Dc-ac converter

Claim 2

A DC-AC converter comprising a pair of input terminals adapted for connection to a source of voltage, a transistor, a transformer having a winding which connects the base and the emitter of said transistor together, a circuit for generating control signals coupled to said transistor base electrode, means coupling the two ends of said transformer winding in electrically conducting connection with the circuit for generating control signals to generate a first current component in said winding, means connecting a series arrangement which includes a second winding of the transformer and the main electrodes of the transistor across the input terminals of the converter, the winding sense of the second transformer winding being arranged in a manner such that a second current component is induced in the first-mentioned transformer winding during the conducting period of the transistor, which second current component flows in the same direction as said first current component in the firstmentioned transformer winding so that the said first and second currents together remove charge carriers from the transistor base through the first-mentioned transformer winding when the transistor becomes non-conducting.

Claim 3

A DC-AC converter as claimed in claim 1 in which the transistor is a high-voltage transistor, characterized in that the operating frequency of the converter is more than 18,000 Hz.

Claim 4

A DC-AC converter comprising a pair of input terminals adapted for connection to a source of voltage, a transistor having base, emitter and collector electrodes, a transformer having first and second windings, means connecting said first winding between the base and emitter electrodes of said transistor, a circuit for generating control signals coupled to said base electrode to cause said transistor to repetitively turn on and off, means electrically connecting said first winding to said signal generating circuit to cause a first current component to flow in said winding, means connecting said second winding in series with the transistor emitter-collector electrodes across said input terminals thereby to induce a second current component in the first winding due to current flow in the second winding during the transistor conduction period, said first and second windings being relatively wound so that said second current component flows in the same direction as said first current component in said first winding whereby said first and second currents are combined to rapidly sweep charge carriers from the transistor base region via the first winding when the transistor is cut-off.

Claim 5

A DC-AC converter comprising a pair of input terminals adapted for connection to a source of voltage, a transistor having base, emitter and collector electrodes, a transformer having first and second windings, means connecting said first winding between the base and emitter electrodes of said transistor, a circuit for generating control signals coupled to said base electrode to cause said transistor to repetitively turn on and off, means electrically connecting said first winding to said signal generating circuit to cause a first current component to flow in said winding, means connecting said second winding in series with the transistor emitter-collector electrodes across said input terminals thereby to induce a second current component in the first winding due to current flow in the second winding during the transistor conduction period, said first and second windings being relatively wound so that said second current component flows in the same direction as said first current component in said first winding whereby said first and second currents are combined to rapidly sweep charge carriers from the transistor base region via the first winding when the transistor is cut-off.

Claim 6

A converter as claimed in claim 3 wherein said circuit for generating control signals comprises a second transformer with a first winding connected in series with the emitter-collector electrodes of said transistor and the second winding of the first transformer across the converter input terminals and a second winding coupled across the base-emitter circuit of the trAnsistor to derive said first current component in said first winding of the first transformer.

Claim 7

A converter as claimed in claim 4 wherein said circuit for generating control signals further comprises a unidirectional current element connected in series with the second winding of said second transformer and with the same polarity as the base-emitter junction of the transistor.

Claim 8

A converter as claimed in claim 4 further comprising a capacitor coupled to the first winding of said second transformer to form therewith a self-oscillating resonant circuit.

Claim 9

A converter as claimed in claim 3 further comprising an auxiliary starting circuit that includes a resistor and capacitor coupled to said input terminals and a voltage breakdown element coupled between the base of the transistor and the junction point of said resistor and capacitor.

Claim 10

A converter as claimed in claim 7 further comprising a diode connected between said junction point and the collector electrode of the transistor and poled so as to discharge the capacitor through said transistor when the transistor is triggered into conduction.

Claim 11

A converter as claimed in claim 3 further comprising a second transistor connected in a push-pull circuit arrangement with the first transistor across said input terminals, a second transformer having a third winding connected between the base and emitter of the second transistor and a fourth winding connected in series with the second transistor emitter-collector electrodes across said input terminals, a second circuit for generating control signals coupled to said second transistor base electrode to cause the second transistor to repetitively turn off when said first transistor turns on and vice versa, means electrically connecting said third winding to said second signal generating circuit to cause a first current component to flow in said third winding, said third and fourth windings being relatively wound so that a second current component is induced in the third winding by the current flow in the fourth winding during the conduction period of the second transistor and in the same direction as said first current component whereby said first and second currents are combined to rapidly sweep charge carriers from the second transistor base region via the third winding when the second transistor is cut-off.