VMOS/Bipolar dual-triggered switch

A method for operating a bipolar power transistor switch having a collector electrode receptive of an operating voltage, a base electrode for receiving a control signal, and an emitter electrode for receiving a source of reference potential, whereby amongst other requirements interelectrode capacitances of said transistor must be charged at the initiation of a given turn-on cycle, before said transistor turns on, and discharged at the initiation of a given turn-off cycle before said transistor turns off, comprising the steps of:

• supplying a current of predetermined magnitude to said base electrode for both initiating the turn-on cycle and turning on said transistor into at least an unsaturated conduction state;
• increasing the magnitude of the current supplied to said base electrode in a step-like manner a sufficient amount for placing said transistor into or as close as possible to a saturated conduction state, depending upon the characteristics of a load being driven by said bipolar transistor switch, for minimizing the power dissipation thereof;
• and
• decreasing the magnitude of the current supplied to said base electrode in a step-like manner first a sufficient amount for both initiating the turn-off cycle and ensuring the placement of said transistor into an unsaturated conduction state, and thereafter second to a magnitude of zero for completing the turn-off of said transistor.

A method for operating a bipolar power transistor switch having a collector electrode receptive of an operating voltage, a base electrode, an emitter electrode, and interelectrode capacitance for connection to a point of reference potential, comprising the steps of:

• initiating the turn-on cycle for said transistor by supplying a first current to said base electrode for turning on said transistor into at least an unsaturated conduction state, whereby said interelectrode capacitances take on charge:
• supplying concurrent with said first current, a second current to said base electrode a predetermined time after turning on said transistor, the sum of the magnitudes of the first and second currents being sufficient for placing said transistor into or as close as possible to a saturated conduction state, depending upon the characteristics of a load being driven by said transistor switch for minimizing the power dissipation thereof;
• providing negative feedback between the collector and base electrodes so that whenever the voltage at said collector electrode increases due to some electrical transient conduction, greater base current is supplied for substantially maintaining said transistor in a saturated conduction state, thereby improving the transient capability of said transistor and further minimizing the power dissipation thereof;
• initiating the turn-off cycle for said transistor by removing said first current from said base electrode for placing saids transistor back into an unsaturated conduction state, whereby said interelectrode capacitances partially discharge;
• and
• removing said second current from said base electrode for completing the turn-off of said transistor.

A high-power switching circuit, comprising:

• bipolar switching transistor means having a collector electrode for receiving a first operating voltage, a base electrode, and an emitter electrode for connection to a point of reference potential;
• a first vertical metal oxide semiconductor (VMOS) field effect transistor having a gate electrode receptive of a first control signal, drain and source electrodes connected individually to the collector and base electrodes, respectively, of said bipolar transistor switching means, said first VMOS being responsive to said first control signal for turning on to substantially lower the impedance between its source and drain electrodes, permitting current flow therebetween;
• and
• current control means having a control electrode receptive of a second control signal, a first electrode for receiving a second operating voltage, and a second electrode connected to said base electrode of said first switching means, said current control means being responsive to said second control signal for turning on to substantially lower the impedance between its first and second electrodes, thereby permitting current to flow between its first and second electrodes;
• said current control means being turned on prior to first VMOS transistor for initiating current flow through the base-emitter electrode current path of said bipolar switching transistor means thereby turning on said bipolar switching transistor means into at least an unsaturated conductive state, thereafter said first VMOS transistor being turned on for supplying sufficient additional current flow through the base-emitter electrodes of said bipolar switching transistor means, for causing the latter to operate in a saturated conductive state, or as close to a saturated state as possible depending upon the characteristics of a load being driven by said curcuit, said first VMOS and current control means being thereafter concurrently turned on for a substantial period of the total conduction time of said bipolar switching transistor means, thereby minimizing the power dissipation of the latter, said first VMOS transistor when conductive providing negative feedback between the collector and base electrodes of first switching device, thereby improving the transient capability of the latter, turn off of said bipolar switching transistor means being initiated by first turning off said current control means, for ensuring said bipolar switching transistor means is placed into a non-saturated conductive state, thereafter said first VMOS transistor is turned off for substantially reducing to zero the magnitude of current flow between the base and emitter electrodes of said bipolar switching transistor means, turning off the latter, such sequence of operation of said second switching means and VMOS transistor also substantially reducing the turn-on and turn-off times of said bipolar switching transistor means.