Project Analog - August 2008 - (Page 12)

mcP6021/2/3/4 oPEraTioNal amPlifiErS In order to choose the right IPM, the engineer starts with information about the application. For example, consider a washing machine controller intended for operation at up to 3-A rms phase current and 16-kHz switching frequency, with dc bus voltage 320 V. If enhanced reliability is an intended selling point for the end-product, the specified maximum junction temperature may be set well within the module vendor’s recommended limit; say 125°C. current ratInGS, heat SInkS The IPMs are available in a number of current ratings and more than one choice may be is suitable for this application. However, because the power losses will be different for each module under the given operating conditions, the heat sink necessary to maintain junction temperature under 125°C will also be different. Calculating the required heat sink thermal resistance (RTH) requires complex knowledge of IPM thermal and electrical behavior to identify conduction and switching losses and predict the junction temperature based on these data. Although modeling steady-state conditions is relatively straightforward, the power losses in practice are not constant. In operation, the junction temperature will fluctuate beyond the steady-state average because power losses vary at a fundamental frequency equivalent to the modulation frequency of the inverter. Another important aspect is mutual heating, since the multiple heat sources within the IPM share the same paths from case to ambient. This effect must be taken into account if the model of the IPM is to be accurate. modelInG toolS Detailed models of IPMs power modules can be a great benefit when identifying and selecting appropriate modules. The module suppliers often have custom tools to with electrical and thermal models for currently available modules. The tools can be used to generate a series of performance curves describing IPM behavior under the application conditions entered by the user. Often the tools allow the users to change parameters such as switching frequency, power factor and modulation index to obtain performance curves customized for the application. The tools usually allow the user to generate useful information to enable easy selection of IPMs: Power loss analysis. To produce power loss versus switching frequency curves.Component comparison. To produce power loss and case temperature curves for heat sink selection. Considering the earlier design example, The modeling tools can be used to calculate the required heat sink Rth. Figure 1 shows the component comparison analysis result from a typical tool, showing both the power loss of the inverter and the maximum heat sink temperature for this application. 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 The MCP602x family of operational amplifiers features high speed, low power, low noise performance that is ideal for feedback control loops. These op amps are available in single, single with power saving chip select, dual, and quad versions. In addition, these amplifiers offer rail-to-rail inputs, low input bias currents, are unity gain stable and are specified over an extended temperature range from -40°C to +125°C. Click here for more information on the MCP6021/2/3/4 Microchip analog page Motor Control Design Center Sample center microchipDIRECT Reference designs/ app notes Technical training 12 · 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/opamps 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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