Available device configurations include the SKIM 3, which was introduced last year, and SKIM 4 and 5, which should both ship in the second quarter of this year. (See www.semikron.com for specifications on these IGBT modules. Select "Products," then "SKIM" to view the datasheet.) The SKIM package can be designed with a choice of ceramic materials for the module's isolating substrate—either aluminum oxide or aluminum nitride. The latter material can be employed when superior thermal performance is needed.
Meanwhile, other vendors are focusing on developing discrete devices. IXYS Corp., a semiconductor vendor, produces MOSFETs for use in SMPSs. Some of these are applied in welding applications. According to Ralph Locher, manager of application engineering at IXYS, customers tend to use discretes in parallel to handle the high current levels rather than opting for a costlier modular solution. "In welding, there's a push to build smaller equipment," Locher says. He believes discretes enable the development of more-compact power supplies for welding.
In its development work, IXYS is trying to reduce gate charge by 40% across the board on all of its MOSFETs. This enhancement in device performance will ease the design of gate-drive circuits.
Another vendor, Intersil, is addressing the welding application by developing advanced IGBTs, free-wheeling diodes, and rectifiers. Two new IGBTs being offered in the high-current ISOTOP package are characterized for 100-kHz switching and a TJ of 125°C, with current ratings of 30 and 40 A under these conditions. These transistors are designated as the HGT1N30N60A4D and HGT1N40N60A4D, respectively.
Such IGBTs will permit reductions in on-state losses and power dissipation, particularly when compared to MOSFET-based designs. This point is illustrated by a case study performed by Intersil that looked at a switched-mode power supply built using size-6-die MOSFETs versus an equivalent circuit built using size-3-die 600-V IGBTs. The transistors were applied in a hard-switched boost converter circuit with 50% duty cycle for conduction. Despite the much larger piece of silicon present in the MOSFET, the IGBT dissipated 25% less power with just a slightly greater rise in junction-to-case temperature. Resulting power densities were 10 to 20 A/cm2 for the MOSFET design versus 100 A/cm2 for the IGBT design. (For more information, visit Intersil's Web site at www.intersil.com/igbt/SMPS_Thermal.asp.)
Because of their higher efficiencies, IGBTs can simplify thermal design. Nevertheless, even when IGBTs are em-ployed, thermal design still demands consideration early on in the design process, observes Alex Craig, lead marketing engineer at Intersil. Craig claims some designers attempt to solve thermal problems by "throwing a bigger IGBT device at the application." That approach may work simply because the larger component is more thermally conductive. Craig explains that this method does nothing to reduce heat dissipation, however. A better thermal-management design that allows for the use of a smaller transistor ultimately offers a more cost-effective solution.
Better recovery diodes provide one way to boost the inverter's power efficiency. To that end, Intersil also is developing a series of 600-V diodes with reverse recovery times of as low as 25 ns. Called Stealth diodes, these devices are copackaged with the IGBTs applied in PFC circuits, such as those applied in high-frequency welding supplies (Fig. 2, again). The diodes are avalanche energy rated and offer soft-recovery switching at rated current, high di/dt, and junction temperatures of as high as 125°C. The Stealth diode reduces EMI, making it possible to eliminate a snubber circuit in some cases, while allowing faster turn on of the associated IGBT, too. That leads to lower turn-on losses in the transistor.
In addition, the company is developing output rectifiers, which it expects to release in the coming months. Housed in the company's ISOTOP package, these components will carry ratings of 200 to 300 V and up to 150 A.
Improvements in device performance and packaging stand to enhance many aspects of high-frequency power-supply design in welding machines, but the benefits aren't limited to these applications. A variety of SMPS applications, such as high-power UPS systems and telecom power supplies, employ similar inverter topologies. The advent of smaller, more-efficient semiconductor components and modules with greater functional integration will help designers of many switching power supplies to satisfy growing demands for designs that are more compact and more manufacturable.
Available device configurations include the SKIM 3, which was introduced last year, and SKIM 4 and 5, which should both ship in the second quarter of this year. (See www.semikron.com for specifications on these IGBT modules. Select "Products," then "SKIM" to view the datasheet.) The SKIM package can be designed with a choice of ceramic materials for the module's isolating substrate—either aluminum oxide or aluminum nitride. The latter material can be employed when superior thermal performance is needed.
Meanwhile, other vendors are focusing on developing discrete devices. IXYS Corp., a semiconductor vendor, produces MOSFETs for use in SMPSs. Some of these are applied in welding applications. According to Ralph Locher, manager of application engineering at IXYS, customers tend to use discretes in parallel to handle the high current levels rather than opting for a costlier modular solution. "In welding, there's a push to build smaller equipment," Locher says. He believes discretes enable the development of more-compact power supplies for welding.
In its development work, IXYS is trying to reduce gate charge by 40% across the board on all of its MOSFETs. This enhancement in device performance will ease the design of gate-drive circuits.
Another vendor, Intersil, is addressing the welding application by developing advanced IGBTs, free-wheeling diodes, and rectifiers. Two new IGBTs being offered in the high-current ISOTOP package are characterized for 100-kHz switching and a TJ of 125°C, with current ratings of 30 and 40 A under these conditions. These transistors are designated as the HGT1N30N60A4D and HGT1N40N60A4D, respectively.
Such IGBTs will permit reductions in on-state losses and power dissipation, particularly when compared to MOSFET-based designs. This point is illustrated by a case study performed by Intersil that looked at a switched-mode power supply built using size-6-die MOSFETs versus an equivalent circuit built using size-3-die 600-V IGBTs. The transistors were applied in a hard-switched boost converter circuit with 50% duty cycle for conduction. Despite the much larger piece of silicon present in the MOSFET, the IGBT dissipated 25% less power with just a slightly greater rise in junction-to-case temperature. Resulting power densities were 10 to 20 A/cm2 for the MOSFET design versus 100 A/cm2 for the IGBT design. (For more information, visit Intersil's Web site at www.intersil.com/igbt/SMPS_Thermal.asp.)
Because of their higher efficiencies, IGBTs can simplify thermal design. Nevertheless, even when IGBTs are em-ployed, thermal design still demands consideration early on in the design process, observes Alex Craig, lead marketing engineer at Intersil. Craig claims some designers attempt to solve thermal problems by "throwing a bigger IGBT device at the application." That approach may work simply because the larger component is more thermally conductive. Craig explains that this method does nothing to reduce heat dissipation, however. A better thermal-management design that allows for the use of a smaller transistor ultimately offers a more cost-effective solution.
Better recovery diodes provide one way to boost the inverter's power efficiency. To that end, Intersil also is developing a series of 600-V diodes with reverse recovery times of as low as 25 ns. Called Stealth diodes, these devices are copackaged with the IGBTs applied in PFC circuits, such as those applied in high-frequency welding supplies (Fig. 2, again). The diodes are avalanche energy rated and offer soft-recovery switching at rated current, high di/dt, and junction temperatures of as high as 125°C. The Stealth diode reduces EMI, making it possible to eliminate a snubber circuit in some cases, while allowing faster turn on of the associated IGBT, too. That leads to lower turn-on losses in the transistor.
In addition, the company is developing output rectifiers, which it expects to release in the coming months. Housed in the company's ISOTOP package, these components will carry ratings of 200 to 300 V and up to 150 A.
Improvements in device performance and packaging stand to enhance many aspects of high-frequency power-supply design in welding machines, but the benefits aren't limited to these applications. A variety of SMPS applications, such as high-power UPS systems and telecom power supplies, employ similar inverter topologies. The advent of smaller, more-efficient semiconductor components and modules with greater functional integration will help designers of many switching power supplies to satisfy growing demands for designs that are more compact and more manufacturable.