Project Analog - August 2008 - (Page 16)

mcP1415/16 DrivEr iN TiNy SoT-23 have been around for decades, they now have sophisticated controls to drive them to their maximum potential. Most ACIMs perform at their highest efficiencies at 75% to 90% of their rated load. For applications that routinely use motors at a fraction of their peak load, it is possible to save 50% of the motor/control’s purchase price in energy savings per year by optimizing efficiency over their load range. The DOE estimates that 44% of all industrial motors are consistently operating at less that 40% of their rated load. Today’s intelligent variable-speed drives (VSDs) can adapt to an application’s needs by providing peak torque or speed only when required. When designing VSDs, careful attention is needed to ensure that the control does not suffer unnecessary losses causing more heat to dissipate into heat sinks, enclosures, and nearby circuitry, leading to higher costs, larger footprints, and reduced lifespan. The VSD will suffer its largest losses in the switches that drive the motor’s windings and in the recovery diodes that carry the phase currents for a short time after the switches turn off. For three-phase ACIM and BLDC drives, there will be six IGBTs or MOSFETs driving three motor phases. For SR drives, as little as two IGBTs and diodes are required, depending on the number of phases used. Most line-voltage controls are based on IGBTs instead of MOSFETs because of their improved conduction performance at higher operating temperatures. At lower voltages, the MOSFET is the preferred device. Conduction losses are dc losses in the turned-on switch. Switching losses occur at both the turn-on and turn-off phases and are proportional to the switching frequency. The drive designer can do little to improve conduction losses other than provide an adequate gate voltage, with a nominal VGE of about 15 V. Switching losses can be mitigated by selecting IGBTs or modules that use either NPT or FieldStop technology to decrease turnon and turn-off losses, decreasing switching frequency, and/or carefully choosing drivers and resistances to optimally drive the IGBT’s gate. Optimizing the gate’s driver can be quite challenging with two objectives to satisfy simultaneously—minimizing switching losses and keeping EMI in check. In integrated motor-control modules, the optimization is fixed and a permanent feature of the module. Semiconductor companies have invested much effort in the development of technologies that allow makers of appliances and industrial machines to implement high-efficiency electronic controls with a minimum of R&D expense and significantly decreased time to market. One example of a costcompetitive power bridge with high efficiency and EMI optimized drivers, diodes, and overcurrent protection features is Fairchild Semiconductor’s Smart Power Module (SPM). Figure 2 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 MCP1415/16 are high speed MOSFET drivers capable of providing 1.5A of peak current. The inverting or non-inverting single channel output is directly controlled from either TTL or CMOS logic. These devices also feature low shoot-through current, matched rise and fall time, and short propagation delays which make them ideal for high switching frequency applications. Click here for more information on the MCP1415/16 Microchip analog page Motor Control Design Center Sample center microchipDIRECT Reference designs/ app notes Technical training 16 · 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/mosfet 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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