IGBT Driver Calculation - Server application notes

Application Note AN-7004Peak Gate CurrentThe IGBT switching time is controlled by charging anddischarging the gate of the IGBT. If the gate peak currentis increased, the turn-on and turn-off time will be shorterand the switching losses reduced. This obviously has animpact on other switching parameters such asovervoltage stress, which have to be watched. The gatecharge currents can be controlled by the gate resistorsR G(on) and R G(off). The theoretical peak current valueI GPEAK can be calculated using the equation below. TheIGBT module's internal gate resistor R G(int) must be takeninto account when calculating the peak gate current. Inpractice, stray inductance reduces the peak value belowthe possible theoretical value.Peak Gate CurrentCalculationThe peak gate current can be calculated as follows:IGPEAKV=RG(on)G− V+ RG(off )G(int)In the data sheet of an IGBT driver, a maximum peakcurrent is given, as are the minimum values for the gateresistors. If both these maximum and minimum ratingsare exceeded, the driver output may be destroyed as aresult.Selection Suitable IGBT DriverWhen selecting the suitable IGBT driver for the individualapplication, the following details have to be considered: The driver must be able to provide the necessary gatecurrent (output current / output power). The maximumaverage output current of the driver must be higherthan the calculated value. The maximum peak gate current of the driver must beequal to or higher than maximum calculated peak gatecurrent. The output capacitors of the driver must be able todeliver the gate charge needed to charge anddischarge the gate of the IGBT. In the data sheet ofSEMIKRON drivers the maximum charge per pulse isgiven. This value must be duly considered whenselecting a suitable driver.Other parameters worth mentioning in the context ofIGBT driver selection are insulation voltage and dv/dtcapability.DriverSel – The Easy IGBT DriverCalculation MethodDriverSel facilitates IGBT driver calculation and theselection of a suitable driver, regardless of theapplication. This software tool takes into considerationthe aforementioned characteristics and equations, andcalculates suitable IGBT drivers on the basis of the IGBTmodule selected, the number of paralleled modules, gateresistor, switching frequency and collector-emittervoltage. This tool can be used for driver calculation andselection for any brand and IGBT package, as well as tocalculate the necessary gate charge and averagecurrent.Link: DrivelSel is a free software tool and is available on the SEMIKRON homepage at http://semisel.semikron.com/DriverSelectTool.asp.6 / 8 2007-10-31 – Rev00 © by SEMIKRON