Patent ID: 8076862

Claim:
A dimmer for connection to a load powered by a power supply, the dimmer comprising: a first switch having a first terminal for receiving a drive current at a drive voltage, and second and third terminals, wherein the first switch is arranged so that when the drive voltage is greater than a switching-threshold voltage, a load current is supplied through the second and third terminals from the power supply to the load, and when the drive voltage is less than said switching-threshold voltage, the first switch switches off said load current; a second switch having a first terminal for receiving a switching current at a switching voltage, and second and third terminals, wherein the second switch is arranged such that when the switching voltage is greater than an overload-threshold voltage, the second switch diverts said drive current away from the first terminal of the first switch and through the second and third terminals of the second switch, thereby reducing the drive voltage at the first terminal of the first switch to a voltage that is less than the switching-threshold voltage, thus causing the first switch to switch the load current off; and wherein, the switching voltage at the first terminal of the second switch is derived from a voltage generated by the load current, such that, when the load current exceeds a threshold value, the second switch is switched on and the first switch, and hence the load current, is thereby switched off.