Bipolar bootstrap top switch gate drive for half-bridge semiconductor power topologies

A method, electrical circuit or apparatus for supplying both positive and negative gate drive power supplies to the “top” semiconductor switch, in a typical half-bridge semiconductor power topology, from the gate drive power supplies of the “bottom” switch and without the use of transformer, capacitive or optical isolation and where the half-bridge circuit topology is, only for the purpose of facilitating a concise description of the invention, defined as two insulated gate bipolar transistor (IGBT) switching devices each with antiparallel diodes and connected in series where the emitter of the “bottom” IGBT is connected to an arbitrary ground reference point, and where the collector of the bottom IGBT, the emitter of the top IGBT and one end of a filter inductor make a common connection and where the other end of said filter inductor is connected to one end of a load and where the other end of said load is connected to a positive DC power source with respect to said ground reference point and where the positive terminal of said positive DC power source is also connected to the negative terminal of a second DC power source having a positive terminal connected to the collector of said top IGBT and where the invention essentially comprises;

• a bipolar arrangement of positive and negative power supplies with respect to the bottom IGBT emitter,
• a bottom gate driver circuit, capable of driving the gate of the bottom IGBT with respect to the bottom IGBT emitter, to turn the bottom IGBT “on” or “off’,
• a top gate driver circuit, capable of driving the gate of the top IGBT positive or negative with respect to the top IGBT emitter, to turn the top IGBT “on” or “off’,
• a bipolar arrangement of positive and negative energy storage capacitors, with respect to the emitter of the top IGBT, to supply power to said top gate driver circuit,
• a diode with anode connected to the positive terminal of said positive power supply referenced to the emitter of said bottom IGBT and with cathode connected to the positive terminal of said positive energy storage capacitor referenced to the emitter of said top IGBT, a third gate driver, which is substantially synchronized with said bottom gate driver circuit,
• a third switching device, a field effect transistor (FET), driven by said third gate driver and with source connected to the negative power supply terminal of said negative power supply referenced to the emitter of said bottom IGBT and with drain connected to the negative terminal of said negative energy storage capacitor referenced to the emitter of said top IGBT and
• where the switching action of the half-bridge IGBTs in substantially typical applications using substantially typical control methods plus the described inclusion and timing of said third switching device cause energy in said positive and negative power supplies referenced to the bottom IGBT emitter to be transferred to said positive and negative energy storage capacitors referenced to the emitter of the top IGBT, respectively.