Circuit for braking and driving an ac motor in the forward and reverse direction utilizing semiconductor elements

Claim 2

A controlling circuit for an AC motor as claimed in claim 1, wherein said first means comprises two transformers and said second means is an AND gate circuit which is inserted between said transformers and said switching element, a primary winding of each of said two transformers connected across two terminals of said two AC controlling elements, whereby when both of said two AC controlling elements are nonconductive said switching element is made conductive to apply braking force to said motor.

Claim 3

A controlling circuit for an AC motor as claimed in claim 1, wherein said first means is an OR circuit consisting of a plurality of diodes which are inserted into the gate circuit of said two AC controlling elements and said second means is a control circuit controlled by said OR circuit for generating a signal to make said switching element nonconductive when either of said two AC controlling elements is conductive.

Claim 4

A controlling circuit for an AC motor as claimed in claim 1, wherein said two diodes are inserted between the gates of said two AC controlling elements and said second means, whereby said two AC controlling elements are made conductive in one direction when no gate signal is applied to the gates of said two AC controlling elements to apply braking force to said motor.

Claim 5

A controlling circuit for an AC motor comprising an AC motor driven by a single-phase AC electric power source having two windings and a capacitor inserted between first ends of said two windings, the other ends of said two windings connected together and to one terminal of said AC electric power source through a circuit means consisting of a diode and a blocking thyristor connected in reverse parallel, two AC controlling elements respectively connected between both terminals of said capacitor and the other terminal of said AC electric power source, two diodes connected between both terminals of said capacitor in reverse polarity, a DC electric power source for supplying DC current to said windings, one terminal of said DC electric pOwer source connected to the connection point of said two reversely connected diodes, a switching element one end of which is connected to the other terminals of said DC electric power source and the other end of which is connected to the connection point of said two windings and said circuit means through a diode which is inserted between the gate and the cathode of said reverse blocking thyristor, a first means for detecting a condition when said two AC controlling elements are both nonconductive, and a second means for making said switching element conductive when said two AC controlling elements are both nonconductive.

Claim 6

A controlling circuit for an AC motor as claimed in claim 6, wherein said first means is a transformer having a primary winding which is inserted between both terminals of said capacitor and a secondary winding which is connected between one electrode and a controlling electrode of said switching element through rectifying elements, said switching element rendered conductive by said DC electric power source and rendered nonconductive by an output of said transformer when either one of said AC controlling elements is conductive.

Claim 7

A controlling circuit for an AC motor as claimed in claim 6, wherein said first means consists of two transformers and said second means is an AND gate circuit inserted between said transformers, a primary winding of each of said two transformers being inserted between two terminals of each of said two AC controlling elements, whereby when there are generated outputs from said transformers said switching element is made conductive by currents supplied from said output of said transformers through said AND gate circuit.