Trigger device and piezo-ignition coupler with galvanic decoupling

A device for triggering a MOS power switch comprising:

• a piezo-ignition coupler for supplying a trigger signal to said power switch, said piezo-ignition coupler consisting of
• a lamina of piezo-ceramic material,
• at least two electrodes disposed on one surface of said lamina and a like number of counter-electrodes disposed on the opposite side of said lamina in at least substantial registry therewith,
• said electrodes on a same surface of said lamina being spaced from each other by an electrically insulating gap for galvanically decoupling said spaced electrodes,
• one electrode on one surface of said lamina and one counter-electrode in at least substantial registry therewith on the opposite surface of said lamina forming an input pair of electrodes, and another electrode on said one surface of said lamina and another counter-electrode in at least substantial registry therewith on the opposite surface of said lamina forming an output pair of electrodes and being connected to a trigger electrode of said power switch,
• said lamina having a shape exhibiting an axis with more than two-fold rotational symmetry with a resonant frequency of vibration determined by a single length dimension of the area of said lamina;
• a current limiting means connected to said MOS power switch for selectively short-circuiting said power switch comprising
• a bipolar transistor having an emitter connected to a gate of said MOS power switch, a collector connected to said counter-electrode of said output pair of electrodes of said coupler, and a base connected to a source terminal of said MOS power switch,
• a resistor connected across said collector terminal and said base terminal of said bipolar transistor, said resistor having a value which is greater than a voltage at which said bipolar transistor becomes conductive across said emitter and base terminals divided by a maximum admissible current to said MOS power switch;
• and
• control electronics connected to said input pair of electrodes for generating an alternating current signal having a frequency which is matched to said resonant frequency of said lamina at a value in the range of 20 kHz to 500 kHz for inducing a selected radial oscillation mode in said lamina.

A device for triggering a MOS power switch comprising:

• a piezo-ignition coupler for supplying a trigger signal to said power switch, said piezo-ignition coupler consisting of
• a lamina of piezo-ceramic material,
• at least two electrodes disposed on one surface of said lamina and a like number of counter-electrodes disposed on the opposite side of said lamina in at least substantial registry therewith,
• said electrodes on a same surface of said lamina being spaced from each other by an electrically insulating gap for galvanically decoupling said spaced electrodes,
• one electrode on one surface of said lamina and one counter-electrode in at least substantial registry therewith on the opposite surface of said lamina forming an input pair of electrodes, and another electrode on said one surface of said lamina and another counter-electrode in at least substantial registry therewith on the opposite surface of said lamina forming an output pair of electrodes and being connected to a trigger electrode of said power switch,
• said lamina having a shape exhibiting an axis with more than two-fold rotational symmetry with a resonant frequency of vibration determined by a single length dimension of the area of said lamina;
• a current limiting means connected to said MOS power switch for selectively short-circuiting said power switch comprising
• a thyrister having an anode connected to a gate terminal of said MOS power switch, a cathode connected to said counter-electrode of said output pair of electrodes of said coupler and a trigger electrode connected to a source terminal of said MOS power switch,
• a resistor connected across said trigger terminal and said cathode, said resistor having a value such that the product of said value and a maximum admissible current to said MOS power switch is greater than or equal to one volt;
• and
• control electronics connected to said input pair of electrodes for generating an alternating current signal having a frequency which is matched to said resonant frequency of said lamina at a value in the range of 20 kHz to 500 kHz for inducing a selected radial oscillation mode in said lamina.