FF400R12KE3HOSA1 Infineon

Application Note Page 1 Date: 15-12-2005 AN-Number: AN-2006-01 Department: AIM PMD ID AE Driving IGBTs with unipolar gate voltage Introduction Infineon recommends the use of negative gate voltage to safely turn-off and block IGBT modules. In areas with nominal currents less than 100tA the negative gate voltage is often omitted for cost reasons. The following paper describes special considerations for a unipolar drive of IGBT modules. Turn-off to 0 V The latest Infineon IGBT chip generations have several advantages. Some highlights especially are a wider dynamic range, faster switching, less switching losses and lower conduction losses. When switching to 0 V two effects may come into play: - parasitic turn-on via the Miller capacitance - parasitic turn-on via stray inductances Turn-on via the Miller capacitance When turning on the lower IGBT in a half-bridge a voltage change dv /dt occurs across the upper IGBT / diode. This causes an approach CE dv CE current i = C to flow which charges the parasitic capacitance CG CG dt C of the upper IGBT. The capacitances C and C form a CG CG GE capacitive voltage divider. Figure 1 depicts the current path via the Miller capacitance of the upper IGBT. C dv CE i = C CG CG dt +15 V Treiber V C CE CG R R R Driver Gon/off Gint C GE dv t CE dt 0 V E v = (R + R + R )i GE Driver Gon/off Gint CG Figure 1: Current via the Miller capacitance of the upper IGBT Infineon Technologies AG Max-Planck-Strae D-59581 Warstein Tel. +49 (0) 29 02 7 64-0 Fax + 49 (0) 29 02 7 64-12 56 www.Infineon.com Author: Baginski Application Note Page 2 Date: 15-12-2005 AN-Number: AN-2006-01 Department: AIM PMD ID AE The current i flows via the Miller capacitance, the serial resistors, C CG GE and the DC-bus. If the voltage drop across the gate resistor exceeds the threshold voltage of the IGBT, a parasitic turn-on occurs. With rising chip temperature the threshold voltage drops by several mV / K. When the upper IGBT switches, a current flows via the Miller capacitance of the lower IGBT and may lead to parasitic turn-on here as well. Turn-on via stray inductances di C2 When turning off the load current a voltage v = L is induced E2 E2 dt across the emitter stray inductance. C 1 T 1 D 1 E /C 1 2 +15 V i C2 T 2 R R R D 2 Driver Gon/off Gint v L E2 E2 0 V E 2 Figure 2: Induced voltage across the emitter inductance When switching the IGBT T on the main current will commutate from 1 the free wheeling diode D to the IGBT. The di /dt produced from 2 C2 decay of the reverse recovery of the diode, induces a voltage on L E2 and shifts the emitter potential of T to the negative. 2 If the induced voltage produced through a high di /dt is higher than the C threshold voltage of the IGBT this will result in a parasitic turn-on of T . 2 Infineon Technologies AG Max-Planck-Strae D-59581 Warstein Tel. +49 (0) 29 02 7 64-0 Fax + 49 (0) 29 02 7 64-12 56 www.Infineon.com Author: Baginski