Improvements in or relating to switched mode power supplies

Claim 2

A switched mode power supply operative on a unidirectional input current from a rectified supply having positive and negative supply lines derived by a full wave rectifier from an alternating supply for providing an output current to a load, the power supply comprising: capacitive smoothing means, two alternately conductive switching means, each switching means comprising two switching elements, the switching means for connecting a load between the positive and negative supply lines of the rectified supply, in use the current through the load alternating as alternate switching means are conductive, each switching element being shunted by a return unidirectional device, the capacitive smoothing means being connected in parallel with one switching element of each of the switching means and to the positive and negative supply lines of the rectified supply by respective further capacitive means shunted by respective unidirectional devices, the arrangement being such that in operation current draw from the supply is substantially continuous.

Claim 3

A switched mode power supply operative on a unidirectional input current derived by a full wave rectifier from an alternating supply for providing an output current to a load, the power supply comprising: two alternately operative switching means, each switching means comprising two switching elements, in use the power supply being connected via a first winding of an electromagnetic coupling device to a load, a capacitive network being arranged to provide a specific capacitive circuit across one switching element of each switching means, a second winding of the electromagnetic coupling device being connected into the capacitive network to be common to each of the specific capacitive circuits, the arrangement being such that in operation current draw from the alternating supply is substantially continuous, the current draw from the alternating supply being controlled at least once in each alternating supply cycle by a component thereof which flows alternately in each of the specific capacitive circuits and being controlled by the e.m.f. generated in the second winding of the electromagnetic coupling device due to the load current which flows in the first winding.

Claim 4

A switched mode power supply operative on a unidirectional input current derived by a full wave rectifier from an alternating supply for providing an output current to a load, the power supply comprising: two alternately operative switching means, each switching means comprising two switching elements, in use the power supply being connected via a first winding of an electromagnetic coupling device to a load, a capacitive network being arranged to provide a specific capacitive circuit across one switching element of each switching means, a second winding of the electromagnetic coupling device being connected into the capacitive network to be common to each of the specific capacitive circuits, the arrangement being such that in operation current draw from the alternating supply is substantially continuous, the current draw from the alternating supply being controlled at least once in each alternating supply cycle by a component thereof which flows alternately in each of the specific capacitive circuits and being controlled by the e.m.f. generated in the second winding of the electromagnetic coupling device due to the load current which flows in the first winding.

Claim 5

A switched mode power supply according to Claim 1 or Claim 2 in which any of the unidirectional devices are diodes.

Claim 6

A switched mode power supply according to Claim 1 or Claim 2 in which the switching elements are MOSFETs.

Claim 7

A switched mode power supply according to Claim 1 or Claim 2 in which the switching elements are gate turnoff thyristors.

Claim 8

A switched mode power supply according to Claim 1 or Claim 2 in which the switching elements are transistors.

Claim 9

A switched mode power supply according to Claim 1 or Claim 2 in which the full wave rectifier is a diode bridge.

Claim 10

A switched mode power supply according to Claim 1 or Claim 2 used to provide a power supply to a load comprising at least one discharge lamp.

Claim 11

A switched mode power supply as herein described and claimed with reference to the accompanying drawings.