Reverse Conducting Drives

Mark Thomas, IGBT Product Marketing Manager, Infineon Technologies


Bringing the IGBT into a new dimension

For the low cost / low power consumer drive market, the RC-Drives family of IGBTs from Infineon has been launched. For the first time Infineon's famous "reverse conducting" (RC) IGBT technology of monolithically integrated IGBT and free wheeling diode in a single die is available for hard switching applications like fans, pumps and motors. By integrating the diode a substantial saving in terms of cost and package size is possible whilst performance is not sacrificed. For the next generation of home appliances, this gives new opportunities to designers in board layout as the new smaller packages offer the chance to reduce PCB area, plus purchasing is kept happy with the savings these products bring. Over the last 10 years, the market forecasts of major home appliances (MHA) sold with variable speed drives (VSD) has been on the optimistic side, with predictions of rapid market acceptance - which never eventuated. High cost has been one of the main reasons for the slow growth with manufacturers selling appliances with VSD as high end products where volumes are not high. The latest market studies continue to predict rapid market growth by indicating, for example, the VSD market in MHA is set to double over the next 5 years. This time, however, there is more confidence in the accuracy of these latest predictions. Government legislation and China's government subsidy program to stimulate the Chinese economy during the 2009 down turn are two reasons why MHA manufacturers are more actively implementing VSD to fulfill tougher efficiency standards. Manufacturers are also using this as a chance to develop products with "unique" features to differentiate themselves from the competition. Without doubt, Intelligent Power Modules (IPM) will enjoy market leadership in this segment, but there is a trend evident that discrete solutions will win more of the market share. Due to cost pressure, OEMs and design-houses are looking more closely at implementing discrete solutions. This has been recently seen by a significant increase in requests for technical support to help with optimizing discrete solution designs. This is the breaking of a new dawn for high efficiency MHA using VSD using discrete solutions.

In response to customer requests, a new family of discrete IGBTs is now available specifically designed with MHA market in mind. The new RC-Drives family is based on Infineon's Trench Field Stop IGBT Technology (TRENCHSTOP™). The new family consists of 4A, 6A, 10A and 15A IGBT + free wheeling diode (FWD) as seen in table.

Since the MHA market is one of the target applications, the device has been optimised accordingly. Price and performance (high efficiency, 5?s short circuit robustness and EMI behaviour) were the key requirements for market acceptance when originally defining the product. Price is seen as the most important feature for the customer; as they are pushing the price of the modules down to bring models offering VSD into the mainstream market and not just for high-end models. The price advantage offered to the customer by the RC-Drives family comes from the reduction in the package size, a single die solution (less test time and bonding requirements) and cost optimization of the technology. Here a 30% cost improvement was achieved over the previous Infineon products offered for this segment. Additionally, due to the package shrink (75% compared to a D²PAK package), a substantial PCB area reduction is possible, as can be seen in figure 1.

Of course, performance is needed and here the advantage of the TRENCHSTOP™ technology comes out on top. Since switching frequencies where VSD is used are rarely seen to exceed 16kHz, the family has been optimised for low conduction losses. This means at low switching frequencies the dominant conductions losses are reduced thanks to the low Vce(sat) (as seen in Figure 2). The resultant high efficiency of the IGBT and diode significantly works towards satisfying the thermal issues when moving to a smaller package.

Easy controllability, via the gate resistor, of the turn on and turn off waveforms further allows the designer to optimise for efficiency. For Infineon IGBTs, low gate resistors (down to 5?) are recommended to get the best efficiency. A feature of all Infineon IGBTs is the soft switching nature, which means excellent EMI behaviour is still maintained even with very low gate resistors.

Starting at the lowest power rated applications, like 30W to 100W air conditioner fans, the 4A device is best suited. Here the 75% footprint reduction over a conventional TO-220 package is the key benefit to the customer whilst being able to operate the devices, when correctly done, without the need for a heat sink. When addressing VSD refrigeration compressors up to 200W, the 4A DPAK (TO-252) version of the RC-Drives shows itself to be the best suited device. Again here, the MHA manufacturers enjoy the 30% cost savings of the RC-Drives family, plus the space-saving credentials are helping them come up with new ways to implement the power board into the fridge unit. To support the release of the new family, a 200W demoboard is available for ordering. Details can be found on the Infineon website. For VSD washing machine motors and inverterised air conditioner compressors up to 800W, when a discrete IGBT solution is preferred, a TO-220 or TO-220 Full Pack package has been used. Application tests have been performed on a commercial washing machine, where the new IKU06N60R in an IPAK (TO-251) using thermal isolation foil has replaced the competitor TO-220 Full Pack devices on the power board. Thermal measurements taken during operation have seen only a 15°C increase in case temperature (as can be seen in Figure 3). This is with a package that is 75% smaller than the TO-220 Full Pack! Here the low conduction losses play a vital role in keeping the case temperature down, even with the higher thermal resistance of the IPAK (TO-251) The application test demonstrates the RC-Drives family really brings the IGBT into a new dimension by offering excellent power handling capabilities in a package that is 75% smaller that the TO-220.

The fully released RC-Drives family specifically targets the price sensitive Major Home Appliance Market that uses Variable Speed Drives. Low conduction losses allow for a 75% package shrink, whilst thermally only a 15°C increase in case temperature is seen during application testing of a commercial washing machine. For more information about discrete IGBTs from Infineon, please visit www.infineon/igbt