Project Analog - August 2008 - (Page 5)

Gate Drive Schemes for Motor Control Applications Contributed by Microchip Technology www.microchip.com Contents Viewpoint Gate Drive Schemes for Motor Control Applications fiG 1 hiGh-aNDloW-SiDE moTor DrivE ExamPlE T he type of motor, powerswitching topology and the power-switching element will generally dictate the necessary gate drive scheme. The two fundamental categories for gate drive are high-side and low-side. High-side means that the source (MOSFET) or emitter (IGBT) of the power element can float between ground and the high-voltage power rail. Low-side means the source or emitter is always connected to ground. An example of both of these types can be seen in a half-bridge topology, shown in Figure 1. voltage applied to the gate must float up as well. This requires some form of isolated, or floating, gate drive circuitry. Q2, however, always has its source or emitter connected to ground so the gate drive voltage can also be referenced to ground. This makes the gate drive much simpler. Various schemes exist for high-side gate drive applications. These include single-ended or doubleended gate drive transformers, floating bias voltages and opto-isolator drive. Examples of these drive schemes are shown in Figures 2 through 4. Microchip’s MOSFET drivers fit a wide variety of applications using the gate drive schemes shown. Microchip’s single output drivers, which have ratings of 0.5A up to 12A, work well for the single-ended gate drive needs for the circuits in Figures 2 and 4. Microchip’s dual output drivers provide an excellent solution for the gate drive solution shown in Figure 3. The gate drive transformer solutions shown in Figures 2 and 3 provide a number of good features. The first feature is that they solve the high-side drive problem. The drive winding(s) that drive the gate of the power MOSFET/IGBT can float at any potential (only limitations to this are the insulation ratings of the wire). The second feature is that it provides both a positive and negative gate drive voltage. As with any transformer, there must be volt- Considerations When Selecting the Proper MOSFET Driver Power Modules for Variable-Speed Motor Control Analog news Microchip analog page Motor Control Design Center Sample center microchipDIRECT Reference designs/ app notes Technical training In this configuration, Q1 and Q2 are always in opposite states. When Q1 is on, Q2 is off and vice-versa. When Q1 goes from being off to on, the voltage at the source of the MOSFET goes from ground up to the highvoltage rail. This means that the 5 · PrOjECT ANAlOG · VOluME 2 / NuMbEr 5 http://www.microchip.com 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

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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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