback-based thermal protection. It is thermally coupled to the thyristor and continuously senses its temperature. When the thyristor approaches maximum operating temperature, the PTC device detects this through thermal coupling and automatically increases resistance to reduce current, providing negative feedback that prevents thermal runaway while allowing maximum efficient operation.
3Ease of manufacture
If cost-sensitive applications avoid large heat sinks, then device cost decreases, but thermal protection capability is insufficient
Solution Approach 1:
The PTC device serves as a cost-effective thermal protection component that can be easily integrated into the thyristor circuit. It provides reliable thermal runaway prevention at a fraction of the cost of large heat sinks or cooling fans, making thermal protection accessible in cost-sensitive applications.
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 effectively prevents thermal runaway by reducing current to the thyristor when it approaches maximum junction temperature, allowing it to operate closer to its rating without risk of damage, improving efficiency and reliability compared to prior designs.
Implementation Method 1
a positive temperature coefficient (PTC) device electrically coupled to the gate of the thyristor device, wherein the PTC device is disposed on the side pad on the first side of the lead frame
Implementation Method 2
a thermal coupler having a first end connected to the thyristor device and a second end attached to the PTC device. The thermal coupler comprises a copper arm which electrically connects the gate to the PTC device
Data Source
Figure 1A~1C
Figure 2A~2C
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AI summary
A device may include a lead frame, where the lead frame includes a central portion, and a side pad, the side pad being laterally disposed with respect to the central portion. The device may further include a thyristor device, the thyristor device comprising a semiconductor die and further comprising a gate, wherein the thyristor device is disposed on a first side of the lead frame on the central portion. The device may also include a positive temperature coefficient (PTC) device electrically coupled to the gate of the thyristor device, wherein the PTC device is disposed on the side pad on the first side of the lead frame; and a thermal coupler having a first end connected to the thyristor device and a second end attached to the PTC device.