Patent ID: 6275093
Filing Date: 2001-08-14
Classification: H03K

Abstract:
A combination comprising:an insulated-gate bipolar transistor (IGBT) having first and second electrodes defining the ends of the main conduction path of the IGBT, and having a control electrode for the application thereto of a control voltage for turning the IGBT on and off; said IGBT being characterized in that a voltage applied between the control and second electrodes must exceed a certain threshold voltage (VT) in order to turn-on the IGBT and in that it has a saturation voltage, V.sub.SAT, which is in the range of a few volts;means for coupling a load between the first electrode of the IGBT and a load power supply terrninal;means connecting the second electrode of the IGBT to a point of reference potential;means for applying a turn-on voltage to the control electrode of the IGBT which is significantly greater than the threshold voltage of the IGBT for operating the IGBT in saturation;means coupled to the first electrode of the IGBT for sensing its voltage level and which is responsive to the voltage at the first electrode exceeding the saturation voltage by a first amount for: appling a preset reduced voltage to the control electrode of the IGBT, said preset reduced voltage being less than said turn-on voltage by a preset amount and being greater than the threshold voltage; and being responsive to the voltage at the first electrode exceeding the saturation voltage by a second amount which is greater than said first amount to gradually decrease the preset reduced voltage applied to the control electrode below the threshold voltage of the IGBT in order to turn it off completely; and wherein said preset reduced voltage is gradually decreased by the gradual discharge of a resistive capacitance (RC) network; where the capacitance of the network includes a distinct, independently manufacture, component, having a capacitance which is substantially greater than the typical gate to source capacitance of a metal oxide field effect transistor, and wherein said gradually decreasing voltage is coupled to the control electrode of the IGBT.