Project Analog - August 2008 - (Page 13)

fiG. 3 PoWEr loSS comParED To SWiTchiNG frEquENcy aS ShoWN By ThE DESiGN Tool. At 3 A rms, the power losses are 31 W for the 6-A module and 21 W for the 10-A module. The maximum allowable case temperature is 84ºC and 99ºC for 6- and 10-A module, respectively. The required heat sink Rth can be calculated as follows: Rth(S-A) = (TC – TA) / P - Rth(C-S) The table (Fig. 4) shows calculated heat sink Rth values assuming ambient temperature of 50ºC and Rth(C-S) of 0.1ºC/W. calculated heat SInk rth valueS show the tradeoffs between 16- and 20-A IPMs. This tool can also be used to analyze the effect of modulation index, switching frequency, heat sink temperature, and power factor on the current rating of the module. For example, one design parameter is the switching frequency. The tool can be used to investigate the maximum motor current and power losses of the IPM at different switching frequencies, as shown in Figs. 2 and 3. Selecting up to three parts in each type of analysis shows the power losses increasing and maximum current decreasing with higher switching frequency. Contents Viewpoint Gate Drive Schemes for Motor Control Applications Considerations When Selecting the Proper MOSFET Driver Power Modules for Variable-Speed Motor Control Analog news fiG. 4 The calculations indicate that the smaller IPM will require a larger heat sink. The final choice would be made based on total system cost and size, including both the IPM and heat sink. The same method can be used to select an IPM for an air conditioner application. These typically combine a 400-Vdc bus and PFC front-end. The switching frequency will be lower than a washer application to limit EMI noise. If the application requires 10 ARMS current at 6-kHz switching frequency, the tool can Microchip analog page Motor Control Design Center Sample center microchipDIRECT Reference designs/ app notes Technical training 13 · PrOjECT ANAlOG · VOluME 2 / NuMbEr 5 http://www.microchip.com http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=79&redirects=analog http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2125¶m=en026178 http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2125¶m=en026178 http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423

Table of Contents Feed for the Digital Edition of Project Analog - August 2008

Project Analog - August 2008 Contents Viewpoint About Project Analog Sponsor Gate Drive Schemes for Motor Control Applications Considerations When Selecting the Proper MOSFET Driver for Your Application Power Modules for Variable-Speed Motor Control Efficient Motor/Controls Save Terrawatt-Hours/Year Analog News Contact Microchip Treelink Microchip Advanced Parts Selector (MAPS)

Project Analog - August 2008

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