Control circuit for an electromagnet

Claim 2

A control circuit for an electromagnet comprising a converter circuit including a main energy storage element, a secondary energy storage element, and circuit means connecting the main storage element to the electromagnet and to the secondary energy storage element and operating to cause energy to be transferred from main energy storage element to the electromagnet, and also effecting transfer of energy from the main energy storage element to the secondary storage element for subsequent use in applying a reverse voltage to the electromagnet when the period of energisation thereof is terminated.

Claim 3

A control circuit as claimed in claim 1 in which said circuit means comprises first and second independent circuit paths connecting the main storage element directly to the electromagnet and the secondary storage element respectively and a further circuit path for connecting the secondary storage element to the electromagnet at termination of energisation of the latter.

Claim 4

A control circuit as claimed in claim 2 in which said first and second independent circuit paths include a common semi-conductor switch element.

Claim 5

A control circuit as claimed in claim 3 in which said first path also includes a diode connecting said switch element to the electromagnet.

Claim 6

A control circuit as claimed in claim 2 in which said secondary storage element is a capacitor, said second circuit path including an inductor into which energy from the main storage element is transferred, means for maintaining current flow in the inductor and for interrupting such current flow, and diode means connecting the inductor to the capacitor so that on interruption of the current flow in the inductor, the energy stored therein is transferred to the capacitor.

Claim 7

A control circuit as claimed in claim 5 in which said further circuit path comprise a semi-conductor switch element for connecting the capacitor in parallel with the electromagnet.

Claim 8

A control circuit as claimed in claim 1 further comprising current control means for maintaining current flow in the electromagnet following the transfer thereto of energy from the main energy storage element.

Claim 9

A control circuit as claimed in claim 7 in which said current control means operates initially to maintain current in the electromagnet at a relatively high level and subsequently acts as a current regulator, which maintains the electromagnet current at a significantly lower level.

Claim 10

A control circuit as claimed in claim 8 in which said circuit means comprises a semi-conductor switch element connecting the main storage element to the electromagnet, a controlled current path connecting the electromagnet to the secondary storage element and active during reduction of the current level from its initial high level to its subsequent lower level to transfer energy already transferred from the main storage element to the electromagnet to the secondary energy storage element and a further controlled current path connecting the secondary storage element to the electromagnet and active only at the termination of energisation of the electromagnet.

Claim 11

A control circuit as claimed in claim 9 in which the secondary storage element is a capacitor.

Claim 12

A control circuit as claimed in claim 1 for controlling a plurality of electromagnets, comprising a common converter circuit, a plurality of secondary energy storage elements a plurality of said circuit means connecting the common converter to respective ones of the electromagnets and to respective ones of the secondary energy storage means and a distribution logic circuit controlling said plurality of said circuit means whereby the electromagnets are energised in a predetermined sequence.