Introduction
The demand for affordable and portable welding equipment is on the rise, especially in developing regions where cost-effective solutions are essential. Discrete IGBTs and MOSFETs have been commonly used in manual arc (MMA) and TIG welding systems with power ranges from 1.5 kW to 6 kW. These welders typically rely on current-mode PWM control along with traditional topologies such as double-tube forward (TTF), half-bridge (HB), and full-bridge (FB). These configurations often operate with zero-current switching (ZCS) during turn-on and hard switching during turn-off. As the need for compact and efficient designs grows, high-frequency operation has become a key trend to enhance performance and reduce system costs.
TRENCHSTOP 5 IGBT technology from Infineon offers significant improvements over previous generations, enabling higher switching frequencies and better efficiency. This makes it an ideal candidate for replacing conventional high-voltage MOSFETs in certain applications, especially when operating at up to 100kHz. Higher switching frequencies can lead to smaller magnetic components and fewer capacitors, which helps reduce overall system size and weight. However, older IGBTs may not always allow for a direct “plug-and-play†replacement due to challenges like voltage overshoot, oscillation, or EMI issues caused by high di/dt and dv/dt during switching.
Improving Half-Bridge Topology
Reducing turn-off losses can bring about major changes in the primary side of the converter, simplifying the overall design. This can also lead to better PCB layouts and more efficient gate driver designs, ultimately reducing the size and weight of the welding machine. For example, a single-phase 4.5kW half-bridge MMA/TIG welder was designed using this approach. By optimizing the power supply loop and layout, two 40A/600V IGBTs were replaced with one IKW50N65H5 TRENCHSTOP 5 IGBT per switch, resulting in improved performance and reliability.
Additionally, the reduced switching and conduction losses significantly lower device temperatures, even allowing for the use of insulating foils. A comparison of case temperatures between different Infineon IGBT technologies shows that the TRENCHSTOP 5 IGBT operates 40K cooler than its predecessor, enhancing thermal management and longevity.
To ensure safe operation, tests were conducted to determine the optimal gate resistance RG(off) that keeps voltage overshoot within 80% of the breakdown voltage, limiting VCE to a maximum of 520V. The lower the stray inductance on the board, the smaller the RG(off) value that can be used without exceeding these limits. The test also evaluated the maximum collector-emitter voltage oscillation, with acceptable values below -200ns set at -25V.
Alternatively, TRENCHSTOP 5 can be used in unoptimized layouts by adjusting the passive gate network. Introducing a turn-off gate resistance and a CGE/RCE gate clamp structure can help maintain acceptable voltage overshoot levels. However, this approach reduces the overall benefits of using TRENCHSTOP 5 IGBTs, highlighting the importance of proper PCB layout and design optimization.
To further minimize stray inductance, TRENCHSTOP 5 IGBTs can be mounted on insulated substrates using surface-mount technology. This results in a more compact solution where both high-side and low-side switches share a common heat sink. While special insulation materials like IMS or Al₂O₃ ceramics may still be required, this advancement leads to a significant reduction in the size and weight of the entire unit. For instance, a new design reduced the size of a half-bridge MMA welder by 35% and its weight by 15%.
This concept allows the overall stray inductance to be as low as 40nH, and with optimized package combinations and full-bridge topology, it can be further reduced to 20nH. Lower stray inductance enables operation at switching frequencies above 100kHz, leading to increased power density, smaller transformers, and fewer DC bus capacitors while maintaining system performance.
Improving Full-Bridge Topology
Figure 4 presents another design example—a 3.5kW full-bridge high-frequency welder. This design replaces traditional MOSFETs with a full-bridge configuration using TRENCHSTOP 5 IGBTs, offering a lower cost, better manufacturability, and higher reliability. The low turn-off losses of TRENCHSTOP 5 IGBTs enable structural improvements in the system, allowing one IGBT to replace three high-voltage MOSFETs. This simplifies integration of power and drive stages onto a single board, reducing the total board area by up to one-third compared to conventional methods.
Moreover, the reduced parasitic inductance in the power loop allows TRENCHSTOP 5 to handle higher di/dt while keeping voltage overshoot within recommended limits. This design demonstrates how to simplify the assembly process, improve manufacturability, and achieve mass production, ultimately lowering system costs. Compared to commercial solutions, this approach reduces material costs by around 30%, size by 30%, and weight by 35%.
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