Switching circuits for energising a load

Claim 2

A circuit for energising a load with unidirectional current from an a.c. supply including; terminals for connection with the load, a first normally non conductive load energising current path for the flow of current between the supply and the terminals; a first control current path for the flow of control current between the supply and the terminals; a first control rectifier means for restricting current flow in the first control path to a first direction; a first switchable rectifier means in the first energising current path and having a control electrode connected to the first control path to be responsive to the first control current for enabling current flow in the first energising current path; and a control switch means for controlling flow of current in the first control path.

Claim 3

A control circuit as claimed in claim 1 and including a transformer secondary winding from which the a.c. supply is derived, the secondary winding having a centre tap connected to one of the terminals; and first and second winding ends; said first control current path and the first energising current path being connected between the first winding end and the other of said terminals.

Claim 4

A control circuit as claimed in claim 2, and including a second normally non-conductive load energising path for the flow of control current betwen the other of said terminals and the second end of said secondary winding; a second switchable rectifier means for enabling current flow in said first direction; a second control current path connecting the second end of said winding to the first control current path at a circuit point between said first control rectifier means and said other terminal; a second controll rectifier means in the second control current path poled in the same sense as the first control rectifier means; and a control electrode to the second switchable rectifier means connected to the second control path to be responsive to current in the second control current path; said control switch means being connected to control current flow in both said paths.

Claim 5

A control circuit as claimed in claim 2, and further including a second normally non-conductive load energising path for the flow of current between the other of said terminals and a second end of the secondary winding; a second control current path for the flow of control current between the other of said terminals and said second end; a second control rectifier means for restricting current flow in the second control current path to said first direction; a second switchable rectifier means responsive to current flow in the second control current path for enabling current flow in said first direction in the second energising current path and second control switch means for controlling flow of current in the second control current path.

Claim 6

A control circuit as claimed in claim 4, in which both of said first and second switchable rectifiers are operationally bidirectional and including; a first current sub-path from the first to the second control path a third control rectifier in said first sub-path poled in the same sense as the first control rectifier in the first control path, said first sub-path enabling current flow from the first control path to the second switchable rectifier means and said second winding end; a second current sub-path from the second to the first control path; a fourth control rectifier in said second sub-path poled in the same sense as the second control rectifier in the second control path, said second sub-path enabling current flow from the second control path to the first switchable rectifier means and said first winding end.